Affiah Telecommunication Systems I

CHAPTER ONE

AN OVERVIEW OF TELECOMMUNICATION SYSTEMS.

1.0 Introduction.The word telecommunication has its roots in two words: Tele in Greek meaning distant and communicatio in Latin meaning connection. Telecommunication is the distant transfer of meaningful information from one location (the sender, transmitter, or source) to a second location (the receiver, or destination). Today, the term telecommunication is used in a very broad sense to imply transfer of information over cable (copper or fiber) or wireless media and includes all of the hardware and software necessary for its transmission and reception.

A first important step in the route toward a modern information society and the information superhighway was the ability to represent information in digital form as binary digits or bits. These bits are then stored electronically, and transmitted either as electrical or light pulses over a physical network or by broadcast signals between sites. An important advantage of digital communication lies in its versatility. Almost any form of information audio, video, or data can be encoded into bits, transmitted, and then decoded back into the desired final form at the receiver. As a result, it is almost always possible to establish a communications system that will transfer the exact types of information needed.

A typical communication system can be partitioned into a transmitter, a channel, and a receiver.

Figure 1. Block Diagram of Communication System.

music, voice, video, data,

“bits” + compression

+ coding

video display, speakers, couch

potato, wed browser

(detect+decode + decompress)

Modulator

mixer, PLL, VCO

TransmitterInformation

Source

Information

SinkDemodulator Receiver

low-noise amplifier (LNA)

mixer

VGA VCO

+ PLL

free-space

fiber

ocean

your house

cables

power line

twisted pair

transmission line

trace on PCB...

Channel

1 Telecommunication Systems

1.0.1 Functional Elements of a Communication System :Figure 1 shows a commonly used model for a communication system . Although suggests a system for communication between two remotely located points, this block diagram is also applicable to remote sensing systems, such as radar or sonar, in which the system input and output may be located at the same site. Regardless of the particular application and configuration, all information transmission systems involve three major subsystems : -a transmitter, the channel , and a receiver .

Input Transducer:The wide variety of possible sources of information results in many different forms for messages. Messages may be analog or digital. The message produced by a source must be converted by a transducer to a form suitable for the particular type of communication system employed. For example, in electrical communications, speech waves are converted by a microphone to voltage variations .Such a converted message is referred to as the message signal .

Transmitter:The purpose of the transmitter is to couple the message to the channel. It is often necessary to modulate a carrier wave with the signal from the input transducer. Modulation is the systematic variation of some attribute of the carrier, such as amplitude, phase, or frequency, in accordance with a function of the message signal.There are several reasons for using a carrier and modulating it. Important ones are :(1) for ease of radiation, (2) to reduce noise and interference, (3) for channel assignment, (4) for multiplexing or transmission of several messages over a single channel, and (5) to overcome equipment limitations.

Channel :The channel can have many different forms; the most familiar is the that exists between the transmitting antenna of a commercial radio station and the receiving antenna of a radio. In this channel, the transmitted signal propagates through the atmosphere, or free space, to the receiving antenna . Other forms of channels are :- Transmission lines (such as open two- wire systems and co-axial

cables) .


- Optical fiber channels.- Guided electromagnetic – wave channels.All channels have one thing in common: the signal undergoes degradation from transmitter to receiver. This degradation results from noise and other undesired signals or interference but also may include other distortion effects as well, such as fading signal levels, multiple transmission paths, and filtering.

Receiver:The receiver's function is to extract the desired message from the received signal at the channel output and to convert it to a form suitable for the output transducer. Although amplification may be one of the first operations performed by the receiver, where the received signal may be extremely weak , the main function of the receiver is to demodulate the received signal . Often it is desired that the receiver output be a scaled, possibly delayed, version of the message signal at the modulator input .

Output Transducer:The output transducer completes the communication system. The device converts the electric signal at its input into the form desired by the system user. The most common output transducer is a loudspeaker . There are many other examples, such as tape recorders, personal computers, meters, and cathode – ray tubes.

1.1 Telecommunications TechnologiesThe information age began with the telegraph, which was invented by Samuel F.B. Morse in 1837. This was the first instrument to transform information into electrical form and transmit it reliably over long distances. The telegraph was followed by Alexander Graham Bell's invention of the telephone in 1876. The magneto-telephone was one of the first telephones on which both transmission and reception were done with the same instrument. After Heinrich Hertz discovered electromagnetic waves in 1888, Guglielmo Marconi invented the radio the first wireless electronic communications system in 1901. The earliest form of electrical communication, the original Morse telegraph of 1837 did not use a key and sounder. Instead it was a device designed to print patterns at a distance. These represented the more familiar dots (short beeps) and dashes (long beeps) of the Morse code, shown in Figure 2. At the transmitting end a


telegrapher closed a switch or telegraph key in a certain pattern of short and long closures to represent a letter of the alphabet. The electrical energy on the wire was sent in the same pattern of short and long bursts. At the receiving end, this energy was converted into a pattern of sound clicks that was decoded by a telegrapher. The code used by both transmitter and receiver is the Morse code.

The Telephone Invented by Bell and his assistant, Thomas A. Watson, marked a significant development in the history of electrical communications systems. In the earliest magneto-telephone of 1876, the speaker’s voice was converted into electrical energy patterns that could be sent over reasonably long distances over wires to a receiver, which would convert

Figure 1.2 Morse code.

A

B

C

D

E

F

G

H

I

J

K

L

M

N

O

P

Q

R

S

T

U

V

W

X

Y

Z

1

2

3

4

5

6

7

8

9

0

.

.

?


these energy patterns back into the original sound waves for the listener. The first commercial wireless voice transmitting system utilizing electromagnetic waves, the radio, was built in the United States in 1906. Hertz discovered the electromagnetic wave in 1888, and in 1895, Marconi began experimenting with wireless telegraphy. Once man learned to encode and decode the human voice in a form that could be superimposed onto electromagnetic waves and transmitted to receivers, this communication approach was used directly with human speech. Now the human voice was transmitted to remote locations, thousands of miles away, picked up by receivers, and converted to speech by speakers. This development opened new opportunities for wireless communications.The key developments that have brought us to our present state of computing include the development of numbers, the introduction of mechanical aids to calculation, the evolution of electronics, and the impact of electronics on computing. Although no one person may be credited with the invention of the computer, we will begin to track its history with an American mathematician and physicist, John Vincent Atanasoff, who designed the first electronic computer in early 1939. The marriage of computers and communications in 1941 was a major milestone that had synergistic effects on both technologies as they developed.

1.2 Telecommunications NetworksA network is a series of points or nodes interconnected by communication paths. The connection points are known as network nodes or switching exchanges. Networks can interconnect with other networks and can therefore contain subnetworks. Every network has a backbone, which is a larger transmission line that carries data gathered from smaller lines that interconnect with it. Traditionally, the telephone network was the largest network of computers interconnecting networks owned by different carriers. The Public Switched Telephone Network (PSTN) still remains the lifeline of most communications. The advent of data communications and a need to interconnect computers resulted in an emergence of data networks. Networks can be characterized in several different ways and classified by:

I. Spatial distance, such as Local Area Network (LAN), Metropolitan Area Network (MAN), and Wide Area Network (WAN);

2. Topology or general configurations of networks, such as the ring, bus, star, tree, mesh, hybrid, and others;


3. Network ownership, such as public, private or virtual private;4. Type of switching technology such as circuit, message, packet, or cell

switching;5. Type of computing model, such as centralized or distributed

computing.6. Type of information it carries such as voice, data, or both kinds of

signals.

1.3 Communications System ParametersThe cost of a system interacts with and relates to each of the requirements listed in the following sections. Obviously, the user always wants the most performance at the least cost, with good reliability and convenience. This is measured in terms of price to performance ratio. The type of information to be transmitted and bandwidth requirement are prime system parameters that determine network design and architecture. The other requirements fall behind them

Type of InformationInformation, data, voice, and video has specific transmission system requirements. The major requirement is that voice and video communications require a constant rate of information transfer and cannot tolerate any delays, which is in direct contrast with bursty data communications that transfer information at a variable rate and on demand. Networks have traditionally been separated by the type of information because of these significant differences in traffic characteristics.

BandwidthBandwidth (BW) is the range of frequencies that can be transmitted with minimal distortion. BW is equal to the rate of information transfer, which is the amount of information that is communicated from the source to the destination in a fixed amount of time, typically one second. BW is also a measure of the transmission capacity of the communications medium. There is a general rule that relates BW and information capacity. Hartley’s Law, which states that the amount of information that can be transmitted in a given time is directly proportional to bandwidth. The expression that links the two is given by


I = ktBW (2–1)where I = amount of information that can be transmittedk = a constant that depends on the type of modulationt = transmission time in secondsBW = channel bandwidth

From the above equation, it is clear that the greater the channel bandwidth, the greater the amount of information you can transmit in a given time. You can still transmit the same amount of information over a narrower channel except that it will take longer.

Broadband and BasebandThere are two types of transmission systems: broadband and baseband. The term broadband, which originated in the CATV industry, involves the simultaneous transmission of multiple channels over a single line. The channel allocation is based on different multiplexing schemes. Baseband refers to the original frequency range of a signal before it is modulated into a higher and more efficient frequency range, but the term is more commonly used to indicate digital transmission of a single channel at a time. It offers advantages such as low cost and ease of installation as well as maintenance, and most importantly, high transmission rates. Most data communications use baseband transmission, however, the push is toward broadband communication that integrates voice, data, and video over a single line.

Synchronous versus AsynchronousCommunications are designated as synchronous or asynchronous depending on how the timing and framing information is transmitted. The framing for asynchronous communication is based on a single character, while that for synchronous communication is based on a much bigger block of data. Synchronous signals require a coherent clock signal called a data clock between the transmitter and receiver for correct data interpretation. The clock recovery circuit in the receiver extracts the data clock signal frequency from the stream of incoming data and data synchronization is achieved. Also, there are a special series of bits called synchronization (SYNC) characters that are transmitted at the beginning of every data block to achieve synchronization. Each data block represents hundreds or even thousands of data characters. Asynchronous transmission incorporates the use of framing bits start and stop bits to signal the beginning and end of each


data character because the data clock signals at the transmitter and receiver are not synchronized, although they must operate at the same frequency. It is more cost-effective but inefficient compared with synchronous transmission. For every character that is transmitted, the asynchronous transmission system adds a start bit and a stop bit, and some also add a parity bit for error-detection.The efficiency of transmission is the ratio of the actual message bits to the total number of bits, including message and control bits and is given by the expression below;

In any transmission, the synchronization, error detection, or any other bits that are not messages are collectively referred to as overheads.

Simplex, Half-Duplex, and Full-DuplexSimplex refers to communications in only one direction from the transmitter to the receiver. There is no acknowledgment of reception from the receiver, so errors cannot be conveyed to the transmitter. Half-duplex refers to two-way communications but in only one direction at a time. Full-duplex refers to simultaneous two-way transmission. For example, a radio is a simplex device, a walkie-talkie is a half-duplex device, and certain computer video cards are full-duplex devices. Similarly, radio or TV broadcast is a simplex system, transfer of inventory data from a warehouse to an accounting office is a half-duplex system, and videoconferencing represents a full-duplex application.

8

M

+ CMEfficiency

=

OverheadM

M C+ 1 100%

100%

where M

C =

Number of message bits

Number of control bits

In other words,

Efficiency% = 100 - Overhead %

( (

x

x

Telecommunication Systems

Serial and ParallelSerial transmission refers to the method of transmitting the bits (0s and 1s) one after another along a single path. It is slow, cost-effective, has relatively few errors, and is practical for long distances. Parallel transmission is described as transmitting a group of bits at a single instant in time, which requires multiple paths. For example, to transfer a byte (8-bit data word), parallel transmission requires eight separate wires or communications channels. It is fast (higher data transfer rate) but expensive, and it is practical only for short distances. Most transmission lines are serial, whereas information transfer within computers and communications devices is in parallel. Therefore, there must be techniques for converting between parallel and serial, and vice versa. Such data conversions are usually accomplished by a Universal Asynchronous Receiver Transmitter (UART).

Analog and DigitalInformation that needs to be communicated may be in analog or digital form. Analog signals are continuously varying quantities, while digital signals are discrete quantities, most commonly binary (On or Off, High or Low, 1 or 0). Voices, images, and temperature readings from a sensor are all examples of analog data. In digital transmission, as all information is reduced to a stream of 0s and 1s, you can use a single network for voice, data, and video. Analog data can be encoded as an analog signal, for example, cassette tape player, and audio as well as video components of a TV program. Digital data is regularly represented by digital signals, for example, e-mail. Also, analog data is commonly encoded with digital signals. When you scan an image or capture a sound on the computer, you are converting analog data to digital signals. This analog-to-digital conversion is usually accomplished with a special device or process referred to as a codec, which is short for coder-decoder.

NoiseThis consists of undesired, usually random, variations that interfere with the desired signals and inhibit communication, noise originates both in the channel and in the communication equipment. Although it cannot be eliminated completely, its effects can be reduced by various means. It is helpful to divide noise into two types: internal noise, which originates within the communication equipment, and external noise, which is a property of the channel. External noise consists of man-made noise, atmospheric, and


space noise. Man-made noise is generated by equipment that produces sparks, such as automobile engines and electric motors with brushes. Atmospheric noise is often called static because lightning, which is a static-electricity discharge, is its principal source. Since it occurs in short, intense bursts with relatively long periods of time between bursts, it is often possible to improve communication by simply disabling the receiver for the duration of the burst. This technique is called noise blanking. Space noise is mostly solar noise, which can be a serious problem with satellite reception when the satellite is in line between the antenna and the sun. Internal noise is generated in all electronic equipment, both passive components like resistors and cables, and active devices like diodes and transistors. Thermal noise is produced by the random motion of electrons in a conductor due to heat. It is an equal mixture of noise of all frequencies, and is sometimes called white noise, by analogy with white light, which is an equal mixture of all colors. The term noise is often used alone to refer to this type of noise, which is found everywhere in electronic circuitry. The noise power in a conductor is a function of its temperature given by the expression

P = kTBW N

where P = internal noise power in wattsN

k = Boltzmann’s constant, 1.38 x 10-23 joules/Kelvin (J/K)T = absolute temperature in Kelvin (K)BW = operating bandwidth in Hertz

The temperature in degrees Kelvin can be found by adding 273 to the Celsius temperature. The previous equation shows that noise power is directly proportional to bandwidth, which means that high bandwidth communications are associated with higher noise. The only way to reduce noise is to decrease the temperature or the bandwidth of a circuit, or both. Shot noise has a power spectrum that resembles that for thermal noise by having equal energy in every hertz of bandwidth, at frequencies from dc into the GHz region. It is created by random variations in current flow in active devices such as transistors and semiconductor diodes. Excess noise, also called flicker noise or pink noise, varies inversely with frequency. It is rarely a problem in communication circuits, because it declines with increasing frequency and is usually insignificant above approximately one kHz. In communications, it is not really the amount of noise that concerns us, but


rather the amount of noise compared to the level of the desired signal. That is, it is the ratio of signal to noise power that is important, rather than the noise power alone. This Signalto- Noise Ratio (SNR), usually expressed in decibel (dB), is one of the most important specifications of any communication system. The decibel is a logarithmic unit used for comparisons of power levels or voltage levels. In order to understand the implication of dB, it is important to know that a sound level of zero dB corresponds to the threshold of hearing, which is the smallest sound that can be heard. A normal speech conversation would measure about 60 dB. The SNR is given by the expression;

SNR dB 10 log = P / P10 S N

where P is the signal power and P is the noise powerS N

1.4 ModulationModulation (a means of controlling the characteristics of a signal in a desired way) is the act of translating some low-frequency or baseband signal (voice, music, data) to a higher frequency . Why do we modulate signals? There are at least two reasons: to allow the simultaneous transmission of two or more baseband signals by translating them to different frequencies, and to take advantage of the greater efficiency and smaller size of higher-frequency antennas. In the modulation process, some characteristic of a high-frequency sinusoidal carrier is changed in direct proportion to the instantaneous amplitude of the baseband signal. The modulation is done at the transmitter, while an inverse process, called demodulation or detection, takes place at the receiver to restore the original baseband signal. There are many ways to modulate a signal, such as Amplitude Modulation (AM), Frequency Modulation (FM), Phase Modulation (PM), and Pulse Modulation. Both AM and FM are used in radio broadcast. Pulse modulation is mainly used for analog-to-digital conversion. In modulation, the amplitude, frequency, or phase of a carrier wave is changed in accordance with the modulating signal in order to transmit information. The resultant is called a modulated wave. This concept is illustrated in Figure 3.


Figure 1.3. Concept of modulation.

A carrier, which is usually a sine wave, is generated at a frequency much higher than the highest modulating signal frequency. The expression below is a general equation for a sine wave carrier:

e(t) = Ec sin (ωct + θ) where e(t) = instantaneous amplitude or voltage of the sine wave at time tEc = maximum amplitude or peak voltageωc = frequency in radians per second t = time in secondsθ = phase angle in radians

In modulation, the instantaneous amplitude of the modulating signal is used to vary some parameter of the carrier. The parameters that can be changed are amplitude Ec, frequency ωc, and phase θ. The information content (analog waveform or digital bits) are mapped onto the carrier wave using different modulation schemes;

1. Classic analog techniques: Amplitude Modulation (AM), Frequency Modulation (FM), Phase Modulation (PM)

2. Simple digital modulation: On/Off Keying (OOK), Amplitude Shift Keying (ASK), Frequency Shift Keying (FSK), Phase Shift Keying (BPSK), Quadrature Amplitude Modulation (QAM)

3. Sophisticated digital modulation: Minimum Shift Keying (MSK), Pulse-Position Modulation (PPM), Orthogonal Frequency-Division Multiplexing (OFDM), Discrete Multi-Tone (DMT).

ModulatingSignal

Modulator

Carrier Wave

ModulatedCarrier


1.4.1 Amplitude Modulation: Modulation Degree and Sideband Amplitude.Amplitude modulation of a sine or cosine carrier results in a variation of the carrier amplitude that is proportional to the amplitude of the modulating signal. In the time domain (amplitude versus time), the amplitude modulation of one sinusoidal carrier by another sinusoid resembles Figure 4a. The mathematical expression for this complex wave shows that it is the sum of three sinusoids of different frequencies. One of these sinusoids has the same frequency and amplitude as the unmodulated carrier. The second sinusoid is at a frequency equal to the sum of the carrier frequency and the modulation frequency; this component is the upper sideband. The third sinusoid is at a frequency equal to the carrier frequency minus the modulation frequency; this component is the lower sideband. The two sideband components have equal amplitudes, which are proportional to the amplitude of the modulating signal. Figure 4b shows the carrier and sideband components of the amplitude modulated wave of Figure 4(a) as they appear in the frequency domain (amplitude versus frequency).

Figure 1.4. Domain display of amplitude modulated carrier

A measure of the amount of modulation is m, the degree of modulation. This is usually expressed as a percentage called the percent modulation. In the time domain, the degree of modulation for sinusoidal modulation is calculated as follows, using variables shown in Figure 5:

Figure 1.4(a). Time domain display Of an amplitude modulated carrier.

Am

pli

tud

e

(Vo

lts)

t

Figure 1.4(b). Frequency domain (spectrum analyzer) Display of an amplitude modulated carrier

Am

pli

tud

e

(Vo

lts) LSB USB

mffC- fC fC mf+


Figure 1.5.

M = E - E / E , Since the modulation is symmetrical, max c c

And E - E = E - E , and E + E / 2 = Ecmax c c min max min .

From this it is easy to show that, m = E - E / E + E for sinusoidal max min max min

modulation.When all three components of the modulation signal are in phase, they add together linearly and form the maximum signal amplitude , as shown in figure 6.

M = E - E / E = / Emax c c

since E = E = EUSB LSB SB,

M = 2E / E SB, c

Then For 100% modulation (m=1.0), the amplitude of each sideband will be one-half of the carrier amplitude (voltage). Thus, each sideband will be 6 dB less than the carrier, or one-fourth the power of the carrier. Since the carrier component does not change with amplitude modulation, the total power in the100% modulated wave is 50% higher than in the unmodulated carrier.

Figure 1.6.

Calculation of degree of amplitude Modulation from time domain display.

Emaxm

E = E + E + Emax c USB LSB

E + EUSB LSB c

Calculation of degree of amplitude modulation displayed in both time and frequency domain.

EmaxFc

Emin

E c

E I s b

m = 0.5

E u s b

f c f mf mf mf c +

Emax

Ec

Emin


Although it is easy to calculate the modulation percentage M from a linear presentation in the frequency or time domain (M = m •100%), the logarithmic display on a spectrum analyzer offers some advantages, especially at low modulation percentages. The wide dynamic range of a spectrum analyzer (over 70dB) allows measurement of modulation percentages as low as 0.06%.

Special Forms of Amplitude modulationChanging degree of modulation of a particular carrier does not change the amplitude of the carrier component itself. Instead, the amplitude of the sidebands changes, thus altering the amplitude of the composite wave. Since the amplitude of the carrier component remains constant, all the transmitted information is contained in the sidebands. This means that the considerable power transmitted in the carrier is essentially wasted. For improved power efficiency, the carrier component may be suppressed (usually by the use of a balanced modulator circuit), so that the transmitted wave consists only of the upper and lower sidebands. This type of modulation is called double sideband-suppressed carrier, or DSB-SC. The carrier must be reinserted at the receiver, however, to recover this modulation. In the time and frequency domains, DSB-SC modulation appears as shown in Figure 7.

Figure 1.7. Frequency and time domain presentations of balanced modulator output.

An important type of amplitude modulation is the single sideband with suppressed carrier (SSB). Either the upper or lower sideband can be transmitted, written as SSB-USB or SSB-LSB (or the SSB prefix may be omitted). Since each sideband is displaced from the carrier by the same frequency, and since the two sidebands have equal amplitudes, it follows that any information contained in one must also be in the other. Eliminating one of

(a) Frequency domain (b) Time domain


the sidebands cuts the power requirement in half and, more importantly, halves the transmission bandwidth (frequency spectrum width). SSB has been used extensively throughout telephone systems to combine many separate messages into a composite signal (baseband) by frequency multiplexing. This method allows the combination of up to several thousand 4-kHz-wide channels containing voice, routing signals, and pilot carriers. The composite signal can then be either sent directly via coaxial lines or used to modulate microwave line transmitters. The SSB signal commonly generated at a fixed frequency by filtering or by phasing techniques. This necessitates mixing and amplification in order to get the desired transmitting frequency and output power. These latter stages, following the SSB generation, must be extremely linear to avoid signal distortion, which would result in unwanted in-band and out-of-band intermodulation products. Such distortion products can introduce severe interference in adjacent channels.

1.4.2 Angular Modulation The carrier as we saw earlier was given by the expression e(t) = A • cos (wt + f) and, angular modulation can be characterized as either frequency or phase modulation. In either case, we think of a constant carrier plus or minus some incremental change.

Frequency ModulationThe instantaneous frequency deviation of the modulated carrier with respect to the frequency of the unmodulated carrier is directly proportional to the instantaneous amplitude of the modulating signal.

Phase ModulationThe instantaneous phase deviation of the modulated carrier with respect to the phase of the unmodulated carrier is directly proportional to the instantaneous amplitude of the modulating signal.

For angular modulation there is no specific limit to the degree of modulation, so there is no equivalent of 100% AM. Modulation index is expressed as:


m = ∆f / f = ∆φp m p

wherem= modulation index,∆f = peak frequency deviation,p

F = frequency of the modulating signal, andm

∆φ = peak phase deviation in radians.p

This expression tells us that the angular modulation index is really an indication of peak phase deviation, even in the FM case. Also, note that the definitions for frequency and phase modulation do not include the modulating frequency. In each case, the modulated property of the carrier, frequency or phase, deviates in proportion to the instantaneous amplitude of the modulating signal, regardless of the rate at which the amplitude changes. The frequency of the modulating signal is important in FM. In the expression for the modulating index, it is the ratio of peak frequency deviation to modulation frequency that equates to phase. Comparing this basic equation with the two definitions of modulation, we find;(i) A carrier sine wave modulated with a single sine wave of constant frequency and amplitude will have the same resultant signal properties (that is, the same spectral display) for frequency and phase modulation. A distinction in this case can be made only by direct comparison of the signal with the modulating wave, as shown in Figure 8.

Figure 1.8. Phase and frequency modulation of a sine wave carrier by a sine-wave signal.

Modulating Wave

Phase modulated Wave

Frequencymodulated Wave


(ii) Phase modulation can generally be converted into frequency modulation by choosing the frequency response of the modulator so that its output voltage will be proportional to l/f (integration of the modulating m

signal). The reverse is also true if the modulator output voltage is proportional to f (differentiation of the modulating signal). Since phase modulation can be m

applied at the amplifier stage of a transmitter, a very stable crystal-controlled oscillator can be used. Thus, “indirect FM” is commonly used in VHF and UHF communication stations where highly stable carrier frequencies are required. We can see that the amplitude of the modulated signal always remains constant, regardless of modulation frequency and amplitude. The modulating signal adds no power to the carrier in angular modulation as it does with amplitude modulation. Mathematical treatment shows that, in contrast to amplitude modulation, angular modulation of a sine-wave carrier with a single sine wave yields an infinite number of sidebands spaced by the modulation frequency, fm. In other words, AM is a linear process, whereas FM is a nonlinear process. For distortion-free detection of the modulating signal, all sidebands must be transmitted. The spectral components (including the carrier component) change their amplitudes when the modulation index m is varied. The sum of the squares of these components always yields a composite signal with an average power that remains constant and equal to 28 the average power of the unmodulated carrier wave.

The curves in figure 1.9, show the relation (Bessel function) between the carrier and sideband amplitudes of the modulated wave as a function of the modulation index m.


Figure 1.9. Carrier and sideband amplitudes for angle modulated signals.

The carrier component J and the various sidebands J go to zero amplitude 0 n

at specific values of m. From these curves we can determine the amplitudes of the carrier and the sideband components in relation to the unmodulated carrier.

FM SpectrumThe spectrum of an FM signal is not infinite. The sideband amplitudes become negligibly small beyond a certain frequency offset from the carrier, depending on the magnitude of m. We can determine the bandwidth required for low distortion transmission by counting the number of significant sidebands. (Significant sidebands usually means all those sidebands that have a voltage at least 1 percent (-40 dB) of the voltage of the unmodulated carrier.) We will now investigate the spectral behavior of an FM signal for different values of m. In Figure 1.10 we see the spectra of a signal for m=0.2, 1, 5, and 10. The sinusoidal modulating signal has the constant frequency fm, so the m is proportional to its amplitude. In figure 1.11 amplitude of the modulating signal is held constant and m is varied by changing the modulating frequency. the individual spectral components are shown for m=5, 10, and 15. For m→∞, the components are not resolved, but the envelope is correct. Two important facts emerge from Figures 1.10 & 1.11:

19

0.8

-0.40 m=3 5 10 15 20 25

1.0

0.6

0.4

Am

plit

ud

e

0.2

0.0

-0.2

1st ordersideband

Carrier

2nd ordersideband

Jn


Figure 1.10. Amplitude-frequency spectrum of an FM signal (with sinusoidal modulating signal, fm, fixed and amplitude varying).

(I) For very low modulation indices (m less than 0.2), we get only one significant pair of sidebands. The required transmission bandwidth in this case is twice fm, as for AM.

(ii) For very high modulation indices (m more than 100), the transmission bandwidth is twice Δfp. For values of m between these margins, we have to count the significant sidebands to determine the transmission bandwidth.

fc- fm fc cf fm+

f

f

m = 0.2

m = 1

m = 5

2Δf

fc- fm fc fc+ fm22

2 f

f

Bandwidth

Bandwidth

ffc cc fff

m

m+-

Bandwidth

f cfcf -

88

14

2m = 10

f

f


Figure 1.11. Amplitude-frequency spectrum of an FM signal (with amplitude of Df fixed and fm decreasing).

Bandwidth of FM Signals.The main effects of varying the modulation index m, on a frequency modulated signal are visualized in Figure 1.12. The main points to observe are:

21

m = 5

f c

2Δf

m = 10

fc

m = 15

f

c

m → ∞

f

f

f

f

f

2Δf

2Δf

2Δf


(I) As m increases, the time domain shows increasing variation in the instantaneous frequency.(ii) As m increases, higher-order sidebands in the frequency domain become more and more significant.(iii) At special values of m, various sideband amplitudes become zero.

Figure 1.12. Variation of a frequency modulated signal in the time and frequency domain as m is

changed from 0 to 7.

The bandwidth requirements for a low distortion transmission in relation to m is shown in figure 1.13.

Figure 1.13 Bandwidth requirements vs. modulation index, m.

m = 7

f c + 9 f mf cm9 f cf _

87654321

0 2 4 6 8 10 12 14 16m

Ban

dw

idth

/∆f


For voice communication, a higher degree of distortion can be tolerated; that is, we can ignore all sidebands with less than 10% of the carrier voltage (-20 dB). There are many more sideband pairs for this signal, but their amplitudes (and therefore their power content) are negligible. The total bandwidth is given by:Bandwidth = f × # of sideband pairs × 2 or, for this example,M

Bandwidth = 10 kHz × 3 × 2 = 60 kHz.

This is three times the bandwidth of an AM signal having the same modulating tone. The bandwidth of an FM signal is usually determined by the number of significant sidebands. For the example just cited, over 99% of the signal power is contained in the three pairs of sidebands.We can calculate the necessary bandwidth B using the approximate expression given by;

B = 2∆f + 2f or B = 2f (1+ m)peak m m

In the commercial, radio the modulating signal is not just a simple sinusoid but a more complex audio signal such as speech or music. Each radio station modulates its specific carrier by an audio signal producing a modulated signal that occupies a small band of frequencies centered about the station’s carrier frequency. As shown in Figure1.14 , the signal received by a radio consists of the signals sent from all stations, whose signals are spaced far enough apart to prevent overlap. Tuning the radio to a specific station selects the narrow band of frequencies transmitted by that station.

Figure 1.14. Signals sent from all stations, separated in frequency to prevent their signals from overlapping.

Frequency Modulation in AM/FM Radio

Station 1 Station 2 Station 3

Frequency

Am

plit

ud

e23 Telecommunication Systems

AM and FM radio stations are spaced specific kHz apart depending on the country and the prevailing regulatory agency specification. Tuning of the radio dial selects one of the small frequency bands of a given station. A demodulator in the radio extracts the modulating audio signal from the received signal. FM radio has a number of performance advantages over AM radio, including better power efficiency and noise rejection, but FM radio provides these advantages at the expense of using a larger channel bandwidth.


CHAPTER TWO

MODULATORS AND TRANSMITTERS

Methods of TransmissionSingle Sideband:The intelligence of an AM signal is contained solely in the sidebands. In fact, each sideband alone contains all the intelligence we need for communications. Since this is true, it may be correctly inferred that one sideband and the carrier signal can be eliminated. This is the principle on which single sideband (SSB) communications is based. Although both sidebands are generated within the modulation circuitry of the SSB radio set, the carrier and one sideband are removed before any signal is transmitted. The sideband that is higher in frequency than the carrier is called the upper sideband (USB). The sideband that is lower in frequency than the carrier is called the lower sideband (LSB). Either sideband can be used for communications as long as both the transmitter and the receiver are adjusted to the same sideband. The transmission of only one sideband leaves open that portion of the RF spectrum normally occupied by the other sideband of an AM signal. This allows more emitters to be used within a given frequency range. Single sideband transmission is used in applications where it is desired to: Obtain greater reliability. Limit size and weight of equipment. Increase effective output without increasing antenna voltage. Operate a large number of radio sets without heterodyne interference (whistles and squeals) from radio frequency carriers. Operate over long ranges without loss of intelligibility due to selective fading.

Radiotelegraphy (Continuous Wave Transmission):Radiotelegraph information can be transmitted by starting and stopping the carrier by means of a switch or key. Each letter and number of a message is indicated by combining short and long pulses (dots and dashes) in groups according to a determined sequence or code. The process of transmitting information, called radiotelegraphy, is also called continuous wave transmission or, more simply, CW. Radiotelegraph information can also be transmitted by using a tone modulated radio wave. In tone transmission, the carrier is modulated at a fixed audio rate usually between .5 and 1 kilohertz. The carrier signal is again stopped and started to form dots and dashes. This is called modulated continuous wave or MCW. Because tone emission


occupies a broader band, it may be used successfully against some types of jamming. However, the broad signal used in tone transmission is an easy target for radio direction finding equipment. The distance range of a tone modulated transmitter is less than that of a nonmodulated CW transmitter of the same power output.

2.1 Principle of AM GenerationAmplitude modulation (AM) is a linear modulation. This is because the superposition principle holds. If a carrier s (t) is amplitude modulated c

separately by the modulating signals m (t) and m (t) producing modulated 1 2

signals sm (t) and sm (t), respectively, then the effect of modulating the same 1 2

carrier by the sum of the two signals is a modulating signal that is the sum of the two modulated waveforms [sm (t) + sm (t)].1 2

But the process involved in generating AM must be non-linear because multiplication is a non-linear process. When same frequencies are contained in the input and output signals of a processor, then the operations performed by the processor on the signals is linear. However if new frequency components are introduced at the output, then the processor has performed a non-linear operation on the input signals.

In AM, new sideband frequencies are produced which are not present either in the carrier or the modulating frequencies. So the multiplication operation that produces AM must be a non-linear operation and involve a non-linear system. In AM, there are two types of modulators that could introduce multiplication by very simple methods. These modulators involve non-linear devices involving diodes or transistors. They are as follows:

(i). The gated modulator made up of electronic switches: The gating action of the gated modulator can be implemented either passively by using a passive switching circuit (Fig. 2.1a) or actively with the help of active devices making up the switching circuit.

(ii). The square-law modulator: The square-law or power law modulator utilizes the non-linear input output characteristics of non-linear devices like the diode or the transistor biased in the non-linear region.


The AM can be easily produced if diodes and transistors are driven into non-linear operation. The most popular modulator is built with a Class C transistor amplifier. A common emitter transistor amplifier coupled with a tank circuit tuned to the carrier frequency can produce AM-DSB-TC. The carrier is fed to the emitter while the modulating signal can be applied to either the emitter or the base or the collector. A Class C amplifier is basically a power amplifier and has high efficiency Passive switching can be achieved either by a mechanical switch operated manually or a diode circuit acting as an electronic switch (Fig. 2.1b). But the speed of mechanical switching is very slow. Usually the carrier frequencies are in the range of mega-hertz. Typical diode switching can be accomplished with the help of a ring modulator or a diode bridge shown in Figure 2.1c. The carrier signal is fed to the input of the switch to cause switching at the carrier frequency.

Fig. 2.1. Different types of gated amplitude modulators.

Mechanical switch SAM (t) m(t)m(t) SAM (t)

ResistanceResistance

Diode bridge

(b) Bridge modulator

Carrier

A B

(a) Passive AM modulator using mechanical switch

m(t) Transformer

Carrier

SAM(t)Transformer

(c) Ring modulator


In the diode bridge, the diodes get forward biased when the carrier signal passes through the negative cycle because in that case the point A (Fig. 2.1b) is at a higher potential than point B. The bridge acts as a closed switch and the output is zero. On the other hand, when the carrier passes through the positive cycle the diodes are reversed biased as point B is at a higher potential than point A. The switch is open and the input appears across the output. The limit on the switching speed is imposed by the non-ideality of the diodes. In the case of the ring modulator the carrier is a train of rectangular pulses. The output is a gated version of the input. It can be passed through a filter to obtain a proper amplitude-modulated signal. Active devices like transistors can also be used as switches. They operate between cutoff and saturation.

2.2 AM Modulating Circuits / AM ModulatorsThere are two levels of modulation: low-level modulation and high-level modulation.With low-level modulation, the modulation takes place prior to the output element of the final stage of transmitter. In high-level modulators, the modulation takes place in the final element of the final stage of transmitterLow-level versus high-level modulation:• With low-level modulation, less modulating signal power is required to

achieve a high percentage of modulation. For high-level modulation, the carrier signal is at its maximum amplitude at the final element, therefore much higher amplitude modulating signal is required to achieve high percent modulation

• However, low-level modulation is not suitable for high-power applications when all the amplifiers that follow the modulator stage must be linear

2.2.1 Emitter Modulator (low-level AM modulator)The emitter modulator is basically a small signal amplifier, and is shown in figure 2.2:


Figure 2.2: Single transistor, emitter modulator

• When no modulating signal present, the circuit operates as a linear amplifier. The output is simply the carrier amplified by the quiescent voltage gain

• When a modulating signal is applied, the amplifier operates nonlinearly, and signal multiplication occurs

• The modulating signal varies the gain of the amplifier at a sinusoidal rate equal to the frequency of the modulating signal and can be expressed as:

A = A [1 + mSin(2πf t)] ---------------------- (2.1)v q m

Where A = amplifier voltage gain with modulationv

A = amplifier quiescent (without modulation) voltage gainq

As sine function goes from a maximum of +1 to a minimum of -1, above equation can be reduced to

A = A [1 + m] v q

At 100% modulation, A (max) = 2A A (min) = 0v g v

Operation of the modulator is briefly described below:• Modulating signal is applied through isolation transformer to the

emitter of transistor and the carrier is applied directly to the base.

V = 30 V dccc

R 1

Rc C 2

RLQ1

c

C 1

C 3

V out

R 2V c

R E

V m


• The modulating signal drives the circuit into both saturation and cut-off states, producing the nonlinear amplification necessary for modulation to occur

• The collector waveform includes the carrier, upper and lower side frequencies as well as a component at the modulating frequency

• Coupling capacitor 2 C removes the modulating signal frequency from the waveform, producing a symmetrical AM envelope at Vout

See the waveforms in figure 2.3;

Figure 2.3: Output waveforms for emitter modulator

Characteristics:• Amplitude of the output signal depends on the amplitude of input

carrier and the voltage gain of amplifier• Coefficient of modulation depends entirely on the amplitude of

modulating signal• Simple but incapable of producing high-power output waveforms.

2.2.2 Collector Modulator (medium-power AM modulator)Similar to emitter modulator, the collector modulator is practically a transistor amplifier with the modulating signal is applied to the collector. The schematic diagram for the collector modulator is shown in figure 2.4.

Modulated carrier superimposedonto modulating signal

Collectorvoltage( )0

Modulating signal( m)

AM DSBFCenvelope

(V )out

Modulating carrier with modulatingsignal frequency removed

Time

Time


Figure 2.4: Schematic diagram of simplified collector modulator

• The RFC is a radio-frequency choke that acts as a short to DC and an open to high frequencies. Therefore, it isolates the DC power supply from high-frequency carrier and side frequencies while allowing low-frequency modulating signal to modulate the collector of the transistorOperation of the circuit:1. Without an applied modulating signal, the collection of wave forms is shown in figure 2.5.

Figure 2.5: Collector waveforms with no modulating signal

Vp Vcc=

Vm

Vcc

Single-frequencymodulating signal

T1 =1.1

RFC

Vout

T2 =1.1

C1R1

Vc

Unmodulatedcarrier

Q1

0.7 Vo VVc

Ic

Vout

Vcc

VCE (sat) = 0 V


Figure 2.6: Practical collector modulator

The operation of this circuit is almost identical to the previous circuit except the addition of a tank circuit (C and L ) in the collector of the transistor as 1 1

shown in figure 2.6. The waveforms of the circuit are shown in figure 2.7:

Figure 2.7: Collector and output waveforms

Vm

Vp Vcc=

Modulatingsignal

T1 1 :1=

Vcc

C1

C3

T2

VoutL1C1

Q1

C1

C2R1

T3 = 1 :1

Vo

Unmodulatedcarrier

Antenna

CN

V V= p cc

m

V c

I c

V out

(b)

O V

O.7 V O V

+ 2 V CC

O V

- 2 VCC


• The waveforms for the modulating signal, carrier and collector current are identical as before and the output is symmetrical AM DSBFC signal

• The positive half-cycle of the envelope is produced in the tank circuit by the flywheel effect As the transistor is conducting, C charges to 1

V + V = 2V . When the transistor is off, C discharges through L . CC m CC 1 1

When L discharges, C charges to a minimum value of − 2V1 1 CC

• The resonant frequency of the tank circuit is equal to fc , and the bandwidth extends from fc − fm to fc + fm . Consequently, the modulating signal, the harmonics and all the higher-order cross products are removed leaving a symmetrical AM DSBFC wave. To achieve symmetrical modulation, maximum efficiency operation, high output power while requiring as little modulating signal drive power as possible, emitter and collector modulators as used simultaneously as shown in Figure 2.8.

Figure 2.13: High-power AM DSBFC transistor modulator

Circuit operation:• The modulating signal is simultaneously applied fed into the collectors

of the push-pull modulators ( Q and Q ) and to the collector of the drive 2 3

amplifier Q1

• Collector modulation occurs in Q . Thus the carrier signal on the base 1

of Q and Q has already been partially modulated, and the modulating 2 3

signal power can be reduced.

Partially modulated wave

Unmodulatedcarrier input

c

T1

Q1

C1

Cc

Cbp

Cc

Rb

Rb

Q2

C2

Q3

T2

Antenna

Modulatedsignal

Fully modulated wave

Cbp

T3

RFC

Modulatingsignal input m

VCC


• The modulators are also not required to operate over entire operating curve to achieve 100% modulation.

2.2.3 Balanced ModulatorThe constraint on the non-linear device may be relaxed if the balanced modulator is designed for producing amplitude modulation. It gives rise to the suppressed carrier variety of amplitude modulation, both for double sideband (DSB) and single sideband (SSB) cases. Figure 2.9 gives the block diagram of a balanced modulator.

Figure. 2.9: Balanced modulator

In this case an additional component, formed by subtracting the modulating signal from the carrier, is taken to their sum. As far as the difference is concerned, let us now consider the difference signal

y (t) [s (t) - s (t)]2 c m

If this difference is applied to the input of the non-linear device then we have2 3

y(t) = a + a [S (t) - s (t)] + a [s (t) - s (t)] + a [s (t) - s (t)] +...2 1 2 c m 3 c m 4 c m

2_ = a +a [s (t) - s (t)]+a [s (t)] +a [s (t)] 2a s (t)xs (t) + higher order terms.1 2 c m 3 c 2 3 m 3 c m

When the output currents are fed to a difference amplifier then the resultant becomes

S (t)m

o180 phase

S (t)m-

ShifterS (t)c

Subtractor

Nonlinears device

BPF

4 a S (t)Sm(t)3 c

+

+

+

+

-

Nonlinear device

Nonlinear device

Nonlinear device

S (t)c

S (t)m

Tank Circuit


-y(t) = y(t) y(t) = 4a s (t) x s (t)1 2 3 c m2 3

[Since y(t) = a +a [s (t)+ s (t)]+ a [s (t)+ s (t)] + a [s (t)+ s (t)] +...1 2 c m 3 c m 4 c m2 3_a +a [s (t)-s (t)]+ a [s (t)-s (t)] +a [s (t)-s (t)] +...1 2 c m 3 c m 4 c m

= 4 a s (t).3 c

S (t) and the odd terms cancel out.]m

As for the third order terms are concerned, the only term remaining from [s (t) c3

+ s (t)] that overlaps the frequency band of the modulating signal is [s (t) m c2 3s (t) ]. This term remains unchanged in the expansion of [s (t) − s (t)] and m c m

cancels out from the final result. Therefore, the resultant output is a double sideband, suppressed carrier amplitude modulated carrier (AM-DSB-SC) because the first order term of the carrier signal is eliminated.

AM TransmitterThe transmitter is an electronic system that acts at the source end. It converts the message into a suitable electrical form so that it could be launched into the atmosphere as an electromagnetic wave.The transmitter (i) generates the carrier signal that carries the message, (ii) modulates the carrier by the message, and (iii) supplies sufficient power or energy to the modulated carrier so that it may travel from the source to the destination without being affected by noise.There are various types of circuits for designing the transmitter. But whatever be its design, a transmitter invariably has the following three parts or sections—the exciter section, the power section, and the modulator section. An AM transmitter must have these three major sub-divisions.

2.3.1 Low-Level Transmitters:Figure 2.9 shows a block diagram for a low-level AM DSBFC transmitter:

Figure 2.10: Block diagram of low-level AM DSBFC transmitter

RF carrieroscillator

Bufferamplifier

Carrierdriver

Modulator

Modulatingsignalsource

Modulating

signal

driver

BandpassFilter

Preamplifier

BandpassFilter

Linear

intermediate

Power

amplifier

Linea

final power

amplifier

Bandpass

Filter

Coupling

network

Antenna


The preamplifier (linear voltage amplifier with high input impedance):To raise source signal amplitude to a usable level with minimum nonlinear distortion and as little thermal noise as possible

Modulating signal driver (linear amplifier):Amplifies the information signal to an adequate level to sufficiently drive the modulator• RF carrier oscillator

To generate the carrier signal, usually crystal-controlled oscillators are used

The buffer amplifier (low-gain, high-input impedance linear amplifier):To isolate the oscillator from the high-power amplifiers• The modulator can use either emitter or collector modulation• The intermediate and final power amplifiers (push-pull modulators)

Required with low-level transmitters to maintain symmetry in the AM envelope

The coupling network:Matches output impedance of the final amplifier to the transmission line/antenna

The applications in low-power, low-capacity systems: wireless intercoms, remote control units, pagers and short-range walkie-talkie.

2.3.2 High-Level Transmitters:The block diagram for a high-level AM DSBFC transmitter is represented in figure 2.11 and operates as follows;


Figure 2.11: Block diagram of a high-level AM DSBFC transmitter

1. The modulating signal is processed similarly as in low-level transmitter except for the addition of power amplifier: To provide higher power modulating signal necessary to achieve 100% modulation (carrier power is maximum at the high-level modulation.

2. Same circuit as before for carrier oscillator, buffer and driver but with addition of power amplifier.

3. The modulator circuit has three primary functions:Provide the circuitry necessary for modulation to occur.It is the final power amplifier.Frequency up-converter: translates low-frequency information signals to radio-frequency signals that can be efficiently radiated from an antenna and propagated through free space

2.3.3 Operation of Am Transmitter Showing Am Modulator In DetailFigure 2.2 shows the details of the AM modulator. The operation of the modulator consists of two stages. First, the information signal and carrier are passed through a nonlinear device, e.g., a transistor or diode, to generate the required upper and lower sidebands along with unnecessary sinusoids of many other frequencies. [The figure mentions an "ideal" nonlinear device; "ideal" means that most of the unnecessary harmonics have been omitted for clarity.] Second, a high-frequency bandpass filter removes the unnecessary sinusoids and passes only those in the required AM-modulated carrier.

Modulatingsignal source

Bandpassfilter

PreamplifierModulating

signal driveramplifier

Modulatingsignal power

amplifier

AM modulatorand output

power amplifier

Antenna

Bandpassfilter

Matchingnetwork

Carrier poweramplifier

Carrier driver

Bufferamplifier

RF carrieroscillator


Figure 2.12: FM Modulator Detail

2.4: Generation of Angle-Modulated Waves. A carrier frequency modulated by signal m(t) can be regarded as phase modulated by the integral of this modulating signal. Similarly, a phase-modulated carrier may be taken to be a frequency modulated by the

AM MODULA TOR IDEAL NON-

LINEARDEVICE

BAND-PASSFILTER

Voltage (Volts)

Time(Sec.)

Time(Sec.)

Time(Sec.)

Time(Sec.)

Filter selects carrier and sidebands.

Voltage (Volts)

Combined Signal

V(t)=[E +Em COS(2pf t)]COS(2pf t)o m o(f = f )m o

Amplifier gain = constant K > 1.

Voltage (Volts)

Combined Signal

Antenna Passes only high frequencies.

Voltage (Volts)

Combined Signal

Amplitude (Volts)

E m E c

f cf m Frequency(H z)

Frequency(H z)

(fc-fm)fc(fc+fm)f md c

Amplitude (Volts) E c

E /2m E /2m

Gain of Filter

0

1

Frequency(H z)

(fc-fm)fc(fc+fm)Frequency(H z)

f m

E /2m E /2m

E cAmplitude Input (Volts)

Amplitude GainK>1

(H z)Amplitude (Volts)

(fc-fm)fc(fc+fm)Frequency(H z)

f m

1Antenna Gain

0

Amplitude (Volts)

(fc-fm)fc(fc+fm) Frequency(H z)

AMPLIFIER

ANTENNA

Voltage (Volts)

Time(Sec.)

Low FrequencyInformation (blue)

High FrequencyCarrier (red)

Amplifier


derivative of the modulating signal. These methods are different for narrow and wideband angle modulation. We shall consider the methods one after the other.

2.4.1 Narrowband angle modulation: Taking our cue from the expression for narrowband angle modulation whose spectrum resembles that of an amplitude-modulated signal, we may use a modulator to produce such narrowband angle modulation. In case of frequency modulation, we have the integral ∫m(t) dt inside the angle. If m(t) is cos (ωmt) then the integration produces sin (ωmt). For narrowband modulation this integrated signal is multiplied with the carrier to produce the desired modulation. For phase modulation the angle varies directly with m(t). So m(t) is directly multiplied to the carrier. The block diagram for narrowband angle modulator is shown in figure 2.13.

Fig. 2.13. Block diagram for narrowband angle modulation.

2.4.2 Wideband Angle Modulation: When the modulation index β is large, i.e., β >> 1, then the simple expression for the angle-modulated wave no longer holds. The number of sidebands increases and modulation can be generated either directly or indirectly. In the indirect method, a narrowband angle modulated signal is first generated by the usual method of narrowband angle modulation technique. Then the narrowband angle modulated carrier is passed through a frequency multiplier that enhances both the frequency deviation as well as the unmodulated carrier frequency. The block diagram is shown in Figure 2.14

m(t)

Integrator

Oscillator

FM

FM Mixer Adder


Fig. 2.14. Indirect method of wideband angle modulation.

The narrowband angle modulated carrier is

y(t) = A cos (nw t + nj[m(t)])c c

where φ[m(t)] is the part of the argument that is being modulated by the carrier. For FM the derivative of φ[m(t)] with respect to time is proportional to the modulating signal while for PM φ[m(t)] is proportional to the message or modulating voltage. As the deviation in frequency is augmented by the multiplier, the carrier frequency is also amplified n times as seen from the following expression:

y(t) = A cos (nw t + nj[m(t)])c c

The instantaneous frequency becomes w = nw + n[dj(t)/ dt] = nw + nbm(t)1 c c

The multiplication of the carrier is not desirable. So the carrier frequency is adjusted to its original value ωc by using frequency translation. Frequency translation means passing the frequency multiplier output through a mixer which has a carrier of frequency [(n − 1)ωc] as its other input so that two the sidebands [(2n − 1)ωc + nβm(t)] and [ωc + nβm(t)] are produced. After passing through a suitable bandpass filter the wideband angle-modulated signal sA(t) = Ac cos (ωct + n φ[m(t)]) is obtained. Mixing only relocates the wideband FM (or PM) without affecting the frequency deviation.

In the direct method a voltage-controlled reactance is used to generate the wideband angle-modulated signal. The basic principle depends on the ability to vary the reactance of a device by the application of the modulating voltage. In a tank circuit consisting of parallel combination of an inductance and a capacitance, the resonant frequency or frequency of oscillation f = 1/√LC

Narrow band FM/PM generator

Frequencymultiplier

Mixer BPF

Oscillator


depends on the values of the capacitor C and inductor L. If any one of the elements can be varied directly with the modulating voltage, then the oscillator frequency will also vary with the modulating voltage as desired for producing angle modulation. Any controlled electrical or electronic phenomenon that provides capacitance variation can be used as a voltage variable reactance across a tank circuit. The tank circuit is first tuned to the unmodulated carrier frequency. The larger the voltage variation from zero the larger is the reactance variation from its unmodulated value. The frequency of oscillation varies accordingly. At the carrier frequency the oscillation is due to the fixed capacitance. For modulation, the variable reactance is superposed on this capacitance. There are various electronic devices that produce voltage variable reactances. These are the field effect transistor (FET), the bipolar junction transistor (BJT), the vacuum tube, the varactor diode, etc. Varactor diodes are usually used in the reverse biased condition. The oscillators on which the reactance modulator operates cannot be crystal controlled. However, this voltage variable oscillator must have the stability inherent to a crystal-controlled oscillator if it is part of a commercial transmitter. Any drift in the stability in the carrier frequency must be controlled giving it a high degree of frequency stability. This frequency stabilization of the reactance modulator may be achieved by a process, which is very similar to the widely used automatic frequency control (AFC) system.

The FET has a capacitance C and a resistance R in its biasing arm as shown in figure 2.15. The circuit must offer a pure reactive impedance across its output terminals A-A'. Basic FET reactance modulator acts as a three terminal reactance that may be connected across the tank circuit. The value of the reactance is proportional to the transconductance g of the FET. This m

transconductance varies with the gate bias. If the modulating signal is superposed on the FET bias, then it will vary with the transconductance.

Figure 2.15: Circuit diagram of a FET reactance modulator.

C

R

Xcibi

D

SG Z

vb

A’

A

o


In order that the output impedance of the FET circuit is purely reactive, the components should be selected in such a way that the following conditions are satisfied:

(i) The bias current ib is small compared to the drain current I or ib << i.(ii). The drain-to-gate impedance X is very large compared to the gate-to-c

source impedance. Here X > R.If a voltage e is applied between the c

drain source terminals of the FET resulting in a current i in the drain, then the impedance seen between the terminals AA' is Z = v/i. This impedance will be purely reactive (capacitive or inductive) if the above criteria are satisfied. Now the gate-to-source voltage v = ibR = Rv/[R − g

jXc] and the FET drain current is given by

i = g v = v g R/[R − jX ]. m g m c

Therefore, the impedance isZ = v / I = 1 / (g R / [R jX ])m c

= (1 / g ) / [R jX ] / Rm c

= (1 / g ) / [R jX / R]m c

If X > R then Z − j [X /R g ] c c m

and the equivalent reactance is X = X /g R = 1/(2 π fC ) eq c m eq

and the equivalent capacitance is C = RC g . eq m

The equivalent capacitance depends on the device transconductance and hence can be varied by bias. The capacitance is originally adjusted to any value by varying R and C.

If R << X , then the voltage v between the course and drain is not 90° out of c g

phase with the applied voltage v. There are three other variations of this basic reactance modulator. In all cases the drain current far exceeds the bias current and the drain-to-gate impedance is much larger than the gate-to-source impedance. If R-C components are used in the biasing arm then the output impedance is purely capacitive with C = RC g as shown earlier. The eq m

dimension is purely capacitive as R in ohms and gm in siemens cancel each other dimensionally. C has the dimension of capacitance. In this case the eq


the resistance is between the gate and source while the capacitance is between the drain and gate. If R and C are reversed with R coming between gate and drain and capacitance between source and gate with R >> X then c

the impedance between terminals A-A' is purely inductive with equivalent inductance L = RC/g . Instead of R-C combination L-R combination may be eq m

taken. For R between the gate and drain, L between the source and gate and with the condition that X > R, Z is inductive with equivalent inductance L = L eq

L/Rg . With R and L reversed and X < R, Z is capacitive with equivalent m L

capacitance C = g L/R. eq m

The varactor diodes are used frequently in the frequency modulator circuit (in Figure 2.16). They are often used in conjunction with a reactance modulator to

Fig. 2.16 Varactor diode frequency modulator.

Provide automatic frequency correction of the FM modulator. The p-n diode is reverse biased to produce a voltage varying capacitive effect. The modulating voltage is applied in series with the reverse bias hence the junction capacitance of the diode varies with the modulating voltage. This simple reactance modulator has the disadvantage of being a two-terminal device. Therefore, it is limited in its applications except for AFC and remote tuning.

2.5 Modulators

There are two types of FM modulators - direct and indirect. Direct FM involves varying the frequency of the carrier directly by the modulating input. Indirect FM involves directly altering the phase of the carrier based on the input (this is actually a form of direct phase modulation.

To oscillator tank circuit

A F in varactor diode

GND

Cc RFC

Cb(RF)

-Vb


2.5.1 Varactor Diode Frequency Modulator

Figure 2.17: Varactor diode Frequency Modulator

Figure 2.19 Varactor diode circuit for Phase modulation.

This circuit in figure 2.17 deviates the frequency of the crystal oscillator using the diode. R1 and R2 develop a DC voltage across the diode which reverse biases it. The voltage across the diode determines the frequency of the oscillations. Positive inputs increase the reverse bias, decrease the diode capacitance and thus increase the oscillation frequency. Similarly, negative inputs decrease the oscillation frequency. The use of a crystal oscillator means that the output waveform is very stable, but this is only the case if the frequency deviations are kept very small. Thus, the varactor diode modulator can only be used in limited applications. A varactor diode circuit for indirect FM is shown in figure 2.18.

The modulating signal varies the capacitance of the diode, which then changes the phase shift incurred by the carrier input and thus changes the phase of the output signal.

Vcc

R1

Crystal FMoutput

Modulatinginput

R2VD1

CrystalOscillator

Input

R1

R2

R1

ModulatingSignalInput

L1

PhaseModulated

Output


Because the phase of the carrier is shifted, the resulting signal has a frequency which is more stable than in the direct FM case.

2.5.2 Voltage Controlled Oscillator (VCO)The second method of direct FM involves the use of a voltage controlled oscillator, which is depicted in figure 2.19 below;

Figure 2.19 Voltage controlled oscillator block diagram

The capacitor repeatedly charges and discharges under the control of the current source/sink. The amount of current supplied by this module is determined by V and by the resistor R. Since the amount of current in

determines the rate of capacitor charging, the resistor effectively controls the period of the output. The capacitance C also controls the rate of charging. The capacitor voltage is the input to the Schmitt trigger which changes the mode of the current source/sink when a certain threshold is reached. The capacitor voltage then heads in the opposite direction, generating a triangular wave. The output of the Schmitt trigger provides the square wave output. These signals can then be low-pass filtered to provide a sinusoidal FM signal. The major limitation of the voltage controlled oscillator is that it can only work for a small range of frequencies. For instance, the 566 IC VCO only works a frequencies up to 1MHz.

2.6 Frequency Modulated (FM) TransmitterThe diagram below shows the signals at various stages through an Frequency Modulated (FM) transmitter.

5V

R

Vin

Current

Source/Sink

BufferSchmitt

TriggerInverter

Triangular

Wave Output

Square Wave

Output

C


Figure 2.20 FM Transmitter Block diagram.

1. Audio Stage: Amplifies (increases) the weak signal coming from the microphone.

2. Modulator: The audio (or data) signal is modulated onto the radio frequency carrier in this modulator stage. Modulation can be by varying the amplitude (or height) of the carrier known as amplitude modulation (am) or by slightly changing its frequency waveform known as Frequency Modulation (fm).

3. Frequency Generator or Oscillator: The Frequency generation stage (often known as the oscillator) defines the frequency on which the transmitter will operate. Incorrect setting of this stage can easily result in operation outside of the amateur band, and hence interference to other (non-amateur) radio users. The Foundation Licence only permits the use of commercially available equipment or commercial kits built strictly in accordance with the instructions. The Foundation

` Licence does NOT permit you to design and build your own transmitters.

4. RF Power Amplifier: The power amplification of the radio signal is carried out in the final stage of the block diagram. It makes the signal stronger so that it can be transmitted into the aerial. The r.f. power amplifier output must be connected to a correctly matched antenna (the “Load”) to work properly. Use of the wrong antenna, or no antenna, can result in damage to the transmitter.

1 - Audio Stage2 - Modulator (FM)3 - Radio Frequency Generator4 - Radio Frequency Power Amplifier

1 2

3

4


2.6.1 Crosby direct FM transmitter If a crystal oscillator is used to provide the carrier signal, the frequency cannot be varied too much (this is a characteristic of crystal oscillators). Thus, crystal oscillators cannot be used in broadcast FM, but other oscillators can suffer from frequency drift. An automatic frequency control (AFC) circuit is used in conjunction with a non-crystal oscillator to ensure that the frequency drift is minimal. Figure 2.20 shows a Crosby direct FM transmitter which contains an AFC loop. The frequency modulator shown can be a VCO since the oscillator frequency as much lower than the actual transmission frequency. In this example, the oscillator centre frequency is 5.1MHz which is multiplied by 18 before transmission to give ft = 91.8MHz. When the frequency is multiplied, so are the frequency and phase deviations. However, the modulating input frequency is obviously unchanged, so the modulation index is multiplied by 18. The maximum frequency deviation at the output is 75kHz, so the maximum allowed deviation at the modulator output is

Δf = 75 /18 =4.1667HzSince the maximum input frequency is f = 15kHz for broadcast FM, the m

modulation index must be β = Δf / f reduces the amount of phase variationm

Figure 2.21: Crosby Direct Fm Transmitter

ModulatingSignal Input

5.1MHz

Frequency Modulator& Master Oscillator

3x 2x 3x

Frequency Multipliers

30.6MHz 91.8.MHz

28.6MHz

Mixer

Buffer and2 x Multiplier

CrystalReferenceOscillator

14.3MHz

LPF

AFC Loop

Discriminatortuned to 2MHz

BPF


The AFC loop aims to increase the stability of the output without using a crystal oscillator in the modulator. The modulated carrier signal is mixed with a crystal reference signal in a non-linear device. The band-pass filter provides the difference in frequency between the master oscillator and the crystal oscillator and this signal is fed into the frequency discriminator. The frequency discriminator produces a voltage proportional to the difference between the input frequency and its resonant frequency. Its resonant frequency is 2MHz, which will allow it to detect low frequency variations in the carrier. The output voltage of the frequency discriminator is added to the modulating input to correct for frequency deviations at the output. The low-pass filter ensures that the frequency discriminator does not correspond to the frequency deviation in the FM signal thereby preventing the modulating input from being completely cancelled.

2.6.2 Amstrong Indirect Fm Transmitter:Indirect transmitters have no need for an AFC circuit because the frequency of the crystal is not directly varied. This means that indirect transmitters provide a very stable output, since the crystal frequency does not vary with operating conditions. Figure 2.22 shows the block diagram for an Armstrong indirect FM transmitter. This works by using a suppressed carrier amplitude modulator and adding a phase shifted carrier to this signal. The effect of this is shown in figure 2.23, where the A signal is the output and the B signal the AM input. The output experiences both phase and amplitude modulation. The amplitude modulation can be reduced by using a carrier much larger than the peak signal amplitude, as shown in figure 2.24. However, this reduces the amount of phase variation.


Figure 2.22 Armstrong Indirect FM Transmitter

Figure 2.23 Phase modulation using amplitude.

Figure 2.24 Better phase modulation with less Amplitude

CrystalCarrier

Oscillator

BufferAmplifer

Combiningnetwork

BalancedAmplitudeModulator

o90 PhaseShifter

ModulatingSignal Input fm

FrequencyMultipliers

72x

72x Mixer

BufferAmplifier

CrystalOscillator

13.15kHz

200kHz

Amplitude

A

B

Amplitude

Time

A

B


The disadvantage of this method is the limited phase shift it can provide. The rest of figure 2.22 shows the frequency shifting to the FM broadcast band by means of frequency multiplication (by a factor of 72), frequency shifting and frequency multiplication again. This also multiplies the amount of phase shift at the antenna, allowing the required phase shift to be produced by a small phase variation at the modulator output. It is worthy of note that a phase modulator can be used as a frequency modulator if the input signal is integrated with respect to time.

2.6.3 General Operation of an Fm Transmitter:Before the information signal is applied to the modulator, only in the FM transmitter is the signal passed through a preemphasis stage. Preemphasis distorts the signal by amplifying high frequencies more than low frequencies, i.e., the high frequencies are "emphasized" before modulation. The purpose of this signal distortion in the FM transmitter is to facilitate later on in the FM receiver the detection of these high frequencies of the signal in the presence of much high-frequency noise generated in the FM demodulator in the receiver. See figure 2.25.


Frequency(Hz)

(f -2f ) (f -f ) f (f +f ) (f +2f ) - Frequencyc m c c c c m c m

(Hz)

(f -2f ) (f -f ) f (f +f ) (f +2f ) Frequencyc m c c c c m c m

(Hz)

EcJ0(m)

EcJ (m)1

EcJ (m)2

EcJ (m)1

EcJ (m)2

Ec

fc Frequency(Hz)

Frequency(Hz)

Frequency(Hz)

Frequency(Hz)

Amplitude (Volts)

fm

fm

Amplitude (Volts)

Antenna Gain1

0

fm (f -2f ) (f -f ) f (f +f ) (f +2f )Frequencyc m c c c c m c m

(Hz)

Amplitude (Volts)

Amplitude (Volts)

fm

Em

fm

Amplitude (Volts)Em

1

Gain

fm

Amplitude (Volts)

PREEMPHASIS

FMMODULATOR

AMPLIFIER

ANTENNA

Voltage (Volts)

Amplitude1 Time(Sec.)

Low Frequencyinformation

Preemphasis amplifies high frequenciesto overcome high-frequency noise

in FM receiver

Voltage (Volts)

Time(Sec.)


Voltage (Volts)

Time(Sec.)


High FrequencyCarrier

Voltage (Volts)

Time(Sec.)

Voltage (Volts)

Combined SignalV(t) =E COS[2 f t+m SIN(2pf t)]o c r mp

(fm << fc)

Combined Signal

Time(Sec.)

Antenna passes only high frequencies.

Voltage (Volts)

Combined Signal

Time(Sec.)

Figure 2.25 General Operation of an FM Transmitter.


CHAPTER THREE

RECEIVERS

3.0 Introduction Radio Frequency (RF):There are two general kinds of signals that can be received by a radio receiver. They are the modulated RF signals that carry speech, music, or other audio energy and the continuous wave signals that are bursts of RF energy conveying messages by means of coded (dot/dash) signals. The process of recovering intelligence from an RF signal is called detection, and the circuit in which it occurs is called a detector. The detector recovers the intelligence from the carrier and makes it available for direct use or for further amplification. In an FM receiver, the detector is usually called a discriminator. An RF signal diminishes in strength at a very rapid rate after it leaves the transmitting antenna. Many RF signals of various frequencies are crowded into the radio frequency spectrum. Therefore, some means must be used to both select and amplify the desired signal. This is accomplished by an RF amplifier. It is included in the receiver to sharpen the selectivity (the ability to choose one frequency out of many) and to increase the sensitivity (the ability to respond to very weak signals). The RF amplifier normally uses tunable circuits to select the desired signal. It contains transistors, electron or integrated circuits (IC) to amplify the signal to a usable level. The signal level of the output of a detector, with or without an RF amplifier, is generally very low. To build up the signal level to a useful value that will operate headphones, a loudspeaker, a teletypewriter, or data devices (one or more AF amplifiers) are used in the receiver.

3.1 Radio Wave Reception: Electrical Resonant CircuitsThe first stage of most radio receivers comprises of some sort of electrical resonant circuit, the workings of which will need to be understood for a better understanding of RF signal reception.

3.1.1 Pure Resistive Circuit:An ac flows through a resistance of R ohms, see Figure 3.1. From ohms law we know that V = IR. Thus for a pure resistance, the potential difference R

across it, V , is IN PHASE with the current flow through it.R

I IN PHASE with VR


Figure 3.1 Phase Diagram for Pure Resistance

shows the curve for a sinusoidal current (I), which is flowing through a coil of inductance L henrys. It can be shown that the current lags the applied voltage by 90°. I LAGS VL

Figure 3.2 Phase Diagram for Pure Inductance

Inductive Reactance. Reactance/Frequency Graph. Figure 3.3 is the reactance – frequency graph for an inductor.V / I = 2πfLL

V / I is called the INDUCTIVE REACTANCE, X , and is measured in ohmsL L

X = 2πfLL

3.1.2 Pure Inductive Circuit:Figure 3.2

R

I

VR

VR

IVR

VR

I

I

IVR

VL

II

VL

VR

VL

VL

IL

I


Figure 3.3: Effect of Frequency on Inductive Reactance

Pure Capacitive CircuitFigure 3.4 shows the curve for a voltage (Vc) developed across a pure capacitor of capacitance C farads. It can be shown that the current leads the applied voltage by

o90 .

Figure 3.4: Phase Diagram for Pure Capacitance

Figure 3.5 is the reactance frequency graph for a capacitor.V /I = 1/2πFCc

V /I is called the CAPACITIVE REACTANCE, X , and is measured in ohmscc

X = ½ πFCc

=X α1/Fc

c I

Vc

Vc

Vc I

I

Vc

I

0

xL


Figure 3.5 Effect of Frequency on Capacitive Reactance

.

3.1.5 Series CircuitA coil, of self inductance L henrys and resistance R ohms, is connected to a capacitor of C farads. An emf of e volts and of variable frequency is connected to the circuit. Figure 3.6 shows the circuit details

Figure 3.6 Series LCR Circuit and Phase Diagram

X

0F

c

R L C

I VV V

e

V

=

Ф

R L C

L XL

VC

I

VL VC-e

VR RI

I

VC XI C

=

=


A phase diagram for the circuit is also shown in Figure 3.6. In this the potential difference (pd) across L is taken as greater than that across C and therefore the applied voltage leads the input current by the phase angle. The expression E / I is called the IMPEDANCE, Z of the circuit and is measured in ohms.

2 2 1/2Z = [R + (X - X ) ]L C

Resonance: When V = V , φ = 0 i.e., the input current is IN PHASE with the L C

applied voltage. In this special condition, the circuit is said to be at RESONANCE.As V = V then I X = I i.e. X = XL C L XC L C

Z is a minimum and is equal to R (from above equation).Resonant Frequency: The frequency at which X = X may be determined L C

as follows: X = XL C1/2

2πFL = 1 / 2π[FC]This value of frequency is denoted by

F = 1 /2 π LCO

Response CurveAt frequencies other than the resonant frequency, VL is not equal to VC and the impedance of the circuit is higher than that at resonance, see Figure 3.7. For an applied voltage of constant amplitude, the current (rms value, I) varies as the frequency of the supply changes, see Figure 3.8. The curve shown in Figure 3.8 is called a RESPONSE CURVE.

Variation of Impedance with Frequency Figure 3.7

0 F

R

FO

Z


Figure 3.8 Va

BandwidthThe BANDWIDTH, B, of the circuit is the difference between the two frequencies either side of resonance at which the current has fallen to 0.707 of its maximum value, see Figure 3.9.

Figure 3.9 Bandwidth in a Series LCR Circuit

riation of Current with Frequency

The bandwidth, B = F – F2 1

The sharpness of the response curve over a range of frequencies near resonance indicates the SELECTIVITY of the circuit. Selectivity is the ability of a tuned circuit to respond strongly to its resonant frequency and to give a poor response to other frequencies either side of resonance. A sharp

Selectivity

0 Fo F

I max

I

0.707

B 0

I

Imax

Imax

F0

I

F1 F2F


response curve indicates high selectivity; poor selectivity is indicated by a flat response curve. For good selectivity, a circuit should have a low value of R and a high L\C ratio.

Figure 3.9 Narrow Bandwidth/Good Selectivity

Figure 3.10 Wide Bandwidth/ Poor Selectivity

3.1.6 Parallel CircuitA coil, of self-inductance L henrys and resistance R ohms, is connected across a capacitor of C farads. An emf of e volt and of variable frequency is connected to the circuit, see Figure 3.11. This type of parallel ac circuit is very common in radio equipments and has many important applications.

B F

I

FB

I


Figure 3.11 Parallel LCR Circuit

The pd across the coil, the phasor sum of VR and VL, is equal to the pd across the capacitor, VC. The supply current is the vector sum of IL and IC. A phase diagram for the circuit is shown in Figure 3.12. For the condition shown, the supply current LAGS the applied voltage by a phase angle of degrees and the circuit is therefore INDUCTIVE (I > I ).L C

Figure 3.12 Phase Diagram for a Parallel LCR Circuit

For a certain value of frequency, I is in phase with E, i.e. the circuit is at RESONANCE. Once again it can be shown that the value of the Resonant Frequency (F ) is given by:O

1/2F = 1 /2 π [LC]O

At resonance, the impedance of a parallel circuit is a maximum and the supply current is a minimum. This circuit arrangement is called a REJECTOR circuit.

I R L

V

e

L

R VL

IC

VCI

VL VE C

IC

VR IL

I

Ф


SelectivityThis is defined in the same way as for a series tuned circuit; namely, the ability of the circuit to respond strongly to the required signal, which is at the resonant frequency, and to give a poor response to all other signals. At resonance, the supply current is a minimum and the impedance is maximum. If the circuit is mis-tuned either side of resonance, e.g. by altering the value of C, the supply current increases and the impedance decreases, see Figure 3.13 and Figure 3.14

Figure 3.13 Variation in Current with Frequency

Figure 3.14 Variation in Impedance with Frequency

Z

FFO

I

Fo F

I


BandwidthParallel circuits reject signals near to the resonant frequency. The BANDWIDTH of the circuit is the difference between the two frequencies, either side of resonance, at which the voltage has fallen to 0.707 of its maximum value. See Figure 3.15

Figure 3.15 Bandwidth in a Parallel LCR Circuit

3.2 The TRF or Tuned Radio Frequency ReceiverThe TRF, or Tuned Radio Frequency receiver, became popular as soon as the electronics industry got to the point where it was possible to build amplifiers cheaply enoug. TRF receivers are probably the simplest designed radio receiver available today. Figure 3.16 shows the block diagram of the three-stage TRF receiver that includes an RF stage, a detector stage and an audio stage. Two or three RF amplifiers are required to filter and amplify the received signal to a level sufficient to drive the detector stage. The detector converts RF signals directly to information. An audio stage amplifies the information signals to a usable level. TRF receivers are simple and have a relatively high sensitivity. However, they have 3 distinct disadvantages:

1. The bandwidth is inconsistent and varies with center frequency when tuned over a wide range of input frequencies. As frequency increases, the bandwidth (f/Q) increases. Thus, the selectivity of the input filter changes over any appreciable range of input frequencies.

F F F F

max

0.707

V

Voltage

maxV

201


Figure 3.16: TRF receiver block diagram

2. Instability due to large number of RF amplifiers all tuned to the same center frequency. High frequency, multi stage amplifiers are susceptible to breaking into oscillation3. The gains are not uniform over a very wide frequency range. The nonuniform L/C ratios of the transformer-coupled tank circuits in the RF amplifiers

3.3 Superheterodyne ReceiverThe nonuniform selectivity of the TRF receiver led to the development of the superheterodyne receiver. It is still used today for a wide variety of radio communication services because its gain, selectivity and sensitivity characteristics are superior to those of other receiver configurations. Heterodyne means to mix two frequencies together in a nonlinear device or to transmit one frequency to another using nonlinear mixing. So the superhet’s significant feature is that the signal in the IF portion of the radio stays at a constant frequency regardless of what station you tune to. This is done by heterodyning or beating two signals. Heterodyning is so important to radio that we have to look at it some more. Consider the circuit of Figure 4.18. We have a box containing some circuitry, and two inputs into the box; one is a 100 Hz sine wave, the other a 1000 Hz sine wave Assuming there is something inside the box , the two input signals will usually somehow combine into the output. There are two main possibilities:

RF stage

Receive antenna RF stage

RF signal

Detector stage

Audio stage

Audio amplifiers

Audio detector

Audio frequencies

RF amp.l

Antenna coupling network

RF amp.

RF amp.

Speaker

Ganged Capacitors


(i) If the circuitry in the box contains only resistors, inductors, and capacitors, it is called a linear circuit. In linear circuits, the output is proportional to the inputs;

Figure 3.17. Mixing two signals in some circuit

there is nothing in the output which did not come from the input. This is just a way of saying that, if 100 Hz and 1000 Hz go in, then only 100 Hz and 1000 Hz can come out.

(ii) But if the circuitry in the box also contains some diodes, transistors, tubes, or other non-linear components, then this becomes a different ball game as the signals can come out that did not go in.

Non-linear circuits can distort; they can change the wave shape of the sine waves going in. So the 100-Hz signal could now produce harmonics of 200, 300, 400, or more Hz, while the 1000-Hz signal could now have harmonics at 2000, 3000, Hz. etc. Much more important for us, though, is that the two input signals can interact with each other. This process is called heterodyning or beating. When two signals interact like this, they produce new signals whose frequencies are the sum and difference of the original two signals. In our case, the sum would be 1100 Hz (1000 + 100), and the difference would be 900 Hz (1000 - 100). These new frequencies would be called heterodynes. As usual, things are just a bit more complicated. The distortion harmonics also produce sums and differences. For example, the 200 Hz harmonic of the 100-Hz signal could heterodyne with the 3000 Hz harmonic of the 1000-Hz signal to produce 2800 and 3200 Hz, and so on. Fortunately, the harmonics are usually smaller than the fundamentals, and so these heterodynes are also smaller than the main ones at 1100 and 900 Hz. At a first glance, you may think this heterodyning is a terrible complication. But remember that, without heterodyning, the superheterodyne receiver would be impossible, and radio and TV reception would be a lot worse today. Figure 3.18 shows the block diagram of a superheterodyne receiver. There are five sections to a superheterodyne receiver:

100 Hz

1000 HzCircuitry Output?


1. RF section: This consists of a preselector and an amplifier. The preselector is a broad-tuned bandpass filter with an adjustable center frequency used to reject unwanted radio frequency (image frequency) and to reduce the noise bandwidth. The RF amplifier determines the sensitivity of the receiver and a predominant factor in determining the noise figure for the receiver.

Fig

ure

3.1

8: B

lock

dia

gra

m o

f s

uperh

ete

rodyn

e r

ece

iverIF

am

pli

fie

rs

(str

ip)

Ban

dp

ass

filt

er

IF s

ecti

on

M

ixe

r/c

on

ve

rte

r s

ec

tio

n

Mix

er

Lo

cal

oscllato

r

RF

am

plifi

ers

P

resele

cto

r

An

ten

na

Gan

ged

tu

nin

g

RF

sig

na

l

RF

se

cti

on

Sp

ea

ke

r

IF s

ign

al

Au

dio

am

plifi

er

secti

on

Au

dio

d

ete

cto

r

Au

dio

dete

cto

rsecti

on

Au

dio

a

mp

lifi

ers

Au

dio

fr

eq

uen

cie

s


2. Mixer/converter section: This consists of a radio-frequency oscillator and a mixer. The choice of oscillator depends on the stability and accuracy desired. The mixer is a nonlinear device to convert radio frequencies to intermediate frequencies (i.e. heterodyning process). The shape of the envelope, the bandwidth and the original information contained in the envelope remains unchanged although the carrier and sideband frequencies are translated from RF to IF.3. IF section: It consists of a series of IF amplifiers and bandpass filters to achieve most of the receiver gain and selectivity. The IF is always lower than the RF because it is easier and less expensive to construct high-gain, stable amplifiers for low-frequency signals. The IF amplifiers are also less likely to oscillate than their RF counterparts4. Detector section: It converts the IF signals back to the original source information (demodulation). It can be as simple as a single diode or as complex as a PLL or balanced demodulator.5. Audio amplifier section: This comprises several cascaded audio amplifiers and one or more speakers

3.3.1 Receiver OperationFrequency conversion: Frequency conversion in the mixer stage is identical to frequency conversion in the modulator except that in the receiver, the frequencies are down-converted rather than up-converted. Mixer: In the mixer, the RF signals are combined with the local oscillator frequency.Local Oscillator: The local oscillator is designed such that its frequency of oscillation is always above or below the desired RF carrier by an amount equal to the IF center frequency. Therefore, the difference of RF and oscillator frequency is always equal to the IF frequency. The adjustments for the center frequency of the preselector and the local oscillator frequency are gang tuned (the two adjustments are tied together so that single adjustment will change the center frequency of the preselector and at the same time, change local oscillator). When local oscillator frequency is tuned above the RF, it is called high-side injection. When local oscillator is tuned below the RF, it is called low-side injection.The mathematical expression of the local oscillator frequency is given as follows:High-side injection: f = f + f lo FR IF

Low-side injection: f = f − f lo RF IF


The illustration of the frequency conversion process for an AM broadcast-band superheterodyne receiver using high-side injection is shown in figure 3.19:

Figure 3.19: Superheterodyne receiver RF-to-IF conversion

Image frequencyAn image frequency is any frequency other than the selected radio frequency carrier that will produce a cross-product frequency that is equal to the intermediate frequency if allowed to enter a receiver and mix with the local oscillator It is equivalent to a second radio frequency that will produce an IF that will interfere with the IF from the desired radio frequency. If the selected

Preselector

(535 kHz to

565 kHz)

Receiver RF input (535 kHz to 1605 kHz)

Tuned to center frequency of

channel 2 (550 kHz) with a

30 kHz bandwidth

Preselector

outputs

Preselector blocks all but three RF channels

Channel 1 Channel 2 Channel 3

535 540 545 550 555 560 565 kHz

Mixer/converter Local oscillator

(1005 kHz)

IF Filters

(450 kHz to

460 kHz)

440 445 450 445 460 465 470 kHz

Channel 3 Channel 2 Channel 1

Channel 2

450 445 460 kHz

IF Filter

output

channel 2

only

1005 kHz-535 kHz = 470 kHz

1005 kHz-540 kHz = 470 kHz

1005 kHz-545 kHz = 460 kHz

1005 kHz-550 kHz = 455 kHz

1005 kHz-555 kHz = 450 kHz

1005 kHz-560 kHz = 445 kHz

1005 kHz-565 kHz = 440 kHz

(1005-(535 to 565) kHz

Mixer/co nerter outputs (channels 1,2 and 3)v

Channel 1

Channel 2

Channel 3


RF carrier and its image frequency enter a receiver at a same time, they both mix with the local oscillator frequency and produce difference

Consequently, two different stations are received and demodulated simultaneously. Figure 3.20 shows the relative frequency spectrum for the RF, IF, local oscillator and image frequencies for a superheterodyne receiver using high-side ejection:

Figure 3.20: Image frequency

For a radio frequency to produce a cross product equal to IF, it must be displaced from local oscillator frequency by a value equal to the IF.With high-side ejection, the selected RF is below the local oscillator by amount equal to the IF. Therefore, the image frequency is the radio frequency that is located in the IF frequency above the local oscillator as shown above. i.e.

f = f + f = f + 2 f Im lo IF RF IF

The higher the IF, the farther away the image frequency is from the desired radio frequency. Therefore, for better image frequency rejection, a high IF is preferred. However, the higher the IF, the more difficult is to build stable amplifiers with high gain. i.e. there is a trade-off when selecting the IF for a radio receiver (image-frequency rejection vs. IF gain and stability)

3.3.3 Image-frequency rejection ratioThe image-frequency rejection ratio (IFRR) is a numerical measure of the ability of a preselector to reject the image frequency. The mathematical representation of IFRR is given as,

2 2 1/2IFRR = (1+ Q ρ )

frequencies that are equal to the IF.

IF2f

IFIF

IF

f f

RF LO Image Frequency


where ρ = (f / f ) - (f /f ) im RF RF im

Q= quality factor of a preselector

Once an image frequency has down-converted to IF, it cannot be removed. Thus, to reject the image frequency, it has to be blocked prior to the mixer stage. I.e. the bandwidth of the preselector must be sufficiently narrow to prevent image frequency from entering the receiver.

3.4 Double-conversion ReceiversAs stated before, for good image-frequency rejection, a relatively high IF is desired. However, for high-gain selective amplifiers that are stable, a low IF is necessary. The solution for this problem is to use two intermediate frequencies. i.e. by using double conversion AM receiver:

Figure 3.21: Double-conversion AM receiver

The first IF is a relatively high frequency for good image rejection. The second IF is a relatively low frequency for good selectivity and easy amplification.

3.4.1 Net Receiver GainNet receiver gain is simply the ratio of the demodulator signal level at the output of the receiver to the RF signal level at the input to the receiver In essence, net receiver gain is the dB sum of all gains to the receiver minus the dB sum of all losses. Figure 3.22 shows the gains and losses found in a

RF stage 1st detector stage 2nd detector stage IF amplifier stage

2nd IF

amplifiers To audio detector

Bandpass

filter

2nd IF 2nd detector

mixer/converter 1st detector

mixer/ converter Bandpass

filter

1st IF

1st local oscillator

2nd local oscillator

RF amplifier and

preselector

Antenna


Figure 3.22: Receiver gains and losses

3.4.2 Practical analysis of Receiver operation.Example: Figure. 3.23 shows a superhet AM radio tuned to a radio station at 880 kHz. Coming into the antenna is not just this station’s signal, but also signals from all sorts of other stations radio, TV, radar, etc. The tuned circuits in the RF section remove most of the undesired signals, but not all, so that the signal coming into the mixer is mostly 880 kHz, but still has many other signals at nearby frequencies.

typical radio receiver: G dB = gains dB − losses dBwhere gains = RF amplifier gain + IF amplifier gain + audio amplifier gainand losses = preselector loss + mixer loss + detector loss

The mixer is a nonlinear circuit; it receives this combined signal, but it also gets a 1335 kHz signal from the oscillator below it. Since it is nonlinear, it heterodynes these signals. There are a lot of different signals going in so it produces a lot of heterodynes, but the most important ones are the sum and difference of the desired station at 880 kHz, and the oscillator signal at 1335 kHz. This gives us 2215 kHz, the sum, and 455 kHz, the difference. But note that the tuned circuits in the IF section are all tuned to 455 kHz, so they keep the 455 kHz signal and reject the others. By the time signal gets to the detector, the filtering has been pretty much completed, and the signal is almost pure 455 kHz (plus any nearby sidebands.

Antenna

Loss Gain

Preselector

Loss Gain Loss Gain

RF

amplifier

Mixer-converter

IF

amplifiersDetector

Audio

amplifier

Local

oscillator

Audio output power Receiver input power


Figure 3.23. Superhet with a 455 kHz IF, tuned to 880 kHz

fIF

Now, suppose we re-tune the radio to a different station, say one at 770 kHz. We re-tune the RF tuned circuits, but these only do a rough job of removing faraway signals, we also re-tune the oscillator to 1225 kHz. The difference between 1225 kHz and 770 kHz is again 455 kHz. And so the IF section again amplifies the resulting signal, without having to be itself re-tuned. So the trick when changing stations is to re-tune the RF circuits, and also re-tune the oscillator so the difference frequency between the station you want, and the oscillator, stays at 455 kHz. Since the RF tuning adjustment is not that critical, it is possible to use a single knob to adjust all the tuned circuits at the same time, without having to worry about whether all of them are right on target. FM broadcast receivers usually use 10.7 MHz IF, and other IF frequencies are also used in other kinds of receivers.If we let f be the frequency of the station we want, and F be the IF station IF

frequency, then the oscillator, the oscillator frequency f should beosc

f = f + fosc station IF

But it’s also possible to letf = f − osc station

Either way, the difference between f and f is equal to the IF frequency f , station osc IF

so either will work.

880 kHz and other stations mostly

880 kHz

All 455 kHzMostly 1335 + 880 kHz = 2215 kHz

and 1335 - 880 kHz = 455 kHz

tuned to

880 kHzMixer

455 kHz

IF

Amp

AF

Amp

RF

Amp 1335 kHz

Local

Oscillator mostly 455 kHz

880 kHz

tuned to tuned to 455 kHz

tuned to Detector

Speaker


3.4.3 The Image FrequencyThe radio in figure 4.18 is tuned to 880 kHz, has a 455 kHz IF, and an oscillator frequency of 1335 kHz. Here we see that 1335 kHz – 880 kHz = 455 kHz. So far, so good. But suppose there was a station at 1790 kHz. Look at the following calculation: 1790 kHz – 1335 kHz = 455 kHz In other words, the difference between the new station at 1790 kHz and the 1335 kHz oscillator frequency is also 455 kHz. This new radio station could also now be heard, though not as well as the one at 880 kHz because the RF tuned circuits largely remove it. But if it were strong enough, it would come through anyway. The 1790 kHz frequency is called the image frequency. The image frequency is calculated as follows:

Desired station 880 kHz + IF frequency +455 kHzOscillator frequency 1335 kHz + IF frequency +455 kHzImage frequency 1790 kHzThat is, the image frequency f is f = f ± 2 f image image desired station IF

We used the ± sign in the equation because in some radios the oscillator could also be below the desired station frequency; in that case, the image frequency would be below the oscillator frequency, and we would need the minus sign. This brings us to a problem bandwidth; “In theory, at least, we could get the bandwidth as narrow as we want, simply by going to a lower IF frequency.” But if we do that, then the image frequency gets closer to the desired frequency, and then the RF tuned circuits may not be able to get rid of it. To get better selectivity and lower bandwidth, lower the IF frequency and to get better rejection of the image frequency, raise the IF frequency. This is particularly a problem with high-frequency receivers intended to receive narrow-band signals.

3.5 Double Conversion Super Heterodyne ReceiverConsider an FM receiver for 146.94 MHz. Since the bandwidth of FM signals on this frequency is typically only 10 or 15 kHz, a low IF frequency (such as 455 kHz or even less) would be ideal. But then the image would be at 146.94 MHz + (2 × 455 kHz) = 147.85 MHZ which is not even 1% away from the desired frequency. There is no way that a typical RF tuned circuit could keep the image out as such we need a tremendous Q to do it. Typical receivers solve the problem one of two ways. A few use a much higher IF frequency


(around 10 MHz), but with special crystal or ceramic filters which can achieve the narrow bandwidth even at this higher IF frequency. But a much more common alternative is to use two separate IF sections and double conversion. Figure 3.24 shows the block diagram of a double-conversion superhet to receive 146.94 MHZ. Since 10.7 MHz and 455 kHz IF transformers are not very expensive many communications radios use them as well, and we show them here.To receive 146.94 MHz, the first oscillator runs at;

146.94 - 10.7 MHZ = 136.24 MHZ The oscillator could be either 10.7MHz above the desired signal, or 10.7 MHZ but here we chose to use the lower frequency. The second oscillator and mixer converts the 10.7 MHz first IF signal to 455 kHz by using an oscillator at;

10.7 MHz + 0.455 MHZ = 11.155 MHz.By using two IF frequencies, the double-conversion receiver solves our two problems. The high first IF frequency does not provide much selectivity, but it

Figure 3.24 Double-conversion superheterodyne Receiver

helps to eliminate the image. Since the image frequency is at:f = f − 2 fimage desired station IF

The minus sign used here indicates that the oscillator is below the desired signal, so the image must be even farther below that. The image frequency becomes;

146.94 MHz − (2 × 10.7 MHz) = 125.54 MHZwhich is far enough away from 146.94 that the RF tuned circuits can remove it (or at least significantly reduce it). The second IF frequency of 455 kHz, on the other hand, is low enough that even transformers with reasonable Q can

Antenna

146.94 MHz 10.7 MHZ

RE

Section

1

Mixer

1

IF

2Mixer

2IF

Detector

AF

Amp

Speaker

2Oscillator

1Oscillator

11.155

St St nd nd

ndSt

157.64 MHz MHz

455 kHz


provide a narrow bandwidth. Incidentally, suppose we wanted to use a similar circuit to receive 145.015 MHz instead of 146.94 MHZ. This circuit would not do, and for an interesting reason: The 11.155 MHz signal from the second oscillator goes into the second mixer, and the mixer is intentionally non-linear (to produce a heterodyne.) Hence it also generates harmonics of all the signals going in. It turns out that the 13th harmonic of 11.155 MHz is exactly 145.015 MHz. Although this harmonic is weak, a slight amount of it will still sneak back into the RF stage, and fool the receiver into thinking there is a weak, unmodulated signal at that frequency. Unless your desired signal is substantially stronger than this false signal it will not be heard. The solution in this case is to change the second oscillator frequency from

10.7 + 455 kHz to 10.7 - 455 kHz, or 10.245 MHZ. This new oscillator frequency has harmonics at different places; while this removes the birdie at 145.015 MHz, it introduces birdies elsewhere, such as 143.43 (which is the 14th harmonic of 10.245 MHz.) Designing wide-band receivers (receivers designed to receive a wide range of frequencies) is thus always a problem; there are always some false signal somewhere, and the designer has to carefully choose his oscillator and IF frequencies to try to place the birdies at places where they will not interfere with normal operation.

3.5.1 The ConverterMany radios combine the mixer and the oscillator into one circuit called the converter. Figure 3.25 shows the converter used in many popular

Figure 3.25 An AM receiver converter

1C 1 1L R

C 1

R R

C2 Q 3

3 2

5 C

V

1 IF

Transformer

T

4

Oscillator coil

C

2

IF Output

T

Antenna coil

V cc

cc

st

1


AM broadcast radios; there are several useful techniques that are worth mentioning. L and C are the RF tuned circuit, with C being the tuning 1 1 1

capacitor. But L does several different jobs. The top part of the winding 1

(above the ground connection) is the part that actually resonates with the capacitor; the bottom part (connecting to C ) acts as the secondary of a 2

transformer, to bring the signal from L to the transistor without loading down 1

the tuned circuit (which would reduce the Q.) At the same time, L is also the 1

antenna. As we have seen, coils or loops of wire can act as antennas; in this case, L is wound on a ferrite core (a ceramic core which contains ferrous 1

metal particles); the core helps to pick up the energy from the radio signal, and concentrate it in the coil. The transistor also does two jobs. First, it oscillates at a frequency 455 kHz above the signal you want to pick up. To do this, we need an amplifier with positive feedback. The transistor is the amplifier, with its output coming out of the collector, going through oscillator coil T , and back through C into the emitter of the transistor. Capacitor C 1 3 4

resonates with the secondary of this coil to control the oscillator frequency. At the same time, however, the transistor amplifies the RF signal coming from the antenna coil, and mixes it with the oscillator signal. Because the transistor is non-linear, it also produces the sum and difference heterodyne frequencies. The primary of IF transformer T and capacitor C resonate at 2 5

455 kHz, and send the 455 kHz difference frequency on to the IF amplifier. Notice that T and T both use taps on one winding (the tap is a third 1 2

connection part way into the winding.) This reduces the loading on the resonant circuit, and keeps the Q from being lowered.

3.5.2 Receiver Sensitivity and Selectivity Sensitivity: Sensitivity describes the ability of a radio to pick up weak signals. Our crystal radio has low sensitivity, because it can only pick up really strong stations. Sensitivity has to be judged in relation to noise. Just picking up a station is not enough, if the station is so noisy that it is not pleasant to listen to. Spec sheets and advertising literature usually specify receiver sensitivity by measuring how much voltage from the antenna (usually measured in microvolts) is required to make the desired signal (usually the sound out of the speaker) 10 times or 100 times stronger than the noise. This ratio of signal to noise is then called the signal-to-noise ratio; a decent radio might provide a 10-to-1 or 100-to-1 signal-to- noise ratio with an antenna signal of under 1 microvolt. This definition of sensitivity is useful for most radio receivers, but not for a crystal


radio. Typical receivers have amplifiers which produce noise when tuned to a weak or no station, so measuring the signal-to-noise ratio is possible. Desired signal (usually the sound out of the speaker) 10 times or 100 times stronger than the noise. This ratio of signal to noise is then called the signal-to-noise ratio; a decent radio might provide a 10-to-1 or 100-to-1 signal-to- noise ratio with an antenna signal of under 1 microvolt. This definition of sensitivity is useful for most radio receivers, but not for a crystal radio. Typical receivers have amplifiers which produce noise when tuned to a weak or no station, so measuring the signal-to-noise ratio is possible. With a crystal set, however, there is really no noise to be heard from the headphones, so measuring the ratio is tough. Still, you need several hundred thousand microvolts of antenna signal to hear anything at all, so sensitivity is clearly bad.

Figure 3.26: Actual and ideal resonant response

(i). A flat top; this lets the carrier and all sidebands get through the tuned circuit equally well.

(ii). Steep skirts; the skirt is the vertical part at the left and right. Steep skirts make sure that the response drops very fast, so that no adjacent stations get through.

(iii). A definite bandwidth; ideally this should be just as wide as the bandwidth of the signal we are trying to receive - no more, and no less. The actual tuned circuit response on the left of Figure 4.21a has none of these.

0.8

0.6

0.4

0.2

0

1

Re

sp

on

se

Frequency


The top is not flat, so the carrier can get through, but the farther out a sideband is, the less of it gets through. The sides are not steep enough to keep out adjacent stations, since even pretty far away from the peak, the curve still has fairly high response. And finally, there is no definite bandwidth to the circuit. The top can be flatten out a bit by widening the whole curve. The bandwidth of a tuned circuit determines the relative width of the curve. The bandwidth in turn is determined by the Q or Quality Factor of the circuit. The higher the Q, the narrower the response is; the lower the Q, the wider it is. Unfortunately, there is a conflict here a lower Q would flatten out the top and thus provide more even transmission of the desired signal, but it also widens the bandpass and makes the skirts even less steep. It now becomes obvious that a single tuned circuit simply cannot provide the right selectivity for a radio, even under ideal conditions.

3.5.3 Superheterodyne Sensitivity and SelectivityBy splitting the amplification into separate sections, a superhet can provide more total gain without the danger of signals feeding back and causing oscillation. Further, because the IF amplifier does not need to be re-tuned each time you change stations, it can be optimized, and carefully adjusted at the factory, to provide the best possible bandpass characteristics — steep skirts and a flat top. But there is more to it than that. Recall our definition of the Quality factor Q of a resonant circuit:

Q = resonant frequency / 3−db bandwidth BThe 3-db bandwidth doesn’t really specify how well the circuit will reject adjacent stations; in order to reject such interference, the response of the tuned circuit has to be 30, 40, or even more db down from the top of the curve at the frequencies of any adjacent stations. We can rewrite the above equation as

3−db bandwidth BW = resonant frequency / QTo get a small bandwidth, we have to either make the resonant frequency small, or make the Q big. But in most resonant circuits, there is a limit on how big Q can get; it is affected by the resistance of the rest of the circuit, and is should be 20 or 30. Increasing Q is not a feasible approach to making the bandwidth small. So, to get a small bandwidth, it would help if you could make the resonant frequency small. But in a TRF receiver, you must tune the resonant circuits to the frequency of the station you want to receive, so you really can not make the resonant frequency small to get a good bandwidth. The bandwidth will change as you tune to different stations, further


complicating the design. As against this, in a superhet all the selectivity is obtained in the IF stages, and their frequency stays the same for all stations.

3.6 Summary of Operation of AM and Superheterodyne Receiver(a) Operation of TRF AM Receiver:The main point of interest here is the structure of the AM detector. The basic structure of the AM detector and of the AM modulator are the same: a nonlinear device followed by a bandpass filter. In the detector, the nonlinear device reproduces the original signal sinusoid from the AM-modulated carrier and also produces many unnecessary sinusoid of other frequencies; the filter removes these unnecessary sinusoid and passes the original information signal. The main difference between the AM modulator and the AM detector is the frequency band passed by the filter: the modulator passes a band at high radio frequencies; the detector passes a band at low audio frequencies. see figure 3.27.


Figure 3.27 Operation of AM and Superheterodyne Receiver

ANTENNA

RE AMP. & bandpass filter

DETECTOR IDEAL NON-

LINEAR

DEVICE

BAND-PASSFILTER

AUDIOAMPLIFIER

SPEAKER

Amplitude (Volts)

Time (Sec.)

Voltage (Volts)

Voltage (Volts)

Time (Sec.)

Time (Sec.)

Time (Sec.)

(fC-f ) Frequency (Hz)

(Hz)

Frequency (Hz)

dc fm

Gain

0

1

Amplitude

m fC fC+fm)(

Amplitude (Volts)

-

(fC-f )m fC fC+fm)( Frequency

(fC f )m fC fC+fm)( Frequency

Amplitude (Volts)

Frequency (Hz)

Frequency (Hz)

Amplitude (Volts)

Amplitude (Volts)

fm

fm

Voltage (Volts)

Voltage (Volts)

Voltage (Volts)

Time (Sec.)


(b) Operational summary of Superheterodyne AM ReceiverThe structure of this receiver and that of the TRF receiver are very similar. The main difference is the frequency range in which most of the signal amplification is done. The TRF receiver amplifies the signal at the same high radio frequencies at which it is received initially by the antenna. Unfortunately, amplification at these high frequencies is inefficient, i.e., the amplifier gains are low. To correct this error, the superheterodyne receiver does most of its signal amplification at a lower "intermediate frequency" band for greater efficiency. Since this intermediate frequency band is the fixed passband of the filter in the IF amplifier, each incoming signal must be lowered to this fixed intermediate frequency band by using a frequency converter, which consists of a mixer (which is a nonlinear device) connected to an oscillator of variable frequency. This is called the "local oscillator." By changing the oscillator frequency appropriately, any station's signal can be lowered to the given intermediate frequency range for efficient amplification. This is shown in figure 3.28.


Figure 3.28 Operation Of Superheterodyne AM Receiver

ANTENNA

RFAMP. & bandpass filter

DEVICE (mixer)

DETECTORIDEAL NON-

LINEARDEVICE

BAND-PASSFILTER

AUDIOAMPLIFIER

SPEAKER

LO

Voltage (volts)

Time (Sec.)

Amplitude (Volts)

Amplitude (Volts)

Amplitude (Volts)

Amplitude (Volts)

Amplitude (Volts)

Amplitude (Volts)

Amplitude (Volts)

Filter selects information signal

Amplitude

Amplitude

Filter selects band around fithe intermediate frequency

Amplitude (Volts)

(fC-fm) Frequency (Hz)

Frequency (Hz)

( ) Frequency (Hz)

Frequency (Hz)

Frequency (Hz)

(Hz)

Frequency (Hz)

Frequency (Hz)

Frequency (Hz)

Frequency (Hz)

dc

Gain

0

1

Voltage (volts)

Time (Sec.)

Time (Sec.)

Voltage (volts)

Voltage (volts)

Voltage (volts)

Voltage (volts)

Voltage (volts)

Time (Sec.)

Time (Sec.)

Time (Sec.)

Time (Sec.)

Time (Sec.)

fC (fC fm)+

fLOAmplitude (Volts)

(fC-fm) fC (fC- fm)

(fm < fI < fC fLO ) fLO

(f-fm) fI (fI+fm) fC-fm fC ( )fC fm+

O

(f I-fm) f ( )If fm+

fm (f -fm)I fI (fI+fm)

fm

fm

IF amplifier

FILTER

IF AMPLIFIERPERSE


3.7 Mesurement Of Amplitude Modulatlated WavesWith a d.s.b. a.m. Wave form, the parameter that is generally measured in the depth of modulation (m). This can be measured by means of a cathode ray oscilloscope (c. r. o.), a modulation meter, or a true r. m. s. responding ammeter or voltmeter.

3.7.1 Use of a C. R. O.An amplitude- modulated wave can be displayed on a c.r.o. in two different ways. The signal and the time base set to operate at the frequency of the modulating signal or perhaps two or three times the modulating frequency if more than one cycle of the envelop is to be displayed. The modulation envelop is then stationary, and an amplitude- modulation envelop, such as that shown in fig 3.29, in displayed.

An alternative method, that makes the detection of waveform distortion easier, is to connect the modulated wave to the Y- input and terminals the modulating originalss to the X- input terminals with the internal time base switched off (see fig 1.11a). The resulting display in then trapezoidal, as shown at fig b. it can be shown that the depth of modulation of the displayed waveform is given by (a-b)/ (a+b) percent. The accuracy of the methods is limited mainly by the lack of discrimination the results from the need to reduce the peak- to- peak variation of the modulated wave into the area of the c. r. o. screen. The reduction in measurement accuracy is particularly

Fig. 3.29 Measurement of modulating factor using a C.R.O.

b

(b)

a

Modulating Signal

Modulating wave

C. R.Ox Y

(a)


noticeable when there is little difference between the maximum a and minimum b dimensions in centimeters, i.e. when the modulation factor is small.

3.7.2 Use of a modulator AmmeterA modulation ammeter is an instrument which has been designed for the direct measurement of modulation depth. Essentially the instrument consists of a radio receiver with a direct- coupled diode detector. If the measurement procedure specified by the manufacturer is followed carefully, accurate measurements of modulation depth can be carried out.

3.7.3 Use of an R. M. S. responding ammeterThe r. m. s. value of an amplitude- modulated current wave is, given by

2I = I N (1 + ½ m ) ................................... (3.1)C

Where I is the r. m. s. value of the unmodulated current waveform. The C

measurement procedure is as follows. The r. m. s. value of the current with no modulation applied is measured first then the modulation is applied, and the new indication of the true r. m. s. responding ammeter is noted. The modulation factor can be calculated using equation (3.1), or in practice, read off from a graph of modulation factor plotted against the ratio I/I .c

Example: In a measurement of modulation depth using an r. m. s. responding ammeter the unmodulated current was 50A, use the graph in figure 3.30. to determine the depth of modulation if the r. m. s. current with modulation applied is (a) 55A, (b) 50. 5A

Figure 3.30 the relationship between I/Ic of the r. m. s. current of amplitude- modulated and unmodulated waves and the modulation factor

Mo

du

lati

on

fa

cto

rm

1. 0

0. 90. 8

0. 7

0. 6

0. 5

0. 4

0. 3

0. 2

0. 1

0. 01.05 1.1 1.15 1.250 1.25 I/IC


Solution:

(a) I/I = 55/50 = 1.1c

Therefore, from the graph, Depth of modulation m = 65% (Ans)

(a) I/I = 50.5/50 = 1.01c

Therefore, depth of modulation m = 14% (Ans)

This method of measurement is capable of accurate result for higher value of modulation depth, out for smaller values below about 30%, the accuracy suffer because of lack of discrimination. Alternatively, if an instrument known as spectrum analyzer is available, the component displayed of the waveform can be individually displayed on the analyzer c.r.t. screen and their amplitudes measured. Fig 1.13b shows the kind of display to be expected. The required degree of linearity can then be quoted in terms of the maximum permissible amplitude of the intermodulation products.

Figure 3.3.1 (a) The signal waveform, (b) the spectrum diagram at the o/p of an ISB channel whose linearity is under test.

3.8 Receiver Test and MeasurementsMeasuring instrument used for receiver and transmitter tests and measurements includes signal generators, electronic voltmeters, power meters and multi- range moving- coil instruments. In addition, certain auxiliary pieces of equipment, such as dummy aerial, are regarded. Signal generators for use in receiver tests should be accurate to belter than 1% and should be directly calibrated. The output voltage should be precisely known and variable from 1mv upwards. It is convenient if the output can be varied using a control which is calibrated in decibels. Alternatively, an extra calibrated attenuator may be used.

Voltage

+

-(a)

Time

f1 f2

f21 f2-

2 f2 f1

f - f f + f2 1 2 1

-

(b)


Standard modulation frequencies which should be available are 400hz and less frequently used 1000hz. It's often useful to be able to vary the modulation between 50 Hz and a few thousand hertz. The standard modulation depth is 30% but it is convenient, additionally to be able to vary the modulation. The output impedance should be low; it is often 50Ω, sometimes 10Ω. The signal generator should be well screened so that signals cannot be coupled into the equipment under test except through the proper connection. Likewise, output from the generator should not be able to reach the equipment being tested through common main supply leads or in any other extraneous way. During any test on relievers the impedance at the receiver input terminals should be about the same as the impedance of the aerial system with which the receiver is likely to be used. The input impedance of communication relievers is commonly 75Ω.

This may substantially match the signal generator impedance. For 10Ω signal generator (figure 3.32(a) a 65Ω resistor series with the output suffices to provide a reasonable match. For a balanced input receiver the signal generator resistance and the additional input resistance should be balanced, i.e. divided between the two input lines. For broadcast- type receiver an “average” circuit shown in figure 3.32(b). This, over the range of frequencies from below 1Mhz to about 2.0MHz, roughly equates to the average aerial impedance likely to be encountered. Bearing in mind the wide variety of aerial type in use, it is clear that a large degree of approximation is involved.

Figure 3.32 Receiver Testing and input circuits

For a sound receiver the output should properly be measured and evaluated at a loudspeaker or telephone headset. To do this is very complicated and methods are not standardized. In practice, therefore the output is measures

Signal Gen

Signal

Gen

Receiver 65Ω

10Ω 75Ω

200PF20NF

Receiver

400PF 400Ω

(a)

(b)

C L RC


either as a power in a power meter, or as a voltage. Output power should be measures in a non – inductive resistance of ohmic value equal to the effective speech coil impedance at 400 hz. Standard output power for loudspeaker sets is usually 50mw: if the output is to be taken to a land line or, if the head phone operation is to take place in a noisy situation, the higher standard of 1mw may be adopted.

3.8.1 Measurement of A Frequency- Modulated WaveThe parameter of a frequency modulated wave that is usually measured is the frequency deviation. Commercial f. m. deviation meters are available but the measurement can be carried out by the CARRIER DISAPPEARANCE METHOD The amplitude of the c carrier frequency component of an fm.

wave is a function of the modulation index. The carrier voltage is zero for v values of modulation index of 2.405, 5.52, 8.65, e. t. c. If, for any one of these is known, the frequency deviation can be calculated using the following formula;

Kf = m f d f m

To measure the frequency deviation of an f. m. wave the signal is applied to an instrument known as the “spectrum analyzer”. The spectrum analyzer is an instrument which displays voltage to a base frequency (as opposed to a c. r.o. which displays voltage to a base of time). The spectrum analyzer therefore displays the spectrum diagram of the f. m. signal. It is adjusted to display only the carrier and the first- order side frequencies.

With the modulating frequency kept at a constant value, the amplitude of the modulating signal is increased from zero which varies the frequency deviation until the carrier first goes to zero. Then m = 2.405 and the frequency f

deviation can be calculated. Further increase in the modulating signal voltage will cause the carrier component to reappear and then again go to zero when the modulating index becomes 5.52.

For example, in a measurement of the frequency deviation of an f. m. signal, the frequency of a signal generator was not at 3KHz. Calculate the frequency deviation at (a) the first and (b) the second carrier disappearance.


Solution3

(a) m = 2.405 / 3 x 10 = Kf f d

3Kf = 2 405 x 3 x 10 = 7.215 KHz (Ans)d

3(b) Kf = 5.52 x 3 10 = 16. 56 KHZ (Ans)d

3.8.2 Measurement of Performance of Amplitude Modulated ReceiversA number of measurements can be carried out to determine the performance of a super heterodyne radio receiver. Some of these tests are appropriate for both amplitudes while others only apply to one type of receiver. In this treatment only the more important of the amplitude modulation receiver measurements will be described; these are adjacent channel ratio, and (d) image channel response ratio.

(a) Sensitivity: The sensitivity of an amplitude modulation radio receiver is the smallest input signal voltage, modulated to a depth of 30% by a 1000HZ (or 400HZ) tone, needed to produce 50mw output power with signal – to – noise ratio of 20dB. The circuit used to carry out a sensitivity measurement is shown in fig.3.33. The signal generator is set 30% modulation depth at the required frequency of measurement and its output voltage is set to about a value about 10dB above the expected Sensitivity.

Figure 3.33: Measurement of radio receiver sensitivity.

The audio: frequency gain of the receiver is the then set to approximately its half maximum position and the receiver is tuned to the measurement frequency. The signal generator frequency is then varied slightly to give the maximum reading on the output power meter. The input voltage producing the necessary audio output condition can now be determined. The input voltage is varied until the power meter indicates 50M.W; then the signal generator modulation is switched off and the power meter indication is noted say1mW. The output signal –to-noise ratio is now 10log x (50/P) dB. If this 10

ratio is not equal to the required 2.0dB the modulation of again signal

Signal

Generator

Receiver

Under text

Power Output

Meter


generator is switched on again and the input voltage to the receiver in increased or decreased as appropriate.

The A.F. gain is adjusted to obtain 50mW indication on the power meter before the modulation is again switched off and the new signal-to-noise ratio determined. This procedure is repeated until the required power output of 50mw is obtained together with 20dB signal-to-noise ratio. The input signal voltage giving the required output conditions is the sensitivity of the receiver.

(ii). Noise Factor: The noise factor F of a radio receiver is the ratio

F = (Noise Power appearing at the output of the Rx) / (that part of the above which is due to thermal agitation at the input terminals).

This definition of noise factor is, for most conditions, is equivalent to

F = (Input signal – to noise ratio) / (Output signal-to-noise ratio)

Figure 3.34: Measurement of radio receiver noise figure

Figure 3.34 shows the circuit used for the measurement of the noise generator of a receiver with the noise generator switched off, the indication of the power output meter is noted. The noise generator is then switched on and without altering any of the receiver controls; its noise output is increased until the indication of the power meter is exactly double its previous value. The noise output of the generator is directly proportional to the current indicated by an noise milli-ammeter and do the noise factor of the receiver is equal to

F = 20I R .......................... (3) a

Where I is the indication of the milli-ammeter and R is the (matched). a

impedance of the receiver and the noise generator . As is often the case at V.H.F. and at U.H.F., R = 50Ω, the noise factor of the receiver is equal to the milli-ammeter reading.

Noise Generator

Receiver Under Text

Power OutputMeter


For example, In a measurement of the noise factor of a 50Ω input impedance radio receiver the reading of the output power meter is doubled when the noise generator's milli-ammeter indicates 6mA. Calculate the noise factor of the receiver in dB.

Solution: F = 6 or 10log 6 = 7.78dB10

(c) Adjacent Channel SelectivityThe selectivity of a radio receiver is its ability to select the wanted signal present at the aerial. The selectivity curves given in figure 3.36 indicates how well the wanted rejects unwanted signal when the wanted signal is not present. This is of course, not of prime interest since the important factor is the adjacent channel voltage needed to adversely affect reception of the wanted signal. This feature of a receiver is expressed by its adjacent channel response ratio which can be measured using the arrangement shown in figure 3.35. With signal generator 2 producing zero output voltage, signal generator 1 is set to the required test frequency and then is modulated to a depth of 30%. With the input signal voltage at 10mV,

- 0Frequency off tune

Figure 3.36 plot of output power and frequency of tune

10mV

inp

ut

vo

ltag

e r

ed

to

p

rod

uce -

30d

B o

utp

ut

po

wer

+


Figure. 3.35: Measurement of radio receiver adjacent channel response ration

the a.f. gain of the receiver is adjusted to give an audio output power greater than 50mW but below the overload point. The modulation below the overload point. The modulation of signal generator 1 is then switched off. Signal generator 2 is than set to a frequency that is 9KHz above the test frequency and modulation to the signal of 30%. The output voltage of the signal generator 2 is then increased until the audio output power is 30dB less than the previous value. The adjacent channel response ratio of there voltages. The measurement can be carried our at a number of other frequencies and the results plotted in figure.

3.36 Image Channel Response RatioThe image channel response ratio (or rejection ratio) is the ratio: 20log (Input voltage at image frequency / Input voltage at signal frequency) 10

To produce the name audio output power the measurement can be carried out using the circuit given in figure 3.33 the signal generator and the receiver are each tuned the text frequency and the input voltage adjusted to given an audio output power 50mW. Then, without altering to the image frequency. The input voltage is then increased until 505mW audio output power is again registered by the power meter. The ratio response ratio is then, given by the ratio of the two necessary input voltages, expressed in dB.

3.3 Measurement of V.S.W.R. The V.S.W.R. on a mismatched transmission line can be determined by measuring the maximum and minimum voltages that are present on the line. In practice the measurement is generally carried out using an instrument known as a STANDING-WAVE INDICATOR. Measurement of V.S.W.R. not only shoes up the presence of reflection on a line but it also offers a most convenient method of determining the nature of the load impedance. The measurement procedure is as follows;

Signal

Signal

generator

generator

2

1Combining Power

networkoutputmeter

UnderReceiver

Test


The V.S.W.R. is measured and the voltage in Wavelength this from the load to the voltage minimum nearest to it is determined. The values obtained allow the magnitude and angle of the voltage reflection coefficient to be calculated. Then, using equation (3.3), then unknown load impedance can be worked out unfortunately, the arithmetic involved in the latter calculation is fairly lengthy and tedious, and it is customary to use a graphical aid known as the smith chart which simplifies the work. If the load impedance is “purely” restive, a much easier method of measurement is available. Suppose for example that E = R , = 3R . (Remember that R is always purely resistive at L L o o

radio frequency) then,

0ρ Z - Z = 3R - R = ½ Ov 1 0 0 0

Z + Z 3R + RL 0 o o

Therefore: S = 1 + Iρ I = 1 + ½ = 3v

1 - (ρ ) 1 - ½ v

Now suppose that Z = R = 1/3 RL L o

0ℓ = 1/3R - R = ½ 180v o o

1/3R + Ro o

and S = 1 + ½ = 3 as before 1- ½

It should be noted that the V.S.W.R is equal to the ratio R /Z or Z /R .L o o L

This simple relationship is always true provided the line losses are negligibly small and the load impedance is purely resistive.


CHAPTER FOUR

TRANSCEIVER AND SSB TECHNIQUES

4.0 Introduction A transceiver is a combination of transmitter and receiver in a single package. The term applies to wireless communications devices such as cellular telephone and cordless telephone sets, handheld two-way radios, and mobile two-way radios. In a radio transceiver, the receiver is silenced while transmitting. An electronic switch allows the transmitter and receiver to be connected to the same antenna, and prevents the transmitter output from damaging the receiver. With a transceiver of this kind, it is impossible to receive signals while transmitting. This transmission mode is called half duplex. Transmission and reception often, but not always, are done on the same frequency. Some transceivers are designed to allow reception of signals during transmission periods. This mode is known as full duplex, and requires that the transmitter and receiver operate on substantially different frequencies so the transmitted signal does not interfere with reception. Cellular and cordless telephone sets use this mode. Satellite communications networks often employ full-duplex transceivers at the surface-based subscriber points. The transmitted signal (transceiver-to-satellite) is called the uplink, and the received signal (satellite-to-transceiver) is called the downlink. Another mode of communication is called simplex, which a device can only act as a transmitter or receiver, but not both. Thus the direction of communication is constantly one way. Thus communication modes are: Simplex, Half-Duplex and Full-Duplex.

Transmission MediaTransmission media is classified into two groups: Guided and unguided.

Guided media. The waves are guided along a physical path, e.g.: twisted pair, coaxial cable and optical fiber.

Two-wire open line. Two-wire open line is the simplest transmission medium, which supports up to 50m transmissions with 19.2kbps. This type of medium must be protected from cross coupling (cross talk) of electrical signals, it is also susceptible to noise signals and electromagnetic radiation.


Duchie

Highlight

Twisted-pair line. Twisted pair is the ordinary copper wire that connects home and many business computers to the Telephone Company. To reduce cross talk or electromagnetic induction between pairs of wires, two insulated copper wires are twisted around each other. Each connection on twisted pair requires both wires. This type of media can support up to 1Mbps over short distance (100m). For some business locations, twisted pair is enclosed in a shield that functions as a ground. This is known as shielded twisted pair (shielded twisted pair or STP), which has protective screen to reduce signal interference effect. Ordinary wire to the home is unshielded twisted pair (Unshielded Twisted Pair or UTP), which is used in telephone and networks (data communication) communication.

Coaxial Cable. To overcome the skin effect, Coaxial cable use protective layers to shield the center conductor from external interference from the outer conductor and electromagnetic radiation. It can be used with various signal types and can reach several hundred meters in 10Mbps.

Optical Fiber. FO carries the transmission in the form of light beam in a glass fiber. A light wave has much wider bandwidth than electrical signal in a wire. It also immune from electromagnetic interference and cross talk, thus it can be used for high-speed transmission or low speed transmission in a noisy environment. FO can reach hundreds of Mbps

Unguided media. Provides means for transmitting electromagnetic waves but not guide them, e.g. propagation through air, vacuum and seawater.

Satellite. A microwave beam is transmitted to the satellite on board circuit (transponder), which then relayed to a pre-defined destination. Communication using satellite usually requires 2 channels, one for up-link and the other for downlink connection both will use extremely high frequency band. E.g. of the communication application using this type of medium is ATM machine with its VSAT (Very Small Aperture Terminal) and mobile cell phone.

Terrestrial Microwave. Terrestrial microwave links is widely used to provide communication links when it is too expensive to establish physical transmission medium. Terrestrial microwave link requires the existence of unobstructed line of sight and it can be used reliably over 50Km distance. E.g. of the application using this type of media would be the PSTN/Cell-phone provider transmission between ground stations in different provinces.


Radio link. Radio wave is almost similar with terrestrial microwave, but it over much shorter area coverage and usually used in distributed computer networks where it would be much too expensive to establish extensive wired connection.

4.1 Transceiver TypesMeter Transceiver: A meter transceiver is basically a two-way radio capable of both receiving and transmitting. A basic 2 meter radio makes use of the amateur radio band in the VHF spectrum and uses frequencies from 144.000 megahertz (MHz) to 148.000 MHz within North and South America, Hawaii, Asia and Oceania. Europe, Russia and Africa can make use of frequencies of 144.000 MHz to 146.000. Since 2 meter transceivers use the VHF frequencies, height means how far away it is possible to communicate clearly. To get the necessary height, repeaters are used and are located in skyscraper tops in cities or mountain range tops in country sides. Repeaters are meter transceivers that pick up a signal from a 2 meter transceiver and retransmit the received signal on their antenna at the same time as received and allow a 2 meter to transmit a long distance. If the repeater is high enough, reception is good for around 100 miles, though the usual repeater rate is for somewhere between 30 to 40 miles distance. A typical FM meter transceiver setup would have a 50 watt set and rooftop vertical antenna for transmission to the local repeater. Transceivers come with three main capabilities: scanners for listening only on airband frequencies, com-only transceivers for receiving and transmitting on airband, and nav-com transceivers for transmitting, receiving, and interpretations and displays of VHF omnidirectional range (VOR) signals for navigation. Most popular and most widely used of the types of transceivers are the com-only meter transceivers and, with headset adapters, they can even be used with aviation headsets in a cockpit. A feature called channel recall allows storage of around ten most frequently used frequencies to scroll through on a trip without having to program them into the unit on some transceivers. Emergency services make use of these types of transceivers as well; not only police and fire services, but also Red Cross shelters and ambulance services. The 2 meter transceivers and frequencies are most useful when mounted units and hand-held units can work together to spread emergency efforts over large areas of a community. Satellite communications to achieve longer distance communications are even possible with smaller transceivers like the 2 meter transceiver, which can share with 10 meter bands, 70 meter bands and even


microwave bands using cross-band repeating. Software modes on board can dictate a satellite's frequency at any given time from a published schedule and uplink and downlink from amateur radio satellites can achieve communication distances of up to 3,000 miles from low Earth satellites. From the higher orbit satellites, distances of up to 30,000 miles can be achieved via what are called satellite “footprints” and these higher flying satellites are basically just elliptically orbiting repeaters.

VHF Transceiver: A very high frequency (VHF) transceiver is a device that is composed of a transmitter and receiver that operates between 30 megahertz (MHz) to 300 megahertz (MHz). The wavelength of a VHF transceiver varies between 39.37 inches (1 m) to 393.70 inches (10 m), mainly depending on the frequency used. Wavelength combined with line-of-sight (LOS) propagation determines VHF devices such as walkie-talkies' and citizen band (CB) radios' receiving and transmitting range. VHF propagation is generally not affected by the ionosphere in the same manner high frequencies (HF) are. As a result of non-ionospheric interference VHF radio transmissions are restricted to a local area; which prevents cross-talk interference several thousand miles away. Propagation distances for VHF devices also depend on environmental topography, antenna height and several other factors. In order for VHF transceiver devices to effectively transmit and receive information with one another, LOS radio propagation should not be obstructed. Solid objects such as trees and buildings usually weaken or completely block LOS propagation. HF and ultra-high frequency (UHF) bands are often included in a VHF transceiver device to increase transmission reliability. Many countries have certain VHF bands restricted to navigational and emergency use. In some countries the VHF radio frequencies of 108 MHz to 118 MHz are reserved for navigational beacons; while 118 MHz to 137 MHz is used for air traffic control. The VHF frequency of 121.5 MHz is often used for emergency signals. VHF transceiver devices are also used in personal and business use. Personal use of VHF devices usually involves leisure activities where cellular devices are not appropriate. For businesses such as taxi cabs and other transportation industries, base station repeaters are used to extend a VHF device's communication range. Transceiver devices vary in aesthetics, radio bands and operating settings. Despite differences in models and settings, basic operating principles remain the same. Most VHF transceivers will have a push-to-talk button for easy and fast communication. The push-to-talk button on most transceivers


will allow a party to transmit or communicate to another party on the same frequency and channel. When using the button only one person at a time can transmit while the other is receiving. For greater peace-of-mind many transceiver devices such as walkie-talkies include encryption and privacy channel options. Without security options sensitive information can still be intercepted by an unauthorized third party. To secure a channel, the walkie-talkie's encryption function will generate a code or password to be used between parties. Another security option that is often used in conjunction with private codes is the use of voice scrambling.

UHF Transceiver: An ultra-high frequency (UHF) transceiver is a device which usually houses a transmitter and receiver operating between the radio frequencies of 300 megahertz (MHz) to 3 gigahertz (GHz). Depending on the frequency used, the corresponding wavelength of a transceiver using a UHF band ranges between 3.94 inches (10cm) to 3.28 feet (1m). Due to the relatively short wavelength, UHF transceivers such as walkie-talkies and citizen band (CB) radios are limited to a radius of several miles. The actual operating distance of the devices will largely depend on several factors including environmental topography, use of repeaters and antenna height. A UHF transceiver relies on line-of-sight radio propagation, which means the devices communicate with one another in a direct path. Physical objects such as trees and buildings will often weaken or even block line-of-sight propagation, decreasing communication reliability. To increase reliability, UHF transceivers bands such as high frequency (HF) and very high frequency (VHF). UHF and multi-band transceivers such as walkie-talkies and CB radios are used for short range communications between two or more parties. Walkie-talkies and CB radios are used by a variety of sectors including public, commercial and military. Public use may involve leisure activities that require communication mobile phones cannot provide due to a weak or non-existent signal. Some countries may reserve certain UHF frequencies for military use only and require a special permit to operate a UHF transceiver. In many commercial and military settings, base station repeaters are utilized to extend a UHF transceiver operating range. Operating instructions for a UHF transceiver will most likely vary due to differing device models and settings. While there are a few differences in how to access certain features in transceiver devices, most operating principles remain the same. For example, most walkie-talkies will have a push-to-talk button which allows a person to transmit or communicate with a device on the


same frequency and channel. The person will receive the message and will be able to respond after the incoming communication is done transmitting. Care should be taken while transmitting sensitive information. Interception of a radio transmission by a third party is entirely possible, especially if the channel is not encrypted or secure. For this reason many walkie-talkie manufacturers have implemented encrypted or privacy channel options. Generally a code or a password is either entered or generated to secure a transmission session between communicating parties. In addition to privacy codes, a voice scrambling function is offered in some transceivers to ensure maximum transmission security.

FM Transceiver: The FM transceiver is a type of radio transceiver that is capable of receiving and transmitting a frequency modulation (FM) signal. Equipment of this type ensures the signal is within a certain band range and can be easily picked up by other transceivers that are structured to receive and send FM signals. Equipment of this type is used in basic and sophisticated communication equipment used by the military and other organizations in various parts of the world. With the FM transceiver, the device is capable of sending and receiving frequency modulation signals. The nature of the signals may be voice communications, music, or any other type of audio transmission. Unlike an FM transmitter, which can only send signals on the FM receiver that is capable of receiving the frequency modulation broadcast, the FM transceiver is configured for both transmission and reception of signals within a certain bandwidth.

This makes the device ideal for a number of applications, ranging from enjoying conversations with people located halfway around the world as well as a providing a means to manage proprietary communications on protected bandwidths. Among the different types of FM transceivers, there are sets designed for basic as well as professional use. Other communication tools have largely replace the use of the FM transceiver in some applications, there are still areas of the world in which this particular type of equipment is used by professional organizations, including military and law enforcement units. Since using an FM transceiver is relatively simple, requiring nothing more than adjusting the gain and using the tuner on the equipment to find the right position on the band to send and receive, this remains a viable option, especially during natural disasters that may render other communication options such as telephone communications temporarily unavailable.


Transceiver Circuit: A transceiver circuit is electrical circuitry with the ability to both transmit and receive signals. Though transceiver use was originally confined to two-way radios in military and police applications, they now are incorporated into a wide range of consumer electronics, from lightweight consumer walkie-talkies and citizen's band (CB) radios, to cell phones, computer wireless networks, cordless telephones, high frequency (HF) and ultra-high frequency (UHF) radio transmitters, and more. Early forms of radio wave transceiver circuitry could only send signals or receive them, but not do both at the same time, known as simplex or half duplex circuits. Most modern transceiver circuits are duplex, however, allowing for simultaneous transmission of two signals over one channel, with reception of the signals at the same time. Devices virtually identical to transceivers in function are ransmitter-receivers, where separate circuitry exists inside a casing for each function of transmitting signals and receiving them. Transponders are another form of circuitry related to a transceiver circuit, where signals are transmitted and received simultaneously, but only in automated fashion, with one application being as a form of safety and identification beacon on aircraft. Transverters are another application of transceiver circuit technology. Amateur radio operators often use a transverter, which can convert HF or very high frequency (VHF) transceiver circuit signals to intermediate frequency (IF) ranges to amplify reception. Using a transceiver circuit in the past meant carrying on audio conversations that required taking turns sending and receiving voice messages, and standard cell phones and radio frequency (RF) radios today allow constant back-and-forth voice transmission.

As broadband transmission capability has advanced, fourth-generation (4G) smartphones and other devices now allow video transmission on transceiver circuits as well. If a transceiver circuit in a smartphone is in motion as someone rides on public transport or drives a car, maximum data transmission speed is 100 megabits per second (Mbit/s). A stationary user of a 4G transceiver-based device can send and receive signals at up to one gigabit per second however (Gbit/s), making video transmission practical on such devices for the first time in history. Such 4G transceiver circuit systems are also being built into laptop computers and other mobile devices as well. Every time someone purchases a telecommunications device in one form or another that incorporates current technology, they are likely buying a transceiver circuit. Transceivers are at the core of most modern


communications technology, and are built into everything from satellites to electronic keys for expensive automobiles that won't start unless the code transmission in the key housing is validated by the computer built into the car's ignition system. Even the radio frequency identification (RFID) chips built into some consumer product packaging to prevent theft and certain credit cards, contain transceivers for decoding, along with transponders to continuously send out information on the card or passport for scanners to read .If drawn on several pages, there will be labels on edges of the schematic indicating connection to other pages. For instance, “+Vcc” is a common positive direct current (DC) supply voltage. The negative side of the power supply is usually indicated by a small triangle with one tip pointing downward. A transmitter schematic indicates a stage usually with a crystal oscillator circuit, which is the frequency reference that controls the carrier generator for the transmitter. Very simple transmitters have one crystal-controlled stage that operates on a single frequency. Multiple-frequency transmitters usually employ one reference crystal with an integrated circuit that usually synthesizes the various frequencies for a multiple-channel transmitter.

The transmitter needs to have a fairly accurate crystal to make sure remote receivers will find the carrier it is sending out. Schematic symbols are accompanied by a single letter or a single identifier followed by a number. A resistor may be labeled as “R1,” a transistor as “Q1,” an integrated circuit as “IC1” or “U1,” and a capacitor as “C1.” A transceiver schematic also has abbreviations such as power supply unit (PSU), local oscillator (LO), receiver (RCVR), transmit (TX), crystal (XTAL), and many others. Standard transceivers can be placed on a desk, such as a base transceiver, while handheld transceivers are portable transceivers. Making a transceiver can be an interesting hobby. In the early days of radio, hobbyists and enthusiasts had fun building the electronics as well as the cabling for the antenna system. Usually, the bigger the antenna, the farther is the range of the signal. When using a transceiver, you have to know the needed receiver frequency and be able to set it on the transceiver. Digital controls allow the frequency to be preset. This way, you can select the right frequency to listen to or monitor.


4.2 Transceiver Operation

(a) AM Transmitter simplified block diagram.

Modern transceivers are based on superheterodyne (superhet) architecture. Prior to the advent of SSB in the mid-1950’s, an amateur HF station generally used separate transmitter and receiver: " A superhet receiver, usually single-conversion with 455 kHz IF. " An AM/CW transmitter consisting of a crystal oscillator or VFO, buffer/multipliers, driver, PA and modulator. The receiver and transmitter had no common subsystems other than the transmit/receive (T/R) relay and possibly an antenna tuner. The acceptance of the heterodyne SSB exciter with crystal or mechanical filters (a superhet in reverse) drove research into sharing RX and TX subsystems. Figure 4.1(a) and (b) shows the block diagrams of an AM and SSB transmitters. Early SSB stations featured separate receivers and transmitters. The transmitter’s antenna relay switched the antenna between RX and TX, and muted the receiver on transmit. Many transmitter-receiver pairs allowed one-knob “transceive” operation by tuning both the receiver and transmitter with the RX or TX VFO. Figure 4.2(a) and (b) shows a simple superhet receiver and SSB/CW receiver

Antenna

RF Power

Amplifier

Amplitude

Modulator

Driver/ Buffer

Speech

Amplifier

Carrier

Oscillator

Microphone

Tuning Dial - VFO

14.1 MHz

14.1 MHz14.1 MHz

audio audio

14.1 MHz

Class C for Audio higher efficiency

Isolates Osc & Amp

speech


(b) SSB Transmitter simplified block diagram.

Figure 4.1 Transmitter Block Diagrams

(a) Simple Superhet Receiver: frequency relationships

Antenna Microphone

Carrier

Oscillator

Balanced

Modulator

RF Power

Amplifier

(RF) 4.0 MHz

Speech

Amplifier

Filter Mixer

& FilterVFO

speech

14.103 MHz

14.103 MHz

(Linear Amplifier)

6.097

MHz rejected by filter

3 kHz audio

USB

LSB

10.1MHz

Tuning Dial

14. 1 MHz

double sideband

Lower Side Band = 3.997 MHz

Upper Side Band = 4.003 MHz

no carrier

4.003MHz

Up-converts signalto transmit frequency

Variable Freq.Oscillator VFO.Sets Transmit Frequency

selects sideband

RF RF IF AFIF AFIFTUNED CIRCUIT MIXER

AMPLIFIER DETECTOR AMPLIFIER

IF+RF

OSCILLATOR LOCAL

A.G.C AF


R F RXAmplifier Filier

Product Amplifier

Antenna

Detector Amplifier I F I F A F

Speaker,Phones

Oscillator

CarrierLocal

Oscillator

Mixer

(b)

Figure 4.2 Receiver Block Diagrams:

Basic SSB/CW Superhet Receiver

The Complete Transceiver Circuit.If we add the transmitter and receiver sections of the basic AM and SSB/CW together we will get a complete transceiver circuit shown in figure 4.3. The Tx/Rx relay routes antenna to Rx input or Tx output as required. Referring to figure 4.3a, The Carrier oscillator, IF filter and local oscillator are shared between receiver and transmitter. The Carrier oscillator feeds the carrier signal to the Balanced Modulator. The Mic audio is amplified and mixed the with carrier to yield the upper side band (USB) and lower side band signals. IF Filter passes USB and suppresses LSB. The Local oscillator is tuned to the required frequency.

The transmitter mixer mixes the IF with local oscillator output to yield USB TX signal. The RF power amplifier raises TX signal power.

Receiver AGC (automatic gain control): An AGC detector samples the average audio or IF output signal level, and feeds it back to the RF and/or IF stages to hold the gain constant over a range of input signal levels. The AGC line also drives the S-meter.Transmitter ALC (automatic level control): A reflectometer samples the forward and reflected power at the output of the RF power amplifier , and feeds it back to the transmit IF amplifier to level the transmitter output at a preset value and protect the transmitter against damage due to load mismatch. Automatic Antenna Tuner (Auto ATU): A T-network (series C – shunt L – series C) located between the antenna socket and the TX/RX relay. It can be


RF Power

Amplifier

TX

Mixer

I FAmplifier

Balanced

Modulator Speech

Amplifier

Product-

meker

Relay TXRX Local

Oscillator Auto

ATU

ANT S-Mixer

R FBandpass

Filters

R F

Amplifier RX

Mixer

I F Product

Filier

I F

Amplifier Detector A F

Amplifier

AGC Line

Receiver

Speaker,Phones

Carrier

Oscillator

Side

Tone

Osc Key

Transmitter

MicALCLine

ATU Control Line ATU Control Line

R F RXAmplifier

Product

Mixer Filier I F

Amplifier I F

Detector Amplifier A F

Receiver

TXFXRelay

ANT

Local

Oscillator

RF Power

Amplifier Mixer

TX

Carrier

Oscillator

Side Tone Osc

Speaker,Phones

Key

Transmitter

Mic

Speech

Amplifier

Balanced Modulator Amplifier

I F

switched out of signal path if desired. Auto ATU matches complex antenna impedance to the 50Ω load required by the transmitter. It will also provide near optimum noise matching for the receiver. Auto ATU is controlled by reflected-power signal from reflectometer in transmitter. RF Bandpass Filters (pre-selector filters) suppress image response, and protect receiver RF amplifier (pre-amp) against overload by strong out-of-band signals.

(a) SSB Transceiver

(b) SSB-CW Transceiver (a CW IF filter is narrower than the SSB filter)


RF Gain & Attenuator:

Transmit signal flow: Audio - Third IF kHz - 2nd IF MHZ - 1st IF MHz RF and Receive signal flow: RF - 1st IF MHz - 2nd - 3rd IF MHz - Audio. Almost all modern HF transceivers employ up-converting architecture. Many current transceivers have DSP (digital signal processing) at the final IF.

Figure 4.5 Audio Amplification

Audio Amplification: Demodulator output drives the pre-amplifier, the pre-amplifier may incorporate adjustable audio filter. Power amplifier typically delivers 2 ~ 5W at 10% THD (total harmonic distortion). Power amplifier drives internal speaker, external speaker or headset. Internal speaker muted

Figure 4.4 shows the gain controlled RF amplifier with front end RF attenuator. RF front-end attenuator is located between antenna input and preselector filter. The RF Gain control increases AGC bias on gain-controlled RF amplifier (and/or 1st IF amplifier in some designs); raises AGC threshold. Receiver dynamic range increases by amount of attenuation inserted. Usually, band noise is 10 to 12 dB above Rx noise floor; attenuation does not significantly degrade noise figure. Attenuator & RF Gain can be used together.

Figure 4.4 Gain-controlled RF amplifier with front end front end RF attenuator

R F

Antenna

R FAttenuator Preselector

Filter Amplifier

Low-pass

Filter to Mixer

AGC Line

DC

Amplifier

RFGain Control

Select

Loudspeaker

Pre-amplifier

Volume

Control

Power Amplifier


when external speaker or headset is plugged in. Figure 4.5 shows the audio amplification section of the transceiver.

4.3 Overview of Single Sideband 4.3.1 Introduction Single Sideband Modulation, SSBSSB modulation offers a far more effective solution for two way radio communication because it provides a significant improvement in efficiency. Single sideband modulation is widely used in the HF portion, or short wave portion of the radio spectrum for two way radio communication. There are many users of single sideband modulation. Many users requiring two way radio communications will use single sideband and they range from marine applications, generally HF point to point transmissions, military as well as radio amateurs or radio hams. Single sideband modulation or SSB is derived from amplitude modulation (AM) and SSB modulation overcomes a number of the disadvantages of AM. Single sideband modulation is normally used for voice transmission, but technically it can be used for many other applications where two way radio communication using analogue signals is required. As a result of its widespread use there are many items of radio communication equipment designed to use single sideband radio including: SSB receiver, SSB transmitter and SSB transceiver equipment's.

Single sideband, SSB modulation is basically a derivative of amplitude modulation, AM. By removing some of the components of the ordinary AM signal it is possible to significantly improve its efficiency. It is possible to see how an AM signal can be improved by looking at the spectrum of the signal. When a steady state carrier is modulated with an audio signal, for example a tone of 1 kHz, then two smaller signals are seen at frequencies 1 kHz above and below the main carrier. If the steady state tones are replaced with audio like that encountered with speech of music, these comprise many different frequencies and an audio spectrum with frequencies over a band of frequencies is seen. When modulated onto the carrier, these spectra are seen above and below the carrier. It can be seen that if the top frequency that is modulated onto the. carrier is 6 kHz, then the top spectra will extend to 6 kHz above and below the signa1. In other words the bandwidth occupied by the AM signal is twice the maximum frequency of the signal that is used to modulated the carrier, i.e. it is twice the bandwidth of the audio signal to be carried. Amplitude modulation is very inefficient from two points. The first is


that it occupies twice the bandwidth of the maximum audio frequency, and the second is that it is inefficient in terms of the power used. The carrier is a steady state signal and in itself carries no information, only providing a reference for the demodulation process. Single sideband modulation improves the efficiency of the transmission by removing some unnecessary elements. In the first instance, the carrier is removed - it can be re-introduced in the receiver, and secondly one sideband is removed - both sidebands are mirror images of one another and the carry the same information. This leaves only one sideband - hence the name Single Side Band/SSB.

SSB Receiver.While signals that use single sideband modulation are more efficient for two way radio communication and more effective than ordinary AM, they do require an increased level of complexity in the receiver. As SSB modulation has the carrier removed, this needs to be re-introduced in the receiver to be able to reconstitute the original audio. This is achieved using an internal oscillator called a Beat Frequency Oscillator (BFO) or Carrier.

Insertion Oscillator (CIO). This generates a carrier signal that can be mixed with the incoming SSB signal, thereby enabling the required audio to be recovered in the detector. Typically the SS8 detector itself uses a mixer circuit to combine the SSB modulation and the BFO signals. This circuit is often called a product detector because (like any RF mixer) the output is the product of the two inputs. It is necessary to introduce the carrier using the BFO/CIO on the same frequency relative to the SSB signal as the original carrier. Any deviation from this will cause the pitch of the recovered audio to change. Whilst errors of up to about 100 Hz are acceptable for communications applications including amateur radio, if music is to be transmitted the carrier must be reintroduced on exactly the correct frequency. This can be accomplished by transmitting a small amount of carrier, and using circuitry in the receiver to lock onto this.

When receiving SSB it is necessary to have a basic understanding of how a receiver works. Most radio receivers that will be used to receive SSB modulation will be of the superheterodyne type. Here the incoming signals are converted down to a fixed intermediate frequency. It is at this stage where the BFO signal is mixed with the incoming SSB signals. It is necessary to set the BFO to the correct frequency to receive the form of SSB, either LSB or


USB, that is expected. Many radio receivers will have a switch to select this, other receivers will have a BFO pitch control which effectively controls the frequency. The BF 0 needs to be positioned to be in the correct position for when the signal is in the centre of the receiver passband. This typically means that it will be on the side of the passband of the receiver. To position the BFO, tune the SSB signal in for the optimum strength, i.e. ensure it is in the centre of the passband, and then adjust the BFO frequency for the correct pitch of the signal. Once this has been done, then the main tuning control of the receiver can be used, and once a signal is audible with the correct pitch, then it is also in the centre of the receiver passband. Tuning an SSB signal with the BFO set is quite easy. First set the receiver to the SSB position or the BFO to ON, and then if there is a separate switch set the LSB/USB switch t6 the format that is expected and then gradual1y tune the receiver. Adjust the main tuning control so that the pitch is correct, and the signal should be comprehensible. If it is not possible to distinguish the sounds, then set the LSB/USB switch to the other position and re-adjust main tuning control if necessary to return the signal to the correct pitch, at which point the signal should be understandable. With a little practice it should be possible to easily tune in SSB signals.

Single sideband power measurementIt is often necessary to define the output power of a single sideband transmitter or single sideband transmission For example it is necessary to know the power of a transmitter sued for two way radio communication to enable its effectiveness to be judged for particular applications. Power measurement for an SSB signal is not as easy as it is for many other types of transmission because the actual output power is dependent upon the level of the modulating signal. To overcome this a measure known as the peak envelope power (PEP) is used. This takes the power of the RF enve10pe of the transmission and uses the peak level of the signa1 at any instant and it includes any components that may be present. Obviously this includes the sideband being used. but it also includes any residual carrier that may be transmitted. The level of the peak envelope power may be stated in Watts, or nowadays figures quoted in dBW or dBm may be used. These are simply the power levels relative to 1 VVatt or 1 milliwatt respectively. As an example a signal of 10 watts peak envelope power is 10 dB above a 1 Watt signal and therefore It has a power of 10 dBW. Similar logic can be used to determine powers in dBm.


SSB AdvantagesSingle sideband modulation is often compared to AM, of which it is a derivative. It has several advantages for two way radio communication that more than outweigh the additional complexity required in the SSB receiver and SSB transmitter required for its reception and transmission.1. As the carrier is not transmitted, this enables a 50% reduction in

transmitter power level for the same level of information carrying signal. (for an AM transmission using 100% modulation, half of the power is used in the carrier and a total of half the power in the two sideband - each sideband has a quarter of the power.)

2. As only one sideband is transmitted there is; a further reduction intransmitter power.

3. As only one sideband is transmitted the receiver bandwidth can be reduced by half. This improves the signal to noise ratio by a factor of two, i.e. 3 dB. because the narrower bandwidth used will allow through less noise and interference.

4.3.2 SSB Transmission.The “double side band with full carrier” (DSBFC) is the conventional amplitude modulation technique, in which both the side bands along with the carrier are transmitted This has been found as an uneconomical technique. The two side bands are exact “image” of each other, hence it is not necessary to transmit both the side bands. Usually one side band with or without carrier is transmitted. This is called “Single side band transmission. In the theory of amplitude modulation (AM), we have seen that a carrier and two sidebands (SB’s) are required for AM transmission. But it is not necessary to transmit all the three signals (1 carrier and 2 sidebands). The carrier or one of the sidebands may be removed (or attenuated). The SSB modulation is the fastest spreading form of analog modulation. The greatest advantage is its ability to transmit signals by using a very narrow band, width, very low power for the distances involved. For 100% modulation (m = 1), only 1/3rd of the total power is present in one of the sidebands, while 2/3rd power is carried by the carrier, which contains no information. Thus if the carrier and one of the sidebands is eliminated from the signal, the transmission will need only 1/6th of the total power. The Fig.4.6(a) shows double sideband with full carrier (DSBFC) and (b) shows double sideband with suppressed carrier (DSBSC) and (c) shows single sideband transmission with suppressed carrier (SSBSC). It can be noted that (c) requires only half the bandwidth (BW) as required to (a) and (b).


Figure 4.6 DSBSC Spectrum

The evolution of SSB amplitude modulation may be done in following steps:(i) The carrier contains no power and all the power is contained in the

sidebands.(ii) Therefore there is no need to transmit carrier. V.(iii) The modulated wave contains three frequencies, f , f +f and f -fc c m c m

(iv) Two sidebands are exact images of each other; since each is affected by changes in the modulating voltage via the exponent m EJ . Recall 2

that m is the modulation index and E the carrier voltage.(v) Therefore all the information may be transmitted by the use of one

sideband only, as the carrier is superfluous and the other sideband is redundant.

(vi) If the carrier is suppressed only the two sidebands power remains and 2

which is equal to = Pc.m /4 about 66% saving will be done. Recall that is the carrier power.

(vii) It one of the sidebands is also suppressed, the remaining power is Pc. 2

m /4 a further saving of 50% power will be achieved.The SSB system is not used for broadcasting due to following reasons.

(a)

(b)

( c)

Carrier

USBLSB

fc fm fc fc fm+

fc fm fc fm+

f

c

f

m+

USBLSB

USB

-

f f

-


(i) The SSB transmitters and receivers require an excellent frequency stability. Even a small shift in frequency, the quality of the transmitted signal is degraded. Thus it is not suitable for transmission of good quality music by SSB system.

(ii) This is not possible to design a tunable receiver oscillator with a very high frequency stability. However with the advent of ‘frequency’ synthesizers, this has become possible, but the synthesizers are very expensive. The major application of SSB system is in long distance radio telephone

4.3.3 Generation of SSBThe following are used for suppression of one of the two sidebands:1. Filter method2. Phase shift method3. Weaver (third) methodThe Balanced modulator suppresses the carrier. To obtain SSB signal, the un wanted sideband (frequency) is to be removed. All of the above three methods have the capability of removing any of the two sidebands.

4.3.4 Forms of amplitude modulationThe forms of amplitude modulations are:1. Double sideband with full carrier (DSBFC) or, A32. Double sideband with suppressed carrier (DSBSC) or, A5C3. Single sideband (SSB) techniques:

(i) Single side band with full carrier (SSBFC) or A3H.(ii) Single band with suppressed carrier (SSBSC) or A3J.(iii) Single side band with reduced carrier (SSBRC) or A3A.(iv) Independent side band (ISB)(v) Vestigial side band with full carrier (VSBFC).

4.3.5 Block diagram and analysis of SSBSC In SB&SC, power is saved by eliminating the carrier component. Further increases in the efficiency of transmission is possible by eliminating one more sideband since the two side band are images of each other, each is affected by changes in the modulating Voltage amplitude and each is equally affected by changes in modulating frequency which changes the frequency of side band itself. It is seen that all the information can be conveyed by the


use of single side band only. The carrier is superfious and the other side band is redundant. Suppose a lower side band is required say

Figure 4.7 Block Diagram of SSBSC

Analysis : Modulating signal as it is and carrier signal (by 90° phase) shift at the input of modulator M then o/p of modulator M will contain sum 1 1

and difference frequencies.

Similarly the modulator M as its input has carrier signal as it is and 2

modulating signal by 90° phase shift at the input. Then the o/p of M2

The Figure 4.8 shows the block diagram showing the complete process.

Signal

AF

Amplifier Carrier

Balanced Modulator

M11

SSB-SCAdder

signal

Modulator Balanced

M2

2VPhase Shifter

+π/2

V

Modulating AF

Amplifier

+π/2

]wv = COS

COS=

[( )

C

C

w wt

90t + w t COS

COS- 90t +

- -

-

w

w t

t

C

C

t 090

90m

w+

+

+

- w t ][

LSB USB

1)(

( ) ( )

v2

= COS wC

90t +- w t( )[ ] - COS wCt + w t 90+ ][ ( )

= COS wCt - w t - 90 - COS w

Ct + w t + 90 )(

V0 V1w

Ct +w t + 90 )(V2 2 COS== +

The output of adder is

oo

m

m

o

m

o o

mm

(o o

mm

LSB USB

o

m


Figure 4.8 Block Diagram of Complete Process

The figure 4.9 shows the modulating signal, carrier SSBSC output and frequency spectrum of the output signal.

Figure 4.9 Frequency Spectrum

Crystal Osc

Buffer

Balanced modulator

USB filter

Crystal Osc

Balanced mixer

USB filter Pilot

Carrier

SSB Signal

Amp.AF

AFC

Modulating signal

Carrier

DSB-SC Output

Frequency spectrum of DSB-SC signal fc mf )( fc fc mf )(fc mf )(_ + t

Phase Reversal


Advantages: The SSB - BC system has the following advantages.1. Bandwidth required for the system is half of that required for DSB

system.2. The effect of selective fading is minimum as only one side band exists.

In long range high frequency communication, particularly in audio-range, SSB technique is employed. The quality of communication is better in this system.

3. It requires relatively low power for communication and efficiency of transmission increased.

Application: The system is used in point to point radio telephony and in marine mobile communication, specially at distress call frequencies.

Achieving frequency stability: In SBSSC system, the carrier should be suppressed at least by 45 db at the transmitter. Earlier this system was not successful because highly stable oscillators are required but with introduction of “Frequency synthesizers”, this system is now improved a lot. If a 100 Hz “frequency shift” occurs in a system through which signals of 300, 500 and 800 Hz are passed, all these signals are shifted to 200;300 and 600 Hz just deterioting the performance of the system. So this system is not suitable for music, speech etc. The frequency stability can be obtained by using temperature controlled crystal oscillators with the transmitter which give highest transmitting stability. As told earlier, the introduction of “Frequency synthesizers” with the receiver the frequency stability. also improves a lot at the reception side. As the SSBSC system does not transmit the carrier, it may cause a “frequency shift”, if highly stable oscillators are not used at the transmitter as well at the receiver.

4.3.6 Single side band with reduced carrier (SSBRC-A3A) systemThis is an old system and was used before invention of frequency synthesizers. In SSBRC or “Pilot carrier” system a pilot carrier is transmitted along with the SSB signal. Block diagram of this system is just an addition of “Pilot carrier” to the SSB system. An attenuated (reduced amplitude) carrier is added to the final SSB signal output. The inserted carrier level is of the order of 15 to 25db below the unsuppressed carrier level. This pilot carrier is used at the receiver for demodulation and tuning. The frequency of pilot carrier is same as that of the original carrier. This system is identical to the SSB systems studied so far. The reduced carrier and SSB signal are added


in the adder to get SSBRC signal. This system is used in transmarine point to point radio telephony and mobile communication. The block diagram is shown in figure 4.10.

Figure 4.10 Block Diagram of a SSBRC System

Independent side band (ISB) system/technique.This system is usually used for medium density traffic. It is mostly a four channel transmission system. The system carries two independent channels simultaneously as two side bands with carrier reduced. Each sideband is independent of the other and different transmissions can be made on them. Each channel has a BW of 6 kHz and is fed to separate “Balanced modulators” along with a 100 kHz signal from a crystal oscillator. The balanced modulator suppresses the carrier by about 45 dB. The USB and LSB channels are selected by Filters and “Added” together with a carrier attenuated by 26 dB. The output of the “Adder” is mixed in a Balanced mixer with 3 MHz oscillator’s output.

The proper frequency is selected from the Balance mixer output and amplified. The signal is then given to the transmitter section, where it is again mixed in a mixer with the output of a “frequency synthesizer” and frequency multiplier to raise its frequency. The usual transmitting frequency is between 3 to 30 MHz. The resulting ISB signal is amplified to a power level of about 60 KW; and then fed to the antenna.

modulating signal

SSB modulator

signal SSB

Adder

Carrier oscillator

Carrier attenuator

Reduced carrier


Note: For high density point to point communication, multiplexing techniques are used such as frequency division multiplexing (FDM). However, for low or medium density traffic, ISB transmission is often employed. ISB essentially consists of two SSB channels added to form two side band around the reduced carrier. However each side band is quite independent of each other. It can simultaneously convey a totally different transmission, to the extent what the upper side band could. It is not advisable to mix telephone and telegraph channels in one side band since “key clicks’ may be heard in the voice circuit. However such hybrid arrangements are sometime unavoidable.

4.3.7 Vestigial Side Band (VSB) technique.In TV, where large BW is required, SSB system is very important for reducing the BW. The BW occupied by TV video signal is at least 4 MHz. If we use DSBFC system, minimum BW of 9 MHz will be required. If SSB system can be used, considerable BW can be saved. Therefore a compromise between SSBSC and DSBSC has been found which is known as Vestigial sideband system. In VSB system the desired sideband is allowed to pass completely but also a portion (called vestige) of the undesired sideband is also allowed to pass through. The vestige of the undesired sideband compensates for the loss of the desired sideband. Moreover, the VSB system does not need a short filter. In this system 1.25 MHz of the lower side band (along with the complete Upper side band) is also transmitted to ensure that the lowest frequencies of the desired USB will not be distorted. As only 1.25 MHz of LSB is transmitted net saving of 3 MHz of VHF spectrum results with every TV channel, thus making possible to allow more number of channels in the same BW. The sound occupies band near the video because it is required with the picture and it is not feasible to have a separate receiver for sound operating at some distant frequency i.e. much away from the video frequency. The VSB frequency spectrum is shown in figure 4.11

Note: The VSB signals are easy to generate, whereas SSBSC signals are relatively difficult to generate. In SSB signal generation using filtering technique, the filter must have very sharp characteristics. Basically such filters must have a flat pass band and extremely high attenuation outside the pass band.


Figure 4.11 VSB Frequency Spectrum

4.3.8 SSB receivers and Their QualitiesThe SSB receivers are of the following types:1. Pilot carrier receiver2. Suppressed carrier receiver.

They may also be of the following types:1. Coherent receivers2. Non Coherent receiver

The SSB receivers demodulate the SSB signals and process them. The SSB receivers are not used as broadcast receivers. They are required to receive signal in crowded frequency bands such as short wave bands. So, these are usually made double (or multi) conversion type. There special qualities are(i) High reliability(ii) Simple maintenance(iii) Ability to demodulate SSB signals(iv) Suppression of adjacent channel signals.(v) High SN ratio(vi) In case of Independent side band (ISD) receivers it should be capable

to separate independent side bands.

Rela

tive a

mp

litu

de

Picture carrier

Sound carrier

Video LSB

Video USB

0.5

0.5

1.2

5

5.2

5

5.5

5

Relative Channel frequency (MHZ )

1.0


4.3.9 Demodulators for SSB signals.The demodulators used for SSB signals are:(i) Product modulator(ii) Balanced modulator

Telecommunication Systems116

CHAPTER FIVE

TELEVISION SYSTEM

5.0 Introduction.The aim of a television system is to extend the sense of sight beyond its natural limits, along with the sound associated with the scene being televised. The TV system is an extension of the science of radio communication with the addition of picture details transmitted together. The picture signal is generated by a TV camera and sound signal by a microphone.

The image source is the electrical signal representing the visual image, and may be from a camera in the case of live images, a video tape recorder for playback of recorded images, or a film chain-telecine-flying spot scanner for transmission of motion pictures (films).

The sound source is an electrical signal from a microphone or from the audio output of a video tape recorder or motion picture film scanner.

The transmitter generates radio signals (radio waves) and encodes them with picture and sound information. An antenna coupled to the output of the transmitter is for broadcasting the encoded signals and a receiving antenna to receive the broadcast signals is coupled th the receiver.

The receiver (also called a tuner), decodes the picture and sound information from the broadcast signals, and whose input is coupled to the antenna. A display device turns the electrical signals into visual images and an audio amplifier and loudspeaker turns the electrical signals into sound waves (speech, music, and other sounds) to accompany the images.

5.1 Basic Theories Applied in TV System(a) 1. Units of measurementsVoltage, current, and resistance are basic measurements of electricity, but when you need to apply electricity to television, you will need to know some other measurements. Among these are frequency, hertz, and AC frequency.

FrequencyFrequency is an action that repeats itself. If you have an electrical circuit that puts out repeated and equal bursts or pulses of energy at 100 of those pulses


a second, the frequency of that circuit is 100 pulses per second. But we measure frequency in hertz (Hz), so the frequency is 100 Hz.

AC FrequencyThe flow of electrons in AC current constantly changes direction. If the electricity in your home is 240 V AC, the electricity will go from 0 V up to 240 V, back down to 0 V, continue down to 240 V, and then go back up to 0 V. This alternation between 240 V of positive electricity and 240 V of negative electricity is one cycle. Your household electricity does this 50 times a second. So the frequency of your household electricity is 50 Hz. Thus, the full description of electricity in your house is 240 V 50 Hz AC.

ImpedanceJust as DC circuits had resistance, AC circuits have impedance. Impedance is the combination of resistance, capacitance, and inductance. Impedance can help to tell if two or more circuits will interact well. The following oversimplified example may help you understand the concept. If your stereo amplifier has a speaker impedance of 8 , this means that it is designed to hook up to speakers that have 8Ω of resistance. If you connect your 8- amplifier to your 8- speakers, everything works great. But if you connect that 10,000- amplifier to speakers that have 8- resistance, you will have problems, because they are not designed to work with that amplifier. You have what’s called a mismatch. Impedance is an important factor when integrating electrical components.

(b). Fields (Induction) and NoiseThese is another set of theories that are very necessary for understanding the operation of the television.

(I) Fields (Induction)Any electrical circuit that has a changing flow of electrons will create an electromagnetic field around itself. For example, if you turned a flashlight on and off several times, the flow of electrons would be starting and stopping and a small electromagnetic field would be created. However, if you left the flashlight on, the flow of electrons would be continuous and unchanging and there would not be an electromagnetic field. Since the flashlight uses very small amounts of electricity, its field would be very small almost unmeasurable. But a high-tension power line running cross-country has an


extremely strong electromagnetic field. When another circuit is placed within this electromagnetic field, a signal from the more powerful circuit is forced, or coupled, into the weaker circuit. The signal may take the form of static, as when you try to play the AM radio in your car near high-power lines, or it may be actual information, as when you sometimes hear very weak background voices on the telephone.

(ii) NoiseAnother thing that can create problems is noise. To see what noise looks like in video, unhook the antenna and/or cable from your TV. Turn your TV on. What you see is noise. If you happen to be near a transmitter and have your TV tuned to its channel, you will also see some picture. This noise is obviously an undesirable feature. Too much of it will interfere with the picture or signal. Inherent in every electrical circuit is a certain amount of this noise. If there is too much noise, then there is a problem.

Signal-to-Noise RatioThe measure of the relationship between the strength of the signal and the amount of noise the circuitry creates is called the signal-to-noise ratio. We use the decibel (dB) scale to measure this relationship. The dB scale is a logarithmic ratio. The signal-to-noise ratio is doubled for every 3-dB difference between the strength of the signal and the strength of the noise. For example, if the noise in our system is 0 dB and the signal is 3 dB, then the signal is twice as strong as the noise; if the signal is 6 dB, then it’s four times as strong as the noise; if the signal is 9 dB, it’s eight times as strong; 12 dB, 16 times as strong; 15 dB, 32 times as strong; and so on. In video we have a signal-to-noise ratio of at least 60 dB.

5.2 Properties of Human Visual System:Frame MergingPersistence of vision: the eye (or the brain rather) can retain the sensation of an image for a short time even after the actual image is removed, this property is applied in TV and allows the display of a video as successive frames as long as the frame interval is shorter than the persistence period, the eye sees a continuously varying image in time. When the frame interval is too long, the eye observes frame flicker. The minimal frame rate (frames/second or fps or Hz) required to prevent frame flicker depends on display brightness, viewing distance. Higher frame rate is required with


closer viewing and brighter display; for TV viewing: 50-60 fps, for Movie viewing: 24 fps and for computer monitor: > 70 fps. Since the human eye does not perceive separate lines/frames when the rate is sufficiently high we should use just enough frame/line rate at which the eye perceives a continuous video.

Line MergingAs with frame merging, the eye can fuse separate lines into one complete frame, as long as the spacing between lines is sufficiently small. The maximum vertical spacing between lines depends on the viewing distance, the screen size, and the display brightness. For common viewing distance and TV screen size, 500-600 lines per frame is acceptable. Similarly, the eye can fuse separate pixels in a line into one continuously varying line, as long as the spacing between pixels is sufficiently small. This the principle behind fully digital video representation.

5.3 Generating the Video SignalThe video signal is most often generated by a TV camera, a very sophisticated electronic device that incorporates lenses and light-sensitive transducers to convert the scene or object to be viewed to an electric signal that can be used to modulate a carrier. All visible scenes and objects are simply light that has been reflected and absorbed and then transmitted to our eyes. It is the purpose of the camera to take the light intensity and color details in a scene and convert them to an electric signal.

5.3.1 Video Raster and Frame Rates: Video raster: The video raster is the rectangular formation of parallel scanning lines that guide the electron beam on a television screen: The rectangular area of a display screen actually being used to display images. The raster is slightly smaller than the physical dimensions of the display screen. Also, the raster varies for different resolutions. Real-world scene is a continuously varying 3-D signal (temporal, horizontal, vertical). Analog video is captured and stored in the raster format; Sampling in time: consecutive sets of frames.

Sampling in vertical direction: successive scan lines in one frame.Video-raster = 1-D signal consisting of scan lines from successive frames. Video is displayed in the raster format displays successive frames and


successive lines per frame. To enable the display to recognize the beginning of each frame and each line, special sync signals are inserted.

Frame: A frame is a single still image within a video clip. As with any digital image, a frame consists of pixels (picture elements), with each pixel representing a colour within the image. The higher the number of pixels, the more accurately an image can be represented. This is called resolution and is measured in megapixels. Frame Size describes the size of a single video frame: width x height, measured in pixels.The width of the frame can vary depending on whether the pixels in the frame are square pixels or non-square pixels.

Frame Aspect Ratio: Frame Aspect Ratio describes the relationship between he width and height of a single video frame. Video is landscape, so the width of a frame is greater than the height. Typical Frame Aspect Ratios for video are 4:3 and 16:9. Digital stills cameras often use 4:3 or 3:2. 4:3 is referred to as standard. 16:9 is referred to as wide-screen. The frame rates Depends on

(i) Human visual system properties. (ii) Viewing conditions. (iii) Capture/Transmission/Display technology.

Ideally we want the rate to be as high as possible to get best possible quality but higher rates mean the capture and display devices must work with very high data rate, and transmission of TV signals would take significant amount of bandwidth

Scanning is a technique that divides a rectangular scene into individual lines. The standard TV scene dimensions have an aspect ratio of 4:3; that is, the scene width is 4 units for every 3 units of height. To create a picture, the scene is subdivided into many fine horizontal lines called scan lines. Each line represents a very narrow portion of light variations in the scene. The greater the number of scan lines, the higher the resolution and the greater the detail that can be observed.

5.3.2 Scanning

A video frame is made of horizontal lines that are scanned from one side of a display to the other. Progressive video scanning happens when each line of a video frame is scanned, one after another. Interlaced scanning fills the entire frame with only half the lines, which requires half the time, thus doubling the perceived frame rate and reducing flicker.


5.3.1 Progressive scanningProgressive scan differs from interlaced scan in that the image is displayed on a screen by scanning each line (or row of pixels) in a sequential order rather than an alternate order, as is done with interlaced scan as shown in figure 5.1. In other words, in progressive scan, the image lines (or pixel rows) are scanned in numerical order (1,2,3) down the screen from top to bottom, instead of in an alternate order (lines or rows 1,3,5, etc... followed by lines or rows 2,4,6). By progressively scanning the image onto a screen every 60th of a second rather than "interlacing" alternate lines every 30th of a second, a smoother, more detailed, image can be produced on the screen that is perfectly suited for viewing fine details, such as text, and is also less susceptible to interlace flicker. The primary intent of progressive scan is to refresh the screen more often. Progressive scanning is much simpler than interlaced scanning: each line is scanned consecutively until a complete frame is drawn

(a) progressive scanning (b) interlaced scanning

Figure 5.1 Scanning methods

Interlaced ScanningInterlaced scan-based images use techniques developed for CRT (Cathode Ray Tube) TV monitor displays, made up of 576 visible horizontal lines across a standard TV screen. Interlacing divides these into odd and even

Fields and Frame: Each scan of the scene is called a field and only involves half of the total scan lines. Two complete scans of the scene is called frame. Because the fields are scanned in rapid sequence (50 per second), the viewer only perceives the complete picture.

5.3.2

Progressive Frame

Horizontal retrace

Interfaced Frame Field 1 Field 2

Vertical retrace


lines and then alternately refreshes them at 30 frames per second. The slight delay between odd and even line refreshes creates some distortion or 'jaggedness'. This is because only half the lines keep up with the moving image while the other half waits to be refreshed. Because the fields are changing at twice the frame rate, there is less perceived flicker than if each frame was scanned progressively. For example, with NTSC, a field of odd lines is scanned in 1/60 of a second and a field of even lines follows in the next 1/60 of a second, resulting in a complete frame every 1/30 of a second. Frame rates lower than 40 fps can cause noticeable flicker. When NTSC and PAL were invented, faster frame rates were not practical to implement. Interlaced scanning was devised to create a perceived frame rate of 60 fps (NTSC) or 50 fps (PAL). Interlaced video scans the display twice, using two fields, to complete a single frame. A single field contains only the odd lines (1, 3, 5, 7, and so on) or the even lines (2, 4, 6, 8, and so on) of the frame. If you could stop the video scanning process to observe a single video field, you would see that every other line is missing, like a comb. Figure 5.2 explains the interlaced scanning as obtained in the Television screen.

Figure 5.2 Interlaced scanning as obtained in real life TV

At the time TV systems were first developed (1939-41), 60 frames/s, 525 lines/frame is technologically infeasible. Interlacing using 60 fields/s and 252.5 lines/field is a good compromise. For a display device to know when does a line/field end, special synchronization signal (with a constant voltage level) are used, this signals are shown in figure 5.3.


Figure 5.3 Synchronization signals

Example: Using the letter F Explain in detail the scanning principle.Solution: In this example, the scene is a large black letter F on a white background. The task of the TV camera is to convert this scanning scene to an electric signal. The camera accomplishes this by transmitting a voltage of 1 V for black and 0 V for white. The scene is divided into 15 scan lines numbered 0 through 14. The scene is focused on the light-sensitive area of a vidicon tube or imaging CCD which scans the scene one line at a time, transmitting the light variations along that line as voltage levels. The simplified scanning diagram is shown in figure 5.10(a). Where the white background is being scanned, a 0-V signal occurs. When a black picture element is encountered, a 1-V level is transmitted. The electric signals derived from each scan line are referred to as the video signal. They are transmitted serially one after the other until the entire scene has been sent as shown in figure 5.10(b). This is exactly how a standard TV picture is developed and transmitted.

Interfaced Frame

Field 1 Field 2

Horizontal retrace Reduce the actual time

used to scan a line

Vertical retrace

Reduce the actual number

of lines (active lines) that is used to describe

the video


(a) Simplified explanation of scanning.

(b) The scan line voltages are transmitted serially. These correspond to the scanned letter F in Figure 5.5a.

Figure 5.4 Principle of scanning explained|.

FScan line

aspect ratio4:3

Scan line

Corresponding video voltage

1 V0 V1 V0 V1 V

0 V1 V

0 V

0 V

1 V

1 V

0 V

0 V

1 V

black -- white

0123456789

1011121314

1

2

3

4

5

6. 7. 8.

Line 1 Line 2 Line 3 Line 4

One line of video

Line 5 Line 5 Line 7 Line 8


Detailed explanation.A more detailed illustration of the scanning process is given in Figure. 5.6. The scene is scanned twice. One complete scanning of the scene is called a field and contains 262.5 lines. The entire field is scanned in 160 s for a 60-Hz field rate. In color TV the field rate is 59.94 Hz. Then the scene is scanned a second time, again using 262.5 lines. This second field is scanned in such a way that its scan lines fall between those of the first field. This produces what is known as interlaced scanning, with a total of 2 x 262.5 = 525 lines. In practice, only about 480 lines show on the picture tube screen. Two interlaced fields produce a complete frame of video. With the field rate being 1/ 60 s, two fields produce a frame rate of 1 /30 s, or 30 Hz. The frame rate in color TV is one-half the field

(

Figure 5.5 Interlaced scanning.

rate, or 29.97 Hz. Interlaced scanning is used to reduce flicker, which is annoying to the eye. This rate is also fast enough that the human eye cannot

262Lines

525

Line

-12

Start of field 1

Start of field 1

Field 1Start of field 2

End of field 1

Start of field 2

End of field 1

Trace

Retrace

End of field 2

262Lines

-12

Start of field 1

Field 2Start of field 2

Field rate - 60 Hz Frame rate - 30 Hz

Trace

End of field 2

Retrace


detect individual scan lines and therefore sees a stable picture. The rate of occurrence of the horizontal scan lines is 15,750 Hz for monochrome, or black and white, TV and 15,734 Hz for color TV. This means that it takes about 1/15,734 s, or 63.3μs to trace out one horizontal scan line. After one line has been scanned, a horizontal blanking pulse comes along. At the receiver, the blanking pulse is used to cut off the electron beam in the picture tube during the time the beam must retrace from right to left to get ready for the next left-to-right scan line. The horizontal sync pulse is used at the receiver to keep the sweep circuits that drive the picture tube in step with the transmitted signal. The width of the horizontal blanking pulse is about 10μs. Since the total horizontal period is 63.6μs, only about 53.5μs is devoted to the video signal. At the end of each field, the scanning must retrace from bottom to top of the scene so that the next field can be scanned. This is initiated by the vertical blanking and sync pulses. The entire vertical pulse blacks out the picture tube during the vertical retrace. The pulses on top of the vertical blanking pulse are the horizontal sync pulses that must continue to keep the horizontal sweep in sync during the vertical retrace. The equalizing pulses that occur during the vertical retrace period help synchronize the half scan lines in each field. Approximately 30 to 40 scan lines are used up during the vertical blanking interval. Therefore, only 480 to 495 lines of actual video are shown on the screen.

Bandwidth and Resolution: The resolution of the picture refers to the amount of detail that can be shown. Pictures with high resolution have excellent definition, or distinction of detail, and the pictures appear to be clearly focused. A picture lacking detail looks softer, or somewhat out of focus. The bandwidth of a video system determines the resolution. The greater the bandwidth, the greater the definition and detail.

5.4 Television Signals The standard television signal consists of the following four elements: The picture information, the picture blanking pulses, the picture average dc component and the picture synchronizing pulses.

5.4.1 Picture Information: The picture information is the basic part of the signal. It is a series of waves and pulses generated during active scanning of the camera tube. As the scanning line travels across the tube, it is amplitude modulated in proportion to the brightness variation in the scene it is


scanning. For commercial television, the amplitude variations are such that the maximum video amplitude produces black, and the minimum amplitude produces white. Ordinarily, the maximum and minimum video amplitude values represent 75 and 15 percent of the maximum carrier voltage, respectively.

5.4.2 Picture Blanking Pulses: To prevent undesirable signals from entering the picture during retrace time, blanking pulses are applied to the scanning beams in both the camera tube and the receiver picture tube . Camera blanking pulses are used only in the pickup device. They serve only to close the scanning aperture on the camera tube during retrace periods, and never actually appear in the final signal sent to the receiver. In some systems, the same pulse that triggers the scanning circuit and blanks the receiver picture tube also closes the camera aperture. The function of the blanking pulses is to suppress the scanning beam during both vertical and horizontal flyback times. The blanking pulses are simple rectangular pulses, somewhat wider than the corresponding camera blanking pulses. They have a duration slightly longer than the actual retrace time. The reason for the slightly longer blanking time is to trim up the edges of the picture and to provide a clean, noise-free period during flyback. Figure 5.1 shows a complete video signal that contains pulses for the removal of visible lines during horizontal retrace periods only. The horizontal pulses

Figure 5.6.The complete video signal for three scanned lines.

recur at intervals of 1/15,750 of a second. At the bottom of the picture, they are replaced by vertical blanking pulses. These are similar to the horizontal pulses, except they are of much longer duration (approximately 15 scanning lines) and have a recurrence of 1/60 of a second. Note that the blanking

100

% A

MP

LIT

UD

E

75

50

25

0

15. 75 0SEC HORIZ. SYNC. PULSE

BLANKINGVOLTAGE LEVEL

BLACK LEVEL

INFRA-BLACKREGION

CAMERASIGNAL REGION

BRIGHTEST LEVEL

GRAYLEVEL

CAMERA SIGNAL(IMAGE DETAIL)

TIMEVISIBLE PART

OF LINE


pulses (and synchronizing pulses) are added at a relatively high-level point in the transmitter because they are considered to be noise-free at that level. The importance of noise-free blanking and synchronizing pulses should be emphasized. They determine the stability of the viewed picture or the degree to which a picture remains locked-in on the picture tube, even under the most adverse transmission conditions.

5.4.3 Picture Average Dc Component: If a television picture is to be transmitted successfully with the necessary fidelity, it needs the dc component of the picture signal. This component is a result of slow changes in light intensity. The loss of the dc component occurs in ac or capacitive coupling circuits. The loss is evidenced by the picture signal tending to adjust itself about its own ac axis. The dc component is returned to the video signal by means of a dc restorer or inserter circuit.

5.4.4 Picture Synchronizing Pulses: Synchronizing the scanning beams in the camera and the receiver must be exact at all times to provide a viewable picture. To accomplish this, synchronizing information is provided by electrical pulses in the retrace intervals between successive lines and between successive pictures (figure 5.6). The retrace periods should be as short as circuit considerations will allow. These periods are in areas where synchronization pulses may be inserted without interfering with the picture. Synchronizing pulses are generated in the equipment that controls the timing of the scanning beam in the pickup device. They become a part of the complete signal that is transmitted to the receiver. In this manner, scanning operations at both ends of the system are always in step with each other. In general, synchronizing signals should provide positive synchronization of both horizontal and vertical sweep circuits. They should be separable by simple electronic circuits to recover the vertical and horizontal components of the composite sync signal. They should be able to be combined with the picture and blanking signals to produce a standard composite television signal. Most television systems produce synchronizing information that conforms to the basic requirements of synchronization. Figure 5.7 shows how the synchronizing signal waveform is added to the picture information and blanking signals to form a complete composite picture signal ready to be transmitted. Note that the duration of the horizontal sync pulses is considerably shorter than that of the blanking pulses. Vertical sync pulses are rectangular, but they are of much shorter duration than the horizontal pulses.


Thus, they provide the necessary means for frequency discrimination. Another series of pulses is added before and after the vertical sync pulses to prevent the pairing problem and to maintain continuous horizontal synchronizing information throughout the vertical synchronization and blanking interval. These are equalizing pulses (figure. 5.7).

Figure 5.7.Vertical synchronizing and equalizing pulses

The time between the last horizontal sync pulse and the first equalizing pulse changes from a full horizontal line interval to one-half of a horizontal line interval every other field. This is caused by the ratio between 15,750 Hz and 60 Hz. The ratio produces the necessary difference between fields to provide interlaced scanning. Since the horizontal oscillator is adjusted to the frequency of the horizontal sync pulses, it is triggered only by every other equalizing pulse or serration of the vertical sync pulse.

The sync pulses of a television waveform need to be able to allow the receiver or monitor to reliably produce an accurate picture. The form of the synchronization waveforms is described here. The description given here applies to the PAL signals but the arguments can be applied to other interlaced tv systems. A television picture is built up of a spot scanned rapidly on the faceplate of a cathode ray tube horizontally and (relatively slowly) vertically to produce a 'raster. The brightness of the spot is varied to produce the picture. A synchronizing signal to control the position of the spot on the screen is combined with the brightness (or luminance) information producing

5.5 TV Synchronisation

AM

PL

IT

UD

E

H IS 64MICROSECONDS

EQUALIZING PULSES

SERRATED VERTICAL

SYNC PULSE

H 3H 3H 3H 9 TO 12H

TIME FOR VERTICAL RETRACE

FIRST LINE

OF VIDEO OF VIDEO LAST LINE

100 %

50 %

0

-

-

-

-

TIME


a 'composite' television signal. The sync and brightness information are kept separate by assigning them unique signal level ranges (see line waveform below). Normally, the total range of a monochrome (black and white) signal is 1 Volt peak-to-peak although the absolute dc levels may vary (usually the signal is ac coupled). The luminance information occupies a range of around 0.7 V and the sync 0.3 V as shown in figure 5.8. With respect to the lowest sync level, the brightest parts of the picture are at a level of 1 V with the black level at 0.3 V. Black level is the same as the blanking level in CCIR system which is not necessarily the case for other systems. Blanking occurs in non-picture parts of the waveform when it is necessary for the electron gun of the crt to be 'off' so that retrace is not visible on the screen.

Figure 5.8. Signal's voltage level

The television waveform carries pulses that allow synchronization of both the horizontal and vertical deflection circuits. These pulses are separated by the video information using a 'sync separator', this can be just a comparator with its threshold set around halfway between black level and the sync tips. There are two deflection generators (timebases) - horizontal and vertical. Both must be triggered at the right time to ensure that the picture is correctly reproduced. Therefore both timebases need to be synchronized and there needs to be a method of triggering either one independently using the same single set of sync pulses. The method used to allow the receiver to distinguish between the two types of sync is to use different widths for the horizontal and vertical sync pulses. The sync pulse is separated from the active picture information by the 'porches': the 'back' and 'front' porches. These avoid the picture detail affecting the accuracy of the synchronization.

Peak white level

Video Signal

Banking level

(Black level)

Sync level

0.7 V

OV DC

0.3 V


5.5.1 Synchronization Pulse: Starting of each Horizontal line is marked by a Horizontal sync pulse and the starting of each field by a vertical sync pulse. There are 625 Horizontal sync pulses per frame and 50 vertical sync pulses per second. Synchronisation pulses ensure that the video image is locked on a video monitor (or VCR etc) vertically and horizontally without any jitter or rolling. If vertical sync is lost, picture may move/tear vertically. If horizontal sync is lost, picture may move/tear horizontally. Video information is carried on each line except portions which are in blank periods (Horizontal & Vertical blanking / retrace period). For monochrome video signals, video information is basically the intensity or luminance information (Y signal). 0V represents the black level and 0.7V represents the peak white level . Sync pulses have an amplitude of -0.3V with respect to blanking level.

5.5.2 Horizontal and Vertical Synchronization Horizontal Sync Pulse: The synchronizing pulse at the end of each line that determines the start of horizontal retrace. For accurate reproduction, both the camera and the television receiver must be synchronized to scan the same part of the scene at the same time. At the end of each horizontal line the beam must return to the left side of the scene. This is called horizontal retrace. Coordination of the horizontal retrace is handled by the horizontal sync pulse.

Figure 5.9 Horizontal sync pulse at the end of each line determines the start of horizontal retrace

At the bottom of the scene, when the last line in first field of the horizontal lines have been scanned, it is time for the beam to return to the top of the scene.

Vertical Sync Pulse: The synchronizing pulse at the end of each field which signals the start of vertical retrace. The start of vertical retrace is signaled by the vertical sync pulse which is different in width than horizontal sync pulses. Since the vertical retrace takes much longer than horizontal retrace, a longer

Horizontal Sync Pulse

1st Line 2nd Line


vertical synchronizing interval is employed. See figure 5.10.

signals the start of vertical retrace.Figure 5.10

Vertical sync is obtained from the last few and first lines of each field. These lines contain a series of special sync pulses which differ on alternate fields shown in figure 5.11: - The format for the first field starting at line 623 ends at line 5 inclusive): 6 Pre-equalizing pulses.. 5 long sync pulses... 5 Post-equalizing pulses. The format for the second field (starting at line 311ends at line 317 inclusive): 5 Pre-equalizing pulses.. 5 long sync pulses... 4 Post-equalizing pulses. The pre- and postequalizing pulses are "short syncs" (active low as usual) of 2 microseconds followed by a delay of 30 microseconds, therefore they last half a scanline each. The "long syncs" are 30 microsecond low pulses with a 2 microsecond delay after them, they last half a line each too. The different vertical sync pulse trains of each field is the means by which the raster beam is offset half a scan line for the interlacing

Figure 5.11 Vertical sync pulses

Vertical sync pulse at the end of each field

line 312 line 312.5

etc.

Horizontal SyncPulse

Vertical SyncInformation

EQUALIZING PULSE

VERTICAL SYNCPULSE

EQUALIZING PULSE

HORIZONTAL SYNC PULSES

H H

3 H 3 H 3 H

VERTICAL BLANKING INTERVAL(21 H)

BOTTOMOF

PICTURE

BEGIN LINE 1OF FIELD 1

TOPOF

PICTURE


5.5.3 The blanking pulses. The composite video signal contains horizontal and vertical blanking pulses to blank the corresponding retrace intervals by raising the signal amplitude slightly above the black level (75 per cent) during the time the scanning circuits produce retraces. The repetition rate of horizontal blanking pulses is therefore equal to the line scanning frequency while the frequency of the vertical blanking pulses is equal to the field-scanning frequency, the values here are 15625 Hz and 50Hz respectively. During the time when horizontal and vertical retrace are taking place, the electron beams in the camera and home TV are cut off. This time period is called blanking. Blanking means that nothing will be written on the television screen or the time period when picture information is shut off. Blanking is the same voltage levels the black picture level. Synchronizing signals which control invisible retrace of scanning are active during the blanking period.

During horizontal blanking, sync and burst occur. During vertical blanking, vertical sync ,vertical equalizing pulses, and vertical serrations occur. The equalizing pulses are inserted to ensure that the video fields begin at the proper points to achieve interlace. The vertical serrations keep the television receiver's horizontal sync circuitry from drifting off frequency during the time when no horizontal picture information is present. figure 5.12 shows the horizontal and vertical blanking pulses.

Figure 5.12 Horizontal and vertical blanking pulses in video signal.

ACTIVE

PICTURE

Equalizing

Pulses

Vertical

Sync

Equalizing

Pulses

Horizontal Pulses

Vertical Serration

BLANKING FOR

VERTICAL SYNC

& FIELD FLYBACK BLANKING FOR

HORIZONTAL

SYNC & LINE

FLYBACK

BLANKING LEVEL

Burst


5.5.1 The horizontal and vertical sync details

Front porch: This is a brief period of 1.5 μs inserted between the end of the picture detail for that line and the leading edge of the line sync pulse which allows the receiver video circuit to settle down from whatever picture voltage level exists at the end of the picture line to the blanking level before the sync pulse occurs

μ

Figure 5.11

Line sync pulse: At the end of the front porch of blanking, horizontal retrace is produced when the sync pulse starts. The flyback is blanked out because the sync level is blacker than black. The duration for the line sync pulses is 4.7 μs, during this period the beam on the raster almost completes its retrace and arrives at the extreme left end of the raster.

The horizontal line and sync details compared to horizontal deflection sawtooth and picture space on the raster is illustrated in figure 5.11.

t

Horizontal sync details

H represents he interval between horizontal scanning lines. The line blanking period is divided into three sections. These are the ‘front porch’, the ‘line sync’ pulse and the ‘back porch’. Their location and effect on the raster is as shown in figure 5.13.

Back porch (blanked)Front porch (blanked)

8075

60

40

2012 5

0

Picture space on

the raster

Horz syncpulse = 4.7 μs

Back porch= 5.8 μs

Horz blanking pulse = 12 μs

t

t

Blanking ends

Retrace

Trace

Blanking begins Retracebegins

information = 52 μs Picture

Front porch = 1.5 μs H = 64 μsPicture

Retrace ends

Horz deflection sawtooth

0

Am

plit

ud

e %

100


Back porch: 5.8 μs and his period of 5.8 μs at

the blanking level allows plenty of time for line flyback to be completed. It also permits time for the horizontal time-base circuit to reverse direction of current for the initiation of the scanning of next line. The back porch also provides the necessary amplitude equal to the blanking level or reference level and enables to preserve the dc content of the picture information at the transmitter.

5.5.5 Video Signal Details and ExplanationThe black-and-white information contained in a scene is made up of the varying light intensity of that image. This information is referred to as the luminance information or the luminance signal. The luminance signal is generated at the electronic camera by measuring the light intensity of each element of the image to be transmitted. To reproduce the luminance information properly, the receiver must be perfectly synchronized with the transmitting camera. This synchronization is controlled by synchronization

Back-Porch is where colour synchronisation occurs and is empty for monochrome. It has a period of t

Horizontal Blanking Period: Horizontal Blanking Period = Front-Porch + H-Sync pulse + Back-Porch. The Start of H-Sync signifies start of scanline. Many more details (rise/fall times etc.) left out here.Timing Details: The sync timing details for PAL and NTSC television system is give in table 5.1.

Table 5.1 Sync Timing Details

Area PAL NTSC

Whole Scanline 64μs 63.55μs

Front Porch 1.65μs 1.5μs

H-Sync pulse 4.7μs 4.7μs

Back Porch 5.7μs 4.5μs

Blanking period (total) 12.05μs 10.7μs

‘Active Display' period 51.95μs 52.9μs

Contains the 'start of scanline' sync pulse.


signals or sync signals as they are commonly called. These sync signals fine tune the receiver's horizontal and vertical sweep generators. There also needs to be a signal that will turn off the reproducing spot at the receiver between scan lines and fields. Therefore, four signals are required to transmit a black-and-white image. These signals are summarized as follows: the luminance signal carrying instantaneous brightness information, a sync signal to control the horizontal sweep, a sync signal to control the vertical sweep, and blanking signals between lines and between frames. These four signals are combined into a unique composite picture signal combining video, blanking, and synchronization information (abbreviated to VBS, also described as video baseband signal suitable for broadcast as shown in figure 5.13. The level of the video signal when the picture detail being transmitted corresponds to the maximum whiteness to be handled, is referred to as peak-white level. This is fixed at 10 to 12.5 percent of the maximum value of the signal while the black level corresponds to approximately 72 percent. The sync pulses are added at 75 percent level called the blanking level. The difference between the black level and blanking level is known as the ‘Pedestal’ which indicates average brightness since it measures how much the average value differs from the black level. The final radiated signal has a picture to sync signal ratio (P/S) equal to 10/4.. Hence the video information may vary between 10 percent to about 75 percent of the composite

Figure 5.13 Video signal details

v/v max%

Co

mp

osit

e v

ideo

sig

nal (p

erc

en

t o

f m

ax)

Da

rke

r t

ha

n d

ark

Horz syncpulses

One line duration

64 μs

64 μs

Active line

period 52 μs

S

Dark

level

Ped

. hei

gh

t D

.C l

ev

el

Blanking level

Pe

d.

he

igh

t

Pe

de

sta

l h

eig

ht

Picture details

D.C

. le

ve

l

Peak white Level

D.C

le

vel

100

8075

60

40

20

12.5

0

P

0.4

0.2

0

0.4

0.2

0.6

0.8

1.0

t


video signal depending on the relative brightness of the picture at any instant. The darker the picture the higher will be the voltage within those limits. In addition to continuous amplitude variations for individual picture elements, the video signal has an average value or dc component corresponding to the average brightness of the scene. The dc component of the video signal is the average value for complete frames rather than lines since the background information of the picture indicates the brightness of the scene. In the absence of dc component the receiver cannot follow changes in brightness as the ac camera signal, say for grey picture elements on a black background will then be the same as a signal for white area on a grey back-ground.

5.6 Basic Television Standards Two basic standards have been adopted for the international exchange of TV programs:

FCC Standard CCIR Standard Lines / frame 525 625 Fields/s 60 50 Colour system NTSC PAL/SECAM Video Bandwidth 4.2 MHz 5 / 5.5 / 6 MHz Colour Subcarrier 3.58 MHz 4.43 MHz

The different video bandwidths of the CCIR standard are not so much due to field and line scanning procedures, but rather to the bandwidth available in the TV transmitter channels.

5.6.1 Line StandardsThe choice for the number of lines per frame is not easy. Because the interlaced systems require accurate placement of scanning lines it is necessary to make sure that the horizontal and vertical timebases are in a precise ratio. This is achieved by passing the one through a series of electronic 'divider' circuits to produce the other. Each division is by a small number, usually odd and prime. 243 for example is 3 x 3 x 3 x 3 x 3, and 343 is 7 x 7 x 7. The 30-line standard, being purely mechanical, has no oscillators to synchronize together. The prime factors for the line standards are as follows:.

90. 2 x 3 x 3 x 5 96. 2 x 2 x 2 x 2 x 2 x 3

180. 2 x 2 x 3 x 3 x 5 240. 2 x 2 x 2 x 2 x 3 x 5


243. 3 x 3 x 3 x 3 x 3 343. 7 x 7 x 7

375. 3 x 5 x 5 x 5 405. 3 x 3 x 3 x 3 x 5

440. 2 x 2 x 2 x 5 x 11 441. 3 x 3 x 7 x 7

450. 2 x 3 x 3 x 5 x 5 455. 5 x 7 x 13

525. 3 x 5 x 5 x 7 605. 5 x 11 x 11

625. 5 x 5 x 5 x 5 819. 3 x 3 x 7 x 13

5.6.2 Line and Field NumberingLine numbering: Lines are numbered consecutively in time, eg from 1 to 625, and not in the order in which they are displayed down the screen. Odd fields do not contain only odd numbered lines. Even fields do not contain only even numbered lines. In an interlaced line standard the second field starts half-way along the middle line in the series, eg halfway along Line 313. Line 1 always occurs in Field 1 (and therefore also Field 3), though its actual position depends on the line standard.

Field numbering: In an interlaced standard there are two fields in every frame. In monochrome standards they are numbered 1-2. In colour standards, the fields are numbered 1-4 because there are patterns of colour subcarrier phase and burst blanking which repeat every four fields. In the PAL standard there is a relationship between subcarrier phase and line sync pulses which repeats every eight fields, but the fields are still numbered 1-4.

Field 1 is defined as the field in which the leading edge of the field sync pulse is coincident with the leading edge of the line sync pulse. Field 2 is therefore the field in which the field pulse occurs mid-way through a line.

In the 625-line standard the lines of Fields 1 and 3 appear on the screen above those of Fields 2 and 4, (ie the half line at the top belongs to Field 1 or 3) whilst in all other standards they are displayed below (ie the half line at the top belongs to Field 2 or 4). In all line standards a full frame comprises Field 1 followed by Field 2 (or Field 3 followed by Field 4). Abrupt changes in picture content (ie 'cuts') should occur between Field 2 and Field 3 of Frame n, or Field 4 of frame n and Field 1 of Frame n+1. Where the picture information contained in two consecutive fields comes from the same time period (eg when originated on film) these should be Field 1 and Field 2, or Field 3 and


Field 4, of Frame n (this is often not possible in 60fps standards, where the '3:2' pull-down form of telescene is used).

Odd/Even: Alternate fields are labelled as Odd or Even. The definition is such that in the 625-line standard Fields 1 and 3 are 'Even', whilst Fields 2 and 4 are 'Odd'. This is because of the odd number of equalization pulses (5 of them) preceding each field sync pulse in the 625-line standard. In all other standards Fields 1 and 3 are 'Odd' whilst Fields 2 and 4 are 'Even'. The odd fields are defined as the ones that end in a half-line and even fields are those ending in a full line.

5.6.3 Obsolete and Current Standards: Tabulated below is a summary of the obsolete and current standards used in television system and the country they are deployed..

The 405-Line StandardSummary of features: Although the 405-line standard was a development of previous systems, and its requirements seem modest by today's standards, it was touch-and-go whether the system would actually work properly. It was the first standard to employ interlace, which, together with the 2.5MHz vision bandwidth effectively doubled the resolution of the Baird system in the horizontal, vertical and temporal dimensions. In fact because the Kell effect was unknown at the time, the horizontal resolution was made greater than that required to match the vertical resolution - especially since

Obsolete Standards Current Standards 405-lines: System A (monochrome, obsolete) Republic of Ireland until 23 Nov 1982 United Kingdom until 2 Jan 1985

819-lines: System E (monochrome, obsolete)

France until 1984, Monaco until 198

: System F (monochrome, obsolete)

RTB Belgium until February 1968 Luxembourg until 1 September 1971

525-lines: System M (NTSC colour) United States of America, Japan and most other territories with 60Hz mains

625-lines: Systems B, D, G, K, K1 and L (SECAM colour)

France from 1982 Luxembourg

People's Republic of China :Systems B, D, G, H, I, K, K1 and

N (PAL colour) Most other territories.


many receivers were incapable of displaying 100% accurate interlace (resulting in 'line pairing' which reduced the apparent vertical resolution and emphasised the coarse line structure even further). The choice of horizontal and vertical blanking times was generous to give receiver timebases plenty of time for the flyback stroke to occur while the signal was at black level. The pulses were fairly primitive, there being no equalising pulses nor pedestal, often called 'set up'. Narrow horizontal synchronising pulses were detected by a 'differentiating' circuit in the receiver and made to trigger the flyback of the line timebase which was set to free-run slightly slowly. Similarly, several broad field pulses were detected by an 'integrating' circuit, directly triggering the vertical timebase. The choice of positive modulation, with sync tips at 0% and peak white at 100% modulation levels meant that 30% of the vision carrier modulation was devoted to video. However, with positive modulation it is difficult to implement an automatic gain control in the receiver that is independent of the video level, and impulse interference results in white spots which are noticeable and annoying.

The 525-Line StandardSummary of featuresThe 525-line NTSC standard was developed in the USA which has a 60Hz mains electricity supply and so was given a 60 field-per-second interlaced repetition rate. Apart from the improved vertical, horizontal and temporal resolutions, there are several features not found in the 405-line standard. Firstly, a set of equalising pulses at twice the line frequency was added at the end of each field, allowing the field pulse integrator to fire at precisely the same moment on both odd and even fields, allowing much better interlace in the receiver. Black level was made higher than blanking level, which means that during line and field flyback the beam current is always cut off and no flyback lines are visible on the display tube face. The vision bandwidth of 4.2MHz was chosen so that the horizontal and vertical resolutions would be the same after Kell adjustment. Negative modulation was chosen which allows receivers to measure the carrier level simply and accurately by sampling the sync level which is always 100% modulation. However, interference pulses, while black and therefore less visible, confuse the sync separater circuits causing false triggering of the line and field oscillators. This was less of a problem when 'flywheel' rather than direct synchronisation began to be used. Peak white level is set to give 10% carrier level, though colour subcarrier excursions take the level lower. Only around 60% of the carrier modulation is


devoted to video. The sound carrier is frequency modulated, which allows the 'intercarrier sound' technique to be used, making fine tuning much easier and less critical. When the NTSC colour system was introduced, it became impossible for the original line and field frequencies to co-exist with the 4.5MHz vision-sound carrier spacing, and so slightly different timebase frequencies were chosen. In fact the field and line frequencies were each multiplied by (1000/1001) so that there was no longer an integral number of frames per second. Because of the necessarily low colour subcarrier frequency the resolution of the NTSC colour system (both luminance and chrominance) is severely limited when compared to the 625 line standard. Also the colour system itself often led to hue errors that could not be corrected automatically. Later decoders featuring 'comb' filters largely overcame these limitations.

The 625-Line StandardSummary of features: The 625-line standard was developed in Germany after the second world war as a 50Hz version of the US NTSC standard. The horizontal timebase frequencies are almost the same, but because of the higher number of scanning lines, the vision bandwidth was increased to 5.0 (CCIR), 5.5 (UK) or 6.0MHz (OIRT). Generally no pedestal is used, and black level is the same as blanking level. Most countries used the NTSC method of negative vision modulation and frequency modulated sound, but France (and Belgium originally) opted for positive modulation and amplitude modulated sound. Intercarrier sound therefore cannot be used in France, though where Nicam digital sound is present, the vision modulation depth is reduced so that there is at least 5% carrier during sync pulses.

The 819-Line StandardSummary of features: The 819-line standard was developed in France after the war as a high-definition alternative to the 441-line standard used previously. Because it had more than twice the number of lines of the 405-line standard, and therefore over twice the horizontal timebase frequency, it required four times the vision bandwidth (10MHz). Otherwise, the standard was very similar to 405-lines. There were no equalising pulses or pedestal in the French version, and instead of a series of broad field sync pulses there was just a single one, half a line period in length, though the Belgian version differed (in this respect


only) by having seven broad field pulses preceded and followed by sets of seven equalizing pulses in a similar way to the 625-line standard. Positive modulation vision and amplitude modulated sound were used, together with the usual vestigial sideband, though a mixture of upper and lower sideband channel allocations was devised whereby adjacent channels in Band III overlapped, allowing more transmitters to be accommodated in the same spectrum. It could be said that 819-lines was a High Definition standard before its time. In modern digital parlance it would be described as '800x738 50 2:1', though the aspect ratio was 4:3 and the pictures were monochrome only. For comparison, the coarsest current (16:9) digital HD standard is '1280x720 50 1:1', of which the centre 4:3 portion would be 960x720 pixels. Modern HD standards use 'square pixels' rather than Kell-factor elongated ones since they are expected to be displayed on dot matrix rather than rasterised displays, and so the horizontal and vertical resolutions are compromised equally by being separated into discrete pixels in both directions instead of only the vertical.

5.6.4 Difference Between Television Standards.There is no major differences between the three world standards (NTSC, PAL, SECAM) have been highlighted. The differences that do exist mainly concern the way of modulating this subcarrier and its frequency.

NTSCThis system uses a line-locked subcarrier at 3.579545MHz, amplitude modulated with a suppressed carrier following two orthogonal axes (quadrature amplitude modulation, or QAM), by two signals, I (in phase) and Q (quadrature), carrying the chrominance information.These signals are two linear combinations of (R −Y ) and (B−Y ). NTSC was very sensitive to phase rotations introduced by the transmission channel, which resulted in very important tint errors, especially in the region of flesh tones, thus, leading to the necessity of a tint correction button accessible to the user on the receivers and to the famous “never twice the same color” expression. This led Europeans to look for solutions to this problem, which resulted in the SECAM and PAL systems


SECAMThis standard eliminates the main drawback of the NTSC system by using frequency modulation for the subcarrier, which is insensitive to phase rotations; however, FM does not allow simultaneous modulation of the subcarrier by two signals, as does QAM. The clever means of circumventing this problem consisted of considering that the color information of two consecutive lines was sufficiently similar to be considered identical. This reduces chroma resolution by a factor of 2 in the vertical direction, making it more consistent with the horizontal resolution resulting from bandwidth reduction of the chroma signals. Therefore, it is possible to transmit alternately one chrominance component, on one line and the other on the next line. It is then up to the receiver to recover the two signals simultaneously, This system is very robust, and gives a very accurate tint reproduction, but it has some drawbacks due to the frequency modulation: the subcarrier is always present, even in non-colored parts of the pictures, making it more visible than in NTSC or PAL on black and white, and the continuous nature of the FM spectrum does not allow an efficient comb filtering; rendition of sharp transients between highly saturated colors is not optimum due to the necessary truncation of maximum FM deviation. In addition, direct mixing of two or more SECAM signals is not possible.

PALThis is a close relative of the NTSC system, whose main drawback it corrects. It uses a line-locked subcarrier at 4.433619MHz, which is QAM modulated by the two color difference signals U = 0493 (B −Y ) and V = 0877 (R −Y ). In order to avoid drawbacks due to phase rotations, the phase of the V carrier is inverted every second line, which allows cancellation of phase rotations in the receiver by adding the V signal from two consecutive lines by means of a 64 s delay line In order to synchronize the V demodulator, the phase of the reference burst is alternated from line to line between +135 and −135 compared to the U vector. Other features of PAL are very similar to NTSC. In addition to the main PAL standard (sometimes called PAL B/G), there are two other less well-known variants used in order to accommodate the 6MHz channels taken from NTSC: PAL M used in Brazil (525 lines/59.94 Hz, subcarrier at 3.575611 MHZ) and PAL N used in Argentina (625 lines/50 Hz, subcarrier at 3.582056 MHZ).


5.7 Colour Television Basic PrinciplesThe Sound and Light Spectrum: Video is a combination of light and sound, both of which are made up of vibrations or frequencies. We are surrounded by various forms of vibrations: visible, tangible, audible, and many other kinds that our senses are unable to perceive. We are in the midst of a wide spectrum which extends from zero to many millions of vibrations per second. The unit we use to measure vibrations per second is Hertz (Hz). Sound vibrations occur in the lower regions of the spectrum, whereas light vibrations can be found in the higher frequency areas. The sound spectrum ranges from 20 to 20,000 Hertz (Hz). Light vibrations range from 370 trillion to 750 trillion Hz. When referring to light, we speak of wavelengths rather than vibrations. As a result of the very high frequencies and the speed at which light travels (300,000 km per second), the wavelength is extremely short, less than one thousandth of a millimeter. The higher the vibration, the shorter the wavelength. Not all light beams have the same wavelength. The spectrum of visible light ranges from wavelength of 780 nm to a wavelength of 380 nm. We perceive the various wavelengths as different colors. The longest wavelength (which corresponds to the lowest frequency) is seen by us as the color red followed by the known colors of the rainbow: orange, yellow, green, blue, indigo, and violet which is the shortest wavelength (and highest frequency). White is not a color but the combination of the other colors. Wavelengths which we are unable to perceive (occurring just below the red and just above the violet area), are the infrared and ultraviolet rays, respectively. Visible light is only visible because we can see the source and the objects being illuminated. The light beam itself cannot be seen. The beams of headlights in the mist for instance, can only be seen because the small water drops making up the mist reflect the light. Figure 5.14 shows the electromagnetic spectrum.

(a) Electromagnetic Spectrum

radio microwave infrared ultraviolet

X- rays gamma

rays

wavelength

in narometres(1 nm =

1 billionth

of a metre)

109 10 10 10 10 108 7 6 5 4 3 2 1 0 -1 -2 -310 10 10 10 10 10 10

light visible

red orange yellow green blue indigo violet

380 nm780 nm


(b) Visible Light Spectrum Figure 5.14 Visible light as part of the electromagnetic spectrum.

LuminosityBesides differing in color (frequency), light can also differ in luminosity, or brightness. A table lamp emits less light than a halogen lamp, but even a halogen source cannot be compared with bright sunlight, as far as luminosity is concerned. Luminosity depends on the amount of available light. It can be measured and recorded in a numeric value. In the past, it was expressed in Hefner Candlepower, but nowadays Lux is used to express the amount of luminosity. Luminosity is the basic principle of the black-and-white television. All shades between black and white can be created by adjusting the luminosity to specific values.

Brightness Values:Candle light at 20 cm 10-15 LuxStreet light 10-20 LuxNormal living room lighting 100 LuxOffice fluorescent light 300-500 LuxHalogen lamp 750 LuxSunlight, 1 hour before sunset 1000 LuxDaylight, cloudy sky 5000 LuxDaylight, clear sky 10,000 LuxBright sunlight > 20,000 Lux

Red Orange Yellow Green Blue Indigo Violet


5.7.1 Color MixingThere are two kinds of color mixing: additive and subtractive color mixing. The mixing of colorants, like paint, is called subtractive mixing. The mixing of colored light is called additive mixing. Color TV is based on the principle of additive color mixing. Primary colors are used to create all the colors that can be found in the color spectrum.

Additive Color Mixing: In video, the color spectrum contains three primary colors, namely red, green and blue. By combining these three, all the other colors of the spectrum (including white) can be produced.red + blue = magenta (cylamen)red + green = yellowblue + green = cyan (turquoise)green + magenta = whitered + cyan = whiteblue + yellow = whitered + blue + green = whiteMaking colors in this way is based on blending, or adding up colored light, which is why it is called additive color mixing. Combining the three primary colors in specific ratios and known amounts enables us to produce all possible colors.

Subtractive Colour Mixing: White light is derived from a ratio of 30% red, 59% green, and 11% blue, see figure 5.15. This is also the ratio to which a color TV is set for black-and-white broadcasts. Shades of grey can be created by maintaining the ratio percentages and by varying the luminosity to specific values. 30% red + 59% green + 11% blue = white

Figure 5.15 subtractive colour mixing: By combining the three primary colors red, green and blue, other colors can be mixed, including white.

Additive color mixing Yellow (red and green)

(red and blue) Magenta or violet

White (all three primary

colors)

Green

Cyan or blue-green(blue and green)

Red

Blue


5.7.2 Light RefractionLight refraction is the reverse process of color mixing. It shows that white light is a combination of all the colors of the visible light spectrum. To demonstrate refraction a prism is used, which is a piece of glass that is polished in a triangular shape. A light beam traveling through a prism is broken twice in the same direction, causing the light beam to change its original course. Beams with a long wavelength (the red beams) are refracted less strongly than beams with a short wavelength (the violet beams), causing the colors to fan out. The first fan out is enlarged by the second fan out, resulting in a color band coming out, consisting of the spectrum colors red, orange, yellow, green, blue, indigo, and violet. There are no clear boundaries between the various colors, but thousands of transitional areas. A rainbow is a perfect example of the principle of light refraction in nature. When white light, such as sunlight passes through a prism, it is refracted in the colors of the rainbow.

5.7.3 Color TemperatureColor temperature relates to the fact that when an object is heated, it will emit a color that is directly related to the temperature of that object. The higher the color temperature, the more 'blue' the light, and the lower the color temperature the more 'red' the light. Color temperature of light can be measured in degrees Kelvin (K). Daylight has a color temperature between 6000 and 7000 K. The color temperature of artificial light is much lower: approximately 3000 K. In reality, color temperatures range from 1900 K (candlelight) up to 25,000 K (clear blue sky). Television is set to 6500 K, simulating 'standard daylight’

5.7.4 The Human EyeThe eye tends to retain an image for about 80 milliseconds after it has disappeared. Advantage is taken of this in television and cinematography, where a series of still pictures (25 per second) create the illusion of a continuously moving picture. Other characteristics of the human eye are that it is less sensitive to color detail than to black-and-white detail, and that the human eye does not respond equally to all colors. The eye is most sensitive to the yellow/green region, and less in the areas of red and (particularly) blue.

5.7.5 Colour video signal generation and connectionsThe term “black and white” is rather misleading because there is all the different shades of grey in between, as well. Monochrome (one colour) is the


term to use, but even that is not totally correct (neither black, white, nor grey are colours, so it is not even “one colour”).

An image passes through the camera lens, and lands on the video target, where it is scanned and turned into an electronic signal that is representative of the picture. If it were done this simply, though, the picture would look rather wierd, as some things would look brighter than they should do, and other things too dark, because our eyes are sensitive to different colours in a certain ratio. So the spectral response of the camera is set up to mimic human vision, which is mostly sensitive to green light, with lesser sensitivities to red and blue light (the ratios being approximately 59% green, 30% red, and 11% blue), so that the monochrome image looks natural. Using photographic filters and/or the photosensitive characteristics of the target, the amount of red, green, and blue light reaching the target is adjusted to produce a natural response.

5.7.6 Colour VideoWhen we see colour, it is due to receptors in our eyes that are mostly sensitive to red, green, and blue light, and between the three of them, we see the full spectrum of colours. So the colour television system, again, is designed to work in a similar way using red, green, and blue light-sensitive components to produce a colour signal. At the simplest level, there are three video targets, one for each colour, with optical filters and prisms (or mirrors), between the lens and targets separating the colours. Those targets are scanned and gamma corrected, this gives three separate red, green, and blue (RGB) video signals. Since we want just one video signal (composite video) that carries all that information, and it is desirable for it to be compatible with monochrome televisions, too. So there must be a way to combine all the signals together in a way that they could be separated, again, in the colour television receiver, and in a way that the colour signals wouldn't be noticed by the older monochrome television sets. The light in any scene can be divided into its three basic color components by passing the light through red, green, and blue filters. This is done in a color TV camera, which is really three cameras in one (see figure 5.16). The lens focuses the scene on three separate light-sensitive devices such as a vidicon tube or an imaging CCD by way of a series of mirrors and beam splitters. The red light in the scene passes through the red filter, the green through the green filter, and the blue through the blue filter. The result is the generation of three


simultaneous signals (R, G, and B) during the scanning process by the light-sensitive imaging devices.

Figure 5.16 Generating colour signals using camera

The red, green, and blue signals are combined together in the right proportions to produce a natural monochrome video signal; the “luminance” signal (“Y” being the abbreviation used for it). This gives us a picture signal for the old monochrome television sets to use, and provides the majority of the picture detail on the colour sets.

Next was needed a way to send the colour information. The technique used is called a “colour-difference” system, where information is transmitted that are the differences between the black and white image and the colour one. Technically, it is done by electrically combining the red and blue signals with the luminance signals, producing a red minus the luminance signal, and a blue minus the luminance signal. At this stage we have what's known as “component video” (separate signals for luminance, and the two colour-difference signals of R-Y & B-Y) (see figure 5.17a), as used in professional analogue video systems and found on the back of many DVD players. Those colour-difference signals are encoded into a single “chrominance” signal (see figure 5.17b), which will be added to the luminance video signal in a manner that is not noticed by most monochrome sets , to produce a “composite video” signal.

Assembly of beam splitters

and mirrors

Lens

Filters

Scen

e

Light-sensitive imaging device (CCD, etc)

Color

Amplifiers

signals

R

G

B

Blu

eG

ree

nR

ed


Figure 5.17 Video signal encoding

The R, G, and B signals also contain the basic brightness or luminance information. If the color signals are mixed in the correct proportion, the result is the standard B&W video or luminance Y signal. The Y signal is generated by scaling each color signal with a tapped voltage divider and adding the signals, as shown in Fig. 5.18. Note that the Y signal is made up of 30 percent red, 59 percent green, and 11 percent blue. The resulting Y signal is what a B&W TV set will see. The color signals must also be transmitted along with the luminance information in the same bandwidth allotted to the TV signal. This is done by a frequency-division multiplexing technique shown in figure 5.17(a). Instead of all three color signals being transmitted, they are combined into I and Q color signals. These signals are made up of different proportions of the R, G, and B signals according to the following specifications:Q = 21 percent red, - 52 percent green, 31 percent blue I = 60 percent red, 28 percent green, - 32 percent blue

(b) The chrominance signals are phase-encoded.

(a) Simplified diagram of colour video encoding

Red video

Green video

Blue video

Sync

Signal matrixing

Red-Y

Blue-Y

Y

Colour encoder

(e.g. PAL or NTSC)

C

Y

Pass filters &

mix amps CVBS

Composite video

S-Video

(luminance + sync)

Component videoRGB video

(Orange)(R Y)

(B Y) (B Y)

(B Y)

(b)

Q

I

Q

(Burst phase)

I

o57

(a)


The minus signs in the above expressions mean that the color signal has been phase inverted before the mixing process.

The I and Q signals are referred to as the chrominance signals. To transmit them, they are phase-encoded; i.e., they are used to modulate a subcarrier which is in turn mixed with the luminance signal to form a complete, or composite, video signal. These I and Q signals are fed to balanced modulators along with 3.58-MHZ (actually 3.579545-MHz) subcarrier signals that are out of phase see figure 5.18. This type of modulation is referred to as a quadrature modulation, where quadrature means a 90° phase shift. The output of each balanced modulator is a double-sideband 90°

Figure 5.18 NTSC composite video signal is generation

Different countries uses different approaches as to how they encoded the colour- difference signals into a chrominance signal; PAL, NTSC, SECAM, etc. We have separate luminance (“Y”) and chrominance (“C”) signals which can be used directly between equipment (as “Y/C” signals, as found in “S-Video” connectors), but will be combined together to form a “composite video signal” (known as “CVBS,” which is short for composite video, blanking, and sync) to be used for analogue television broadcasting, or simply for cabling video equipment together that's designed for composite video. For the color signals to be accurately recovered, the subcarrier at the receiver must have a phase related to the subcarrier at the transmitter. To ensure the proper conditions at the receiver, a sample of the 3.58-MHz subcarrier signal

Cam

era

ou

tpu

t si

gn

als

R

G

B

Inverting amplifier

31% B

52% G

11% B

32% B

28% G

59% G

30% R60% R

21% R

Linear mixer

Linear mixer

Linear mixer

(adder)

(Chrominance)(I + Q)

LPF0.5 MHz

LPF1.5 MHz

Balanced modulator

o90

Linear mixer

Y (luminance)

Y + Cto main mixer

3.579545-oscillator

(subcarrier)

Balanced modulator

Q

MHz

-

-

-


developed at the transmitter is added to the composite video signal. This is done by gating 8 to 12 cycles of the 3.58-MHz subcarrier and adding it to the horizontal sync and blanking pulse as shown in figure 5.19. This is called the color burst, and it rides on what is called the back porch of the horizontal sync pulse. The receiver uses this signal to phase-synchronize the internally generated subcarrier before it is used in the demodulation process.

Figure 5.19 The composite video, blanking, and sync signal

The combining of the Y & C signals also requires some reduction in the resolution of the luminance signal, so that they don't interfere with each other. This means that the composite video signal is almost the worst choice, of the lot, for connecting a signal from one thing to another.

5.7.7 Color SpacesColour television CRT’s typically have three electron guns that illuminate three different kinds of phosphor dots on the screen. Those phosphor dots, when illuminated, glow with the red, green, and blue primary colors of light. From these primary colors, all other shades are generated. A combination of real world physical characteristics determines what the human vision system perceives as color. A color space is a mathematical representation of these characteristics. Color Spaces are always three-dimensional. There are many possible color space definitions:

Front Porch

75%

50%

25%

12.5%

BackPorch

Am

plitu

de

Blacker Than Black

A

Blanking Pedestal

Video

Time

63.5 µSec[15,750 Hz]

White Level

Next Pedestal

Blanking Level

Blank Level

White Level

A

Color Burst (at least 8 cycles)

SyncPulse

100%


(i) Digital imagery often uses the red/green/blue color space, known simply as RGB.

(ii) The cyan/yellow/magenta space, known as CYM, is used in printing.

(iii) Hue, saturation, and intensity, (or HSI) is the color space typically used by artists.

(iv) Intensity-chromaticity color spaces, YUV and YIQ, are used for television broadcast.

Though most work in digital imagery is performed in RGB, image processing applications require transformation to the other color spaces.

5.7.7.1 Luminance-Chrominance Luminance and chrominance is the colour models that correspond to brightness and color. These color models are denoted as YUV and YIQ. The YUV space is used for the PAL broadcast television system used in Europe. The YIQ color space is used for the NTSC broadcast standard in North America. The two methods are nearly identical, using slightly different conversion equations to transform to and from RGB color space. In both systems, Y is the luminance or brightness component and the I and Q (or U and V) are the chrominance, or color, components. These are the variables that are changed by the brightness, color, and tint controls on a television.

The advantages of using YUV or YIQ for broadcast is that the amount of information needed to define a color television image is greatly reduced. However, this compression restricts the color range in these images. Many colors that can appear on a computer display cannot be recreated on a television screen.

5.7.7.2 RGB to YIQ & YIQ to RGB (NTSC)The YIQ system is the color primary system adopted by National Television System Committee (NTSC) for color TV broadcasting. The YIQ color solid is made by a linear transformation of the RGB cube. Its purpose is to exploit certain characteristics of the human eye to maximize the utilization of a fixed bandwidth. The human visual system is more sensitive to changes in luminance than to changes in hue or saturation, and thus a wider bandwidth should be dedicated to luminance than to color information. Y is similar to perceived luminance, I and Q carry color information and some luminance information. The Y signal usually has 4.2 MHz bandwidth in a 525 line system.


Originally, the I and Q had different bandwidths (1.5 and 0.6 MHz), but now they commonly have the same bandwidth of 1 MHZ.

RGB-to-YIQ (NTSC) Y = .299R + .587G + .114B I = .596R - .274G - .322B Q = .212R - .523G + .311B

YIQ-to-RGB R = 1.00Y + .956I + .621Q G = 1.00Y - .272I - .647Q B = 1.00Y - 1.105I + 1.702Q

5.7.7.3 RGB to YUV & YUV to RGB (PAL)Listed below are the equations for converting RGB colors into YUV and back to RGB. These equations assume that the red, green, and blue components have values between 0.0 and 1.0. Since this range is typical represented using 8-bit values between 0 and 255, they need to be scaled and processed as floating-point numbers:

RGB-to-YUV (PAL) Y = .299R + .587G + .114B U = -.147R - .289G + .436B V = .615R - .515G - .100B

YUV-to-RGB R = 1.00Y + .000U + 1.14V G = 1.00Y - .396U - .581V B = 1.00Y + 2.029U + .000V

5.7.8 SynchronisationWhether colour or monochrome, there's a common requirement for them both, that the television screen is synchronised with the transmitted video signal, so that the picture is drawn in the right place. A video signal is a serialised signal, the picture is scanned from left to right across the screen, from the top down to the bottom. Sync signals indicate where the edges of the frames are, both horizontally and vertically.


For RGB systems the sync signals may be carried on separate cables (one for horizontal sync, the other for vertical sync), or the two may be combined into composite sync and supplied with just one cable, or that composite sync may be added to one or more of the video signals (adding it to the green signal is quite common). For all the other systems, composite sync is added to the luminance signal.The encoded colour systems also have a colour synchronisation signal, the “colour burst.” This is added to the chrominance signal. It's appears, briefly, for a moment before the start of a horizontal line of video. It's not something that's seen by the viewer, it's off the edge of the visible frame. In the receiver, the colour decoding circuitry uses it to align its colour sub-carrier oscillators with the encoder's.The complete spectrum of the transmitted color signal is shown in figure 5.20. Note the color portion of the signal. Because of the frequency of the subcarrier, the sidebands produced during amplitude modulation occur in clusters that are interleaved between the other sidebands produced by the video modulation. Remember that the 3.58-MHZ subcarrier is suppressed by the balanced modulators and therefore is not transmitted. Only the filtered upper and lower sidebands of the color signals are transmitted. To demodulate these double-sided (DSB) AM signals, the carrier must be reinserted at the receiver. A 3.58-MHz oscillator in the receiver generates the subcarrier for the balanced modulator-demodulator circuits.

Figure 5.20 Transmitted video and color signal spectrum

3.58-MHz suppressed subcarrier

6 MHz Total signal bandwidth

4.5 MHz 80 kHz

Sound carrier (FM)

0.5 MHz 1.5 MHz

Band width of / and Q signals

Picture carrier (AM)

Total video bandwidth

1.25 MHz


5.7.9 ConnectionsWhen connecting a device to a video monitor, and they both have choices of different connection types, you should pick the best one possible. Some connection options are quite noticeably better than others. The least amount of stages between source and display, the better the results (picture clarity, colour response, etc.). For analogue video, the following list is in order of best to worst choices:RGB, Component, S-Video, Composite video and RF.If you have digital video connections, and you're dealing with signals which are digital, then you're best to use them, but passing analogue signals through digital connections is not a good idea (it will involve conversion to digital, and back to analogue, which will introduce losses). When you have analogue and digital signals to monitor, use different inputs on your monitor appropriate for each of them. For digital video, you have a list of choices like:HDMI, DVI and VGAAudio-wise, you want to pick the same route as the video connections. If you are connecting the video digitally, you should do the audio the same way (particularly as sometimes there can be a delay between the sound and picture, and you want them to be in time with each other). With digital audio, you have connection choices of optical or electrical digital audio.

5.8 Complete Television Encoder and Decoder.Figure 5.21 shows a simplified block diagram of an NTSC color TV decoder. with the functions of each component explained as follows;

Figure 5.21 Simplified block diagram of an NTSC color TV encoder

+

Audio

R(t) Y(t)

B(t)

I(t)

Q(t)

G(t)

RGBto YIQ

LPF 10-4.2MHz

LPF 20-1.5MHz

LPF 30-0.5MHz

2/מ-BPF

2-4.2MHz VSB

FM modulator 4.5MHz

To transmit antenna

Acos(2מf t)c

+


The RGB to YIQ converter converts the original signal from RGB to YIQ coordinates. The three low pass filters (LPF1,LPF2, LPF3) band limit each signal according to its expected bandwidth and the allocated frequency band. The dashed box implements the QAM function, which multiplex the I and Q components into a single signal at a color sub-carrier frequency of fc. The BPF is a bandpass filter, which band limits the multiplexed I and Q signal to the range of 2-4.2 MHz. This is necessary because at fc=3.58 MHz, the multiplexed signal would have a bandwidth of 3.58-1.5=2.08 to 3.58+1.5=5.08MHz because the bandwidth of the I signal is 1.5 MHz. Without the BPF, the multiplexed signal will interfere with the audio signal. This BPF essentially leaves the Q signal as is, but cut off some of the upper sideband of the I signal. The FM modulator shifts the audio signal to the audio subcarrier frequency of 4.5 MHz. Then the modulated audio, the Y signal and the multiplexed I and Q signal are added together. Finally they go through the VSB modulator, which modulate the combined signal to a designated picture carrier frequency and removes most of the lower side band.

5.9 The Receiver.Figure 5.22 shows a simplified block diagram of an NTSC color TV decoder with the functions of each component explained as follows;

Figure 5.22 Simplified block diagram of an NTSC color TV decoder.

Composite

video

BPF.4.4-4.6MHz

BPF.0.4-4.2MHz

LPF 10-4.2MHz

FM demodulator

LPF 20-1.5MHz

LPF 30-0.5MHz

2/מ-

YIQtoRGB

VSB

Demodulator

From antenna

2Acos(2מf t)c

_ +

Q(t)

I(t)

Y(t) R(t)

AudioTo

Speaker

G(t) Tomonitor

B(t)

+


The VSB demodulator brings the received signal from its picture carrier frequency to the baseband. The BPF at left extracts the audio signal, the BPF at the right extracts the composite video signal. The extracted audio signal is still at the audio sub-carrier frequency. The FM demodulator brings the audio signal back to the baseband, which is then sent to the speaker. The LPF1 extracts the luminance signal (Y) from the composite video signal. The difference between the composite video and the extracted Y signal is the multiplexed I and Q signal. The dashed box implements QAM demodulator and separates the I and Q signal and bring each back to its baseband. The YIQ to RGB converter converts the YIQ components to RGB components, which are then sent to the monitor.

5.10 Complete Television Transmitter and ReceiverThe block diagram of a TV transmitter is shown in Figure 5.23. The sweep and sync circuits create the scanning signals for the vidicons or CCDs as well as generate the sync pulses that are transmitted along with the video and color signals. The sync signals, luminance Y, and color signals are added to form the final video signal that is used to modulate the carrier. Low-level AM is used. The final AM signal is amplified by very high-power linear amplifiers and sent to the antenna via a diplexer, which is a set of sharp bandpass filters that pass the transmitter signal to the antenna but prevent signals from getting back into the sound transmitter.

At the same time, the voice or sound signals frequency-modulate a carrier that is amplified by class C amplifiers and fed to the same antenna by way of the diplexer. The resulting VHF or UHF TV signal travels by line-of-sight propagation to the antenna and receiver.


Figure 5.23 Complete TV transmitter.

5.11 TV ReceiverThe block diagram of a monochrome and colour television receiver is shown in figure 5ccc and 5ddd. A simplified block diagram of a black and white TV receiver is shown in figure 5.24. The receiving antenna intercepts radiated RF signals and the tuner selects desired channel’s frequency band and converts it to the common IF band of frequencies. The receiver used two or three stages of intermediate frequency (IF) amplifiers. The output from the last IF stage is demodulated to recover the video signal. This signal that carries picture information is amplified and coupled to the picture tube which converts the electrical signal back into picture elements of the same degree of black and white.

H

V

R

G

S

TVcamera

Lens

Image

3.58MHzVH

H +

V + C

burst High-power

linear amplifier

Antenna

Diplexer

High-power class C amplifier

Sound carrier oscillator

FM modulator

Audio amplifiers Microphone

Picture carrier oscillator

Finalvideo

Composite video

Color processing (from Fig.19-10a)

Color burst

generator

Horizontal and vertical sync

pulse generators

Horizontal and vertical sweep

circuits for scanning

Mixer (adder)

Low-levelAM modulator


Figure 5.24 Block diagram a monochrome television Receiver

The block diagram of a colour receiver is similar to the black and white receiver shown in figure 5.25. The colour picture tube has three guns corresponding to the three pick-up tubes in the colour camera. The screen of this tube has red, green and blue phosphors arranged in alternate stripes. Each gun produces an electron beam to illuminate corresponding colour phosphor separately on the fluorescent screen. The eye then integrates the red, green and blue colour informations and their luminance to perceive actual colour and brightness of the picture being televised. The sound signal is decoded in the same way as in a monochrome receiver The main difference between the monochrome and colour tubes is the need of a colour or chroma subsystem which accepts only the colour signal and processes it to recover (B-Y) and (R-Y) signals. These are combined with the Y signal to obtain VR, VG and VB signals as developed by the camera at the transmitting end. VG becomes available as it is contained in the Y signal. The three colour signals are fed after sufficient amplification to the colour picture tube to produce a colour picture on its screen.

Receiver antenna

Sound IFamplifier

FM sound demodulator

Audioamplifier

Loudspeaker

Picture tube

RFtuner

Common IF

amplifiers

Video detector

Video amplifier

Light

Scanning and synchronizing

circuits


Figure 5.25 Block diagram of a colour television receiver

5.11.1 The Picture TubeThe basic elements of a CRT are the envelope, electron gun, and phosphor screen (figure 5.26a). The envelope, typically made of glass, serves as a vacuum enclosure, substrate for the phosphor screen, and for the electron gun. The envelope is typically funnel-shaped, with the small end blocked by a glass stem that supports the electron gun. The electron gun produces, controls, focuses, and deflects the electron beam that causes the phosphor screen to glow. The large end of the funnel is sealed by a glass panel or faceplate on the inside of which the phosphor screen is deposited. The phosphor screen emits light when excited by electron bombardment, and thereby produces a viewable image. CRTs produced with one color phosphor are monochromatic, that is, the image is black-and-white, black-and-green, or any other color contrasted with black. Color CRTs use several colors of phosphor, generally red, green, and blue, and produce full-color images as additive combinations of these colors. To produce a color television picture tube, the most commonly employed CRT is a thin screen of perforated metal called an aperture mask is welded to a frame mounted within the panel. This aperture mask must travel with the glass panel throughout the production process. Using the aperture mask as a pattern, multiple coatings and rinsings of the panel are performed, leaving a surface with thousands of narrow lines of red, green, blue, and black (figure 2.6b). The panel, with aperture mask in place, is then sealed to the envelope. The assembly of

Antenna

IF sound signal trap Sound strip L.S.

To AGC circuit

‘Y’ signal

To sweep circuit

Colour picture tube

‘C’ signal

‘Y’ signal VR

VG

V B

Red gun

Green gun

Blue gun

Detectionyoke

Colour phosphorscreen

BGR

Tuner and IF sections

Chromasignal filter

Videodetector and buffer amp.

Videoamplifier

Chromasub-su

Chromasub-system


(a) Basic elements of CRT

(b) CRT electron gun, aperture mask, and matrix line screenFigure 5.26 The television Picture tube.

electron guns and deflection yoke is fitted to the rear of the envelope, the air is evacuated from the envelope, and the envelope is sealed. The proper alignment of guns, aperture mask, and panel is of critical importance in the assembly of a tube and determines the not only the quality of the image but whether or not the tube will function. Glass forms the outer shell of the CRT and functions as much more than a simple container. The composition of the glass in the tube is designed to minimize optical defects, provide electrical insulation for The thickness of the glass must be increased as tube size is increased, to high voltages, and provide protection against X-radiation

base

connections

three

electron

guns electro-magnetic

deflection

yoke

aperture

mask

fluorescent light-emitting

three-color screen

three

electron

beams

special

glass bulb

electron gun

aperture mask

matrix line screen (inside faceplate)


emissions. withstand the atmospheric pressure exerted on the tube which contains a vacuum.

5.11.2 Picture Yube Oparating PrinciplesThe picture tube is the largest component of a television set, consisting of four basic parts. The glass face panel is the screen on which images appear. Suspended immediately behind the panel is a steel shadow mask, perforated with thousands of square holes. (Connected to the mask is a metal shield to neutralize disruptive effects of the Earth's magnetic field.) The panel is fused to a glass funnel, which comprises the rear of the picture tube. The very rear of the funnel converges into a neck, to which an electron gun assembly is connected. The inside of the panel is painted with a series of very narrow vertical stripes, consisting of red, green and blue phosphors. These stripes are separated by a narrow black graphite stripe guardband. When struck by an electron beam, the phosphors will illuminate, but the graphite will not. This prevents color impurity by ensuring that the electron beam only strikes the phosphor stripes it is intended to light. The electron beam is generated by the electron gun assembly, which houses three electron guns situated side-by-side. Each of the three guns emits an electron beam (also called a cathode ray) into the tube, through the mask and onto the panel. Because the three beams travel side-by-side, the holes in the mask ensure that each beam, because of its different angle of attack, will hit only a specific phosphor stripe - red, green or blue. The three phosphors, lighted in different combinations of intensity, can create any visible color when viewed from even a slight distance. The three electron beams are directed across the screen by a series of electromagnets, called a yoke, which draw the beams horizontally across the screen a line at a time. Depending on the screen size, the beam draws about 500 lines across the entire screen. Each time, the phosphors light up to produce an image. The electron guns and the yoke are electronically synchronized to ensure the lines of phosphors are lighted properly to produce an accurate image. The image lasts only for about a 30th of a second. For that reason, the picture must be redrawn 30 times a second. The succession of so many pictures produces the illusion of movement, just like the frames on movie film. Color combinations produced by a picture tube


Red Green BlueRed X Yellow X X Blue XGreen X White X X XBlack Magenta X XCyan X X

5.12 Television Receiver ControlsMajority of monochrome television receivers have the following controls on their front panel (i) channel selector: The channel selector switch is used for selecting

the desired channel(ii) fine tuning: The fine tuning control is provided for obtaining best

picture details in the selected channel. (iii) brightness: The brightness control varies beam intensity of the

picture tube and is set for optimum average brightness of the picture.(iv) contrast: The contrast control is actually gain control of the video

amplifier. This can be varied to obtain desired contrast between white and black contents of the reproduced picture.

(v) horizontal hold: The hold control is used to get a steady picture in case it rolls up or down.

(vi) volume controls: The volume and tone controls form part of the audio amplifier in sound section, and are used for setting volume and tonal quality of the sound output from the loudspeaker.Besides an ON-OFF switch. Some receivers also provide a tone control.

In colour receivers there is an additional control called ‘colour’ or ‘saturation’ control. It is used to vary intensity or amount of colours in the reproduced picture. In modern colour receivers that employ integrated circuits in most sections of the receiver, the hold control is not necessary and hence usually not provided.

5.13 Other Screen DisplaysApart from the CRT for a display, new display methods have been perfected and brought to market. These include liquid-crystal displays (LCDs), plasma,


projection, Digital Light Processing (DLP), and a few others. These new displays are more expensive than CRTs, but they have brought two major benefits to TV displays.

(i), The displays are flat or thin. CRTs require depth to function properly and so take up a great deal of room on a table or desk. The typical depth of a CRT is 18 to 24 in. LCD and plasma displays are very thin and rarely more than 5 in thick.

(ii) Alternative displays can be made in much larger sizes. The maximum CRT size made today is 36 in. Other displays can be made in sizes from about 37- to 60-in diagonal measurement. Many of these displays are capable of being wall-mounted. A brief summary of the most common types are as follows;

Plasma. A plasma screen is made up of many tiny cells filled with a special gas. When the gas is excited by an electric signal, the gas ionizes and becomes a plasma that glows brightly in shades of red, blue, and green. The cells are organized to form triads or groups of the three colors that are then mixed and blended by your eye to form the picture. Scanning signals turn on the cells horizontally as in a CRT.

LCD. Liquid-crystal displays use special chemicals sandwiched between pieces of glass. These chemicals are designed to be electrically activated so that they block light or pass light. A bright white light is placed behind the screen. Then the red, blue, and green sections of the screen are enabled to pass the desired amount of light. The screen is also made in the form of groups of three color dots or segments to produce any desired color. Electric signals scan across the color dots horizontally, as in other TV sets, to reproduce the picture. LCD screens are very common in computer video monitors but are now practical for TV sets. As prices decline more TV sets will use them.

Projection screens. A popular large screen option is an LCD projection TV. A very bright light is passed through a smaller LCD screen and then through a lens, creating a picture from 40 to 60 in diagonally. Another projection screen uses Texas Instruments’ Digital Light Processing (DLP) chips. These chips are made with microelectromechanical systems (MEMS). They consist of


thousands of tiny mirror segments each whose tilt angle is controllable. These mirrors reflect light through color lenses to create a very large back-projected image.

5.14 Summary of Television OperationThe pictures you see on your TV are drawn by a beam of electrons fired out of a gun at the back of the set. When the beam hits chemicals (called phosphors) that are painted on the inside of the picture tube, the phosphors glow. But because they glow only for a fraction of a second, the beam has to immediately draw another picture. In fact, the beam draws a picture 30 times every second which is so fast that, together, the pictures look like they are moving.

The TV receives electrical signals, either through the air from broadcast stations, or over cable or from a VCR. Those signals are pulses of electrical energy that arrive in waves. Those waves can have many different shapes, and each shape can tell the TV something about what it's supposed to do. A TV uses two kinds of waves, AM (for Amplitude Modulation) and FM (for Frequency Modulation). As their names suggest, AM waves vary in strength but not how frequently they repeat, while FM waves vary in frequency but not their strength.

Each TV channel uses multiple AM signals and one FM signal. And there are several channels broadcast at the same time. It's the job of the tuner in the TV set to filter out all channels except the one you want to watch. For example, if you want to watch channel 7, the tuner blocks out all the channels below 7, and all the channels above 7. The only one it lets through is channel 7, with its AM and FM signals. After the channel passes through the tuner, it travels through a series of filters that separate the FM waves from the AM waves, and then separates the multiple AM waves from each other. The FM signal, which is the same kind used to carry FM radio signals, carries the sound information, just like a radio. FM signals can carry multiple audio channels - in this case, two, for stereo sound. AM waves, which are the same kind used to carry AM radio signals, carry the picture information. The TV uses one AM wave to carry the basic picture information which is needed to draw a black & white picture. In effect, it tells the electron gun how brightly to illuminate the screen at each point along a horizontal line. When it finishes drawing that line, it draws another and another, until it fills the screen with 525 lines. And when it


finishes drawing a screen, it draws a second, and a third, and so on, at a rate of 30 pictures every second.

The TV "draws" pictures by synchronizing the electron guns (which shoot the beams that light the screen) with the yoke, a circle of magnets that deflect, or "pull," the electron beam left and right, and up and down, across the screen. Together, the guns and the yoke can draw pictures, by knowing what to draw and where to draw it. Another AM signal carries the color information - it tells the TV where to put the color. This signal actually consists of two signals on the same wave, separated by time.

On a color TV, black is produced when no colors are lit. White is produced when red, green and blue are lit together. If the TV lights only blue, the TV will, of course, produce blue. But if it lights red and green, the TV will produce yellow. If it lights blue and green, the TV produces cyan. In fact, using only red, green and blue, the TV can produce any color.


CHAPTER SIX

TELEVISION ANTENNA SYSTEM

The antenna (aerial, EM radiator) is a device, which or receives electromagnetic waves. The antenna is the transition between a guiding device line, waveguide) and free space (or another usually unbounded medium).Its main purpose is to convert the energy of a guided wave into the energy of a free-space wave (or vice versa) as efficiently as possible, while in the same time the radiated power has a certain desired pattern of distribution in space.

An antenna, otherwise known as an arial, is a device created to send or receive signals through air waves. The word antenna comes from the Latin, meaning, "sail yard." There are many types of antennae and many ways to categorize them. Man-made antennas are made for the basic purpose communication: to send and receive signals, signs and other forms of communication. They are mostly metal and have many different designs, sizes, and shapes. The major categorical division between those devices that transmit signals called "transmitting antennas" and those that receive signals called "receiving antennas." It is possible to have antennas that function as both, that is, for transmitting and receiving signals. However, transmitting units can handle a great deal more energy than receiving antennas. Antenna types can be used to differentiate between those used for radio, television, radar systems and much more. Since antennae can be built for transmission on different frequencies, another way to categorize them is by their frequency. For a radio antenna, it is important to know whether they are built for frequency modulation (FM) which broadcasts at 88-108 MHZ (megahertz) or amplitude modulation (AM) which broadcasts at 535-1605 KHZ (kilohertz). For television antennae, you can distinguish between UHF (ultra high frequency) and VHF (very high frequency) antennas or perhaps even those which pick up both.

6.0 Definition and circuit theory description.

6.1 General Review of Antenna Geometries and Arrangement.From the general review point of view, a review of antennas based on their geometries and arrangements will be considered in this section. This review will consider the following the single-element radiator’s aperture antennas,


printed antennas, printed slot radiators, leaky waves antennas, reflector antennas and lense antennas.

6.1.1 Single Element Radiators

Figure 6.1. A Wire radiators (single-element)

Figure 6.2. Aperture antennas (single element)

There is a variety of shapes corresponding to each group. For example, loops can be circular, square, rhombic, etc. Wire antennas are simple to make but their dimensions are commensurable with the wavelength. This limits the frequency range of their applicability. At low frequencies, these antennas become increasingly large.

Aperture antennasAperture antennas are those whose beam width is determined by the dimensions of a horn, lens or reflector. They are excited by a propagating wave produced by another transducer which itself is an antenna and provides transmission line connection for the aperture antenna. See fig. 6.2.

(a) Pyramidal horn (b) Conical horn

wire antenna elements

straight-wire elements

(dipoles/monopoles) loops helices


Printed AntennasThe patch antennas consist of a metallic patch etched on a dielectric substrate, which has a grounded metallic plane at the opposite side. They contain some sort of opening through which electromagnetic waves are transmitted or received. They are commonly used in aircraft or spacecraft applications. The feed of a parabolic dish or other type of reflector antenna is often an aperture antenna such as an open-ended wave guide or horn. These types of antennas are preferable in the frequency range of 1-2 GHz. Figure 6.2 shows single element aperture antennas.

(a) circular patch (b) rectangular Patch

( c) Printed Dipole

Figure 6.3 Printed Patch Radiators

There is great variety of geometries and ways of excitation. Figure 6.3 shows three geometries of patch antennas. There are virtually unlimited number of patch patterns, for which the basic configurations used in practice is given in figure 6.4.

Ground plane

t1 Subscribe

tPatch

A

t

A

L

Ground plane

t1 Subscribe

SQUARE DICK DICK WITH SLOT

RECTANGULAR ELLIPSE DISK SECTOR


Figure 6.4. Forms of Patches

They are suited for integration with slot-line circuits, which are usually designed to operate at frequencies > 10 GHz. Both patch and slot antennas share some common features. They are easy and cheap to fabricate. They are easy to mount; they are light and mechanically robust. They have low cross-polarization radiation. Their directivity is not very high. They have relatively high conducting and dielectric losses. These radiators are widely used in patch/slot arrays, which are especially convenient for use in spacecraft, satellites, missiles, cars and other mobile applications.

6.1.4 Leaky-Wave AntennasThis is a waveguide structure that possesses a mechanism that permits it to leak power all along its length shown in figure 6.5 in a leak wave antenna with continuous slit along its length. Since the leakage occurs over the length o f the slit in the waveguide structure, the whole length constitutes the antenna’s aperture. they are classified into uniform leaky wave antenna (ULWA) and periodic leaky wave antenna (PLWA). These are antennas derived from millimeter-wave (mm-wave) guides, such as dielectric guides, microstrip lines, coplanar and slot lines. They are developed for applications at

6.1.3 Printed Slot Antennas (Radiators)A slot antenna is a transmitting aerial which the radiating elements are open slots surrounding a metal sheet. Printed slot antennas comprises a slot on the ground plane of a grounded substrate. The slot can have virtually any shape and can be fed either by a microstrip line or coplanar waveguide.

PENTAGON RINGRIGHT-ANGLED

ISOSCELES TRIANGLE

EQUILATERAL TRIANGLE

SEMI DISK ELLIPTICAL RING


Figure 6.5. Leaky Wave Antennas

Reflector AntennasThis are antennas which the principle of mirror reflection from curvilinear metal surfaces is used to focus high frequently electromagnetic energy. These reflectors is larger than the wavelength. structurally, reflector antennas are metallic or metal-plated surfaces of various shapes. Figure 6.6 shows typical reflectors. The two most important characteristics of directional antennas are directivity and power gain. A reflector is used to concentrate the EM energy in a focal point where the receiver/feed is located. Optical astronomers have long known that a parabolic cylinder mirror transforms rays from a line source on its focal line into a bundle of parallel rays. Reflectors are usually parabolic (paraboloidal). Reflector antennas have very high gain and directivity. Typical applications: radio telescopes,

Frequencies > 30 GHz, infrared frequencies included. Periodical discontinuities are introduced at the end of the guide that lead to substantial radiation leakage (radiation from the dielectric surface).

Intal strips

Reflector

Feed

Reflector

Sub-reflector

Feed

(b) Parabodic reflector with Cruepain feed (a) Parabodic reflector with fecal feed


Figure 6.6. Typical Reflectors

Lens AntennasThis is a microwave antenna with a dielectric lense placed in front of a dipole or horn radiator to concentrate the radiated energy into a narrow beam or focus the received energy on the dipole or horn. The shape of the lense depends on the refractive index n, the ratio of the phase velocity of propagation of a radio wave in a vacuum to that in the lense. If n > 1 we define a decelerating lense antenna, but if n < 1 we define an accelerating lense antenna, See figure 6.7. Lenses play a similar role to that of reflectors in reflector antennas. They collimate divergent energy into more or less plane EM wave. Lenses are often preferred to reflectors at higher frequencies (f > 100 GHz). They are classified according to their shape and the material they are made of.

(a) Lense antenna with index of refraction n > 1

Reflector

Feed

(c) Corner reflector

Convex-plane Convex-convex Convex-concave


6.2 Antenna ArraysAntenna arrays consist of multiple (usually identical) radiating elements. Arranging the radiating elements in arrays allows achieving unique radiation characteristics, which cannot be obtained through a single element. There are two types of antenna arrays: Driven arrays – all elements in the antenna are fed RF from the transmitter Parasitic arrays – only one element is connected to the transmitter. The other elements are coupled to the driven element through the electric fields and magnetic fields that exist in the near field region of the driven element. There are many types of driven arrays. The four most common types are:

(i) Collinear array (ii) Broadside array (iii) Log Periodic Array (iv) Yagi-Uda Array

(b) Lense antenna with index of refraction n < 1

Figure 6.7. Lense Antennas

6.2.1 Collinear Array The collinear array consists of /2 dipoles oriented end-to-end. The center dipole is fed by the transmitter and sections of shorted transmission line known as phasing lines connect the ends of the dipoles as shown figure 6.8a.

Convex-convex Convex-concave Convex-plane


(b) Feed and Phasing lines (b) Phasing lines adjustment.

Figure 6.8 Collinear Array

The length of the phasing lines are adjusted so that the currents in all the dipole sections are in phase, as shown figure 6.b. The input impedance of a collinear array is approximately 300 ohms. The directivity of a collinear array slowly increases as the number of collinear sections is increased.

6.2.2 Broadside Array A broadside array consists of an array of dipoles mounted one above another as shown below. Each dipole has its own feed line and the lengths of all feed lines are equal so that the currents in all the dipoles are in phase.

(a) Vertical (b) Horizontal ( c) Two Dimensional

Figure 6.9. The Broadside Array

Rows of broadside arrays can be combined to form a two dimensional array as shown figure 6.9c. The two-dimensional array is used in high performance radar systems. The amplitude and phase of each input current is adjusted so that the antenna radiates its RF in a narrow beam. By making changes to the input phase and amplitude, the beam can be made to scan over a wide range

ANTENNA

RF CURRENT

MAGNITUDE z

X

Y

Phasing Lines Phasing Lines

Feed Line

Phasing Lines


of angles. Electronic scanning is much faster than mechanical scanning (which uses a rotating antenna) and permits rapid tracking of large numbers of targets. A special type of phased array consisting of 2 or more vertical antennas is widely used in AM broadcasting. Consider an AM transmitter located in a coastal city . It would make no sense to radiate a signal in all directions; there is only water to the east of city. Two or more antennas could be used to produce a directional pattern that would radiate most of the signal to the west.

6.2.3 Log Periodic Dipole ArrayThe log periodic dipole array (LPDA) shown in figure 6.10 is one antenna that almost everyone over 40 years old has seen. They were used for years as TV antennas. The chief advantage of an LPDA is that it is frequency-independent. Its input impedance and gain remain more or less constant over its operating bandwidth, which can be very large. Practical designs can have a bandwidth of an octave or more. Although an LPDA contains a large number of dipole elements, only 2 or 3 are active at any given frequency in the operating range. The electromagnetic fields produced by these active elements add up to produce a unidirectional radiation pattern, in which maximum radiation is off the small end of the array. The radiation in the opposite direction is typically 15 - 20 dB below the maximum. The ratio of maximum forward to minimum rearward radiation is called the Front-to-Back (FB) ratio and is normally measured in dB.

Figure 6.10 Log-Periodic Dipole Array

DIRECTION OF MAXIMUM RADIATION


The log periodic antenna is characterized by three interrelated parameters.as well as the minimum and maximum operating frequencies, f and f . The diagram figure 6.11 shows the relationship between these MIN MAX

parameters. Unlike many antenna arrays, the design equations for the LPDA are relatively simple to work with.

Figure 6.11. Relationship Between Log Periodic Array Parameters

6.3 Television Transmission AntennasHorizontal polarization is standard for television broadcasting, as signal to noise ratio is favorable for horizontally polarized waves when antennas are placed quite high above the surface of the earth. The height of the antenna is determined as follows;Since the height of the antenna is a function of the wavelength “λ”. The minimum height of the antenna is given by λ/4.

i.e the height of the antenna is λ/4 = c / 4fwhere λ = c / f

8c = speed of light = 3 x 10f = transmitting frequency.

Hence from the expression above, as the transmitting frequency is increased the height of the antenna is decreased.

a L n+1 L n

n+1D

D n

LN fMIN

L1 fMAX 4tan(a)

Dn

Dn+1

== = = =500 360 בב ב

Q1-

Ln+1

Ln


6.3.1 Turnstile AntennaEssentially, the turnstile antenna consists of two dipoles at 90 degree angles to each other. One dipole is connected to the main feed line, in this case a 50-Ohm line. Its gain is almost less 3dB than that of a single dipole in its direction of maximum radiation, because each element of the turnstile receives only one-half the transmitter power. It also has very good reception pattern. Figure below shows the basic layout of the turnstile antenna.

Figure 6.12. Turnstile antenna Layout

Another important characteristics of turnstile antenna is SWR value. Since the turnstile impedance is about 36 Ohms, a 50-Ohm feed line will show an SWR of between 1.3:1 and 1.4:1. Do not try to tune the antenna for a 1:1 SWR, since that will require shortening the elements below individual dipole resonance. The resultant pattern will no longer be omni-directional. Figure 6.13a shows the geometry of turnstile antenna and figure 6.13b shows the omni-directional radiation pattern of turnstile antennas.Another important characteristics of turnstile antenna is SWR value. Since the turnstile impedance is about 36 Ohms, a 50-Ohm feed line will show an SWR of between 1.3:1 and 1.4:1. Do not try to tune the antenna for a 1:1 SWR, since that will require shortening the elements below individual dipole resonance. The resultant pattern will no longer be omni-directional. Figure 3.2 shows the geometry of turnstile antenna and figure 3.3 shows the omni-directional radiation pattern of turnstile antennas.

Main Feedline

Dipole 2

Dipole 1

Dipole 1

90 Deg.

Dipole 2

90- DegreePhasing Line

Basic TurnstileOutline


(a) Geometry

(b) Radiation Pattern

Figure 6.13. Turnstile Antenna Geometry and radiation Pattern

Turnstile antennas are most used for FM broadcast reception by take the advantage of their reasonable performance in all directions without the need for a rotor. It also survive at harshest weather. The turnstile antenna also can be a useful antenna for net control stations. However, the turnstile antenna has limitations.

One-Half Wavelength

0Feed 90Out of phase

One-Half Wavelength

- 20 - 10- 90

60

30

0

330

300

270

240

210

180

150

120

Max Null: 1 dB

40 30-

10-Meter Turnstile Azimuth PatternHeight: 35; Elevation Angle : 14 Degrees

Max Gain: 5.0 dBi Max Null: 1 dB

Fig. 2


6.3.2 Vertically stacked turnstile array A system includes an antenna array consisting of a plurality of antenna elements, a plurality of receivers to process the signals from the antenna elements of the antenna array, and a combiner to combine receiver outputs so as to minimize the effect of undesirable signals such as multipath or interference while maintaining a nominal gain in the direction of the desired signal. The combiner takes into account variation or uncertainty in the assumed antenna array response, such as imprecise knowledge of the angle of arrival and uncertainty in the array manifold and multiplicative uncertainties due to gain variations between receivers, as well as non-uniformity in the response due to coupling between elements and coupling with the antenna structure. This system is applicable to antenna arrays with non-uniform responses, such as closely spaced arrays in which the coupling between elements is significant.

Another antenna system that is often used for band I and band III transmitters consists of dipole panels mounted on the four sides at the top of the antenna tower as shown in figure 6.14. Each panel consists of an array of full-wave dipoles mounted in front of reflectors. For obtaining unidirectional pattern the four panels mounted on the four sides of the tower are so fed that the current

oin each lags behind the previous by 90 . This is achieved by varying the field cable length by λ/4 to the two alternate panels and by reversal of polarity of the current.

6.3.3 Dipole Panel Antenna System

6.3.4 Combining NetworkThe AM picture signal and FM sound signal from the corresponding transmitters are fed to the same antenna through a balancing unit called diplexer. As illustrated in figure 6.15, the antenna combining system is a bridge configuration in which first two arms are formed by the two radiators of the turnstile antenna and the other two arms consist of two capacitive reactances. Under balanced conditions, video and sound signals though radiated by the same antenna, do not interfere with the functioning of the transmitter other than their own.


Figure.6.14. Dipole panel antenna system (a) panel of dipoles (b) radiation pattern of four tower mounted dipole antenna panels.

Figure 6.15. Equivalent bridge circuit of a diplexer for feeding picture and sound transmitters to a common turnstile array.

6.4 Television Receiver AntennasFor both VHF and UHF television channels, one-half-wave length is a practical size and therefore an ungrounded resonant dipole is the basic

1 2

1 2

1 2

(a) (b)

Dipole 1

2

3

4Tower

Balun

Picture transmitter

Reactance

Sound transmitter

Reactance

Antenna load north-south turnstile

elements

Antenna load east-west turnstile

elements


antenna often employed for reception of television signals. The dipole intercepts radiated electromagnetic waves to provide induced signal current in the antenna conductors. In fact a single antenna can be designed to receive signals from several channels that be close to each other. While a half-wave dipole will deliver satisfactory signal for receivers located close to the transmitter, elaborate arrays become necessary for locations far away from the transmitter.

6.4.1 Yagi-Uda AntennaA Yagi-Uda antenna is familiar as the commonest kind of terrestrial TV antenna to be found on the rooftops of houses. It is usually used at frequencies between about 30MHz and 3GHz, or a wavelength range of 10 metres to 10 cm. The rod lengths in a Yagi-Uda are about a half wavelength each, and the spacings of the elements are about 1/3 of a wavelength. This puts the overall sizes of Yagi-Udas in the ranges

frequency transverse length length length dimension (λ/2) 3 elements 5 elements 15 elements 30MHz 5 metres 6 metres 13 metres 47 metres 100MHz 1.5 metres 1.8 metres 3.9 metres 14 metres 300MHz 50 cm 60 cm 1.3 metres 4.7 metres 1GHz 15 cm 18 cm 39 cm 1.4 metres 3GHz 5 cm 6 cm 13 cm 47 cm

From table 6.1 one can get a very good idea of the approximate frequency of the link by looking at the antenna from afar. A diagram of a 7 element Yagi-Uda layout is given in figure 6.16.

Figure 6.16. Element Yagi-Uda Layout

reflector directors

forwards direction

driven folded dipole


There are three kinds of elements (or rods) mounted on a longitudinal connecting bar or rod. It doesn't matter if this connecting rod conducts, as it is orientated at right angles to the currents in the elements, and to the radiating electric fields; it supports little or no current, and does not contribute to the radiation. It does not matter what it is made of other than that it should have good structural properties. If it is made of conducting metal as are the elements, it can be connected electrically to the directors and to the reflector (but not to the driven element) without disturbing any of the properties of the antenna.The three types of element are termed the driving element, the reflector(s) and the director(s). Only the driving element is connected directly to the feeder; the other elements couple to the transmitter power through the local electromagnetic fields which induce currents in them. The driving element is often a folded dipole, which by itself would have a driving point impedance of about 300 ohms to the feeder; but this is reduced by the shunting effect of the other elements, so a typical Yagi-Uda has driving point impedance in the range 20-90 ohms. The maximum gain of a Yagi-Uda is limited to an amount given approximately by the gain of a dipole (1.66 numerical) times the total number of elements. Thus, a single element has maximum gain 1.66 = 2.2dBi, a driving element with a single reflector has maximum gain 3.3 (numerical) or 5.2dBi, a three element antenna consisting of a single director, driving element, and reflector has maximum gain about 5 (numerical) or 7dBi and a 15 element Yagi-Uda with 13 directors has maximum gain about 25 (numerical) or 14dBi. There may be compromises in the design to achieve the required front/back ratio, driving point impedance, and bandwidth, so the gains may be somewhat less than these numbers in a practical antenna.

6.4.2 Yagi Antenna DesignThe following expressions can be used as a starting point while designing any Yagi antenna array.Length of dipole (in metres) ≈ 143/f (MHz) ( f is the centre frequency of the channel)Length of reflector (in metres) ≈ 152/f (MHz)Length of first director (in metres) ≈ 137/f (MHz)Length of subsequent directors reduces progressively by 2.5 per cent.Spacing between reflector and dipole = 0.25λ ≈ 75/f (MHz)Spacing between director and dipole = 0.13λ ≈ 40/f (MHz)


Spacing between director and director = 0.13λ 39/f (MHz)The above lengths and spacings are based on elements of 1 to 1.2 cm in diameter. It may be noted that length of the folded dipole is measured from .

centre of the fold at one end to the centre of the fold at the other end. It must be remembered that the performance of Yagi arrays can only be assessed if all the characteristics like impedance, gain, directivity and bandwidth are taken into account together. Since there are so many related variables, the dimensions of commercial antennas may differ from those computed with the expressions given above. However, for single channel antennas the variation is not likely to be much.

In fringe areas where the signal level is very low, high-gain antenna arrays are needed. The gain of the antenna increases with the number of elements employed. A Yagi antenna with a large number of directors is commonly used with success in fringe areas for stations in the VHF band. As already mentioned, a parasitic element resonant at a lower frequency than the driven element will act as a mild reflector, and a shorter parasitic element will act as a mild ‘concentrator’ of radiation. As a parasitic element is brought closer to the driven element, then regardless of its precise length, it will load the driven element more and therefore reduce its input impedance. This is perhaps the main reason for invariable use of a folded dipole as the driven element of such an array.

≈

6.4.3 Indoor AntennasAn aerial device especially designed in order to reach the reception over the air transmission TV signals, which are broadcasted at frequency range of about 41 to 250 MHz in the VHF band, and 470 to 960 MHz in the UHF band in diverse nations is called as a television antenna. In order to cover up this complete range, characteristically antennas have multiple conductors of varying lengths which match up to the wavelength range the antenna is expected to take delivery of.

Indoor TV antennas may possibly be positioned at locations where signals are sufficiently strong enough to get through antenna limitations. They are basically plugged in to the small screen receiver and positioned by rights, habitually on the top of the receiver ("set-top"). At times the display is required


to be tested with to catch up with the finest image quality. In addition an indoor TV antenna can put on from RF amplification, in general called a TV booster. They are to the largest part suitable for yellow zone while an amplified one possibly will work well in green or light green zones as well. Indoor antennas are by no means a good quality option for places with weak signal.A necessity to reallocate an antenna just about while changing channels and spotty or mottled reception and is an exceptionally universal slow down of indoor TV antennas, for the most part of directional indoor antennas. Indoor antennas for TV more or less never have a line of vision to the towers and at all times receive a reverberation, an echoed signal which bounces off the surroundings and off the residential walls. The path and strength of the reverberated signal to a great extent depends on weather, time of a day and frequency. RF emission is absorbed in different ways by different building materials thus making indoor TV antennas presentation be dependent on the manufacturing stuff or the direction in which ones windows are being gazing at. In contrast to outdoor antennas, indoor antennas do not give many benefits. They are by and large better for individuals who only have need of minimal signal gain and can just about get the channels they need. Even so, indoor antennas are being employed for various reasons, with ease of installation being the most ubiquitous one. They are more than ever all the rage with individuals residing in apartments or rented homes, as they are not capable of installing anything on a permanent basis. In strong signal areas it is sometimes feasible to use indoor antennas provided the receiver is sufficiently sensitive. These antennas come in a variety of shapes. Most types have selector switches which are used for modifying the response pattern by changing the resonant frequency of the antenna so as to minimize interference and ghost signals. Generally the switch is rotated with the receiver on, until the most satisfactory picture is obtained on the screen. Almost all types of indoor antennas have telescopic dipole rods both for adjusting the length and also for folding down when not in use.

6.4.4 Conical Dipole AntennaThis antenna consists of two half-wave dipoles inclined at about 30° from the horizontal plane, similar to a section of a cone. In some designs a horizontal dipole is provided in between the two half-wave dipoles.


Figure 6.17. VHF fan (conical) dipole with reflector

The dipoles are tilted by about 30° inward towards the wave front of the arriving signal. This as shown in figure 6.17 results in a total included angle of 120° between the two conical sections in the broadside direction. A straight reflector is provided behind the conical dipoles. This arrangement is an improvement over the conventional dipole where an element cut for the low frequencies will have a multi-lobed pattern on the higher channels, and an element cut for the high frequencies will have a poor response on the lower channels. Though, one conical antenna array may be adequate for all VHF channels, sometimes three or four such arrays are stacked high for better and more uniform reception. Another combination antenna which is known as in-line antenna is shown in figure. 6.18. It consists of a half-wave folded dipole with reflector for the lower VHF band, that is in line with the shorter half-wave folded dipole meant for the upper VHF band. The distance between the two folded dipoles is approximately one-quarter wavelength at the high-band dipole frequency.

Figure 6.18. In-line YAGI antenna array for lower and upper VHF bands

Lead wire

Dipoles

Mast

(a)

Reflector

Low band folded dipole

High-band folded dipole

Directors

Reflector


6.5 UHF AntennasDue to the higher attenuation suffered by the UHF signals, it becomes necessary to have very high gain and directive antennas. Besides this, higher gain is also necessary because receivers are less sensitive and tend to be more noisy at these frequencies than at lower frequencies. At microwave frequencies, some special type of antennas are used, in which the basic optical properties are utilized to concentrate the radiated waves for higher directivity and more gain. The two types that find wide application for television reception are the Bow-Tie or Di-Fan Antenna and Parabolic Reflector Antenna.

Figure 6.19. Fan Dipole UHF Antenna.

6.6 Bow TieBow tie antennas are, not surprisingly, shaped like the outline of a bow tie. Used primarily for UHF TV reception, these antennae feature two conductors---just like a loop antenna. As shown in figure 6.19, the dipoles are triangular in shape made out of metal sheet, instead of rods. This unit has a broad band response with radiation pattern resembling the figure of eight. When a screen reflector is placed at its back the response becomes unidirectional. For greater gain two or four sets of dipoles can be put together to form an array.

Mesh-screen reflector

Specially designed dipoles


However, the antenna does not connect the conductors. More closely related to the dipole "rabbit-ears" antennae, used for VHF TV reception, bow tie antennae consist of two "bows," each of which extends from a single conductor, loops back and reconnects to that same conductor.

6.7 Parabolic Reflector AntennaA reflector is used to concentrate the EM energy in a focal point where the receiver/feed is located. Optical astronomers have long known that a parabolic cylinder mirror transforms rays from a line source on its focal line into a bundle of parallel rays. Reflectors are usually parabolic (paraboloidal). Actually, the first use of a parabolic (cylinder) reflector was used for radio waves by Heinrich Hertz in 1888. Rarely, corner reflectors are used. Reflector antennas have very high gain and directivity.The parabolic reflector antenna shown in figure 6.20 has its dipole placed at the focal point of a parabolic reflector. The incoming electromagnetic waves are concentrated by the reflector towards the dipole. This provides both high gain and directivity. Note that instead of using an entire parabolic structure only a

Figure 6.20 in operation, combination antennas serve to simplify reception problems from all the channels. Various combinations of different VHF and UHF antennas are in use.

section is used. The use of such a reflector provides a gain of 8 db over that of a resonant half-wave dipole. In areas where both VHF and UHF stations are

Parabolic reflector antenna.

Reflector

Dipole

Lead-in wire


6.8 Log-Periodic Dipole Arrays (LPDA)The LPDA has several dipoles arranged in echelon and criss-cross fed from the front. The name comes from the geometric growth, which is logarithmic.

Figure 6.21. Log periodic Antenna Types

This is a very wideband antenna with a gain of up to about 7 dBi. For any frequency, only about three of the elements are carrying much current. The other elements are inactive. As frequency increases, the active elements “move” toward the front of the array. Most VHF TV antennas are LPDAs. TV LPDAs come in two types: straight and Vee shown in figure 6.21. The Vee type (LPVA) has a very slightly higher gain for channels for some channels. The basic construction of a log periodic antenna consisting of a six element array is illustrated in figure 6.22.

Figure 6.22. Six Element Log Periodic Antenna

TV station

LPDAstraight type overhead view overhead view

Vee type LPDA

Staggered feeder system

Transmission line


From figure 6.22, the largest dipole is at the back and each adjacent element is shorter by a fixed ratio typically 0.9. Also the distance between the dipoles becomes shorter and shorter by a constant factor which is typically 35 per cent of quarter wave spacing. As a result, the resonant frequencies for the dipoles overlap to cover the desired frequency range. All the dipoles are active elements without parasitic reflectors or directors. The active dipoles, as shown in the figure, are interconnected by a crossed wire net which transposes the signal by 180°. When this antenna is pointed in the direction of the desired station, only one or two of the dipole elements in the antenna react to that frequency and develop the necessary signal. All the other elements remain inactive, i.e., do not develop any signal at that particular frequency. However, for any other incoming channel some other elements will resonate to develop the signal. When the largest dipole is cut for channel 2, the array will cover all the low-band VHF channels as antenna resonance moves towards the shorter elements at the front. However, for the high-band VHF channels i.e 174 to 223 MH,z the elements operate as 3 λ/2 dipoles.

They are angled in as a ‘V’ to line up with the split lobes in the directional response for third harmonic resonance. Figure 6.23 illustrates a log periodic antenna for colour Tv reception.

Figure 6.23 A colour log periodic antenna. The elements are vee’dto eliminate dual phase problems.

Vee’d elements

Mast


When the largest dipole is cut for the lowest channel in the UHF band of 470 to 890MHz, the array can cover all the UHF channels. The UHF antenna array can be mounted along with the VHF array where a diplexer network (a U/V splitter) connects the two antennas to a common transmission line .

6.9 Antenna InstallationThe following information about antennas is a guide to their installation.

Choosing the right antenna: Outdoor antennas are preferred to the indoor variety whose performance can be affected by wall insulation, plumbing, electrical wiring, roofing materials and even people moving around a room.Choice of an outdoor antenna depends on the channels in your area:Very High Frequency (VHF)

· Band I antennas for channels 0 to 2 · Band II antennas for channels 3 to 5 · Band III antennas for channel 5A to 11 · Multi-channel VHF antennas for channels 0 to 11

Ultra High Frequency (UHF) · Band IV antennas for channels 28 to 35 · Band V antennas for channels 39 to 69 · Band IV/V antennas for channels 28 to 69

The UHF antenna size depends on how close you are to the transmitter. In most areas, where you can see the transmitting station, a yagi antenna with 8 to 10 elements or cross-pieces should be used. At distances greater than 20km from the transmitter, or in difficult terrain, a 10 to 18 element antenna will be needed. This type of antenna, because of its length, may have to be mounted on a stronger mast. In most locations, particularly where channels from both band 4 and band 5 are used, a phased array antenna is usually suitable.

Mounts or Masts:Numerous forms of mounting brackets are available for antennas. These can range from chimney brackets to fascia board mounts to free-standing masts for brackets to be bolted to the wall of your house. Separate antennas for VHF and UHF signals are recommended. These can be mounted on the same post or mast, but always ensure that the UHF antenna is positioned about 1


meter above the VHF antenna. Mount the antenna on the mast in such a way that the antenna and the transmitter are in clear line of sight. It is usually best to mount an antenna on the side of the house closest to the transmitter.

6.9.1 Installation tips:When installing your antenna:· Disconnect the power supply to your television set before starting any

installation work. · Ground your antenna mast electrically, using heavy gauge earthing

wire"6mm" and a grounded rod. This will protect anyone who touches the antenna. It also offers your property some protection against lightening.

· Mount the antenna clear of power lines. · The minimum height is the width of the antenna (above the roof line). · Check local government regulations for mast heights if you are

installing an antenna above your roof line.

Position your antenna:Generally you should point the antenna towards the transmitting station. And it is important that you have the antenna pointed at the correct signal source. For example, in some areas there is a main transmitter and a number of translators. Shrubs and trees, building and hills in the direct path of your antenna may weaken the incoming signal and cause reception problems. If you cannot see the transmitting station, experiment by pointing the antenna in different directions-you may receive a stronger signal reflected off one of the obstacles mentioned above. The antenna cross-pieces will need to be either vertical or horizontal, depending on the ‘polarization’ of the transmission source.

Co-axial cable:Use low loss coaxial feeder cable to connect the antenna to the TV set. This type of cable is suitable for both VHF and UHF signals. Use the shortest possible length of cable as this will mean reduced signal loss. Prevent wind damage by attaching the cable firmly to the outside wall. From the cable into a half-loop where it enters the house so that rainwater will drip off. Seal the entry point.


Connections:It is very important that proper coaxial connections are used at each end of the coaxial cable.When connecting coaxial cable:

· Cut back the outer cover · Cut back the center insulation · Connect the center conductor cable to the antenna · Ensure that the shielding braid is firmly contacting the saddle clamp, being careful not to crush the cable by over tightening the saddle clamp. · Coaxial plugs and joints should be soldered or securely fastened with screw connections.

Antenna connection:Most antenna have a connector box where the coaxial cable is connected to the antenna. If yours does not have such a box, then a balun is required. This piece of equipment has a coaxial connection at one end and a ribbon at the other. If your antenna needs a balun, connect the ribbon end to the antenna terminals, and the coaxial cable down lead to the coaxial connection. Position the antenna balun so that it won’t collect rainwater. A balun will also be needed at the TV end of the cable if the TV has only ribbon-type connections. Connect the ribbon to the terminals on your set, and plug the coaxial into the balun.

Diplexer:A diplexer combines signals from VHF and UHF antennas into one output cable which can then be connected to your TV set. Diplexers can be mounted either near the antennas or near the TV. You only need a diplexer when a TV set has just the one input socket for both VHF and UHF cables. Separate input sockets mean that a diplexer is unnecessary.

Splitter:More than one TV set can be connected to your outdoor antenna. A splitter takes an input signal from one cable and divides it between two or more outputs.

Amplifier If you use a splitter you will find that signal strength is reduced and that you may need a masthead or distribution amplifier. This equipment boosts the signal before it is fed into the splitter and ensures that signals of


adequate strength are supplied to each connected set. Combined Splitter/Amplifiers are also available.

FM rejection filters:FM broadcast signals can sometimes interfere with television signals and cause annoying patterns in the picture. The problem occurs where high level FM signals are present at the input of a television receiver. This can often be solved by fitting an FM rejection filter to the receiver’s antenna input at the back of the television set. This filter is sometimes described as an FM trap. The filter enables receivers to reject FM sound signals, thus preventing them from interfering with most television signals.

Down converter:Older VHF-only TV sets will need a down converter to alter the UHF signal so that it can be used by the VHF set. Most video cassette recorders can used as a down converter. Check the manufacturer’s specifications of your VCR.

Master Antenna Systems "MATV”:Many hotels, apartment buildings, hospitals and office blocks provide wall-mounted antenna sockets which are connected by cable to a master antenna. Ensure that the cable used for such connections is high quality coaxial cable. If it is necessary to install an FM filter to such a system, it should be fitted between the receiving antenna and the first amplifier in the distribution system.


CHAPTER SEVEN

TELEPHONE SYSTEMS

7.0 IntroductionA wire carrying an electric current has a magnetic field around it, i.e., there are lines of force in concentric circles round the wire shown in figure 7.1. This magnetic field will deflect a compass needle and the direction of the field depends on the direction of the current. If the wire: be placed above a magnetic needle lying in the magnetic meridian, i.e., lying in the line of the North and South magnetic poles, a current flowing south to north over the needle will deflect the north-seeking pole to the west.

Figure 7.1 Lines of force around a current carrying wire. Direction of current downwards through the plane of the paper

This is readily remembered by the right hand rule which is explained as follows: Place the right hand (palm downwards) between the wire and the needle. If the current be flowing from the wrist to the fingers, the outstretched thumb will indicate the direction in which the north-seeking pole of the needle will be deflected. By arranging a number of turns of wire in the form of a coil, technically termed a solenoid, figure 7.2 a stronger magnetic field can be obtained. The strength of the field depends on two things-the number of turns of wire and the current flowing. Iron conducts lines of force far better than air, and the introduction of an iron core enormously increases the magnetic field. The softer the iron the greater is its effect. Figure 7.3 illustrates one form of electro-magnet. The two limbs are united at their base by the soft iron yoke, and the armature of similar material is placed above. The path of the lines of


force, termed the magnetic circuit, is shown by the dotted line. In order to obtain opposite polarity on the two poles of the electro the windings are reversed on the two limbs. The effect of the current is to cause the armature to be attracted; and here it may be said that in any electro-magnetic arrangement there is always a tendency for the armature to move in such a way as to shorten the lines

Figure 7.2 A solenoid

of force as though, indeed, a tension or pull existed along their length. When an electro-magnet is carrying sufficient current to perform its function of attracting its armature, it is said to be energized.

Figure 7.3 An electro-magnet.

One of the simplest forms of signaling device consists of an electric bell, battery and press button. By arranging that certain rings shall have definite meanings, simple messages may be transmitted. This arrangement is termed

SOLENOID

S N

N S

SPRING

ARMATURE

ELECTROMAGNET

Yoke


a code of signals, and is adequate for indicating, for example, that a carrier has been placed in a pneumatic tube, that a carrier has been received, that empty carriers are required, or similar messages.

7.1 TelephonyThe common telephone as we know it today is a device connected to the outside world by a pair of wires. It consists of a handset and its cradle with a signaling device, consisting of either a dial or push buttons. The handset is made up of two electroacoustic transducers, the earpiece or receiver and the mouthpiece or transmitter. There is also a sidetone (the sound of the talker’s voice heard in his or her own receiver) circuit that allows some of the transmitted energy to be fed back to the receiver. The transmitter or mouthpiece converts acoustic energy into electric energy by means of a carbon granule transmitter. The transmitter requires a direct-current (dc) potential, usually on the order of 3–5 V, across its electrodes. We call this the talk battery, and in modern telephone systems it is supplied over the line (central battery) from the switching center and has been standardized at −48 V dc. Current from the battery flows through the carbon granules or grains when the telephone is lifted from its cradle or goes “off hook.” When sound impinges on the diaphragm of the transmitter, variations of air pressure are transferred to the carbon, and the resistance of the electrical path through the carbon changes in proportion to the pressure. A pulsating direct current results. The typical receiver consists of a diaphragm of magnetic material, often soft iron alloy, placed in a steady magnetic field supplied by a permanent magnet, and a varying magnetic field caused by voice currents flowing through the voice coils. These currents cause the magnetic field of the receiver to alternately increase and decrease, making the diaphragm move and respond to the variations. Thus an acoustic pressure wave is set up, more or less exactly reproducing the original sound wave from the distant telephone transmitter. The telephone receiver, as a converter of electrical energy to acoustic energy, has a comparatively low efficiency, on the order of 2–3%.

7.1.1 Manual Telephone Exchange.Alexander Graham Bell in 1870 invented the telephone; a wired system for two way voice communication between remote locations. This system was somewhat limited in that it only allowed communication with one fixed location, so it was an obvious advance to have lines going to other locations.


an operator was alerted and you would tell her who you wished to speak to . The operator would then take a wire from your socket on her switchboard and plug you into the other persons socket. When you completed the call, you would hang up your receiver and the operator would remove the plug from the called party's socket. This was very labour intensive and as the popularity of the telephone grew, the number of operators employed by the Post Office grew; large switching centres (exchanges) could have many tens of operators, each with their own switchboard. If you wished to make a call to someone outside your own local exchange, say to the next exchange, your operator would call an operator at the adjacent exchange and then ask her to connect through to the desired subscriber. If you wanted to call someone much further away, then the call would have to be set up with a whole chain of operators, each one calling the next. As such, although long distance calls were possible, it was a very complicated process involving a lot of operators.

7.1.2 Switching Systems7.1.2.1 The magneto system: The magneto system was among the earliest switching systems used in manual telephony. As the name implies the system uses a low frequency subscriber's voltage for the purpose of signaling. The signaling voltage is produced by manually operated generators both at the exchange and at the subscriber’s telephone. When an exchange is handling a large volume of traffic the use of hand operated generators at each position reduces the overall operating efficiency. It is usual, therefore, at large magneto exchanges to instal a machine driven alternator and for the operator to connect the signaling voltage to a circuit by means of a key. In the central battery signaling (C.B.S.) system a direct current is used for signaling, when subscribers call the exchange. The source of e.m.f, for signaling is obtained from a battery situated at the exchange. An important similarity between the two systems discussed in this pamphlet is the need for a local battery at the subscribers telephone. The local battery provides the source of current for the energization of the transmitter. In the magneto system and the central battery signaling system the calling device, on the switchboard consists of an electromagnetic flap indicator. Although, in some cases magneto switchboards have had the indicators replaced by lamps.


Sequence in setting up a connection:1. The subscriber to call the exchange lifts the telephone and turns the

handle of the generator associated with the telephone.

2. The operator to answer the calling subscriber inserts the answering cord into the subscriber's answering jack.

3. The calling subscriber's indicator flap is restored manually by the operator.

4. The speak key associated with the answering cord circuit is thrown by the operator and the number of the wanted subscriber is requested.

5. If the wanted subscriber is connected to the same exchange, the operator inserts the calling end of the same cord circuit into the jack associated with the subscriber to be called.

6. To call the subscriber, the operator throws the ring key and connects ringing current to the required line.

7. When the called subscriber answers, the setting up of the call is complete and the operator withdraws from the circuit by restoring the speak key.

8. To operate the cord circuit supervisory indicator at the completion of the call the subscribers operate their hand generators.

9. When the cord circuit supervisory indicator flap

7.1.2.2 Central Battery Signaling (C.B.S.) Systems: In the C.B.S. systems calling and clearing signals are automatically controlled by the removal and replacement of the subscriber's receiver. Two supervisory relays are provided on each pair of cords, one on the answering side and one on the calling side, these relays operate the supervisory signals when a call is in progress. The central battery located at the exchange is used for all general signaling purposes and a battery of 2 cells for speaking purposes, is associated with each telephone at the subscribers' stations. The advantages of the three C.B.S. systems as compared with the magneto System are:(i) Automatic signaling between the subscriber and the exchange.(ii) Automatic signaling over junction circuits.(iii) The external plant is necessarily maintained in the high condition of

efficiency which the system demands for satisfactory working.(iv) No generator is required at the subscriber's station.


The disadvantages of the systems are:-(i) Relatively large batteries required at small exchanges.(ii) Complexity of the exchange apparatus, and of that at a subscribers’

premises when extension circuits are necessary.(iii) Complexity of junction circuits.

7.1.2.3 Crossbar SwitchingCrossbar, as the name implies, depends on the crossing or intersection of two points to make a connection. The switching matrix is shown in Figure 7.4a. It is called a cross point array. Its operation depends on energizing a vertical line and a horizontal line and the point where they intersect represents the connection made. The crossbar system utilizes a switching matrix, which is externally managed by common control, to route telephone calls. Its operation depends on a connection made by energizing a vertical line and a horizontal line in the matrix

(a) Cross point array

11

12

13

14

15

16

01 02 03 04 05 06 07 08 09 010

OUTPUTLINES


Figure 7.4 Cross-bar switching.

as shown in Figure 7.4b, the crossbar matrix is controlled by common control. Control signals from transmission lines are detected and used to control the matrix to connect the proper lines for the path from the calling telephone to the called telephone.

7.1.2.4 Electro mechanical Switches: An electro mechanical version utilizes electromagnets to open and dose contacts in the matrix. After many operations, the contacts may prove to be unreliable. Reed relay switches, although also electro mechanical devices, are more dependable because they are in a sealed envelope. They open or dose depending on the polarity of the electrical impulses input.

7.1.2.5 Digital Switches: Most central offices employ digital switching. This replaces the maintenance intensive electro mechanical switches with reliable semiconductors.

7.1.2.6 Automatic Switching: Almon B. Strowger was an undertaker in Kansas City, USA. The story goes that there was a competing undertaker locally whose wife was an operator at the local (manual) telephone exchange. Whenever a caller asked to be put through to Strowger, calls were deliberately put through to his competitor. This obviously frustrated Strowger

CROSSPOINTMATRIX

SIGNALING CONTROL SIGNALING

(b) System Organization


greatly and he set about devising a system for doing away with the human part of the system. Strowger developed a system of automatic switching using an electromechanicalcal switch based around around electromagnets and pawls. With the help of his nephew (Walter S. Strowger) he produced a working model in 1888. In this selector, a moving wiper (with contacts on the end) moved up to and around a bank of many other contacts, making a connection with any one of them.

7.1.2.7 Selector Theory: A selector starts in the 'home' position and with each 'impulse' the wiper contacts would progress round the output bank to the next position. Each output would be connected to a different subscriber, thus the caller could connect to any other subscriber who was connected to that bank, without any manual assistance from an operator.

(a) A simple Selector


(b) A Two-Motion "Final" Selector

Figure 7.5 The Telephone Selector

In Figure 7.5a, the selector has 10 outputs, so a caller can choose to connect to any of 10 different subscribers by dialing any digit from 1 to 0 (0=10). This sort of automatic selector is known as a Uniselector, as it moves in just one plane (rotary). By mounting several arcs of outlets on top of each other, the number of outlets can be increased significantly but the wipers are then required to move both horizontally to select a bank and then vertically to move around that bank to the required outlet. Such a selector is known as a Two-Motion Selector. Two-motion selectors typically have 10 rows of 10 outlets, thus 100 possible outlets altogether. A two-motion selector can therefore accept two dialed digits from a subscriber and route the call to any of 100 numbers. The selector 'wipers' always start in their resting 'home' position. The first digit moves the selector vertically up to the corresponding level and then the second digit moves the wipers around the contacts of that level. This is shown in figure 7.5b. The type of selector shown above is known as a Final Selector as it takes the final two digits of the number dialed. Most numbers dialed are several digits longer, and therefore pass through a chain of selectors. Selectors previous to the Final Selectors are different; they are called Group Selectors. Group selectors take only ONE digit from the caller, and step up the number of levels according to the digit dialed. The rotary

Level 5

Sub “58”

Rotary Stepping

( Viewed from above)

Stepped round to level 8Stepped up to level 5

( Viewed from side)

Vertical Stepping

1

2

3

4

5

6

7

9

0

0

9

87

6

5

4

3

2

1


movement is then automatic; the wipers search around that level to find a free outlet - i.e. the next free selector in the chain.

The Rotary Dial: In Strowger's system, selecting digits to dial was done by a complicated system involving five separate wires. Later, the system of Timed Pulse (TP) dialing was invented using a rotary dial. With TP dialing, only one pair of wires is required for a telephone, the speech pair. To dial a digit, the circuit is interrupted according to the number dialed so, for example, if you dialed a '4' then the line would be pulsed four times, quickly in succession. After a moment, it was assumed that the digit was complete and that any further pulses belonged to the next digit. In order to ensure that successive digits did not come too soon and thus be mistaken for pulses belonging to the previous digit, the finger stop on the dial was put some way round so that after removing your finger from the dial, there was a minimum time taken for the dial to return to the home position. It is important to note here that for the purposes of dialing, the digit '0' sends TEN pulses for dialing - i.e. the selector will step around to the 10th position.

Progress Tones: A series of distinctive tones was developed which were produced by a machine called a Ring Generator. The ring generator was entirely electro mechanical; different cadences and tones were produced by rotating cams connected to a generator. As well as generating the tones, the Ring Generator machine also provided timed pulses which were used by various processes throughout the exchange. The progress tones produced were as follows :

(i) Dial Tone (DT). This is a 33 c/s continuous note and is applied to the line after the subscriber has lifted his handset and the switching equipment has allocated him an available outlet for this call to proceed. There would have been a physical limit on the number of calls an exchange could handle so if all equipment was already in use, the subscriber would not get dial tone. The actual pitch of the dial Tone varied from exchange to exchange depending on the adjustment of the ring generator.

(ii) Busy Tone (BT). A higher pitched note of 400 c/s interrupted to give a cadence of 0.75 seconds on, 0.75 seconds off. Busy tone indicated either that the called subscriber is already off-hook (busy) or that the route to the called subscriber is congested. In later systems, a slightly


different cadence was introduced in order to distinguish between these two scenarios.

(iii) Number Unobtainable Tone (NUT). Identical pitch to the busy tone but continuous. This tone is used to indicate that a number is out of service, faulty or that a spare line has been dialed.

(iv) Ring Tone (RT). A tone of 133c/s which interrupted in the same cadence as the ring current which rings the telephone's bell at the called party's end : 0.4 seconds on, 0.2 seconds off.

7.2 Telephone Numbering Schemes: There were many different versions of Strowger type exchanges. The smallest ones, serving small remote villages would handle just a few subscribers. The larger exchanges in urban districts could handle thousands of subscribers. In a small village, there might be just 50 subscribers and so three digits would be plenty to identify them all. For example, subscribers on a very small rural exchange might be allocated numbers in the range 200-299 - on the final selector, level 2. Of course, numbers of just two digits would have been enough to cover 50 subscribers, but three digits were used to allow for special codes (Operator, Emergency, Telegrams etc.) and also to separate payphones onto other 'levels'. On larger exchanges, four or five digits were used, allowing a theoretical maximum of 10000 or 100000 subscribers. The range was limited of course because there were no subscribers on levels '0' or '1' as they were reserved for trunk and operator calls respectively.

7.2.1 The Director System: To connect to another exchange, its code could be dialed and the selectors would route accordingly, but that dialing code would have to vary depending on where the call originated from because obviously routes would vary. From the subscriber's point of view, it would be unacceptable to have to dial a different number depending on where you were. To get around this, a set of uniform dialing codes was introduced so that a subscriber could dial the same exchange from any other exchange always using the same dialing code. Because the actual routing would vary depending on where the call originated from, a piece of equipment called a Translator was introduced. This took the uniform dialing code as the subscriber dialed it and translated it into the necessary impulse trains so that selectors could be routed accordingly. The translator was electromechanical


of course. The translator also includes 'digit absorbtion' facilities so that if a subscriber dials someone on the same exchange, the exchange code is ignored and the call routed locally. When the subscriber dials the exchange code, the translator cannot start 'translating' until it has all three digits, then it can get to work, but in the meantime, the subscriber may dial the rest of the number. To allow for this, the translator must have Digit Storage facilities so that it can store the rest of the digits dialed by the subscriber and repeat them to the remote exchange once the connection has been established.

7.2.2 The Mnemonics System: It was thought that people would have problems remembering seven digit numbers (3 exchange + 4 subscriber) so a system of allocating letters to the dial to make area mnemonics was developed. Each exchange was then given a code according to the location, as closely as possible. The original British lettering scheme was as follows:

Table 7.1 Lettering scheme

This 'letter to number' scheme varies between countries and nowadays even between manufacturers, particularly with mobile telephones. The letter 'O' was mapped to the digit '0' in order to avoid confusion. The letters Q and Z were not used in the original scheme to avoid confusion with 'O' and '2'. When the scheme was first devised, the letters were black and the figures in red (all phones were owned by the Post Office).

Some Examples :BARnet (227)EALing (325)HENdon (436)KINgston (546)MILl Hill (645)PUTney (788)VICtoria (842)

1

2

3

4

5

ABC

DEF

GHI

JKL

MN

PRS

TUV

WXY

0 (Operator)

6

7

8

9

0

Not Allocated


7.3 Automatic Telephone ExchangesThe required features of any automatic switching system is summarized in table 7.2. Figure 7.6 shows an the call routing system with its different components.

Table 7.2 Automatic telephone Exchange Features

Function Performed by

To detect that a caller has lifted his handset

To ‘busy his line so that he is not interrupted

To allocate equipment to the caller, if available

To indicate to that the caller that he may proceed with

dialling

To accept digits from the caller and route accordingly

To connect the call through to the appropriate

subscriber

To either return Busy Tone if busy or apply ring signal

to the called party’s phone

and ring tone to caller and then cease ringing when

the called party answers

To detect the answering of the call and register it

against the caller’s account

To alert engineers in case of fault

Subscriber Line

Circuit

Subscriber Line

Circuit

Line finder &

Allotter

Dial Tone

Group Selectors

Final Selectors

Final Selectors

& Ring Generator

PG/CSH Alarms

etc.

Metering Circuits


Subscriber's Line Circuit: Every subscriber is connected to his local exchange by one pair of wires; this single pair carries the voice in both directions and the ring current to ring the bell when a call is received. Within the subscriber's premises, the line is actually then split into three wires to allow for an anti-tinkling circuit but it's important to bear in mind that only two wires run from exchange to subscriber (known as a & b). Once at the exchange, an additional one or two wires is added to the line. These are used for internal signaling are known as P (or Private) and M (or Meter). At the exchange, every subscriber's line terminates into its own Subscribers Line Circuit (SLC). This consists of a pair of relays dedicated to that subscriber; if there are 1000 subscribers on that exchange, then there are 1000 SLCs. All other equipment onwards in the chain is shared between all subscribers - otherwise if there were 1000 of everything the cost and size of an exchange would be astronomical and wasteful. It would only be necessary if it was expected that every subscriber was going to place a call at exactly the same time, and that would never happen. As such, when an exchange is designed, consideration is given to the maximum amount of traffic that would ever need to be carried at one time, and equipment is therefore provided to allow for that.

Line Finder & Allotter: When the subscriber lifts his handset, current start to flow on the line; this is detected by the SLC. As you will recall, dialing of the digits causes selectors to step up or round the corresponding number of pulses. As there are many subscribers, but only a few selectors, there has to be a method for; (i) Finding a free (available) selector and (ii) Connecting the calling subscriber to that selector. Step (i) is done by the Allotter. Step (ii) is done by the Linefinder. See figure 7.6. Although the linefinder is shown looking like a Uniselector in the diagram it is in fact normally a two-motion selector which means that it can serve up to 100 or 200 subscribers. The Allotter, on the other hand is usually a uniselector, with 25 or 50 outlets, thus allowing access to 25 or 50 first group selectors. n.b. the Subscriber's Line Circuits are not shown in the diagram, but would be in the line between the subscribers' telephones and the linefinders. Another function of the SLC is to 'mark' the caller's line as 'busy' so that incoming calls will detect that the line is in use.


Figure 7.6. Simplified Routing of a Local Call

Charging: With the introduction of automatic exchanges, the need arose for automatic charging. Every subscriber was allocated a digit counter (meter) in the exchange. This consisted of an electromagnet which closed with every metering 'pulse'. The electormagnet's armature drove a set of numerical decimal cams. For every meter pulse, the meter clicked one unit. At the end of each billing period, a photographer would take a photograph of all subscribers' meters. These photographs were then sent to the billing department to be read, and bills sent out accordingly. Meters typically had four or five digits, wrapping round to '0000' after '9999'. The first meter pulse was generated as soon at the called subscriber answers the call. This pulse is generated by the final selector and sent back down the chain of selectors to the caller's meter to register one 'unit'. For local calls, a piece of equipment called a Local Call Timer (LCT) was in circuit between the final selector and previous group selectors. After the initial 'answering' pulse, the LCT starts rotating, clicking round once from each timed pulse. These timed pulses are generated by the Ring Generator. After 10 clicks round, the LCT is back to it's original position and if the call is still active, it sends another metering pulse,

LINE FINDER 1 ALLOTTER 1

2

4

3

6GROUP SELECTOR 2

FINAL SELECTOR (Level 8)

Sub. 836

8


and another unit is charged to the caller. The LCT only stops rotating when the calling party clears. If the called party hangs up, the metering continues for sometime until it is automatically dropped by the system.

For non local calls, a system of multi-metering was introduced. A meter pulse generator produced different pulse rates and the appropriate one of these would be applied to the call timer depending on the destination of the call.

Alarms: In order to facilitate efficient operation of an exchange, all Strowger type exchanges are fitted with a number of alarms to alert the engineer to any problems. Some alarms indicate equipment failure, whereas other alarms just indicate unusual operation which might be cause for concern. The most important alarms are as follows :

· Permanent Glow (PG) : This alarm indicated that a subscriber's phone was offhook and that a call was not in progress. This is not necessarily a fault; a subscriber could have just forgotten to replace their handset properly or deliberately taking their phone off the hook to avoid calls. Doing this meant that the subscriber could be holding onto exchange equipment, thus preventing other subscribers from using it. If enough subscribers left their phone off the hook, no-one else could make any calls. If an engineer spotted a PG alarm, he would work out which selector it was one and release that selector from the subscriber. In unattended rural exchanges(where no engineer was permanently on-site) the subscribers line circuit differed slightly in that a 'parking' relay was provided so that a PG condition was automatically cleared. The term 'Permanent Glow' originates from the days of manual switchboards when a subscriber being off hook would be shown by his light 'glowing' on the board.

· Called Subscriber Held (CSH) : This condition occurs when the called party hangs up his phone but the caller still remains active. A CSH alarm is not harmful, and is common - for instance, if someone puts the phone down to go and take the call in another room, a CSH condition will occur whilst their phone is back on the hook. As soon as a CSH condition is detected, a timer starts. If a period of (say) 3 minutes elapses without the called subscriber picking their handset up again then the call is cleared down and charging ceases.


Release Alarm (RA) : The release alarm is the important one. The earth supply to most selector electromagnets is connected via the release alarm. As these electromagnets are intended to operate for brief moments only (to drive the selectors), then if current is drawn for more than a few seconds, then it is assumed that the selector has jammed. In order to avoid burning out the selector, the PG alarm is raised, drawing the engineers attention to the particular rack at fault and he can rush round and clear it. In an unattended exchange, circuitry is provided to automatically lower the current to the faulty selector in order to stop it burning out until the engineer arrives.

7.4 The Morden Telephone SystemAn early acronym for the telephone company was TELCO, which was replaced by POTS (Plain Old Telephone System). Either one is easier to use than spelling out telephone system or telephone company. Since the divesture of AT&T in 1984, another acronym emerged which was used to describe some of the local telephone companies, RBOC (Regional Bell Operating Company). The elements of the telephone system is shown in figure 7.7.

Figure 7.7 Elements of a Telephone system

TollLine

TrunkSwitch Station

Local Switch Station

TrunkLine

(4-Wire)

Hybrid Circuit

Repeater

Repeater

Trunk Lines

Trunk Lines

TollLine

Local Loop

Subscriber

Subscriber

LocalLoop

(2-Wire)

TrunkSwitch Station


Hybrid Circuit


The most common and familiar use of TELCO begins when a user, known as a subscriber, picks up the telephone handset and initiates a call by going off hook. In the telephone set, a multiganged switch activates with release of the handset from its cradle or hook. This switch completes a direct current path between the subscriber and the local switch station.

7.4.1 Touch Tone PadThe dialer has long since been replaced by the Touch Tone keypad, which is laid out as block numbered push buttons. Each button, when selected and pushed, sends a pair of tones to the local switching office, which interprets the tones as the number associated with the button pushed. The name for this method of sending and detecting phone numbers is dual tone multiple frequency (DTMF). The Touch Tone pad and the tonal frequencies associated with each row and column of the pad are shown in Figure 7.8. Pressing one of the buttons on the pad sends the two tones associated with that button’s row and column.

7.4.2 Long Distance Lines

Figure 7.8 Dual Tone Multiple Frequency (DTMF) Touch Tone Pad and Associated Frequencies

For long distance or message unit calls, the call is routed through trunk lines via toll stations. Toll stations are switching stations used to select which long distance trunk lines are to be used to route your call. These trunk lines are terminated in another toll station, which may connect the call to another trunk line or to a local switch station, depending on the call’s destination. Longer calls may require longer trunk lines and additional intermediate switching

1 2 3

4 5 6

7 8 9

* 0 #

697 H z

770 H z

852 H z

941 H z

1,209 1,336 1,477H z H z H z


stations. The hierarchy of the telephone company switching stations, shown in Figure 7.9, begins with the local switch station, which has direct connections to the local subscribers. Many calls are completed at the local switch station. Other calls require connections through higher levels of switching. Local switch stations are classified as class 5 stations. They are connected to each other and in clusters to a tandem switch, which is also classified as a class 5 station. The subscribers, tandem, and local switch stations are considered as the local loop. Tandem stations, in turn, may connect the incoming call to other tandem

Figure 7.9 hierarchy of the telephone company switching stations

Local

Sectional Center

Regional Center

Sectional Center

Primary Center

TollStation

Tandem Switch


Primary Center

TollStation

Tandem Switch

Local Switch

Local

Local

Toll

Toll

Local Loop

Subscriber Subscriber


stations, which pass the call on to a local switch station to be connected to the called subscriber. Tandem stations are also the beginning of the long distance connection.

(a) (b)

Figure 7.10 Hybrid Two-Wire/Four-Wire Interface.

7.4.3 Two-Wire and Four-Wire Interfaces: A circuit called a hybrid circuit is used to interface the two-wire unbalanced twisted pair (UTP) lines to a four-wire trunk line that transports the conversation in a half duplex mode. The hybrid circuit shown in Figure 7.10 receives the call signals on a pair of wires, sending them through the primary windings of transformers T1 and T2 and impedance matching components, R1, R2, and C. The calls are coupled to the transformer secondaries, amplified, and sent out on one pair of wires. The same signals appear at the output of a second amplifier, but being in phase, have no potential difference and are canceled. Conversations returning are amplified through the second amplifier and fed, out of phase, to the junction of T1 and T2 and to one side of a two-wire connection. The signal traveling through the primaries of T1 and T2 are now out of phase and are coupled across to the secondaries and canceled at the input of amplifier 1. Hence, the signal returns along the two-wire path but is not echoed back along the four-wire line.

Amplifier

Return

4-Wire Send

Active Hybrid Transformer

T1 T2

Active R1

2-Wire Send

Return Amplifier

Signal Flow Direction

R2

C

4-Wire Receive

Send Loops Receive Loops

Return

Active

2-Wire Receive

Signal Flow Direction

T1 T2

Amplifier

4-Wire Send

R1

C

R2

Amplifier Active

Return

2

1

42

1


7.4.4 The Telephone Set.7.4.4.1 FunctionsThe telephone set performs eight electrical functions to provide us with service. The most important ones are:1. It requests the use of the telephone system when the handset is lifted.2. It indicates that the system is ready for use by receiving a tone, called

the dial tone.3. It sends the number of the telephone to be called to the system. This

number is initiated by the caller when the number is pressed (or the dial is rotated in older telephones).

4. It indicates the state of a call in progress by receiving tones indicating the status (ringing, busy, etc.).

5. It indicates an incoming call to the called telephone by ringing bells or other audible tones.

6. It changes speech of a calling party to electrical signals for transmission to a distant party through the system. It changes electrical signals received from a distant party to speech for the called party.

7. It automatically adjusts for changes in the power supplied to it.8. It signals the system that a call is finished when a caller “hangs up’’ the

handset

A single pair of wires connects the telephone to the central switching office. This connection is called a local loop. One connection is called the tip (T) and the other connection the ring. When the “receiver” handset is in the offhook, the offhook signal tells the exchange that someone wants to make a call. The exchange returns a dial tone to the called phone to let the caller know that the exchange is ready to accept a telephone number. The telephone number also may be referred to as an address. Numbers are sent either by a stream of pulses (pulse dialing) or by a series of audio Touch tones (tone Dialing. The connection having been made at the switching office, a ringing signal is sent to the called telephone. Removing the handset at the ringing telephone results in a loop current flow. The transmitter converts acoustical energy into equivalent electric current variations. The receiver converts these electrical variations into the equivalent acoustical energy-calleded sound. If either telephone handset is hung up, the current loop is opened and the central office releases the line connection.


7.4.4.2 Telephone Set ComponentsThere are several components in even the tiniest handset used for making calls. These are described below:Handset: This is the part of the telephone you hold in your hand to speak and listen to a conversation. It is also common to have the “handset” built into a headphone and microphone set for those people who spend a lot of time on the phone or need their hands free while speaking and listening on the phone. Inside the handset are a transmitter and a receiver. You speak into the transmitter and listen from the receiver.Switch hook: This is the switch that is pushed down when the handset rests on its cradle (on-hook). When you lift the handset to place a call, you release the switch hook and it pops up. The circuit is now off-hook and current flows through the telephone. When the telephone is placed back on-hook, current flow ceases.Hybrid 2- to 4-wire converter: Four wires, organized in two pairs, run from the handset, one pair from the transmitter and another pair from the receiver, to the hybrid, which provides the conversion between the 4-wire handset and the 2-wire local loop. The converter is the communications bridge between the handset equipment and the 2 wires to the telephone company.Sidetone: This is a planned, audible result emanating from the hybrid in the phone, through which a portion of speech is allowed to bleed over into the

Speech Circuit

DialingCircuits

Polarity &TransientProtection

Hook Switch

Ring (-48v)

Tip (Ground)

Analogue

Polarity &TransientProtection

RingerCircuits

AnalogueSwitches

DigitalSwitches

BORSCHTBattery Feed

(15-80mA, 56v)

Over VoltageProtection

Ring (20Hz, 90v)Line Cards

Supervision

Coding

Hybrid

Test

Coding

PBX or Central Office

Plain Old Telephone System

7.11. Telephone Set and Central Office Connection


earpiece during a conversation so that users can judge how loudly they are speaking.Dialer: This is the touch pad or rotary dial that signals the telephone company that you are placing a call. When you push the buttons on a touch pad or spin the dial on a rotary telephone that is in the off-hook state, you send a signal to the telephone company, specifying the location you are calling. Keep in mind that for flexibility many push-button phones have a setting that permits them to send either tones or pulses for signaling.Ringer: When someone is trying to call you, the telephone company notifies you by sending alternating current (AC) voltage through the wires to your telephone set. The voltage triggers a device, the ringer, that makes a ringing sound. An electrical component called a capacitor prevents direct current (DC) from flowing through this circuit when the phone goes off-hook and dial tone DC voltage is received.

7.4.4.3 Telephone Set Features Display Screen - Lets you view standard phone information, access menus, and use softkeys to select calling features like Conference and Transfer. In standard view, the screen displays the time, date, and your telephone number; the screen displays an envelope icon when you have messages waiting. Headset: Lets you listen hands-free by inserting the plug of the headset into the headset jack and then toggling the Headset key on or off. Hold Key: Place calls on hold.Indicator Light: Blinks or glows red when you have an incoming call, green when the call has been answered. Dial Pad: Works exactly like the dial pad on a traditional phone. Menu Key: Lets you change the phone settings for contrast (shades of the display screen), select the ring type (multiple ring types are provided), and set caller preferences such as Call Waiting or activate features such as Do Not Disturb and Speed Dial. Mute Key: Lets you toggle one/off the microphone during a conversation. Navigation Arrows - Four keys let you navigate through the menu system and scroll through on-screen text.Services: The Services key is used to access the Public view of the Penn Online Directory.Softkeys: Are used to activate various features and functions (softkeys are displayed along the bottom of your phone screen). The options displayed


above the softkeys will change depending on the state of phone. For example, when you are speaking with someone the End Call option appears; when the phone is idle New Call, Callers and Dir are displayed. Speaker :Toggle speaker phone on/off.Volume: Lets you adjust the volume during a conversation. When the phone is idle, you can also use the Volume key to adjust the ringer volume.

7.4.5 The Public Switched Telephone NetworkThis is the global collection of interconnections originally designed to support circuit-switched voice communication. It provides the traditional pots (Land Line Phone) service to residence and other establishments. It caries analogue data. Most central office exchanges can handle up to 10,000 telephones. But what if we have a need to connect more than 10,000 phones, or to connect phones in different cities, different states, or different countries, a complex network of many telephone exchanges has to be established to accomplish these requirements.

Exchange Destinations: Telephone exchanges exist in a network hierarchy. Usually the first four classes are for long-distance switching, and the fifth for connection to the subscription telephones.

Interconnections: The network attempts to make connection at the lowest possible level, and therefore the shortest path. If the lines are all busy, trunk groups at the next highest level are used.

Structure: The control and voice signals are carried by three types of facilities-local, exchange area, and long-haul.

Local Network: The local network consists of homes and businesses connected via wire pairs to a central office.

Exchange area network: The exchange area network fills the transmission gap between local and long distance trunks. A simplified example is shown in Figure 7.12. Exchanges are interconnected with exchange area transmission systems. These systems may consist of open wire pairs on poles, wire pairs in cables, microwave radio links, and fiber optic cables. The exchange area network normally interconnects local exchanges and tandem exchanges. Tandem exchanges


are those that make connections between central offices when an interoffice trunk is not available.

Figure 7.12. Exchange Area network

Long haul network: Toll or backbone switches (core or tandem switch; high capacity switch positioned in the physical core or backbone of a network) provide long distance connectivity over long distance trunks. each toll switch can handle more than 100,000 simultaneous phone calls. The long-haul network is made up primarily of high capacity fiber optic cables. Long-distance carriers primarily employ fiber optic cables in favor of satellite and microwave links, which are relegated to situations where optical fiber installation is not practical or economical. The long haul network has the following characteristics;(i) Higher level of users(ii) More stringent performance requirements such as high quality circuits(iii) Long distances between users including world wide distances(iv) Higher traffic volumes and densities(v) Larger switches and trunk cross section

CITY D

CITY E

CITY B

CITY C

CITY A

Sectional Center

Primary Center

Toll Center

Central Office

Microwave Land Links

Cable

Open Wire


7.5 Electronic Central officeInterfaces are used to couple two telephone subsystems to each other. They contain the hardware and programming to transfer all voice, data, and power. Subscriber calls are first handled at the central office level. Depending on the ultimate destination, the call will be switched one or more times to different levels and carried through line side and trunkside interfaces.

7.5.1 Line side interface: The largest number of interfaces in the telephone network occur between the telephone set and the local office. Because this interface has evolved through the days of magneto ringers, rotary dials, and step-by-step switches, the line side interface has been more difficult to replace with electronics and still meet the standards and characteristics that have evolved over the years. Because there are so many local loops, this is the interface that will be part of the network longer than any other telephone network are referred to as BORSCHT, which means Battery, Over voltage protection, Ringing, Signaling Supervision, Coding, Hybrid, and Test. Let's now examine the functions of the conventional line side or subscriber interface in more detail. The TELCO term for interfacing calls through the switching station hierarchy has been termed BORSHT, the letters of which are initials for the following elements of the TELCO system:

Battery, signifying the –48V battery used to supply the direct current for off hook and dial detection.Over voltage protection, which is built-in protection against voltage surges and induced voltages from electrical storms.Ringing, designating the 20–Hz ringing signal.Supervision control, which is the response to on-/off-hook, etc.Hybrid circuit, that interfaces two-wire and four-wire lines.Testing, for purposes of checking the system.

7.5.2 Trunkside Interface: A trunk usually refers to the channel(s) between the equipment at two switching locations. A trunk circuit is the interface between the trunk and the switching system. The transmission method may be wire pairs or multiplexed analog or digital signals. The trunk must have a battery supply, supervision signaling, and termination. Short-distance trunks may be pairs of wires, while long-distance trunks are usually implemented through multiplexed analog or digital carrier systems. The trunk itself may be


one way or two way, and either automatic or operator handled. The trunkside interface at the central office accommodates these varying types and provides the same sort of functions that the lineside interface provides, although with more variations and complexity.

7.6 Telephone Wiring

Table 7.3 UTP Cables and Uses

7.6.1 Cable Categories: The Electronic Industries Alliance (EIA) and the Telecommunications Industry Association (TIA) are trade associations that have developed telecommunication industry standards. The category rating system was developed by the TIA in response to industry demands for higher data rate specifications on applications over Unshielded Twisted Pair (UTP) and is now part of standard document EIA/TIA–568A which covers UTP cables as well as connecting devices such as jacks, cross-connect blocks and patch panels for Commercial Building Cabling. EIA/TIA-570-A entitled Residential Telecommunications Cabling Standard provides specifications for premises cabling. Table 7.3 shows the UTP cable category/level, their uses and supported speed.

7.6.2 Color Coding/ Tip and Ring: Standard color codes have been developed to enable the installer to quickly identify a pair within a bundle, thus facilitating termination at different points within a wiring system. Both solid and striped colors are common. Each pair has a tip and a ring conductor. The terms tip and ring originated from the earliest types of telephone systems, where the operator had to physically use patch cords to route the calls. The operator’s switchboard plug had three conductors: tip, ring and

UTP CableCat./Level Uses

Speeds Supported

1

2

3

4

5

Voice, Low Speed Data

Low Speed LAN, 4 Mbps Token Ring (all above)

10 Base T Ethernet, 100 Base T4, 100 VG Any LAN (all above)

16 Mbps Token Ring (all above)

100 Base TX,ATM, TP-PMD (all above)

1

MHz

MHz

MHz

4

10

20 MHz


sleeve. The tip conductor was connected to the very tip of the plug and had a positive voltage. The ring conductor had a negative voltage and was connected to a small collar or ring, just back and isolated from the tip. Located behind the ring, the sleeve or ground conductor provides a shield ground when used. The colors used to identify tip conductors are different from the colors used to identify ring conductors. There are five colors associated with tip conductors, and five different colors associated with ring conductors. Polarity must be maintained within each pair, since telephone systems provide all dialing and voice functions on the polarized tip and ring pair. Further, the tip and ring conductors must be isolated from others, that is, the pairs must be used as pairs. If you use the tip conductor from one pair and the sleeve from another, data transmission will be impaired and crosstalk may result.

7.6.3 Common Outlet Configurations: A standard 4 pair wiring codes is given in table 7.4. Note that for 6-wire jacks: use pair 1, 2 and 3 color codes. For 4-wire jacks: use pair 1 and 2 codes.

Twist: Twisted pair copper wire is most prevalent in telecommunication media. Each pair is twisted to prevent induction and crosstalk from other pairs in the same bundle and from outside power circuits and motors. (The unwanted transfer of intelligence from one or more circuits to other circuits is called crosstalk.) Crosstalk is reduced by twists, cable lay, shielding and physical separation made during the cable manufacturing process.

Table 7.4 Standard 4-pair Wiring Color Code

Pair 1

Pair 2

Pair 3

Pair 4

TR

TR

TR

TR

White/Blue Blue/White

Orange/White White /Orange

White/GreenGreen/White

White/Brown Brown/White


7.6.4 Cabling Installation Techniques:• Use the shortest practical route• Conceal cable for damage protection• When drilling access holes through exterior walls:• Slope holes upward from the outside• Drill holes only slightly greater than cable diameter• Provide cable "drip loop" outside of building to avoid water ingress• Use plastic bushings• Seal holes after installing cable• Fire stopping, bonding and grounding must be performed according to

fire, building and electrical codes that apply• Every connection degrades system performance, so use the minimum

number necessary• Better to provide excess capacity in terms of cable and outlets than not

enough. Later additions are costly and time consuming• Wire to the highest anticipated data rate (speed) or greater – never less• Never install components of unknown/questionable origin or quality. At

the very best, the system will transmit signals to the level of its weakest component. Every element and connection is important

• Document all connections carefully, and keep installations tidy• Tag wires at demarcation point for later troubleshooting• Test everything• Install jacks at the same height as electrical outlets. Wall-mount phone

jacks should be 48 to 52 inches from the floor• Cover unused wall boxes with a blank wall plate to protect and mark

their location• Do not splice cable runs• Pull 4-pair cable per manufacturer’s specifications but not more than

25 lbs. pulling tension. EIA/TIA-568A and -570 recognize 4-pair UTP as a minimum pair count

• Do not run cable parallel to power wiring and do not share bored holes.• Avoid sharp bends and sheath nicks• Maintain polarity. Match wire colors of tip (+) and ring (-) pairs. Polarity

reversal interferes with most data devices and some telephones• Use a recommended 4-pair jack for 2 line telephones• Leave pull cord in conduit, if used, to facilitate running new wire• Do not run power in same conduit with telecommunications cable• Use insulated staples to support wire, leaving wire loose within staples


• Avoid under-carpet wiring runs• Use inner walls whenever possible for reasons of safety and

appearance• Leave 18" of spare wire at outlets• Most importantly, always check for ground, open and shorts after

wiring is roughed in.

7.6.5 Standards and Codes: Standards help to ensure system performance by providing installation guidelines and requirements. Codes generally address safety requirements.

Some standards affecting Telecommunications are:(i). ANSI/EIA/TIA standards influence installation, required cable, designs

and hardware for telecommunication systems in buildings.(ii). National Electrical Code (NEC)(iii). ANSI/ NFPA-70 – published by NFPA provides electrical safety

standards regarding fires and electrical hazards. (iv). Lightning Protection Institute – publishes a Material Standard and

Installation Practice Standard based on ANSI/ NFPA 780 (v) Underwriters Laboratories (UL) – an independent testing laboratory

7.7 The Mobile Telephone System.The traditional telephone system will still not be able to satisfy a growing population of users. People now expect to make phone calls from cars, swimming pools, and while jogging in the park as well as send e-mail and surf the Web from all these locations and more. Consequently, there is a tremendous amount of interest in wireless telephony. Wireless telephones come in two basic varieties: cordless phones and mobile phones (sometimes called cell phones). Cordless phones are devices consisting of a base station and a handset sold as a set for use within the home. The mobile system is used for wide area voice and data communication. Mobile phones have gone through three distinct generations, with different technologies:

(i). Analog voice.(ii). Digital voice.(iii). Digital voice and data (Internet, e-mail, etc.).


Figure 7.13 the mobile Phone system

Figure 7.13 shows a mobile telephone system. The base station can transmit and receive on several different frequencies simultaneously to provide several individual channels for use at the same time. The number of frequencies available depends on the nature of the system.

7.7.1 Mobile Telephone Generations:7.7.1.1 First-Generation Mobile Phones: Analog Voice: In 1946, the first system for car-based telephones was set up. This system used a single large transmitter on top of a tall building and had a single channel, used for both sending and receiving. To talk, the user had to push a button that enabled the transmitter and disabled the receiver. Such systems, known as push-to-talk systems. In the 1960s, IMTS (Improved Mobile Telephone System) was installed. It used a high-powered (200-watt) transmitter, on top of a hill, but

BASE ANTENNA

450 MHz MOBILE UNIT

FROM/TOMOBILE ANTENNA

20 TO 30 MILES

FROM/TOBASE ANTENNA

TELEPHONE LAND LINE

CONTROL TERMINAL

RECEIVER TRANSMITTER RECEIVER TRANSMITTER

CONTROL LOGIC

BASE STATION MOBILE STATION HANDSET

FIXED-POSITIONLAND-BASED TELEPHONE

TRANSMISSIONLINK

CENTRAL OFFICE

CENTRAL OFFICE

SWITCHING NETWORK

SWITCHING NETWORK

NATIONAL/INTERNATIONALTELEPHONE SYSTEM


now had two frequencies, one for sending and one for receiving, so the push-to-talk button was no longer needed. Since all communication from the mobile telephones went inbound on a different channel than the outbound signals, the mobile users could not hear each other unlike the push-to-talk system used in taxis. It had the disadvantages of limited number of channels in the given bandwidth and adjacent system had to be spaced kilometers apart to avoid interference. This limited capacity made the system impractical.

Advanced Mobile Phone System: All that changed with AMPS (Advanced Mobile Phone System), invented by Bell Labs and first installed in in 1982. In England, where it was called TACS, and in Japan it was called MCS-L1. In all mobile phone systems, a geographic region is divided up into cells, which is why the devices are sometimes called cell phones. In AMPS, the cells are typically 10 to 20 km across; in digital systems, the cells are smaller. Each cell uses some set of frequencies not used by any of its neighbors. The key idea that gives cellular systems far more capacity than previous systems is the use of relatively small cells and the reuse of transmission frequencies in nearby (but not adjacent) cells. Whereas an IMTS system 100 km across can have one call on each frequency, an AMPS system might have 100 10-km cells in the same area and be able to have 10 to 15 calls on each frequency, in widely separated cells. Thus, the cellular design increases the system capacity by at least an order of magnitude, more as the cells get smaller. Furthermore, smaller cells mean that less power is needed, which leads to smaller and cheaper transmitters and handsets. The idea of frequency reuse is illustrated in figure. 7.14(a). The cells are normally roughly circular, but they are easier to model as hexagons. In figure 7.14 (a), the cells are all the same size. They are grouped in units of seven cells. Each letter indicates a group of frequencies. Notice that for each frequency set, there is a buffer about two cells wide where that frequency is not reused, providing for


Figure 7.14 frequency reuse; (a) Frequencies are not reused in adjacent cells. (b) To add more users, smaller cells can be used.

good separation and low interference. In an area where the number of users has grown to the point that the system is overloaded, the power is reduced, and the overloaded cells are split into smaller microcells to permit more frequency reuse, as shown in figure 7.14(b). At the center of each cell is a base station to which all the telephones in the cell transmit. The base station consists of a computer and transmitter/receiver connected to an antenna. In a small system, all the base stations are connected to a single device called an MTSO (Mobile Telephone Switching Office) or MSC (Mobile Switching Center).

Frequency Reuse and Cell Splitting: Two essential elements are unique to the cellular concept: frequency reuse and cell splitting. Frequency reuse refers to using the same frequency or channel simultaneously for different conversations, in the same general geographic area. The idea of having more than one transmission on a given frequency is not new; it is done in virtually all radio services. What is unique to cellular is the closeness of the users; two users of the same frequency may be only a few dozen miles apart, rather than hundreds of miles. This is done by using relatively low power transmitters on multiple sites, rather than a single high-power transmitter. Each transmitter covers only its own cell, and cells sufficiently far apart may be using the same frequency. Cell splitting is based on the notion that cell sizes are not fixed, and may vary in the same area or over time. The principle

G

B

C

A

F

E

D

G

B

C

A

F

E

D

G

B

C

A

F

E

D

(a) (b)


is shown in Figure 7.15. Initially, all the cells in an area may be relatively large as shown in Figure 7.15a. When the average number of

Figure 7.15 Cell Splitting

users in some cells becomes too large to be handled with proper service quality, the overloaded cells are split into smaller cells by adding more transmitters, as shown in Figure 7.15b. The same MTSO can continue to serve all of the cell sites, but expansion of its computer and switching facilities probably will be required.

Handoff: At any instant, each mobile telephone is logically in one specific cell and under the control of that cell’s base station. When a mobile telephone physically leaves a cell, its base station notices the telephone’s signal fading away and asks all the surrounding base stations how much power they are getting from it. The base station then transfers ownership to the cell getting the strongest signal, that is, the cell where the telephone is now located. The telephone is then informed of its new boss, and if a call is in progress, it will be asked to switch to a new channel because the old one is not reused in any of the adjacent cells. This process, called handoff, takes about 300 msec. Channel assignment is done by the MTSO, the nerve center of the system. The base stations are really just radio relays. Handoff can be done in two ways. In a soft handoff, the telephone is acquired by the new base station before the previous one signs off. In this way there is no loss of continuity. The downside here is that the telephone needs to be able to tune to two

6

7

2

1

3

4

5

2

3

4

5

6

7

1

Cell Splitting

(a) Initial Cell-Site Pattern (b) No. 1 Cell-Site Split


frequencies at the same time (the old one and the new one). Neither first nor second generation devices can do this. In a hard handoff, the old base station drops the telephone before the new one acquires it. If the new one is unable to acquire it (e.g., because there is no available frequency), the call is disconnected abruptly. Users tend to notice this,

Figure 7.16 handoff between cells

but it is inevitable occasionally with the current design In a larger one, several MTSOs may be needed, all of which are connected to a second-level MTSO, and so on. The MTSOs are essentially end offices as in the telephone system, and are, in fact, connected to at least one telephone system end office. The MTSOs communicate with the base stations, each other, and the PSTN using a packet-switching network. Figure 7.16 shows a typical handoff between cells.

The MTSO: The Mobile Telephone Switching Office (MTSO) is the mobile equivalent to a PSTN Central Office. The MTSO contains the switching equipment or Mobile Switching Center (MSC) for routing mobile phone calls. It also contains the equipment for controlling the cell sites that are connected to the MSC. The systems in the MTSO are the heart of a cellular system. It is responsible for interconnecting calls with the local and long distance landline telephone companies, compiling billing information, etc. Its subordinate

CELLULARSWITCHINGEQUIPMENT

PUBLIC SWITCHEDTELEPHONENETWORK

BASE STATION 1

BASE STATION 2

BASE STATION 3


BSC/RNC are responsible for assigning frequencies to each call, reassigning frequencies for handoffs, controlling handoffs so a mobile phone leaving one cell (formally known as BTS)'s coverage area. It also provides resources needed to efficiently serve a mobile subscriber such as registration, authentication, location updating and call routing. The cell sites are interconnected and controlled by a central mobile telecommunications switching office (MTSO), which is basically a telephone switching office as far as hardware is concerned.

Mobile Units: The mobile units consist of a control unit, a transceiver, and appropriate antennas. The transceiver contains circuits that can tune to any of the 666 FM channels from 826 to 845 MHz and 870 to 890 MHz in the cellular range. Each cell site has at least one setup channel dedicated for signaling between the cell and its mobile units. The remaining channels are used for conversations. Each mobile unit is assigned a 10-digit number, identical in form to any other telephone number. Callers to the mobile unit will dial the local or long distance number for the desired mobile unit. The mobile user will dial 7 or 10 digits with a 0 or 1 prefix, where applicable, as if calling from a fixed telephone.

7.7.1.2 Second-Generation Mobile Phones: Digital VoiceThe first generation of mobile phones was analog; the second generation digital. there was also no standardization during the second generation. Four systems are used: D-AMPS, GSM, CDMA, and PDC. The name PCS (Personal Communications Services) is sometimes used in the marketing literature to indicate a second-generation (i.e., digital) system. Originally it meant a mobile phone using the 1900 MHz band, but that distinction is rarely made now.

D-AMPS: The second generation of the AMPS systems is D-AMPS and is fully digital. D-AMPS uses the same 30 kHz channels as AMPS and at the same frequencies so that one channel can be analog and the adjacent ones can be digital. Depending on the mix of phones in a cell, the cell’s MTSO determines which channels are analog and which are digital, and it can change channel types dynamically as the mix of phones in a cell changes. On a D-AMPS mobile phone, the voice signal picked up by the microphone is digitized and compressed using a model that is more sophisticated than the delta modulation and predictive encoding schemes we studied earlier.


Compression takes into account detailed properties of the human vocal system to get the bandwidth from the standard 56-kbps PCM encoding to 8 kbps or less. The compression is done by a circuit called a vocoder. The compression is done in the telephone, rather than in the base station or end office, to reduce the number of bits sent over the air link. One difference between AMPS and D-AMPS is how handoff is handled. In AMPS, the MTSO manages it completely without help from the mobile devices.

GSM (The Global System for Mobile Communications): Virtually everywhere else in the world, a system called GSM (Global System for Mobile communications) is used, GSM is a cellular system and frequency division multiplexing is used, with each mobile transmitting on one frequency and receiving on a higher frequency. Also a single frequency pair is split by time-division multiplexing into time slots shared by multiple mobiles. However, the GSM channels are much wider and hold relatively few additional users giving GSM a much higher data rate per user.

CDMA (Code Division Multiple Access): CDMA is described in International Standard IS-95 and is sometimes referred to by that name. The brand name cdmaOne is also used in CDMA. Instead of dividing the allowed frequency range into a few hundred narrow channels, CDMA allows each station to transmit over the entire frequency spectrum all the time. Multiple simultaneous transmissions are separated using coding theory. CDMA also relaxes the assumption that colliding frames are totally garbled. Instead, it assumes that multiple signals add linearly. CDMA is comparable to everybody being in the middle of the room talking at once, but with each pair in a different language. The English-speaking couple just hones in on the English, rejecting everything that is not English as noise. Thus, the key to CDMA is to be able to extract the desired signal while rejecting everything else as random noise. In CDMA, each bit time is subdivided into m short intervals called chips. Typically, there are 64 or 128 chips per bit, but in the example given below we will use 8 chips/bit for simplicity. Each station is assigned a unique m-bit code called a chip sequence. To transmit a 1 bit, a station sends its chip sequence. To transmit a 0 bit, it sends the one’s complement of its chip sequence. No other patterns are permitted. Thus, for m = 8, if station A is assigned the chip sequence 00011011, it sends a 1 bit by sending 00011011 and a 0 bit by sending 11100100. Increasing the amount of information to be sent from b bits/sec to mb chips/sec can only be done if


the bandwidth available is increased by a factor of m, making CDMA a form of spread spectrum communication.

Enhanced Second-Generation Mobile Standards: Enhanced second-generation (sometimes referred to as 2.5G or 2+G) builds upon the second-generation standards by providing increased bit-rates and bringing limited data capability. Data rates range from 57.6kbps to 171.2kbps. High-Speed Circuit-Switched Data (HSCSD) provides access to four channels simultaneously, theoretically providing four times the bandwidth (57.6) of a standard circuit-switched data transmission of 14.4kbps. D-AMPS IS-136B Time Division Multiple Access (TDMA) is the intermediate step to Universal Wireless Communication (UWC-136), a third-generation standard. The first phase of D-AMPS will provide up to 64kbps. The second phase will provide up to 115kbps in a mobile environment. General Packet Radio System (GPRS) is an evolutionary path for GSM and IS-136 TDMA to UWC-136. It is a standard from the European Telecommunications Standards Institute (ETSI) on packet data in GSM systems. The Telecommunications Industry Association (TIA), as the packet-data SDO for TDMA-136 systems, has also accepted GPRS. GPRS supports theoretical data rates up to 171.2kbps by utilizing all eight channels simultaneously. This data rate is roughly three times faster than today’s fixed telecommunication networks and about ten times as fast as current circuit-switched data services on GSM networks. GPRS is a universal packetswitched data service in GSM. It involves overlaying a packet-based air interface on the existing circuit-switched GSM network. Packet switching means that GPRS radio resources are used only when users are actually sending or receiving data. Using GPRS, the information is split into separate but related packets before being transmitted and subsequently reassembled at the receiving end. GPRS is a non-voice-added service that allows information to be sent and received across multiple mobile telephone networks. It supplements today's circuit-switched data and short messaging service. GPRS uses packet data technology, a fundamental change from circuit-switched technology, to transfer information. It also facilitates instant connection capability, sometimes referred to as “always connected.” Immediacy is one of the key advantages of GPRS. Immediacy enables time-critical application services


7.7.1.3 Third-Generation Mobile The Third-generation (WCDMA in UMTS, CDMA2000 & TD-SCDMA): The 3G revolution allowed mobile telephone customers to use audio, graphics and video applications. Over 3G it is possible to watch streaming video and engage in video telephony, although such activities are severely constrained by network bottlenecks and over-usage. One of the main objectives behind 3G was to standardize on a single global network protocol instead of the different standards adopted previously. In EDGE, high-volume movement of data was possible, but still the packet transfer on the air-interface behaves like a circuit switch call. Thus part of this packet connection efficiency is lost in the circuit switch environment. Moreover, the standards for developing the networks were different for different parts of the world. Hence, it was decided to have a network which provides services independent of the technology platform and whose network design standards are same globally. Thus, 3G was born. The International Telecommunication Union (ITU) defined the demands for 3G mobile networks with the IMT-2000 standard. An organization called 3rd Generation Partnership Project (3GPP) has continued that work by defining a mobile system that fulfills the IMT-2000 standard. In Europe it was called UMTS (Universal Terrestrial Mobile System), which is ETSI-driven. IMT2000 is the ITU-T name for the third generation system, while cdma2000 is the name of the American 3G variant. WCDMA is the air-interface technology for the UMTS. The main components includes BS (Base Station) or nod B, RNC (Radio Network Controller), apart from WMSC (Wideband CDMA Mobile Switching Centre) and SGSN/GGSN. 3G networks enable network operators to offer users a wider range of more advanced services while achieving greater network capacity through improved spectral efficiency. Services include wide-area wireless voice telephony, video calls, and broadband wireless data, all in a mobile environment. Additional features also include HSPA (High Speed Packet Access) data transmission capabilities able to deliver speeds up to 14.4 Mbps on the downlink and 5.8 Mbps on the uplink. In many countries, 3G networks do not use the same radio frequencies as 2G, so mobile operators must build entirely new networks and license entirely new frequencies; an exception is the United States where carriers operate 3G service in the same frequencies as other services.


Third Generation Mobile Standards: Third-generation systems will provide wide-area coverage at 384kbps and local area coverage up to 2Mbps. The primary motivation for the development of third generation wireless communications is the ability to supplement standardized 2G and 2G+ services with wideband services. Essentially, this offers voice plus data capability. The existing array of incompatible second-generation technologies, together with the restricted amount of information that can be transferred over these narrowband systems, prompted the ITU to work towards defining a new global standard for the next-generation broadband mobile telecommunication systems. Known as IMT-2000 (International Mobile Telecommunications-2000), he project was started to attain authorship of a set of globally harmonized standards for broadband mobile communications. The first set of IMT-2000 recommendations was recently approved by the ITU. IMT-2000 is the term used by the International Telecommunications Union for this set of globally harmonized standards. The initiative was to define the goal of accessing the global telecommunication infrastructure through both satellite and terrestrial mobile systems. IMT-2000 has reflected the explosion of mobile usage and the need for future high-speed data communications, with wideband mobile submissions. IMT-2000 is a flexible standard that allows operators around the world the freedom of radio access methods and of core networks so that they can openly implement and evolve their systems.

7.7.1.4 Fourth Generation( 4G) Mobile NetworksIn contrast to 3G, the new 4G framework to be established will try to accomplish new levels of user experience and multi-service capacity by also integrating all the mobile technologies that exist (e.g. GSM - Global System for Mobile Communications, GPRS - General Packet Radio Service, IMT-2000 - International Mobile Communications, Wi-Fi - Wireless Fidelity, Bluetooth). The fundamental reason for the transition to the All-IP is to have a common platform for all the technologies that have been developed so far, and to harmonize with user expectations of the many services to be provided. The fundamental difference between the GSM/3G and All-IP is that the functionality of the RNC and BSC is now distributed to the BTS and a set of servers and gateways. This means that this network will be less expensive and data transfer will be much faster. The current generation of mobile telephony, 4G has been developed with the aim of providing transmission rates up to 20 Mbps while simultaneously accommodating Quality of Service


(QoS) features. QoS will allow you and your telephone carrier to prioritize traffic according to the type of application using your bandwidth and adjust between your different telephone needs at a moment's notice. Only now are we beginning to see the potential of 4G applications. They are expected to include high-performance streaming of multimedia content. The deployment of 4G networks will also improve video conferencing functionality. It is also anticipated that 4G networks will deliver wider bandwidth to vehicles and devices moving at high speeds within the network area.

Long Term Evolution(LTE) Basics: Long Term Evolution has long been seen as the first advancement towards stronger, faster and more efficient 4G data networks. The technology under LTE can currently reach downlink peak rates of 100Mbps and uplink speeds of 50Mbit/s. The LTE technology is also a scalable bandwidth technology for carriers operating anywhere from 20Mhz town to 1.4Mhz. Long Term Evolution offers some excellent advantages over current 3G systems including higher throughput, plug and play compatibility, FDD (Frequency Division Duplexing) and TDD (Time Division Duplexing), low latency and lower operating expenditures. It also offers legacy modes to support devices operating on GPRS systems, while supporting seamless passthrough of technologies operating on other older cellular towers. The technologies put forth by LTE will not only be implemented over time, they are designed to be scalable. This scalability means the company can slowly introduce LTE technologies over time, without disrupting current services. LTE is also designed with a full Internet Protocol (IP) network infrastructure. This means it can support full voice in packet domains, while also offering advanced radio techniques for achieving higher performance levels beyond what basic CDMA networks and 3G data packets can currently achieve.


7.8 Traffic EngineeringThe telephone exchanges are connected by trunks or junctions. The number of trunks connecting exchange X with exchange Y is the number of voice pairs or their equivalent used in the connection. One of the most important steps in telecommunication engineering practice is to determine the number of trunks required on a route or connection between exchanges. To determine (dimension) a route correctly, we must have some idea of how many people will wish to talk at once over the route. The usage of a transmission route or a switch brings us into the realm of traffic engineering, and the usage may be defined by two parameters: (1) calling rate, or the number of times a route or traffic path is used per unit period, or, more properly defined, “the call intensity per traffic path during the busy hour” and (2) holding time, or “the duration of occupancy of a traffic path by a call,” or sometimes, “the average duration of occupancy of one or more paths by calls.” A traffic path is “a channel, time slot, frequency band, line, trunk, switch, or circuit over which individual communications pass in sequence.” Carried traffic is the volume of traffic actually carried by a switch, and offered traffic is the volume of traffic offered to a switch. To determine the traffic path or size of a telephone exchange, we must know the hourly, daily and weekly traffic intensity. There are weekly and daily variations in traffic within the busy season. Traffic is very random in nature. However, there is a certain consistency we can look for. For one thing, there usually is more traffic on Mondays and Fridays and a lower volume on Wednesdays. A certain consistency can also be found in the normal workday hourly variation. The busiest period, the busy hour (BH), is between 10 A.M. and 11 A.M. From one workday to the next, originating BH calls can vary as much as 25%. To these fairly “regular” variations, there are also unpredictable Variations that may be caused by weather, natural disaster, international events, sporting events, and so on. Nevertheless, suitable forecasts of BH traffic can be made. Some common Busy Hour Definitions are as follows:1. Busy Hour. The busy hour refers to the traffic volume or number of call

attempts, and is that continuous 1-h period lying wholly in the time interval concerned for which this quantity (i.e., traffic volume or call attempts) is greatest.

2. Peak Busy Hour. The busy hour each day; it usually is not the same over a number of days.


3. Time Consistent Busy Hour. The 1-h period starting at the same time each day for which the average traffic volume or call-attempt count of the exchange or resource group concerned is greatest over the days under consideration.

4. The engineering period (where the grade of service criteria is applied) is defined as the busy season busy hour (BSBH), which is the busiest clock hour of the busiest weeks of the year.

5. The average busy season busy hour (ABSBH) is used for trunk groups and always has a grade of service criterion applied. For example, for the ABSBH load, a call requiring a circuit in a trunk group should encounter “all trunks busy” (ATB) no more than 1% of the time.

7.8.1 Measurement of Telephone Traffic: If we define telephone traffic as the aggregate of telephone calls over a group of circuits or trunks with regard to the duration of calls as well as their number, we can say that traffic flow (A) is expressed as

A = C × Twhere C designates the number of calls originated during a period of 1 h and T is the average holding time, usually given in hours.

A is a dimensionless unit because we are multiplying calls/hour by hour/call. Suppose that the average holding time is 2.5 min and the calling rate in the BH for a particular day is 237. The traffic flow (A) would then be 237 × 2.5, or 592.5 call-minutes (Cm) or 592.5/60, or about 9.87 call-hours (Ch). The unit of traffic intensity is the erlang, named after the Danish mathematician A. K. Erlang. The erlang is a dimensionless unit. One erlang represents a circuit occupied for 1 h. Considering a group of circuits, traffic intensity in erlangs is the number of call-seconds per second or the number of call-hours per hour. If we knew that a group of 10 circuits had a call intensity of 5 erlangs, we would expect half of the circuits to be busy at the time of measurement.

There are other traffic units. For instance: call-hour (Ch);1 Ch is the quantity represented by one or more calls having an aggregate duration of 1 h; call second (Cs);1 Cs is the quantity represented by one or more calls having an aggregate duration of 1 s; traffic unit (TU), a unit of traffic intensity. One TU is the average intensity in one or more traffic paths carrying an aggregate traffic


of 1 Ch in 1 h (the busy hour unless otherwise specified). 1 TU = 1 E (erlang) (numerically). The equated busy hour call (EBHC) is a European unit of traffic intensity. 1 EBHC is the average intensity in one or more traffic paths occupied in the BH by one 2-min call or an aggregate duration of 2 min. Thus we can relate our terms as follows:

1 erlang = 30 EBHC = 36 CCS = 60 Cm

assuming a 1-h time-unit interval.

7.8.2 Blockage, Lost Calls, and Grade of Service: Lets say, an isolated telephone exchange serves 50 subscribers and that no more than 10% of the subscribers wish service simultaneously. Therefore, the exchange is dimensioned with sufficient equipment to complete 5 simultaneous connections. Each connection would be, of course, between any two of the 50 subscribers. Now let subscriber 51 attempt to originate a call. The caller cannot because all the connecting equipment is busy, even though the line wishes to reach may be idle. This call from subscriber 51 is termed a lost call or blocked call because the capacity of the system is for 50.

Grade of service expresses the probability of meeting blockage during the BH and is expressed by the letter p. A typical grade of service is ρ = 0.01. This means that an average of one call in 100 will be blocked or “lost” during the BH. Grade of service, a term in the Erlang formula, is more accurately defined as the probability of blockage. It is important to remember that lost calls (blocked calls) refer to calls that fail at first trial. We discuss attempts (at dialing) later, that is, the way blocked calls are handled.Example: Assume that there are 354 lines connected for service and 6 blocked calls (lost calls) during the BH, what is the grade of service?

Grade of service = Number of lost calls / Total number of offered calls= 6 / 354 + 6= 6 / 360

ρ = 0.017

The average grade of service for a network may be obtained by adding the grade of service contributed by each constituent switch, switching network, or trunk group.


7.8.3 Erlang And Poisson Traffic Formulas: When determining a route, we want to find the number of circuits that serve the route. There are several formulas at our disposal to determine that number of circuits based on the BH traffic load. To determine which traffic formula to use given a particular set of circumstances. These factors primarily dealt with are;(1) call arrivals and holding time distribution, (2) number of traffic sources, (3) availability, (4) handling of lost calls.

The Erlang B loss formula has been widely used today . Loss here means the probability of blockage at the switch due to congestion or to “all trunks busy” (ATB). This is expressed as grade of service (EB) or the probability of finding x channels busy. The other two factors in the Erlang B formula are the mean of the offered traffic and the number of trunks of servicing channels available. Thus;

EB = (An/n!) / (1 + A + A2/2! + ·· ·+An/n!)

where n is the number of trunks or servicing channels, A is the mean of the offered traffic.EB is the grade of service using the Erlang B formula.

This formula assumes the following:(i) Traffic originates from an infinite number of sources.(ii) Lost calls are cleared assuming a zero holding time.(iii) The number of trunks or servicing channels is limited.(iv) Full availability exists.

7.8.4 Time and Call Congestion: Time congestion, of course, refers to the decimal fraction of an hour during which all trunks are busy simultaneously. Call congestion, on the other hand, refers to the number of calls that fail at first attempt, which we term lost calls. Keep in mind that the Erlang B formula deals with offered traffic, which differs from carried traffic by the number of lost calls.


CHAPTER EIGHT

TELEGRAPHY

7.0 IntroductionTelegraphy is used to transfer information in the written form. It is a combination of two words. "Tele" means at a distance and "Graph" means to write. Hence telegraphy is to write at a distance. In the early days of civilization, there were various methods of transferring information (messages) over long distances these methods went on improving with the passage of time and today we have the most modern methods of communication. Telegraphy was the first electrical communication system that allowed the people to communicate with each other beyond the limited ranges of voice and vision. Telegraph depends upon the transmission of electrical signals, which are arranged according to some definite code. The information to be sent is first converted into some form of code for ease of transmission and reception. Codes are symbols that represent units of information understandable by both sender and receiver.

7.1 Telegraphy Code Types: In the unequal length code all the characters are represented by marks and spaces, and the time of transmission is not the same (equal). There is no limit to the number of characters combinations possible from this code. The most common unequal length code is the Morse code. In the equal length code each character consists of equal number of elements, each having the same duration, which is also the basic time unit of the system. Five-unit code is an equal length code and is most extensively used in machine telegraphy.

7.1.1 Morse CodeMorse code is named in honor of Samuel F.B. Morse, an American who invented the telegraphic code. The morse code basically consists of two elements, the dot (.), called "dit", which is the shortest element, also called unit element and the lash (-), called "dah", which is the longer element. The dot is about one-fourth the duration of a second. The dash is three times longer than the dot. The relative durations of dots, dashes and other elements have been fixed by international agreement. Thus:


A dot length = l/4lh of a second.A dash length = 3 dots length.Spacing between elements of a character = 1 dot length.Spacing between character of a word = 3 dots length.

This new code was called the "CONTINENTAL" or "INTERNATIONAL" MORSE CODE and became the universal standard for Radio Telegraph Communications Here is a list which shows the dot and dash equivalents of letters and numbers in the Original Morse code (American Morse Code), and the Continental (International) code . An explanation of the timing and length of the characters is shown in table 7.5 with Dot = * Dash = - Long Dash = ---- .

The first telegraph message ever sent was a short one, but very interesting. The message was: “What God Hath Wrought”. The reader should try to put the message in the encoder to see what it looks like.


Table 8.1 Timing and length of the characters

MORSE CODE CONTINENTAL CODECHARACTER: AMERICAN MORSE INTERNATIONAL CODE

A * - * - B - * * * - * * * C * * * - * - * D - * * - * * E * * F * - * * * - * G - - * - - * H * * * * * * * * I * * * * J - * - * * - - - K - * - - * - L ---- * - * * M - - - - N - * - * O * * - - - P * * * * * * - - * Q * * - * - - * - R * * * * - * S * * * * * * T - - U * * - * * - V * * * - * * * - W * - - * - - X * - * * - * * - Y * * * * - * - - Z * * * * - - * * 1 * - - * * - - - - 2 * * - * * * * - - - 3 * * * - * * * * - - 4 * * * * - * * * * - 5 - - - * * * * * 6 * * * * * * - * * * * 7 - - * * - - * * * 8 - * * * * - - - * * 9 - * * - - - - - * 0 ------ - - - - -

Period * * - - * * * - * - * - Comma * - * - - - * * - - Question - * * - * * * - - * *


Explanation of Spacing and Timing:To standardize the International Code Transmission Speed, the 5-letter word PARIS is used to establish the number of ''words-per-minute''. For example, if the word PARIS was sent 5 times in a minute, the transmission speed would be 5-words-per-minute or WPM. The following relationships exist between the elements of the code (dits and dahs), the characters (letters) and the words:

The DIT is the Basic UNIT of Length.The DAH is equal in length to three DITS.The space between the DITS and DAHS within a character (letter) is equal to one DIT.The space between characters (letters) in a word is equal to three DITS.The space between words is equal to seven DITS.

7.1.2 Speed In Words-per-minute Or Wpm: The following information about the calibration of the speed of transmission in WPM (Words-Per-Minute).The speed in WPM is defined as the number of times the word "PARIS" for instance is sent in one minute with normal 1:3:7 spacing and weighting. "PARIS" was chosen because it has the right number of dits and dahs to represent an average word length in Morse.

7.1.3 Machine Telegraph Codes Other codes have been introduced with the development of keyboard operation and machine telegraphy. Codes were developed by Jean Maurice Baudot and Donald Murray using five elements of mark or space in serial form for each character symbol. Five elements are insufficient to separately define all letters of the alphabet, numeric figures and punctuation and hence two character symbols were allocated to shift between letters and figures or punctuation so that each other character symbol performed two functions. Added to each five element symbol were also two additional elements to define the start and stop of the symbol for synchronisation. The five element codes are still in use today in the communications services, including amateur radio, but these codes are quite different to the first code introduced by Baudot. The Baudot code was designed to suit manual operation from a pianoforte type keyboard of five keys, one for each element in a symbol. This original code is also known as the CCITT No 1 code and this is shown in table 7.2. (CCITT is an abbreviation for Consultative Committee for International Telegraph and Telephone).


One limitation of the five element codes is that there are no provision for both upper and lower case alpherbetic letters. This limitation was overcome by the Murray code; A binary code with five binary digits per letter developed on the basis of the CCIT2 code shown in figure 7.3.

The Ascii Code The ASCII code is much more versatile than the five element codes with one bit state difference between upper and lower letters and additional symbols for control and printing operations, particularly suited to use with computers. With the development of computers and high speed data exchange, ASCII has become a common serial data code and this code uses seven mark or space elements or bits to define each character. ASCII is an abbreviation for American National Standard Code for Information Interchange and was adopted by the American National Standards Institute in 1968. The code actually utilises an eight bit byte with the eighth bit often used for parity error check on the other bits. Additional start and stop bits are also included when operated in the non-synchronous mode as used in the teletype service. With seven bits available, all letters (including upper and lower case), all numerals and all punctuation characters are allocated a unique character symbol or byte. The arrangement of the first seven bits, for each of the characters, is shown in table 7.


0 Indicates Space - positive current in a Baudot multiplex.1 Indicates Mark - negative current in a Baudot multiplex.* Indicates Free for internal use by a country or administration.

Table 8.2 - The Baudot or CCITT Code No 1


Table 8.3 The Murray or CCITT No 2 with variations

Notes: Transmission order: Bit 1® Bit 5 * “Black” - no action international alpherbet #2… unassigned (domestic variation not used internationlly


Table 7.4. The ASCII Code

Start & Stop Bits The five element codes and the ASCII code use similar start and stop elements or bits. The start bit is a zero or space signal equal in period of time to a single character bit. The stop bit is a one or mark signal with a minimum period of time between that of one and two character bits, depending on the system. The maximum stop period is as long as desired as the stop mark condition remains until the next character is initiated by the start space pulse.

The ASCII Data Code

7 65

000

001

010

011

100

101

110

111

4321000000010000000110 1 0 00 1 0 10 1 1 00 1 1 110001001101010111100110111101111

NULSOHSTXETXEOXENOACKBELBSHTLFVTFFCASOSI

OLEOCIDC2DC3DC4MAXSYNETBCANEMSUBESCFSGSASUS

SPC1-

‘=%&

().

+

_

/

0123456789

==<=>?

U

ABCDEFGHIJKLMNO

ORSTUVWXYZ[\

>

- -

abcdelghIlk1mn0

pqrsluvwxyz[]]

P

DEL

ACKBELBSCANCRDC1DC2DC3DC4DELDLEENOEMLOTESCETBETX

= acknowledge signal bellbackspace (_)cancel carriage return device control 1device control 2device control 3device control 4(delete)data link escape enquiry (WRU)end of medium end of trans.escape end of block end of text

= = = = = = = = = = = = = = = =

FFFSGSHTLFNAKNULRS SISOSOHSPCSTXSUBSYNUSVT

= = = = = = = = = = = = = = = = =

form feed (horme)file separator group separator

line feed (+))not acknowledgenullrecord separator shill inshill out start of loading space start of text substitute

unit separator vertical tab ( +)


Typical timing formats for a character train in the five unit and ASCII codes are shown in figure 7.1 (a) and (b), respectively.

(a) Time sequence of a typical Baudot character, the letter 0

(b) Time sequence of a typical ASCII character, the letter S. The eighth or parity bit may be set for any of four conditions; (1) always mark, (2) always

space, (3) odd parity or (4) even parity. All four choices are in common usage.

Figure 7.1 Start and Stop bits

REST

CONDITION

MARK

(CURRENT ON)

(CURRENT OFF)

SPACE

START

PULSE

CHARACTER NO.1 CHARACTER NO:2

1 2 3 4 6

(m) (s) (s) (m) (s)

DATA PULSES FOR ‘D’

TIME

(m) (s)

1 2

STOP

PULSE

START

PULSE

CHARACTER NO.1

CHARACTER NO:2‘REST’

CONDITION

MARK

(CURRENT ON)

(CURRENT OFF)SPACE

START

PULSE STOP

PULSE

STAP

PULSETIME

PULSES DATA FOR ‘S’

(m) (s)(s)(m) (m) (s) (m) (s)


7.2 Morse code Telegraph SystemThe morse code telegraph system is a simple electric circuit consisting of the following components:1. A battery: which acts as a source of electrical energy in the circuit.

2. Morse key: It is a manual key and acts as a switch to open and close the circuit. Thus causing pulses of current to flow on the line. When the operator starts opening and closing of the key. The transmission of information and encoding starts at the same time.

3. Transmission line: Acts a medium for the transmission information between the two stations. The dots and dashes flow-on the line in the form of electrical energy and are carried instantly through the wires from the transmitter to the receiver.

i4. Receiver: The receiver used is called a sounder, because it produces click like sound. The receiver consists of electromagnet and a movable armature. When a pulse of current passes through the electromagnet, it attracts the armature and click is produced. When the pulsed stops, the armature returns to its normal position with the help of a spring and again makes a click. The time between the clicks represents a dot or a dash. These clicks are heard by an operator and are decoded into messages in the written form by him. The morse code telegraph system is illustrated in t figure 7.25.

Figure 7.2 The morse code telegraph system

Morse Key Morse Sounder

Morse System


7.2.1 Single and Double Current Morse code SystemThe morse code system may be either single current or double current. In the single current system single battery is used. The current on the line flows only in one direction. There is current on the line when dot or dash is transmitted and no current when neither dot nor dash is transmitted. The advantage of single current system is low power consumption. However, the flow of current is slower and thus is a disadvantage. In the double current system two batteries of opposite polarities are used. There is always current on the line, which may be either positive or negative. For dot or dash the current on the line is positive while for space it is negative. The double current system is more sensitive and speedier than the single current system. This is illustrated in figure 7.3.

Figure 7.3 Single and double current system.

7.3 TeleprinterA teleprinter (teletypewriter, Teletype or TTY) is a electro mechanical typewriter that can be used to communicate typed messages from point to point and point to multipoint over a variety of communication channels that range from a simple electrical connection, such as a pair of wires, to the use of radio and microwave as the transmission medium. They could also serve

letter space word space word space

letter space letter space

U S E O F C O D E

U S E O F C O D E

letter space word space word space

letter space letter space

O

O

(a) Single current Morse code

(b) Single current Morse code


as a command line interface to early mainframe computers and minicomputers, sending typed data to the computer with or without printed output, and printing the response from the computer. The salient features of teleprinter are listed below:1. A teleprinter is a telegraph transmitting receiving machine.2. Teleprinter resembles a typewriter because it has a typewriter like

keyboard.3. A teleprinter is a mechanical device driven by electrical motors,

recently Electronic machine has been introduced, controlled by the microprocessor.

4. Code used by teleprinter machine is the 5-unit code,5. A teleprinter works on the start-stop principle.6. A teleprinter acts both as a transmitter and as a receiver.7. When used as a receiver, the signals are received in the serial form are

converted into Parallel. Then a detector converts it into the character and the printer prints it on the paper.

8. Every teleprinter has also the facility of local record,9. The actual mechanical arrangement of a teleprinter machine is very

Complicated, but a block diagram which shows the different parts of the machine is figure 7.4.

Figure 7.4. Block Diagram of teleprinter

Motor

Platen unit

Selector

unit

Electro

magnet

Type head

Aggregate

motor unit

Keyboard

Clutch

Translater

unit

Tra

nsm

itte

r


7.3.1 Application of the Teleprinter1. The teleprinter is basically used for sending and receiving of Telegraph

signals,2. Teleprinter switching system is used in Telex (teleprinter exchange)

which is a convenient method of sending printed messages. An auto- telex service has the advantage of communication as in telephone astern and transfer of written record as in telegraph system.

3. Due to these two advantages, these services are used both for commercial and industrial purposes,

4. The teleprinter can also be used for typing the local records.

7.4 Wireless TelegraphyAt the transmitter side, when the key is pressed, the telegraph signal current passes through the modulator, where high frequency signal from the oscillator is also received. The two are mixed and then after passing through amplifier, the antenna radiates power in the air and is received by the distant receiving antenna. At the receiver side the signal received, after passing through amplifier, is demodulated and is again converted into telegraph signals. The functions of the various blocks- in the block diagram in figure 7.5.

Figure 7.5 Block Diagram of wireless Telegraphy

Modulator

Telegrapgh

Signal input

Oscillator

Demodulator Rx Amp

Rx Antenna

Tx Amp

Tx Antenna

Telegrapgh

Signal output


ModulatorThe modulator is a circuit, which combines or mixes two frequencies. The telegraph signal, which is a low frequency signal and a carrier, which is a high frequency signal are mixed in the modulator. Both frequencies appear as modulated signal at the output of the modulator. The modulated signal-is a high frequency signal and is more suitable for transmission.

DemodulatorThe demodulator is an essential part of the receiver. It does the reverse function as that of the modulator. The original telegraph signal is separated from the carrier signal by the demodulator circuit.

AmplifierThe amplifier is used to amplify the power level of the signal to a sufficient amount. The transmitting amplifier boosts the signal power level more suitable for transmission. The receiving amplifier raises the power level of the received signal to an adequate amount.

OscillatorThe oscillator is a circuit, which generate radio frequency signal called carrier. At the transmitter side the carrier signal is mixed with the signal containing information and thus resulting in a high frequency modulated wave suitable for transmission. At the receiver side the output of the oscillator is used to select the required signal from the various radio frequency signals picked up by the antenna and reject all others.

7.5 Facsimile FACSIMILE (fax) is a method of transmitting still images over an electrical communications system. The images, called "pictures" or "copy" in fax terminology, may be weather maps, photographs, sketches, typewritten or printed text, or handwriting. The still image serving as the fax copy or picture cannot be transmitted instantly in its entirety. Three distinct operations are performed. These are scanning, transmitting, and recording or receiving. Scanning consists of subdividing the picture in an orderly manner into a large number of segments. This process is accomplished in the fax transmitter by a scanning drum and phototube arrangement. The picture you want to transmit is mounted on a cylindrical scanning drum. This drum rotates at a constant speed and at the same time moves longitudinally along a shaft. Light from an


exciter lamp illuminates a small segment of the moving picture and is reflected by the picture through an aperture to a phototube. During picture transmission, the light crosses every segment of the picture as the drum slowly spirals past the fixed lighted area. The amount of light reflected back to the phototube is a measure of the lightness or darkness of the segment of the picture being scanned. The phototube changes the varying amounts of light into electrical signals. These are used to amplitude modulate the constant frequency output of a local oscillator. The modulated signal is then amplified and sent to the radio circuits. Signals received by the fax receiver are amplified and actuate a recording mechanism. This recorder makes a permanent recording (segment by segment) on paper. The paper is attached to a receiver drum similar to the one in the fax transmitter. The receiver drum rotates synchronously with the transmitter drum. Synchronization of the receiver and transmitter is done to reduce distortion. Synchronization is obtained by driving both receiver and transmitter drums with synchronous motors operating at the same speed. Drum rotation continues until the original picture is reproduced. The recording mechanism may reproduce the picture photographically by using a modulated light source shining on photographic paper or film. It may also reproduce directly by burning a white protective coating from specially prepared black recording paper. The receiver drum is FRAMED with respect to the transmitter drum by a series of phasing pulses that are transmitted just before transmission. The pulses operate a clutch mechanism that starts the scanning drum in the receiver. This ensures proper phasing with respect to the starting position of the scanning drum in the transmitter.

7.5.1 Details of a fax machine1. Facsimile or fax machine is an electronic system. It is used for

transmitting graphical information through wires or through free space (i.e. with the help of electro-magnetic waves).

2. To send a fax means to send graphical information on a paper.3. When we want to send a fax, the graphical information on paper is

SCANNED by strong light beam (its working is fairly similar to Xerox machine).

4. While scanning, reflected light varies depending on the details in graphical information.

5. The variations in light are converted into equivalent electrical signals.


6. This conversion is done with the help of Charge Coupled Device (CCD) and electronic memory circuits.

7. Then the signals are transmitted over telephone line or through free space.

8. By opposite process, the transmitted graphical information is reproduced in printed form (on paper) at receiving end of fax machine.

9. Fax machine is used to send letters, photographs, maps etc. In short, any information in printed form on paper can be sent with the help of fax machine.

7.5.2 Scanning a Document.Figure 7.6 shows the mechanism of scanning used in fax machine. The process of scanning is done electronically. The paper is fed into the rollers. Upper rollers rotate clockwise and lower rollers rotate anticlockwise. So the paper is pulled into the machine. The light source focuses a strong light beam on the paper. The light beam reflects from paper surface and through mirror assembly, it is incident on CCD (Charge Coupled Devices).

The CCD is a light sensitive semiconductor device. It has a very large number of tiny capacitor like devices. These are reverse biased silicon photo diodes arranged in matrix form on a silicon chip. They convert variations in light signals into proportional electrical signals.

Figure 7.6 Scanning mechanism of a Fax Machine

CCD

electronic

circuit

mirror

mirror

refle

cted

light

paper

direction of paper

rollers

(note direction

of rotation)

paper feed

light source

mirror


The complete information on paper is NOT stored on CCD. The beam of light source scans the paper along width of paper, row-by-row. When it goes from one end to another, the CCD becomes occupied. Then charged information on CCD is given out to electronic memory and next scanning process starts, until complete paper is scanned. Block diagram of fax machine is shown in figure 7.7 with the operation of each block as explained below:

Transmitter block: When paper as graphical information is inserted into fax machine, it is scanned row–by–row. The CCD converts this information into proportional analog signals. This output is fed to A/D converter circuit. Its output is in digital form. This digital data becomes extremely huge due to scanning details in the document. So it is compressed with the help of digital data compression circuit. This circuit is made up of VLSI (Very Large Scale Integration) technology. Hence, the size of data in bits (binary digits) is reduced. This size of data in terms of bits is sufficient to represent the image of document. With compression, size of storage memory is reduced and data transmission rate is increased. The compressed data output is fed to modulator. It is the modem, which can modulate & demodulate digital data. In modem, a carrier wave is modulated using the data and transmitted over telephone line. In some cases, PSK or QAM techniques are used in modulation.

Figure 7.7 Block diagram of a Fax Machine

CCDA/D

converter modulator

circuit

digital data

compresion

telephone

line

interface to/from

telephone

line

demodulator

circuit

operator

controls

control

logic

digital data

expansion

motor control

circuits

thermal

printer

roller drive

motors

RECEIVER BLOCK

TRANSMITTER BLOCK


Receiver block: When fax signal reaches receiver block through telephone line, it is demodulated using demodulator within modem. Thus, at its output we get original data only in compressed form. To expand the data it is fed to digital data expansion block. This circuit is also made up of VLSI (Very Large Scale Integration) technology. The data is recovered by removing its data compression into original size. the signals are fed to thermal printer. this printer requires special heat sensitive paper. The head (stylus) of printer, which prints the information on paper, has tiny heating elements (coils). These elements rapidly turn on/off, depending on the signals received. It moves on the paper and actually burns it into black/shades of black (i.e. gray shades). In this way, it prints exact image of original document.

Control blocks: This is very complex circuit used for handshaking between two fax machines, during communication. During this process, different audio tones and beeps are exchanged and produced. This process takes place as follows;(i) When a fax machine is dialed, called machine responds to it by

producing an audio tone.(ii) The calling machine sends synchronous signals, so both machines

start at the same time.(iii) The called machine compares this signal as per its own standards and

acknowledges to sync. signals. Then the printing begins.The operator controls block of a typical fax machine say, the G3 Fax Machine

provides user-friendly controls like start, stop, number to be dialed and a number of other functions. Motor control circuit controls speed of motor and paper rollers. It is a constant speed controller circuit called as governor circuit. The total communication between two fax machines is half-duplex type. The standards of modern fax machine are set as per CCITT (International Telegraph & Telephone Consultative Committee). This is important to avoid compatibility problems.


i

Index

AAA, 42ABC, 207ABSBH, 238absolute, 10, 131ac, 52, 58, 129, 131, 138access, 95, 209, 218, 224, 233, 235accurate, 82-83, 98, 130, 132, 138, 141, 144, 164ACK, 248acoustic, 198action, 26, 117, 247active, 10, 26, 124, 127, 131, 133-134, 177, 190-191, 210-211actuate, 255adapters, 93Adder, 39, 110, 113adder, 110, 113, 152, 160addition, 32, 37, 83, 96, 112, 117, 138, 144, 186Additive, 147additive, 147, 162address, 216, 225adjacent, 16, 75-76, 86, 88-89, 115, 143, 191, 199, 227-229, 231adjust, 70, 106, 129, 219, 236aerial, 46, 83-84, 88, 169, 172, 185AF, 52, 70, 72, 100, 110-111AFC, 41, 43, 47-48, 111AGC, 101-103, 162alarm, 211-212Alarms, 208, 211ALC, 101

align, 156alignment, 163Allotter, 208-209alloy, 198alternate, 122, 133, 161, 181alternating, 218alternation, 118alternator, 199AM, 11-12, 16, 18, 20, 23-28, 30, 33, 35-38, 48, 66, 68-69, 73-74, 77-80, 99, 101, 104-105, 107, 119, 156, 159-160, 167-169, 177, 181amateur, 46, 93-94, 99, 105, 244ammeter, 81-82, 87-88Amp, 70, 72, 99, 111, 253amp, 62, 102, 162amplification, 3, 16, 30, 46, 52, 68, 76, 79, 104, 161, 186amplified, 29, 40, 101, 113, 159-160, 186, 215, 255amplifier, 1, 18, 27-30, 33-37, 46, 52, 64-65, 68-69, 74, 76, 79-80, 101-103, 117-118, 152, 160-162, 165, 194-195, 215, 253-254amplifiers, 28, 36, 52, 61-62, 64-65, 67-69, 75, 159-161amplify, 52, 61, 97, 254amplifying, 50AMPLITUDE, 128Amplitude, 11-13, 15, 19-21, 23, 26, 30, 38, 49, 51, 78, 80-81, 86, 99, 104, 135, 153, 167amplitude, 2, 11-21, 26-28, 30, 34-36, 39, 46, 48-49, 56, 81-83, 85-86, 104, 107-109, 112, 115, 127-128, 132, 134, 136, 138, 142-143, 156, 169, 176, 255amplitudes, 13, 15, 18-19, 22-23, 83, 86AMPS, 227, 231-233Amstrong, 48

ii

Index

analog, 2, 9, 11-12, 107, 221, 231, 257analogue, 104, 150, 152, 157, 219analyzer, 13, 15, 83, 85AND, 25, 91angle, 12, 19, 39-41, 56, 59, 90, 164, 167, 181, 187ANSI, 225antenna, 2, 10, 25, 36-37, 46, 50, 52, 62, 69, 74-75, 79, 91, 93-95, 98-99, 101-103, 113, 117, 119, 157-161, 169-172, 174-195, 228, 253-254aperture, 128, 162-163, 169-172, 255apparatus, 201application, 2, 8, 40, 92, 97, 109, 188, 233, 236applications, 25, 28, 36, 43-44, 58, 96-97, 104-106, 154, 171-173, 222, 234, 236architecture, 6, 99, 103area, 81, 93-94, 120, 124, 138, 145, 192, 207, 219, 225, 227-229, 231, 234-236, 255arial, 169arithmetic, 90Armstrong, 48-49array, 175-177, 181-182, 184-185, 187-188, 190-192, 201, 235arrays, 172, 175-176, 178, 181, 183, 185, 187ASCII, 245, 248-249aspect, 121, 125, 143assembly, 162-164, 256Asynchronous, 7, 9ATB, 238, 240ATM, 92, 222atmospheric, 9, 164attenuated, 107, 112-113attenuation, 103, 114, 188attenuator, 83, 103, 113ATU, 101-102audible, 106, 145, 216-217audio, 1, 9, 23-25, 46, 52, 61, 65, 68-69, 77, 86, 89, 96-97, 99-101, 103-105, 117, 157-159, 165, 167, 216, 234, 258audiorange, 112authentication, 231automated, 97automatic, 41, 43, 47, 101, 141, 203-205, 208, 210, 222Azimuth, 180

Bbackbone, 5, 220background, 119, 124, 138backspace, 248

Baird, 140Balanced, 34, 49, 100-102, 109-111, 113, 116, 152Balun, 182balun, 194BAND, 38, 78, 80band, 16, 23, 26, 35, 40, 46, 48, 50, 71, 73, 77, 79-80, 92-97, 101-104, 107, 109-110, 112-115, 148, 158, 160, 181, 185, 187-188, 191-192, 231, 237Bandpass, 35, 37, 64, 68, 102bands, 24, 93-95, 107, 113, 115, 187bandwidth, 6-7, 10, 16, 19-20, 22-24, 33, 57, 61, 64-66, 68, 71-73, 75-76, 92, 96, 104-105, 107, 121, 127, 138, 140-142, 144, 151, 154-156, 158, 177, 184-185, 227, 232-233, 236BARnet, 207base, 27, 29, 33, 81, 85, 94-95, 98, 136, 163, 196, 225-226, 228-230, 232baseband, 7, 11, 16, 137, 159battery, 197-200, 221, 250-251Baudot, 244, 246, 249beacon, 97beacons, 94beam, 92, 120, 127-129, 132-133, 135, 141, 145, 148-150, 161-162, 164-165, 167-168, 170, 174, 176, 255-257beams, 128-129, 134, 145, 148, 163-164, 168Bearing, 84Beat, 105beeps, 3, 258BEL, 248Bessel, 18BFO, 105-106bias, 41-44, 103biasing, 41-42binary, 1, 9, 245, 257bipolar, 41bit, 8-9, 63, 76, 155, 232-233, 245, 248-249bits, 1, 7-9, 12, 232, 245, 248-249, 257BJT, 41blanking, 10, 127-132, 134-137, 139, 141-142, 152-153block, 2, 7, 34-36, 39, 45-46, 48, 61-63, 72, 94-95, 99-100, 110, 113, 157-161, 166, 213, 248, 252-253, 257-258Blue, 146-147, 150-151, 162, 165, 223Bluetooth, 235Boltzmann, 10booster, 186BORSCHT, 217, 221boundaries, 148BPF, 34, 40, 47, 157-159BPSK, 12broadband, 7, 97, 234-235

iii

Index

broadcast, 1, 8, 11, 47, 50, 70, 74, 84, 96, 115, 117, 137, 154, 167, 180, 195broadcasting, 108, 117, 152, 154, 177-178Broadside, 175-176Brown, 223browser, 1brushes, 10BS, 234, 248BSBH, 238BSC, 231, 235BT, 205BTS, 231, 235Buffer, 35, 37, 45, 47, 49, 99, 111bulb, 163bundle, 173, 189, 222-223burst, 10, 134, 139, 144, 153, 156, 160bus, 5bushings, 224busy, 205-206, 208-209, 216, 219, 237-240BW, 6-7, 10, 76, 107, 113-114byte, 9, 245

Ccable, 1, 91-92, 119, 156, 167, 181, 193-195, 222-225cables, 1-2, 10, 156, 194, 219-220, 222cabling, 98, 152, 222calibration, 244camera, 117, 120, 124, 127-129, 132, 134, 136, 138, 149-150, 160-161Candlepower, 146capacitance, 40-45, 54, 118capacitive, 42-43, 129, 181capacitor, 30, 41, 45, 54-55, 58-59, 74, 98, 218, 256capacity, 6, 36, 220, 224, 227, 234-235, 239capture, 9, 121carbon, 198carriage, 248Carrier, 12, 19, 27, 35, 37-38, 49, 99-102, 105, 108, 110-111, 113carry, 52, 86, 105, 154, 167cascaded, 65casing, 97cassette, 9, 195cathode, 3, 81, 130, 164CATV, 7CCD, 124, 149-150, 256-257CCDs, 159

CCIR, 131, 138, 142CCIT, 245CCITT, 244, 246-247, 258CDMA, 231-234, 236cell, 6, 92, 97, 225, 227-231Cellphone, 92cells, 166, 200, 227-230cellular, 91, 94, 227-228, 230-232, 236Celsius, 10centimeters, 82channel, 1-3, 7, 9, 24, 66, 83, 86, 88-89, 93, 95-98, 113-115, 119, 143, 160, 165, 167, 184-185, 191-192, 221, 226-229, 231, 237channels, 2-3, 7, 9, 16, 66, 92, 113-114, 138, 143-144, 167, 182-183, 186-187, 189-192, 226-227, 231-233, 240, 251Charge, 256charges, 33, 45charging, 45, 210-211chart, 90chip, 232, 256choke, 31chroma, 144, 161chrominance, 142-144, 150-152, 154, 156cinematography, 148CIO, 105circuit, 6-7, 10, 15, 26-27, 29-33, 37, 40-44, 47-48, 52, 55-63, 69, 71, 73-76, 84, 86-87, 89, 92, 97-98, 101, 105, 114, 117-119, 128-129, 135-136, 141, 162, 169, 182, 197-200, 205, 209-211, 215, 217-219, 221, 232-234, 237-238, 250, 254, 256-258circuitry, 10, 25, 37, 62-63, 97, 105, 119, 134, 156, 212circuits, 10, 35, 52, 61-63, 69-72, 76, 84, 97, 118, 127, 129, 131, 134, 138, 141, 156, 159-161, 165, 172, 200-201, 220, 223, 231, 238, 240, 255-257clock, 7-8, 238clusters, 156, 214coarse, 141coaxial, 16, 91, 193-195code, 3-4, 25, 95-96, 98, 198, 206-207, 232, 241-242, 244-245, 248, 250-252codec, 9coded, 52codes, 95-96, 206, 222-224, 244-245, 248-249Coding, 217, 221-222Coefficient, 30coefficient, 90coil, 53, 55, 58-59, 73-74, 83, 85, 196collector, 27, 30-33, 36, 74collinear, 175-176color, 120, 126-127, 143-149, 151-154, 156-159, 162-164, 166-168, 222-223

iv

Index

colors, 10, 144-145, 147-148, 153-155, 162, 166, 168, 222-224colourdifference, 150combiner, 181communication, 1-3, 5, 7, 9-11, 18, 23, 62, 84, 91-92, 94-96, 104-107, 112-114, 117, 169, 198, 219, 225, 227, 233, 241, 251, 253, 258communications, 1-10, 25, 72, 91, 93, 95-96, 98, 104-105, 217, 232, 235, 237, 244, 254comparator, 131compatibility, 236, 258complement, 232component, 13-15, 18-19, 30, 34, 83, 85, 109, 127, 129, 138, 144, 150, 154, 157-158, 164, 218, 224composite, 15-16, 18, 129, 131, 134, 137, 149-150, 152-153, 156, 159computer, 5, 8-9, 93, 97-98, 120, 154, 166, 228-229, 252computing, 5-6conductor, 10, 92, 189, 194, 222-223conductors, 183, 185, 188-189, 222-223conduit, 224configuration, 2, 181configurations, 5, 62, 171congestion, 240connect, 81, 118, 175, 189, 193-194, 199, 202-204, 206, 208, 213-214, 219, 222connection, 1, 5, 74, 84, 92-93, 98, 157, 170, 194, 200-201, 203, 207, 215-216, 219, 224, 233-234, 237, 239, 251connectivity, 220connector, 194construction, 190consumer, 97-98control, 8, 36, 41, 45, 47, 74, 83, 94, 101, 103, 106, 130, 134, 137, 141, 165, 180, 201-202, 219, 221, 229, 231, 245, 248, 257-258controller, 258controls, 45, 87, 98, 106, 129, 154, 162, 165, 257-258converter, 37, 64-66, 68-69, 73, 79, 158-159, 195, 198, 217, 257convex, 174-175coordinates, 158coplanar, 172copper, 1, 92, 223cord, 200, 224cordless, 91, 97, 225core, 74, 97, 196, 220, 235cos, 16, 39-40cosine, 13counter, 210cradle, 198, 213, 217Crosby, 47crossbar, 201-202

CROSSPOINT, 202Crosstalk, 223CRT, 122, 153, 162-163, 165-166CRTs, 162, 166crystal, 18, 36, 41, 44, 47-48, 72, 74-75, 98-99, 112-113, 165-166Current, 45, 57, 60, 140, 198, 251currents, 34, 176, 184, 198Curve, 56curve, 34, 53-54, 56-58, 76curvilinear, 173cutoff, 28CVBS, 151-152CW, 25-26, 99, 101-102cyan, 147, 154, 168cycle, 28, 33, 81, 118cylinder, 173, 189CYM, 154

DDAH, 244DAHS, 244dahs, 244dash, 52, 241-242, 250-251dashes, 3, 25, 241, 250data, 1, 5-9, 11, 46, 52, 92, 97, 121, 219, 221-225, 232-236, 245, 248, 252, 257-258dB, 11, 14-15, 19, 23, 68-69, 86-89, 103, 106-107, 113, 119, 177, 179dBi, 180, 184, 190dBm, 106dBW, 106DC, 31, 44, 98, 103, 118, 131, 218, 248decibel, 11, 119decibels, 83decimal, 210, 240decline, 166decoder, 157-158decoding, 98, 156decompress, 1deflection, 131, 135, 163degrees, 10, 59, 148DEL, 248delay, 123, 133, 144, 157delta, 231demodulated, 67, 160, 253, 258demodulation, 11, 65, 105, 112, 153demodulator, 24, 50, 65, 68, 144, 156, 158-159, 161, 254, 257-258

v

Index

density, 113-114depth, 81-84, 86, 88, 142, 166derivative, 39-40, 104, 107design, 6, 35, 46, 77, 109, 178, 184, 227, 230, 234detection, 8, 11, 18, 50, 52, 81, 221detector, 52, 61-62, 64, 68-69, 77, 82, 101, 105, 161-162, 252deviation, 16-17, 39-40, 47-48, 85, 105, 144device, 3, 8-9, 34, 37, 40, 42-43, 48, 62, 65, 77, 79, 91, 94-97, 117, 120, 123, 128-129, 150, 157, 169, 185, 197-199, 218, 228, 248, 252, 256devices, 8-10, 26, 28, 41, 52, 91, 94-95, 97, 121, 149-150, 169, 202, 222, 224-225, 227, 230, 232, 236, 256diagram, 2, 30-31, 34-37, 39, 41, 45-46, 48, 56, 59, 61-63, 72, 83, 85, 99-100, 109-110, 112-113, 124, 151, 157-162, 178, 183, 209, 252-253, 257dial, 24, 198, 205-207, 216, 218, 221, 231Dialer, 218dials, 207, 221diameter, 185, 224diaphragm, 198dielectric, 171-174differentiating, 141digital, 1-2, 7, 9, 11-12, 103, 120-121, 142-143, 154, 157, 202, 221, 227, 231, 257-258digits, 1, 204-210, 231, 245, 257dimension, 42, 183, 237dimensional, 153, 176dimensions, 82, 120-121, 140, 170, 185diode, 26-28, 37, 41, 43-44, 65, 82diodes, 10, 26-28, 41, 43, 63, 256diplexer, 159, 181-182, 192, 194dipole, 174-177, 179, 181-187, 189, 191-192dipoles, 170, 175-176, 179, 181-182, 186-188, 190-191directional, 173, 177, 179, 186, 191directivity, 172-173, 176, 185, 188-189directors, 183-185, 191discrete, 9, 143discriminator, 48, 52dish, 171DISK, 171-172distortion, 3, 6, 16, 18-19, 22-23, 36, 50, 63, 81, 103, 123, 255DITS, 244domain, 13-15, 22domains, 15, 236dot, 52, 143, 241-242, 250-251dots, 3, 25, 153, 166, 241-242, 250downlink, 91-92, 94, 234, 236downward, 98drain, 42-43driven, 27, 175, 183-185, 199, 234, 252

drives, 30, 97, 101, 103DSB, 15, 27, 34-35, 111-112, 156DSBFC, 30, 33, 35-37, 107, 109, 114DSBSC, 107-109, 114DSP, 103DTMF, 213dual, 191, 213dummy, 83duplex, 8, 91, 97, 215, 258Duplexing, 236DVD, 150

EEALing, 207EBHC, 239EDGE, 234efficiency, 8, 11, 15, 24, 27, 33, 79, 99, 104-105, 109, 112, 198-200, 234EIA, 222, 224-225electormagnet, 210electric, 3, 10, 120, 124, 166, 175, 184, 196-198, 216, 250electrical, 1-4, 35, 41, 52, 91-92, 97, 117-119, 129, 157, 160, 163, 167, 192, 198, 202, 216, 218, 221, 224-225, 241, 250-252, 254-256electricity, 117-118, 141Electro, 202, 252electromagnet, 210, 250electromagnetic, 3, 5, 35, 91-92, 118-119, 145-146, 163, 169, 171, 173, 177, 183-184, 189, 199electromechanical, 206electron, 52, 120, 127, 131, 134, 153, 161-164, 167-168electronic, 3, 5, 10, 26-27, 35, 41, 83, 91, 98, 120, 129, 136, 138, 149, 255-257element, 28, 124, 136, 169-171, 175, 179, 183-185, 187, 190-192, 224, 241, 244-245, 248elements, 41, 105, 121, 127, 138, 160, 162-163, 170, 172, 175, 177, 179, 181-185, 190-192, 212, 221, 228, 241-242, 244-245, 248, 258emf, 55, 58emission, 25, 186emitter, 27-30, 33, 36, 74emitters, 25encode, 5encoder, 151, 156-157, 242encoding, 151, 231-232, 250encryption, 95

vi

Index

energized, 197energy, 4-5, 10, 35, 52, 74, 117, 167, 169, 173-174, 189, 198, 216, 250England, 227equalizing, 127, 130, 133-134, 143equates, 17, 84EQUIPMENT, 230equipment, 2, 9-10, 25-26, 46, 83-84, 96, 104, 129, 152, 194, 205-206, 208-211, 217, 221, 230, 239equivalents, 242Erlang, 238-240erlangs, 238error, 8, 79, 245errors, 8-9, 105, 142-143ESC, 248essence, 68Ethernet, 222ETSI, 233-234ETX, 248

Ffaceplate, 130, 162-163Facsimile, 254-255Fan, 188FCC, 138FDD, 236FDM, 114features, 95, 140-142, 144, 172, 208, 218, 234, 236, 252feedback, 74feeder, 184, 190, 193Feedline, 179FET, 41-42fI, 80fiber, 1, 3, 91-92, 219-220Fidelity, 235Field, 122, 124, 126, 139-140fields, 122-123, 126, 130, 133-134, 137, 139-141, 175, 177, 184Filter, 35, 38, 66, 80, 100-101, 103, 109filters, 65, 72, 99, 102, 114, 142, 149, 151, 158-159, 167, 195FINDER, 210Finder, 209flicker, 10, 119, 121-123, 126fluorescent, 146, 161, 163flyback, 128, 135-136, 141flywheel, 33, 141

FM, 11-12, 17-21, 23-24, 38-40, 43-52, 70-71, 93, 96, 144, 156-161, 167, 169, 180-181, 195, 231focuses, 149, 162, 256fps, 119-120, 123, 140frame, 119-123, 126, 132, 138-139, 156, 162frequencies, 6, 10-11, 13, 18, 23, 26-27, 30-31, 37-38, 45, 50-52, 56-57, 61-65, 67-70, 72-74, 76-77, 79, 84-85, 89, 91, 93-95, 98, 104, 108, 110, 112, 114, 142, 145, 160, 169-170, 172-174, 178, 183, 187-188, 191, 213, 226-227, 230-231, 234, 254frequency, 2, 7-8, 10-27, 29-31, 33, 35, 37-41, 43-48, 50-62, 64-68, 70-74, 76-77, 79-81, 85-86, 88-92, 94-98, 100-101, 104-106, 109, 111-115, 117-118, 130, 134, 141-146, 151, 156, 158-160, 167, 169-171, 177-178, 183-187, 190-191, 199, 213, 227-228, 230, 232, 237, 253-255fuse, 120

Ggain, 29-30, 36, 38, 62, 65, 67-69, 76, 86-87, 89, 96, 101, 103, 141, 165, 173, 177, 179, 181, 184-186, 188-190gateways, 235gating, 26, 153Gbit, 97generation, 16, 46, 97, 114, 148-149, 152, 230-231, 233-235generator, 40, 84-89, 98, 160, 200, 205, 211generators, 83, 131, 137, 160, 199-200geometries, 169, 171Geometry, 180GHz, 10, 95, 171-174, 183gigabit, 97gigahertz, 95glowing, 211GPP, 234GPRS, 233, 235-236Grade, 239graphite, 164gray, 258grey, 138, 147-149ground, 74, 92, 138, 172, 223, 225GSM, 231-233, 235guardband, 164Guided, 3, 91

vii

Index

Hhabitually, 185halfwave, 187Halogen, 146handoff, 229-230, 232handoffs, 231handset, 198, 205, 208-209, 211, 213, 216-217, 225handshaking, 258hardware, 1, 221, 225, 231harmonics, 33, 37, 63, 73Hartley, 6haul, 219-220HD, 143HDMI, 157headphones, 52, 75headset, 84, 93, 103-104, 218henrys, 53, 55, 58hertz, 10, 27, 84, 117-118heterodyne, 25, 63, 73-74, 86, 99heterodyning, 62-63, 65HF, 94-95, 97, 99, 103-104hierarchy, 214, 219, 221highfrequency, 11, 31hook, 118, 198, 205, 211, 213, 217-218, 221HSCSD, 233HSI, 154HSPA, 234HT, 248Hue, 154hue, 142, 154huge, 257Human, 119, 121, 148Hybrid, 212, 215, 217, 221Hz, 47, 51, 62-63, 78, 80, 84, 105, 112, 118-119, 126-127, 130, 134, 140-142, 144-145, 153, 217, 221

IIC, 45, 52, 59, 98IF, 62, 64-74, 76-77, 79-80, 97, 99-103, 160-162IFRR, 67ignition, 98impedance, 36, 41-43, 56, 59-60, 84-85, 87-90, 102, 118, 176-177, 179, 184-185, 215IMT, 234-235

IMTS, 226-227inches, 94-95, 224indicator, 199-200indicators, 199indigo, 145, 148inductance, 40, 43, 53, 55, 58, 118induction, 92, 223inductive, 42-43, 85inductor, 41, 53inductors, 63Industry, 222, 233information, 1-3, 6-7, 9, 11-12, 15, 25, 36-37, 50-51, 61, 65, 77, 80, 94-96, 98, 105, 107-109, 117, 119, 127, 129-132, 134-139, 143-144, 149-151, 154, 160, 167-168, 192, 218, 230, 232-233, 235, 241, 244, 250, 254-258informations, 161infrared, 145, 173Input, 2, 38, 44, 47, 49, 87, 89inputs, 44, 62-63, 105, 157Inside, 217inside, 39, 62, 97, 162-164, 167instal, 199installed, 226-227installer, 222instrument, 3, 82-83, 85, 89insulated, 92, 224integral, 38-39, 142integrated, 39, 50, 52, 98, 165integrating, 118, 141, 235integration, 18, 39, 172integrator, 141intelligence, 25, 52, 223intent, 122Intercarrier, 142Interception, 96intercepts, 160, 183intercoms, 36interconnect, 5interconnected, 5, 191, 219, 231interface, 215, 221-222, 233-234, 252, 257interfacing, 221intermodulation, 16, 83Internet, 225, 236Inverter, 45ionosphere, 94ionospheric, 94IP, 235-236IR, 52ISB, 83, 109, 113-114ISD, 115ITU, 234-235þÿIÁ, 90

viii

Index

Jjack, 200, 218, 224John, 5jXc, 42

Kkbps, 91, 232-233, 235Kelvin, 10, 148key, 3-5, 25, 98, 114, 199-200, 218-219, 227, 232-233, 250, 253keyboard, 244, 252Keying, 12keypad, 213kHz, 10, 16, 23-24, 47, 49, 66, 69-74, 99-100, 103-104, 113, 156, 231km, 145, 192, 227kTBW, 10KW, 113

Llags, 53, 181LAN, 5, 222landline, 230layers, 92LCD, 166LCR, 55, 57, 59, 61leaky, 170, 172lens, 149, 166, 170Level, 35-36, 137, 153, 204, 210, 222LF, 248limit, 16, 28, 76, 158, 205, 241Line, 102-103, 120, 125-126, 132, 135, 138-142, 176, 179, 208-209, 212, 217, 219, 221Linefinder, 209link, 92-93, 183, 232, 248links, 6, 92, 219-220loading, 74, 248lobes, 191local, 65-68, 79, 93-94, 98, 101, 184, 193, 199, 202, 209-217, 219, 221, 230-231, 235, 252-253, 255

location, 1, 135, 198, 207, 218, 224, 231locations, 5, 92, 183, 185, 192, 198, 221, 225logarithmic, 11, 15, 119, 190logic, 106, 257loop, 47-48, 188, 193, 214, 216-217, 224loops, 74, 170, 189, 221Lost, 239-240LOT, 248loudspeaker, 3, 52, 84-85, 117, 165LPDA, 177-178, 190LPDAs, 190LPF, 47, 152, 157-159LPVA, 190LSB, 13-15, 25, 100-101, 105-106, 108, 110, 113-115LTE, 236luminance, 130-132, 136-137, 142, 150-154, 156, 159, 161luminosity, 146-147Lux, 146

MmA, 88, 217machines, 258magenta, 147, 154magnet, 196-198, 252magnetic, 164, 175, 196-198, 255magneto, 3-4, 199-200, 221magnitude, 19, 90, 227mainframe, 252maintenance, 7, 115, 202manage, 96manifold, 181maps, 254, 256Marconi, 3, 5margins, 20masts, 192material, 174, 196, 198mathematical, 13, 65, 67, 153matrix, 143, 163, 201-202, 256matrixing, 151MATV, 195Mbit, 97, 236Mbps, 92, 222, 234-236measurement, 15, 81-83, 85-90, 106, 166, 238mega, 27megabits, 97megahertz, 93-95, 169megapixels, 121

ix

Index

memory, 256-257Merging, 119-120meter, 81, 85-89, 93, 101, 193, 210-211metering, 210-211meters, 3, 83, 85, 92, 210MH, 99, 191MHz, 45, 47-48, 70-73, 84, 93-95, 99-100, 103, 113-114, 138, 140-144, 152-158, 160, 183-185, 192, 222, 226, 231microcells, 228microphone, 2, 46, 117, 217-218, 231microprocessor, 252microstrip, 172microwave, 16, 92-94, 145, 174, 188, 219-220, 251millimeter, 145, 172Mixer, 39-40, 47, 49, 64-66, 69-70, 72, 100, 102-103, 160Mnemonics, 207mobile, 91-92, 95, 97, 112-113, 172, 207, 225-227, 229-235modem, 257-258modulate, 2, 11, 16, 31, 120, 152, 158-159, 255, 257modulating, 2, 11-13, 16-20, 23-24, 26-31, 33-35, 37-41, 43-44, 47-48, 81, 85, 106, 108-111, 113, 143modulation, 7, 11-18, 20-22, 25-26, 28-30, 33-34, 36-37, 39-41, 43-44, 46-50, 81-87, 89, 96, 104-105, 107-109, 141-144, 152, 156, 169, 231, 257modulator, 3, 15, 18, 26-37, 39, 41-44, 46-48, 50, 65, 77, 82, 99, 109-111, 113, 116, 152, 156-158, 160, 253-254, 257modulators, 26-28, 33-34, 36, 43, 113, 152, 156moment, 141, 156, 205, 236monitor, 98, 120, 122, 130, 132, 157-159monochrome, 127, 131-132, 136, 139-140, 143, 149-150, 155, 160-161, 165Morse, 3-4, 241-242, 244, 250-251motor, 252, 257-258motors, 10, 223, 252, 255, 257MSC, 228, 230MTSO, 228-232multipath, 181multiplex, 158, 246multiplexing, 2, 7, 16, 114, 151, 232Murray, 244-245, 247mV, 88mW, 86-87, 89

Nnarrowband, 39-40, 235NEC, 225negative, 28, 44, 98, 118, 142, 223, 246, 251network, 1, 5-6, 9, 35-37, 49, 62, 89, 101, 192, 219-221, 230, 233-236, 239networks, 5, 91-93, 97, 233-236NFPA, 225nodes, 5noise, 1-3, 9-11, 24, 35-36, 50-51, 64, 74-75, 86-88, 91, 102-103, 107, 119, 128-129, 178, 232nonlinear, 18, 27, 30, 36-37, 62, 65, 69, 77, 79nonlinearly, 29NTSC, 123, 136, 138, 140-144, 151-152, 154-155, 157-158

OOFDM, 12ohms, 42, 52-56, 58, 176, 184optical, 91, 149, 157, 163, 188, 220optimum, 102, 106, 144, 165orange, 145, 148Orthogonal, 12oscillator, 18, 35-37, 41, 43-48, 65-74, 79, 98-99, 101, 105, 109, 113, 130, 152, 156, 160, 253-255oscilloscope, 81outlets, 204, 209, 224-225OUTPUTLINES, 201

Ppacket, 6, 230, 233-234, 236packets, 233, 236PAL, 123, 130, 136, 138-140, 143-144, 151-152, 154-155panels, 181-182, 222paraboloidal, 173, 189parameters, 6, 12, 178, 237parasitic, 185, 191parity, 8, 245, 249passband, 79, 106

x

Index

passive, 10, 26patch, 171-172, 222pattern, 4, 162, 169, 177, 179, 181-182, 186-188patterns, 3-5, 139, 171, 195, 232PBX, 217PCB, 1PCM, 232PCS, 231PDC, 231peak, 12, 17, 23, 48, 76, 81, 106, 131-132, 137, 141, 236Pedestal, 137, 153Phasing, 176, 179phone, 85, 92, 208, 211, 213, 216-220, 224-225, 227, 230-231phones, 95, 97, 207, 218-219, 225, 227, 231picture, 114, 117, 119, 121-122, 124, 126-132, 134-139, 148-150, 155, 157-162, 164-167, 181-182, 186, 195, 254-255Pilot, 111-112, 115pink, 10pixel, 121-122pixels, 120-122, 143placed, 98, 119, 166, 174, 178, 188-189, 196, 198, 217plasma, 165-166plate, 224PLL, 1, 65PLWA, 172Poisson, 240polarity, 181, 197, 202, 224polarization, 178, 193police, 93, 97porch, 135-136, 153Postequalizing, 133POTS, 212power, 1, 10-11, 14-16, 18, 23-24, 26-28, 30-31, 33, 35-37, 46, 69, 83, 85-89, 98, 101-102, 105-109, 112-113, 118-119, 159-160, 169, 172-173, 179, 184, 193, 216, 221, 223-224, 227-229, 251, 253-254PPM, 12Preamplifier, 35, 37Preemphasis, 50-51preselector, 64-65, 67-69, 103present, 5, 26, 29, 88-89, 106-107, 134, 142, 144, 195preserve, 136processing, 103, 154, 160Progressive, 121-122propagates, 2propagating, 170propagation, 92, 94-95, 159, 174properties, 17, 121, 184, 188, 232PSK, 257

PSTN, 5, 92, 230PSU, 98pulse, 127-128, 130-133, 135-136, 139-141, 153, 160, 210-211, 216, 248, 250PulsePosition, 12

QQAM, 12, 143-144, 158-159, 257QoS, 236quadrature, 143, 152

Rrabbit, 189radar, 2, 69, 169, 176radiate, 177radiation, 2, 91-92, 163, 172-173, 175, 177, 179-180, 182, 184-185, 188radiator, 169, 174radiators, 170, 172, 181radio, 2-3, 5, 8, 11, 23-26, 31, 37, 46, 52, 58, 61-67, 69-71, 74-77, 79, 82, 86-91, 93-98, 104-107, 109, 112-113, 117, 119, 145, 167, 169, 173-174, 189, 219, 228-229, 233-236, 244, 251, 254-255radios, 71-74, 91, 94-95, 97Radiotelegraphy, 25rainbow, 145, 148raster, 120, 130, 133, 135rays, 145, 173, 189RBOC, 212RCVR, 98reactance, 40-43, 53-54reactive, 41-42receiver, 1-4, 7-8, 10-11, 15, 25, 50-52, 61-69, 71-74, 76, 79, 82-84, 86-89, 91, 94-96, 98-99, 101-102, 104-107, 109, 112, 114-115, 117, 127-132, 134-138, 141, 144, 149, 152-153, 156, 159-162, 165, 173, 181, 185-186, 189, 195, 198-200, 216-217, 226, 228, 241, 250, 252-255, 258receivers, 5, 52, 61, 70-71, 73-75, 97-99, 105-106, 109, 115, 141, 143, 165, 181, 183, 188, 195

xi

Index

reception, 1, 3, 8, 10, 52, 63, 88, 91, 93, 96-97, 107, 112, 179-180, 183, 185-189, 191, 193, 241receptors, 149records, 253Red, 93, 146-147, 150-151, 162, 165Reed, 202reflected, 101-102, 120, 193, 235, 255reflection, 89-90, 173reflectometer, 101-102reflector, 170-171, 173-174, 183-185, 187-189reflectors, 173-174, 181, 189, 191refraction, 148, 174-175refractive, 174relay, 99, 101, 202, 211Repeater, 212repeaters, 93-95resistor, 45, 84, 98resolution, 121, 127, 140-142, 144, 153resolutions, 120, 141, 143resonance, 56-57, 59-61, 179, 191restorer, 129retrace, 122, 124, 127-129, 131-135reuse, 227-228RF, 25, 35-37, 43, 46, 52, 61-62, 64-74, 97, 99-103, 105-106, 157, 160-161, 175-176, 186RFC, 31, 33, 43RFID, 98RGB, 149, 151, 154-159rhombic, 170rid, 71Ringer, 217-218RNC, 231, 234-235rotor, 180RTB, 140

Ssatellite, 10, 91-92, 94, 220, 235satellites, 94, 98, 172saturation, 28, 30, 154, 165sawtooth, 135SBSSC, 112scan, 9, 120-122, 124-127, 132-133, 137, 166, 176scanline, 133, 136scanning, 120-130, 134-136, 138, 142, 150, 159-160, 177, 254-257SCDMA, 234scene, 117, 120-122, 124, 126-127, 132, 136, 138, 149schematic, 30, 98

scrambling, 95-96screen, 81, 83, 92, 120-123, 126-127, 130-131, 134, 139, 153-155, 161-164, 166-168, 185-186, 188, 218SECAM, 138, 140, 143-144, 152selectivity, 52, 58, 61-62, 65, 68, 71-72, 76-77, 88selectors, 204, 206, 209-210, 212semiconductor, 10, 256sender, 1, 241sensitivity, 52, 61-62, 64, 74-75, 86-87sensor, 9separated, 6, 23, 131, 143, 149, 164, 168, 227, 232, 254sequential, 122serial, 9, 244-245, 252settings, 94-95, 218SGSN, 234shunt, 101sideband, 13-15, 18-19, 22-23, 25-26, 34-35, 65, 76, 100, 104-109, 113-114, 143, 152, 158sidebands, 15-16, 18-20, 22-23, 25, 37-40, 69, 75, 105, 107-109, 156sidetone, 198siemens, 42Signal, 12, 38, 44, 47, 49, 51, 81, 83-84, 86, 89, 110-111, 119-120, 131, 136, 151, 215, 253signaling, 197-200, 209, 218, 221, 231signals, 1, 3, 6-9, 11, 16, 19, 23, 26, 37, 45, 52, 60-63, 65, 69-71, 73-74, 76, 84, 91, 93-94, 96-97, 101-102, 104-107, 112, 114-117, 121, 123-124, 128-130, 132-134, 137, 143-144, 149-153, 155-157, 159-161, 166-169, 181, 183, 185-186, 188, 192-195, 198, 200, 202, 215-216, 218-219, 221, 224, 227, 232, 241, 252-258sinusoidal, 11, 13-14, 19-20, 29, 45, 53SLC, 209slot, 170, 172, 237smartphones, 97SNR, 11socket, 101, 194, 199softkeys, 218-219Software, 94SOH, 248solar, 10solenoid, 196-197sonar, 2sounder, 3, 250speaker, 4, 74-75, 103-104, 118, 159, 219spectral, 17-19, 149, 234spectrum, 10, 13, 15-16, 19-21, 25, 39, 52, 67, 83, 85, 93, 104, 111, 114, 143-149, 156, 232-233speech, 2, 5, 11, 23, 52, 85, 99-100, 104, 112, 117, 205, 216-217speed, 27-28, 92, 97, 145, 178, 222, 224, 235, 244-245, 254-255, 258

xii

Index

splitter, 192, 194Splitting, 228-229SSB, 15-16, 25, 34, 91, 99-102, 104-116SSBFC, 109SSBRC, 109, 112-113SSBSC, 107, 109-112, 114stereo, 118, 167storage, 93, 257STP, 92strength, 52, 106, 119, 167, 186, 194-196strip, 64, 162Strowger, 202-203, 205-206, 211subcarrier, 139, 141-144, 152-153, 156, 158subscriber, 91, 199-200, 203-211, 213, 215, 221, 231, 239subscribers, 199-201, 204, 206, 209-211, 214, 239subsystems, 2, 99, 221subtracting, 34superhet, 62, 69, 72, 76-77, 99superheterodyne, 62-63, 66-67, 72, 79, 99, 105superposition, 26Supervision, 217, 221supervisory, 200suppressed, 15, 34-35, 48, 107-109, 112, 143, 156switch, 4, 25, 27-28, 91, 106, 165, 186, 203, 213-215, 217, 220, 229, 234, 237, 239-240, 250switchboard, 199, 222switches, 26, 28, 186, 202, 220-221switching, 5-6, 26-28, 198-199, 201-203, 205, 208, 213-214, 216, 219, 221, 229-231, 233, 239, 253SWR, 179symmetrical, 14, 30, 33sync, 121, 127, 129-137, 139-142, 151-153, 156, 159-160, 258synchronisation, 136, 141, 156, 244synchronization, 7-8, 123, 129-131, 136-137synchronizing, 127, 129-130, 132-133, 161, 168synchronous, 7-8, 245, 255, 258synthesizers, 109, 112systems, 2, 4, 7, 16, 36, 97, 112, 123, 128-131, 138, 140, 143, 150, 154, 156, 166, 169, 176, 198-201, 205, 219, 221-223, 225-227, 230-231, 233, 235-236

TTACS, 227talkie, 8, 36, 96Tandem, 214-215, 219TDD, 236

TDMA, 233techniques, 9, 12, 16, 74, 109, 114, 122, 236, 257TELCO, 212-213, 221Telegrams, 206Telegrapgh, 253telegraph, 3-4, 114, 242, 250, 252-254Telegraphy, 241, 253telephone, 3-5, 16, 84, 91-92, 96, 109, 114, 119, 198-202, 205-206, 208, 212-214, 216-219, 221-223, 225-226, 229-234, 236-239, 253, 256-258telephones, 3, 97, 207, 209, 216, 219, 224-228telephony, 112-113, 199, 225, 234-235teleprinter, 251-253telescene, 140teletypewriter, 52, 251television, 117-118, 120, 127-132, 134, 136, 140, 146, 148-150, 152-155, 160-165, 169, 178, 182-183, 185, 188, 193, 195Telex, 253terminals, 41-43, 81, 84, 87, 194termination, 221-222Terrestrial, 92, 234THD, 103TIA, 222, 224-225, 233timebase, 141-142tip, 98, 216, 222-224Token, 222traffic, 6, 94, 113-114, 199, 209, 220, 236-240transceiver, 91, 93-98, 101, 104, 231transceivers, 91, 93-99, 103transconductance, 41-42transducer, 2-3, 170transformer, 29, 62, 74, 215transistor, 26-27, 29-33, 37, 41, 74, 98transistors, 10, 26-28, 52, 63transmission, 1-3, 5-9, 11, 16, 19-20, 22, 25-26, 36, 47, 76, 89, 91-94, 96-98, 104-107, 109, 112-114, 117, 121, 129, 143, 169-170, 175, 185, 192-193, 202, 216, 219, 221, 223, 227-228, 233-235, 237, 241, 244, 250-251, 254-255, 257transmitter, 1-4, 7-8, 11, 18, 25-26, 28, 35-37, 41, 45-48, 50, 83, 91, 94-96, 98-99, 101-102, 104, 106-107, 112-113, 117, 119, 129, 136, 138, 152-153, 159-160, 175, 177, 179, 181-184, 192-193, 198-199, 216-217, 226, 228, 250, 252-255transmitters, 16, 36, 46, 48, 97-99, 109, 143, 181-182, 227-229transponder, 92TRF, 61-62, 76-77, 79trunk, 206, 213, 215, 219-221, 237-239trunks, 219-221, 237-238, 240TTY, 251tuner, 96, 99, 117, 160-161, 167

xiii

Index

tuning, 43, 64, 70, 74, 99, 106, 112, 142, 165turnstile, 179-182TV, 8-9, 63, 69, 114, 117, 119-124, 126-127, 130, 134, 138, 147, 149, 151, 154, 157-160, 166-168, 177, 183, 185-186, 188-190, 193-195Twist, 223twisted, 1, 91-92, 215, 223TX, 98-99, 101-102, 222

UUART, 9Uda, 175, 183-184UHF, 18, 94-95, 97, 159, 169, 182, 185, 188-189, 192-195ULWA, 172UMTS, 234Uniselector, 204, 209units, 36, 93, 96, 121, 169, 227, 231, 238, 241universal, 186, 233, 242unmodulated, 13-14, 16, 18-19, 39, 41, 73, 82uplink, 91, 94, 234, 236USB, 13-15, 25, 100-101, 106, 108, 110-111, 113-115UTP, 92, 215, 222, 224UWC, 233

Vvaractor, 41, 43-44VBS, 137VCO, 1, 45, 47VCR, 132, 167, 195vestige, 114Vestigial, 109, 114VFO, 99-100VGA, 1, 157VHF, 18, 93-95, 97, 114, 159, 169, 182, 185, 187, 189-195Video, 115, 120-121, 131-132, 136-138, 145, 149, 151, 153, 157, 161-162vidicon, 124, 149violet, 145, 147-148virtual, 6VLSI, 257-258

voice, 1, 4-7, 9, 11, 16, 23, 95-97, 104, 114, 159, 198, 209, 219, 221, 223, 225, 231, 234-237, 241voltage, 2, 11-12, 14, 18-19, 23, 25, 29-30, 36, 40-45, 48, 53-54, 56, 59, 61, 74, 83, 85-90, 98, 108, 123-125, 128, 131, 134-135, 138, 151, 199, 218, 221, 223voltages, 89, 125, 163, 221voltmeter, 81Volts, 13, 38, 51, 78, 80VSAT, 92VSB, 114-115, 157-159VSBFC, 109

Wwalkietalkie, 95WAN, 5watts, 10, 106wave, 2-3, 5, 11-15, 17-18, 25, 31, 33, 35, 39, 45, 52, 62-63, 81-82, 85, 92-93, 97, 104, 108, 115, 167-172, 174, 181-183, 186-187, 189, 191, 198, 254, 257waveform, 12, 30, 44, 46, 81-83, 129-131waveguide, 169, 172wavelength, 94-95, 145, 148, 170, 173, 178, 183, 185, 187waves, 2-3, 5, 63, 82, 91-92, 117, 127, 167, 169-171, 178, 183, 188-189, 255WCDMA, 234Web, 225why, 147, 227wideband, 39-40, 190, 235wire, 2, 4, 74, 91-92, 170, 187, 189, 191, 193, 196, 199, 215, 217, 219, 221, 223-225wireless, 1, 3, 5, 36, 91, 97, 225, 234-235, 253wiring, 192, 222-225WMSC, 234Wpm, 244

YYagi, 175, 183-185YagiUda, 183yellow, 145, 147-148, 154, 168, 186YIQ, 154-155, 158-159

xiv

Index

yoke, 162-164, 168, 196YUV, 154-155

i

Index

AAA, 42ABC, 207ABSBH, 238absolute, 10, 131ac, 52, 58, 129, 131, 138access, 95, 209, 218, 224, 233, 235accurate, 82-83, 98, 130, 132, 138, 141, 144, 164ACK, 248acoustic, 198action, 26, 117, 247active, 10, 26, 124, 127, 131, 133-134, 177, 190-191, 210-211actuate, 255adapters, 93Adder, 39, 110, 113adder, 110, 113, 152, 160addition, 32, 37, 83, 96, 112, 117, 138, 144, 186Additive, 147additive, 147, 162address, 216, 225adjacent, 16, 75-76, 86, 88-89, 115, 143, 191, 199, 227-229, 231adjust, 70, 106, 129, 219, 236aerial, 46, 83-84, 88, 169, 172, 185AF, 52, 70, 72, 100, 110-111AFC, 41, 43, 47-48, 111AGC, 101-103, 162alarm, 211-212Alarms, 208, 211ALC, 101

align, 156alignment, 163Allotter, 208-209alloy, 198alternate, 122, 133, 161, 181alternating, 218alternation, 118alternator, 199AM, 11-12, 16, 18, 20, 23-28, 30, 33, 35-38, 48, 66, 68-69, 73-74, 77-80, 99, 101, 104-105, 107, 119, 156, 159-160, 167-169, 177, 181amateur, 46, 93-94, 99, 105, 244ammeter, 81-82, 87-88Amp, 70, 72, 99, 111, 253amp, 62, 102, 162amplification, 3, 16, 30, 46, 52, 68, 76, 79, 104, 161, 186amplified, 29, 40, 101, 113, 159-160, 186, 215, 255amplifier, 1, 18, 27-30, 33-37, 46, 52, 64-65, 68-69, 74, 76, 79-80, 101-103, 117-118, 152, 160-162, 165, 194-195, 215, 253-254amplifiers, 28, 36, 52, 61-62, 64-65, 67-69, 75, 159-161amplify, 52, 61, 97, 254amplifying, 50AMPLITUDE, 128Amplitude, 11-13, 15, 19-21, 23, 26, 30, 38, 49, 51, 78, 80-81, 86, 99, 104, 135, 153, 167amplitude, 2, 11-21, 26-28, 30, 34-36, 39, 46, 48-49, 56, 81-83, 85-86, 104, 107-109, 112, 115, 127-128, 132, 134, 136, 138, 142-143, 156, 169, 176, 255amplitudes, 13, 15, 18-19, 22-23, 83, 86AMPS, 227, 231-233Amstrong, 48

ii

Index

analog, 2, 9, 11-12, 107, 221, 231, 257analogue, 104, 150, 152, 157, 219analyzer, 13, 15, 83, 85AND, 25, 91angle, 12, 19, 39-41, 56, 59, 90, 164, 167, 181, 187ANSI, 225antenna, 2, 10, 25, 36-37, 46, 50, 52, 62, 69, 74-75, 79, 91, 93-95, 98-99, 101-103, 113, 117, 119, 157-161, 169-172, 174-195, 228, 253-254aperture, 128, 162-163, 169-172, 255apparatus, 201application, 2, 8, 40, 92, 97, 109, 188, 233, 236applications, 25, 28, 36, 43-44, 58, 96-97, 104-106, 154, 171-173, 222, 234, 236architecture, 6, 99, 103area, 81, 93-94, 120, 124, 138, 145, 192, 207, 219, 225, 227-229, 231, 234-236, 255arial, 169arithmetic, 90Armstrong, 48-49array, 175-177, 181-182, 184-185, 187-188, 190-192, 201, 235arrays, 172, 175-176, 178, 181, 183, 185, 187ASCII, 245, 248-249aspect, 121, 125, 143assembly, 162-164, 256Asynchronous, 7, 9ATB, 238, 240ATM, 92, 222atmospheric, 9, 164attenuated, 107, 112-113attenuation, 103, 114, 188attenuator, 83, 103, 113ATU, 101-102audible, 106, 145, 216-217audio, 1, 9, 23-25, 46, 52, 61, 65, 68-69, 77, 86, 89, 96-97, 99-101, 103-105, 117, 157-159, 165, 167, 216, 234, 258audiorange, 112authentication, 231automated, 97automatic, 41, 43, 47, 101, 141, 203-205, 208, 210, 222Azimuth, 180

Bbackbone, 5, 220background, 119, 124, 138backspace, 248

Baird, 140Balanced, 34, 49, 100-102, 109-111, 113, 116, 152Balun, 182balun, 194BAND, 38, 78, 80band, 16, 23, 26, 35, 40, 46, 48, 50, 71, 73, 77, 79-80, 92-97, 101-104, 107, 109-110, 112-115, 148, 158, 160, 181, 185, 187-188, 191-192, 231, 237Bandpass, 35, 37, 64, 68, 102bands, 24, 93-95, 107, 113, 115, 187bandwidth, 6-7, 10, 16, 19-20, 22-24, 33, 57, 61, 64-66, 68, 71-73, 75-76, 92, 96, 104-105, 107, 121, 127, 138, 140-142, 144, 151, 154-156, 158, 177, 184-185, 227, 232-233, 236BARnet, 207base, 27, 29, 33, 81, 85, 94-95, 98, 136, 163, 196, 225-226, 228-230, 232baseband, 7, 11, 16, 137, 159battery, 197-200, 221, 250-251Baudot, 244, 246, 249beacon, 97beacons, 94beam, 92, 120, 127-129, 132-133, 135, 141, 145, 148-150, 161-162, 164-165, 167-168, 170, 174, 176, 255-257beams, 128-129, 134, 145, 148, 163-164, 168Bearing, 84Beat, 105beeps, 3, 258BEL, 248Bessel, 18BFO, 105-106bias, 41-44, 103biasing, 41-42binary, 1, 9, 245, 257bipolar, 41bit, 8-9, 63, 76, 155, 232-233, 245, 248-249bits, 1, 7-9, 12, 232, 245, 248-249, 257BJT, 41blanking, 10, 127-132, 134-137, 139, 141-142, 152-153block, 2, 7, 34-36, 39, 45-46, 48, 61-63, 72, 94-95, 99-100, 110, 113, 157-161, 166, 213, 248, 252-253, 257-258Blue, 146-147, 150-151, 162, 165, 223Bluetooth, 235Boltzmann, 10booster, 186BORSCHT, 217, 221boundaries, 148BPF, 34, 40, 47, 157-159BPSK, 12broadband, 7, 97, 234-235

iii

Index

broadcast, 1, 8, 11, 47, 50, 70, 74, 84, 96, 115, 117, 137, 154, 167, 180, 195broadcasting, 108, 117, 152, 154, 177-178Broadside, 175-176Brown, 223browser, 1brushes, 10BS, 234, 248BSBH, 238BSC, 231, 235BT, 205BTS, 231, 235Buffer, 35, 37, 45, 47, 49, 99, 111bulb, 163bundle, 173, 189, 222-223burst, 10, 134, 139, 144, 153, 156, 160bus, 5bushings, 224busy, 205-206, 208-209, 216, 219, 237-240BW, 6-7, 10, 76, 107, 113-114byte, 9, 245

Ccable, 1, 91-92, 119, 156, 167, 181, 193-195, 222-225cables, 1-2, 10, 156, 194, 219-220, 222cabling, 98, 152, 222calibration, 244camera, 117, 120, 124, 127-129, 132, 134, 136, 138, 149-150, 160-161Candlepower, 146capacitance, 40-45, 54, 118capacitive, 42-43, 129, 181capacitor, 30, 41, 45, 54-55, 58-59, 74, 98, 218, 256capacity, 6, 36, 220, 224, 227, 234-235, 239capture, 9, 121carbon, 198carriage, 248Carrier, 12, 19, 27, 35, 37-38, 49, 99-102, 105, 108, 110-111, 113carry, 52, 86, 105, 154, 167cascaded, 65casing, 97cassette, 9, 195cathode, 3, 81, 130, 164CATV, 7CCD, 124, 149-150, 256-257CCDs, 159

CCIR, 131, 138, 142CCIT, 245CCITT, 244, 246-247, 258CDMA, 231-234, 236cell, 6, 92, 97, 225, 227-231Cellphone, 92cells, 166, 200, 227-230cellular, 91, 94, 227-228, 230-232, 236Celsius, 10centimeters, 82channel, 1-3, 7, 9, 24, 66, 83, 86, 88-89, 93, 95-98, 113-115, 119, 143, 160, 165, 167, 184-185, 191-192, 221, 226-229, 231, 237channels, 2-3, 7, 9, 16, 66, 92, 113-114, 138, 143-144, 167, 182-183, 186-187, 189-192, 226-227, 231-233, 240, 251Charge, 256charges, 33, 45charging, 45, 210-211chart, 90chip, 232, 256choke, 31chroma, 144, 161chrominance, 142-144, 150-152, 154, 156cinematography, 148CIO, 105circuit, 6-7, 10, 15, 26-27, 29-33, 37, 40-44, 47-48, 52, 55-63, 69, 71, 73-76, 84, 86-87, 89, 92, 97-98, 101, 105, 114, 117-119, 128-129, 135-136, 141, 162, 169, 182, 197-200, 205, 209-211, 215, 217-219, 221, 232-234, 237-238, 250, 254, 256-258circuitry, 10, 25, 37, 62-63, 97, 105, 119, 134, 156, 212circuits, 10, 35, 52, 61-63, 69-72, 76, 84, 97, 118, 127, 129, 131, 134, 138, 141, 156, 159-161, 165, 172, 200-201, 220, 223, 231, 238, 240, 255-257clock, 7-8, 238clusters, 156, 214coarse, 141coaxial, 16, 91, 193-195code, 3-4, 25, 95-96, 98, 198, 206-207, 232, 241-242, 244-245, 248, 250-252codec, 9coded, 52codes, 95-96, 206, 222-224, 244-245, 248-249Coding, 217, 221-222Coefficient, 30coefficient, 90coil, 53, 55, 58-59, 73-74, 83, 85, 196collector, 27, 30-33, 36, 74collinear, 175-176color, 120, 126-127, 143-149, 151-154, 156-159, 162-164, 166-168, 222-223

iv

Index

colors, 10, 144-145, 147-148, 153-155, 162, 166, 168, 222-224colourdifference, 150combiner, 181communication, 1-3, 5, 7, 9-11, 18, 23, 62, 84, 91-92, 94-96, 104-107, 112-114, 117, 169, 198, 219, 225, 227, 233, 241, 251, 253, 258communications, 1-10, 25, 72, 91, 93, 95-96, 98, 104-105, 217, 232, 235, 237, 244, 254comparator, 131compatibility, 236, 258complement, 232component, 13-15, 18-19, 30, 34, 83, 85, 109, 127, 129, 138, 144, 150, 154, 157-158, 164, 218, 224composite, 15-16, 18, 129, 131, 134, 137, 149-150, 152-153, 156, 159computer, 5, 8-9, 93, 97-98, 120, 154, 166, 228-229, 252computing, 5-6conductor, 10, 92, 189, 194, 222-223conductors, 183, 185, 188-189, 222-223conduit, 224configuration, 2, 181configurations, 5, 62, 171congestion, 240connect, 81, 118, 175, 189, 193-194, 199, 202-204, 206, 208, 213-214, 219, 222connection, 1, 5, 74, 84, 92-93, 98, 157, 170, 194, 200-201, 203, 207, 215-216, 219, 224, 233-234, 237, 239, 251connectivity, 220connector, 194construction, 190consumer, 97-98control, 8, 36, 41, 45, 47, 74, 83, 94, 101, 103, 106, 130, 134, 137, 141, 165, 180, 201-202, 219, 221, 229, 231, 245, 248, 257-258controller, 258controls, 45, 87, 98, 106, 129, 154, 162, 165, 257-258converter, 37, 64-66, 68-69, 73, 79, 158-159, 195, 198, 217, 257convex, 174-175coordinates, 158coplanar, 172copper, 1, 92, 223cord, 200, 224cordless, 91, 97, 225core, 74, 97, 196, 220, 235cos, 16, 39-40cosine, 13counter, 210cradle, 198, 213, 217Crosby, 47crossbar, 201-202

CROSSPOINT, 202Crosstalk, 223CRT, 122, 153, 162-163, 165-166CRTs, 162, 166crystal, 18, 36, 41, 44, 47-48, 72, 74-75, 98-99, 112-113, 165-166Current, 45, 57, 60, 140, 198, 251currents, 34, 176, 184, 198Curve, 56curve, 34, 53-54, 56-58, 76curvilinear, 173cutoff, 28CVBS, 151-152CW, 25-26, 99, 101-102cyan, 147, 154, 168cycle, 28, 33, 81, 118cylinder, 173, 189CYM, 154

DDAH, 244DAHS, 244dahs, 244dash, 52, 241-242, 250-251dashes, 3, 25, 241, 250data, 1, 5-9, 11, 46, 52, 92, 97, 121, 219, 221-225, 232-236, 245, 248, 252, 257-258dB, 11, 14-15, 19, 23, 68-69, 86-89, 103, 106-107, 113, 119, 177, 179dBi, 180, 184, 190dBm, 106dBW, 106DC, 31, 44, 98, 103, 118, 131, 218, 248decibel, 11, 119decibels, 83decimal, 210, 240decline, 166decoder, 157-158decoding, 98, 156decompress, 1deflection, 131, 135, 163degrees, 10, 59, 148DEL, 248delay, 123, 133, 144, 157delta, 231demodulated, 67, 160, 253, 258demodulation, 11, 65, 105, 112, 153demodulator, 24, 50, 65, 68, 144, 156, 158-159, 161, 254, 257-258

v

Index

density, 113-114depth, 81-84, 86, 88, 142, 166derivative, 39-40, 104, 107design, 6, 35, 46, 77, 109, 178, 184, 227, 230, 234detection, 8, 11, 18, 50, 52, 81, 221detector, 52, 61-62, 64, 68-69, 77, 82, 101, 105, 161-162, 252deviation, 16-17, 39-40, 47-48, 85, 105, 144device, 3, 8-9, 34, 37, 40, 42-43, 48, 62, 65, 77, 79, 91, 94-97, 117, 120, 123, 128-129, 150, 157, 169, 185, 197-199, 218, 228, 248, 252, 256devices, 8-10, 26, 28, 41, 52, 91, 94-95, 97, 121, 149-150, 169, 202, 222, 224-225, 227, 230, 232, 236, 256diagram, 2, 30-31, 34-37, 39, 41, 45-46, 48, 56, 59, 61-63, 72, 83, 85, 99-100, 109-110, 112-113, 124, 151, 157-162, 178, 183, 209, 252-253, 257dial, 24, 198, 205-207, 216, 218, 221, 231Dialer, 218dials, 207, 221diameter, 185, 224diaphragm, 198dielectric, 171-174differentiating, 141digital, 1-2, 7, 9, 11-12, 103, 120-121, 142-143, 154, 157, 202, 221, 227, 231, 257-258digits, 1, 204-210, 231, 245, 257dimension, 42, 183, 237dimensional, 153, 176dimensions, 82, 120-121, 140, 170, 185diode, 26-28, 37, 41, 43-44, 65, 82diodes, 10, 26-28, 41, 43, 63, 256diplexer, 159, 181-182, 192, 194dipole, 174-177, 179, 181-187, 189, 191-192dipoles, 170, 175-176, 179, 181-182, 186-188, 190-191directional, 173, 177, 179, 186, 191directivity, 172-173, 176, 185, 188-189directors, 183-185, 191discrete, 9, 143discriminator, 48, 52dish, 171DISK, 171-172distortion, 3, 6, 16, 18-19, 22-23, 36, 50, 63, 81, 103, 123, 255DITS, 244domain, 13-15, 22domains, 15, 236dot, 52, 143, 241-242, 250-251dots, 3, 25, 153, 166, 241-242, 250downlink, 91-92, 94, 234, 236downward, 98drain, 42-43driven, 27, 175, 183-185, 199, 234, 252

drives, 30, 97, 101, 103DSB, 15, 27, 34-35, 111-112, 156DSBFC, 30, 33, 35-37, 107, 109, 114DSBSC, 107-109, 114DSP, 103DTMF, 213dual, 191, 213dummy, 83duplex, 8, 91, 97, 215, 258Duplexing, 236DVD, 150

EEALing, 207EBHC, 239EDGE, 234efficiency, 8, 11, 15, 24, 27, 33, 79, 99, 104-105, 109, 112, 198-200, 234EIA, 222, 224-225electormagnet, 210electric, 3, 10, 120, 124, 166, 175, 184, 196-198, 216, 250electrical, 1-4, 35, 41, 52, 91-92, 97, 117-119, 129, 157, 160, 163, 167, 192, 198, 202, 216, 218, 221, 224-225, 241, 250-252, 254-256electricity, 117-118, 141Electro, 202, 252electromagnet, 210, 250electromagnetic, 3, 5, 35, 91-92, 118-119, 145-146, 163, 169, 171, 173, 177, 183-184, 189, 199electromechanical, 206electron, 52, 120, 127, 131, 134, 153, 161-164, 167-168electronic, 3, 5, 10, 26-27, 35, 41, 83, 91, 98, 120, 129, 136, 138, 149, 255-257element, 28, 124, 136, 169-171, 175, 179, 183-185, 187, 190-192, 224, 241, 244-245, 248elements, 41, 105, 121, 127, 138, 160, 162-163, 170, 172, 175, 177, 179, 181-185, 190-192, 212, 221, 228, 241-242, 244-245, 248, 258emf, 55, 58emission, 25, 186emitter, 27-30, 33, 36, 74emitters, 25encode, 5encoder, 151, 156-157, 242encoding, 151, 231-232, 250encryption, 95

vi

Index

energized, 197energy, 4-5, 10, 35, 52, 74, 117, 167, 169, 173-174, 189, 198, 216, 250England, 227equalizing, 127, 130, 133-134, 143equates, 17, 84EQUIPMENT, 230equipment, 2, 9-10, 25-26, 46, 83-84, 96, 104, 129, 152, 194, 205-206, 208-211, 217, 221, 230, 239equivalents, 242Erlang, 238-240erlangs, 238error, 8, 79, 245errors, 8-9, 105, 142-143ESC, 248essence, 68Ethernet, 222ETSI, 233-234ETX, 248

Ffaceplate, 130, 162-163Facsimile, 254-255Fan, 188FCC, 138FDD, 236FDM, 114features, 95, 140-142, 144, 172, 208, 218, 234, 236, 252feedback, 74feeder, 184, 190, 193Feedline, 179FET, 41-42fI, 80fiber, 1, 3, 91-92, 219-220Fidelity, 235Field, 122, 124, 126, 139-140fields, 122-123, 126, 130, 133-134, 137, 139-141, 175, 177, 184Filter, 35, 38, 66, 80, 100-101, 103, 109filters, 65, 72, 99, 102, 114, 142, 149, 151, 158-159, 167, 195FINDER, 210Finder, 209flicker, 10, 119, 121-123, 126fluorescent, 146, 161, 163flyback, 128, 135-136, 141flywheel, 33, 141

FM, 11-12, 17-21, 23-24, 38-40, 43-52, 70-71, 93, 96, 144, 156-161, 167, 169, 180-181, 195, 231focuses, 149, 162, 256fps, 119-120, 123, 140frame, 119-123, 126, 132, 138-139, 156, 162frequencies, 6, 10-11, 13, 18, 23, 26-27, 30-31, 37-38, 45, 50-52, 56-57, 61-65, 67-70, 72-74, 76-77, 79, 84-85, 89, 91, 93-95, 98, 104, 108, 110, 112, 114, 142, 145, 160, 169-170, 172-174, 178, 183, 187-188, 191, 213, 226-227, 230-231, 234, 254frequency, 2, 7-8, 10-27, 29-31, 33, 35, 37-41, 43-48, 50-62, 64-68, 70-74, 76-77, 79-81, 85-86, 88-92, 94-98, 100-101, 104-106, 109, 111-115, 117-118, 130, 134, 141-146, 151, 156, 158-160, 167, 169-171, 177-178, 183-187, 190-191, 199, 213, 227-228, 230, 232, 237, 253-255fuse, 120

Ggain, 29-30, 36, 38, 62, 65, 67-69, 76, 86-87, 89, 96, 101, 103, 141, 165, 173, 177, 179, 181, 184-186, 188-190gateways, 235gating, 26, 153Gbit, 97generation, 16, 46, 97, 114, 148-149, 152, 230-231, 233-235generator, 40, 84-89, 98, 160, 200, 205, 211generators, 83, 131, 137, 160, 199-200geometries, 169, 171Geometry, 180GHz, 10, 95, 171-174, 183gigabit, 97gigahertz, 95glowing, 211GPP, 234GPRS, 233, 235-236Grade, 239graphite, 164gray, 258grey, 138, 147-149ground, 74, 92, 138, 172, 223, 225GSM, 231-233, 235guardband, 164Guided, 3, 91

vii

Index

Hhabitually, 185halfwave, 187Halogen, 146handoff, 229-230, 232handoffs, 231handset, 198, 205, 208-209, 211, 213, 216-217, 225handshaking, 258hardware, 1, 221, 225, 231harmonics, 33, 37, 63, 73Hartley, 6haul, 219-220HD, 143HDMI, 157headphones, 52, 75headset, 84, 93, 103-104, 218henrys, 53, 55, 58hertz, 10, 27, 84, 117-118heterodyne, 25, 63, 73-74, 86, 99heterodyning, 62-63, 65HF, 94-95, 97, 99, 103-104hierarchy, 214, 219, 221highfrequency, 11, 31hook, 118, 198, 205, 211, 213, 217-218, 221HSCSD, 233HSI, 154HSPA, 234HT, 248Hue, 154hue, 142, 154huge, 257Human, 119, 121, 148Hybrid, 212, 215, 217, 221Hz, 47, 51, 62-63, 78, 80, 84, 105, 112, 118-119, 126-127, 130, 134, 140-142, 144-145, 153, 217, 221

IIC, 45, 52, 59, 98IF, 62, 64-74, 76-77, 79-80, 97, 99-103, 160-162IFRR, 67ignition, 98impedance, 36, 41-43, 56, 59-60, 84-85, 87-90, 102, 118, 176-177, 179, 184-185, 215IMT, 234-235

IMTS, 226-227inches, 94-95, 224indicator, 199-200indicators, 199indigo, 145, 148inductance, 40, 43, 53, 55, 58, 118induction, 92, 223inductive, 42-43, 85inductor, 41, 53inductors, 63Industry, 222, 233information, 1-3, 6-7, 9, 11-12, 15, 25, 36-37, 50-51, 61, 65, 77, 80, 94-96, 98, 105, 107-109, 117, 119, 127, 129-132, 134-139, 143-144, 149-151, 154, 160, 167-168, 192, 218, 230, 232-233, 235, 241, 244, 250, 254-258informations, 161infrared, 145, 173Input, 2, 38, 44, 47, 49, 87, 89inputs, 44, 62-63, 105, 157Inside, 217inside, 39, 62, 97, 162-164, 167instal, 199installed, 226-227installer, 222instrument, 3, 82-83, 85, 89insulated, 92, 224integral, 38-39, 142integrated, 39, 50, 52, 98, 165integrating, 118, 141, 235integration, 18, 39, 172integrator, 141intelligence, 25, 52, 223intent, 122Intercarrier, 142Interception, 96intercepts, 160, 183intercoms, 36interconnect, 5interconnected, 5, 191, 219, 231interface, 215, 221-222, 233-234, 252, 257interfacing, 221intermodulation, 16, 83Internet, 225, 236Inverter, 45ionosphere, 94ionospheric, 94IP, 235-236IR, 52ISB, 83, 109, 113-114ISD, 115ITU, 234-235þÿIÁ, 90

viii

Index

Jjack, 200, 218, 224John, 5jXc, 42

Kkbps, 91, 232-233, 235Kelvin, 10, 148key, 3-5, 25, 98, 114, 199-200, 218-219, 227, 232-233, 250, 253keyboard, 244, 252Keying, 12keypad, 213kHz, 10, 16, 23-24, 47, 49, 66, 69-74, 99-100, 103-104, 113, 156, 231km, 145, 192, 227kTBW, 10KW, 113

Llags, 53, 181LAN, 5, 222landline, 230layers, 92LCD, 166LCR, 55, 57, 59, 61leaky, 170, 172lens, 149, 166, 170Level, 35-36, 137, 153, 204, 210, 222LF, 248limit, 16, 28, 76, 158, 205, 241Line, 102-103, 120, 125-126, 132, 135, 138-142, 176, 179, 208-209, 212, 217, 219, 221Linefinder, 209link, 92-93, 183, 232, 248links, 6, 92, 219-220loading, 74, 248lobes, 191local, 65-68, 79, 93-94, 98, 101, 184, 193, 199, 202, 209-217, 219, 221, 230-231, 235, 252-253, 255

location, 1, 135, 198, 207, 218, 224, 231locations, 5, 92, 183, 185, 192, 198, 221, 225logarithmic, 11, 15, 119, 190logic, 106, 257loop, 47-48, 188, 193, 214, 216-217, 224loops, 74, 170, 189, 221Lost, 239-240LOT, 248loudspeaker, 3, 52, 84-85, 117, 165LPDA, 177-178, 190LPDAs, 190LPF, 47, 152, 157-159LPVA, 190LSB, 13-15, 25, 100-101, 105-106, 108, 110, 113-115LTE, 236luminance, 130-132, 136-137, 142, 150-154, 156, 159, 161luminosity, 146-147Lux, 146

MmA, 88, 217machines, 258magenta, 147, 154magnet, 196-198, 252magnetic, 164, 175, 196-198, 255magneto, 3-4, 199-200, 221magnitude, 19, 90, 227mainframe, 252maintenance, 7, 115, 202manage, 96manifold, 181maps, 254, 256Marconi, 3, 5margins, 20masts, 192material, 174, 196, 198mathematical, 13, 65, 67, 153matrix, 143, 163, 201-202, 256matrixing, 151MATV, 195Mbit, 97, 236Mbps, 92, 222, 234-236measurement, 15, 81-83, 85-90, 106, 166, 238mega, 27megabits, 97megahertz, 93-95, 169megapixels, 121

ix

Index

memory, 256-257Merging, 119-120meter, 81, 85-89, 93, 101, 193, 210-211metering, 210-211meters, 3, 83, 85, 92, 210MH, 99, 191MHz, 45, 47-48, 70-73, 84, 93-95, 99-100, 103, 113-114, 138, 140-144, 152-158, 160, 183-185, 192, 222, 226, 231microcells, 228microphone, 2, 46, 117, 217-218, 231microprocessor, 252microstrip, 172microwave, 16, 92-94, 145, 174, 188, 219-220, 251millimeter, 145, 172Mixer, 39-40, 47, 49, 64-66, 69-70, 72, 100, 102-103, 160Mnemonics, 207mobile, 91-92, 95, 97, 112-113, 172, 207, 225-227, 229-235modem, 257-258modulate, 2, 11, 16, 31, 120, 152, 158-159, 255, 257modulating, 2, 11-13, 16-20, 23-24, 26-31, 33-35, 37-41, 43-44, 47-48, 81, 85, 106, 108-111, 113, 143modulation, 7, 11-18, 20-22, 25-26, 28-30, 33-34, 36-37, 39-41, 43-44, 46-50, 81-87, 89, 96, 104-105, 107-109, 141-144, 152, 156, 169, 231, 257modulator, 3, 15, 18, 26-37, 39, 41-44, 46-48, 50, 65, 77, 82, 99, 109-111, 113, 116, 152, 156-158, 160, 253-254, 257modulators, 26-28, 33-34, 36, 43, 113, 152, 156moment, 141, 156, 205, 236monitor, 98, 120, 122, 130, 132, 157-159monochrome, 127, 131-132, 136, 139-140, 143, 149-150, 155, 160-161, 165Morse, 3-4, 241-242, 244, 250-251motor, 252, 257-258motors, 10, 223, 252, 255, 257MSC, 228, 230MTSO, 228-232multipath, 181multiplex, 158, 246multiplexing, 2, 7, 16, 114, 151, 232Murray, 244-245, 247mV, 88mW, 86-87, 89

Nnarrowband, 39-40, 235NEC, 225negative, 28, 44, 98, 118, 142, 223, 246, 251network, 1, 5-6, 9, 35-37, 49, 62, 89, 101, 192, 219-221, 230, 233-236, 239networks, 5, 91-93, 97, 233-236NFPA, 225nodes, 5noise, 1-3, 9-11, 24, 35-36, 50-51, 64, 74-75, 86-88, 91, 102-103, 107, 119, 128-129, 178, 232nonlinear, 18, 27, 30, 36-37, 62, 65, 69, 77, 79nonlinearly, 29NTSC, 123, 136, 138, 140-144, 151-152, 154-155, 157-158

OOFDM, 12ohms, 42, 52-56, 58, 176, 184optical, 91, 149, 157, 163, 188, 220optimum, 102, 106, 144, 165orange, 145, 148Orthogonal, 12oscillator, 18, 35-37, 41, 43-48, 65-74, 79, 98-99, 101, 105, 109, 113, 130, 152, 156, 160, 253-255oscilloscope, 81outlets, 204, 209, 224-225OUTPUTLINES, 201

Ppacket, 6, 230, 233-234, 236packets, 233, 236PAL, 123, 130, 136, 138-140, 143-144, 151-152, 154-155panels, 181-182, 222paraboloidal, 173, 189parameters, 6, 12, 178, 237parasitic, 185, 191parity, 8, 245, 249passband, 79, 106

x

Index

passive, 10, 26patch, 171-172, 222pattern, 4, 162, 169, 177, 179, 181-182, 186-188patterns, 3-5, 139, 171, 195, 232PBX, 217PCB, 1PCM, 232PCS, 231PDC, 231peak, 12, 17, 23, 48, 76, 81, 106, 131-132, 137, 141, 236Pedestal, 137, 153Phasing, 176, 179phone, 85, 92, 208, 211, 213, 216-220, 224-225, 227, 230-231phones, 95, 97, 207, 218-219, 225, 227, 231picture, 114, 117, 119, 121-122, 124, 126-132, 134-139, 148-150, 155, 157-162, 164-167, 181-182, 186, 195, 254-255Pilot, 111-112, 115pink, 10pixel, 121-122pixels, 120-122, 143placed, 98, 119, 166, 174, 178, 188-189, 196, 198, 217plasma, 165-166plate, 224PLL, 1, 65PLWA, 172Poisson, 240polarity, 181, 197, 202, 224polarization, 178, 193police, 93, 97porch, 135-136, 153Postequalizing, 133POTS, 212power, 1, 10-11, 14-16, 18, 23-24, 26-28, 30-31, 33, 35-37, 46, 69, 83, 85-89, 98, 101-102, 105-109, 112-113, 118-119, 159-160, 169, 172-173, 179, 184, 193, 216, 221, 223-224, 227-229, 251, 253-254PPM, 12Preamplifier, 35, 37Preemphasis, 50-51preselector, 64-65, 67-69, 103present, 5, 26, 29, 88-89, 106-107, 134, 142, 144, 195preserve, 136processing, 103, 154, 160Progressive, 121-122propagates, 2propagating, 170propagation, 92, 94-95, 159, 174properties, 17, 121, 184, 188, 232PSK, 257

PSTN, 5, 92, 230PSU, 98pulse, 127-128, 130-133, 135-136, 139-141, 153, 160, 210-211, 216, 248, 250PulsePosition, 12

QQAM, 12, 143-144, 158-159, 257QoS, 236quadrature, 143, 152

Rrabbit, 189radar, 2, 69, 169, 176radiate, 177radiation, 2, 91-92, 163, 172-173, 175, 177, 179-180, 182, 184-185, 188radiator, 169, 174radiators, 170, 172, 181radio, 2-3, 5, 8, 11, 23-26, 31, 37, 46, 52, 58, 61-67, 69-71, 74-77, 79, 82, 86-91, 93-98, 104-107, 109, 112-113, 117, 119, 145, 167, 169, 173-174, 189, 219, 228-229, 233-236, 244, 251, 254-255radios, 71-74, 91, 94-95, 97Radiotelegraphy, 25rainbow, 145, 148raster, 120, 130, 133, 135rays, 145, 173, 189RBOC, 212RCVR, 98reactance, 40-43, 53-54reactive, 41-42receiver, 1-4, 7-8, 10-11, 15, 25, 50-52, 61-69, 71-74, 76, 79, 82-84, 86-89, 91, 94-96, 98-99, 101-102, 104-107, 109, 112, 114-115, 117, 127-132, 134-138, 141, 144, 149, 152-153, 156, 159-162, 165, 173, 181, 185-186, 189, 195, 198-200, 216-217, 226, 228, 241, 250, 252-255, 258receivers, 5, 52, 61, 70-71, 73-75, 97-99, 105-106, 109, 115, 141, 143, 165, 181, 183, 188, 195

xi

Index

reception, 1, 3, 8, 10, 52, 63, 88, 91, 93, 96-97, 107, 112, 179-180, 183, 185-189, 191, 193, 241receptors, 149records, 253Red, 93, 146-147, 150-151, 162, 165Reed, 202reflected, 101-102, 120, 193, 235, 255reflection, 89-90, 173reflectometer, 101-102reflector, 170-171, 173-174, 183-185, 187-189reflectors, 173-174, 181, 189, 191refraction, 148, 174-175refractive, 174relay, 99, 101, 202, 211Repeater, 212repeaters, 93-95resistor, 45, 84, 98resolution, 121, 127, 140-142, 144, 153resolutions, 120, 141, 143resonance, 56-57, 59-61, 179, 191restorer, 129retrace, 122, 124, 127-129, 131-135reuse, 227-228RF, 25, 35-37, 43, 46, 52, 61-62, 64-74, 97, 99-103, 105-106, 157, 160-161, 175-176, 186RFC, 31, 33, 43RFID, 98RGB, 149, 151, 154-159rhombic, 170rid, 71Ringer, 217-218RNC, 231, 234-235rotor, 180RTB, 140

Ssatellite, 10, 91-92, 94, 220, 235satellites, 94, 98, 172saturation, 28, 30, 154, 165sawtooth, 135SBSSC, 112scan, 9, 120-122, 124-127, 132-133, 137, 166, 176scanline, 133, 136scanning, 120-130, 134-136, 138, 142, 150, 159-160, 177, 254-257SCDMA, 234scene, 117, 120-122, 124, 126-127, 132, 136, 138, 149schematic, 30, 98

scrambling, 95-96screen, 81, 83, 92, 120-123, 126-127, 130-131, 134, 139, 153-155, 161-164, 166-168, 185-186, 188, 218SECAM, 138, 140, 143-144, 152selectivity, 52, 58, 61-62, 65, 68, 71-72, 76-77, 88selectors, 204, 206, 209-210, 212semiconductor, 10, 256sender, 1, 241sensitivity, 52, 61-62, 64, 74-75, 86-87sensor, 9separated, 6, 23, 131, 143, 149, 164, 168, 227, 232, 254sequential, 122serial, 9, 244-245, 252settings, 94-95, 218SGSN, 234shunt, 101sideband, 13-15, 18-19, 22-23, 25-26, 34-35, 65, 76, 100, 104-109, 113-114, 143, 152, 158sidebands, 15-16, 18-20, 22-23, 25, 37-40, 69, 75, 105, 107-109, 156sidetone, 198siemens, 42Signal, 12, 38, 44, 47, 49, 51, 81, 83-84, 86, 89, 110-111, 119-120, 131, 136, 151, 215, 253signaling, 197-200, 209, 218, 221, 231signals, 1, 3, 6-9, 11, 16, 19, 23, 26, 37, 45, 52, 60-63, 65, 69-71, 73-74, 76, 84, 91, 93-94, 96-97, 101-102, 104-107, 112, 114-117, 121, 123-124, 128-130, 132-134, 137, 143-144, 149-153, 155-157, 159-161, 166-169, 181, 183, 185-186, 188, 192-195, 198, 200, 202, 215-216, 218-219, 221, 224, 227, 232, 241, 252-258sinusoidal, 11, 13-14, 19-20, 29, 45, 53SLC, 209slot, 170, 172, 237smartphones, 97SNR, 11socket, 101, 194, 199softkeys, 218-219Software, 94SOH, 248solar, 10solenoid, 196-197sonar, 2sounder, 3, 250speaker, 4, 74-75, 103-104, 118, 159, 219spectral, 17-19, 149, 234spectrum, 10, 13, 15-16, 19-21, 25, 39, 52, 67, 83, 85, 93, 104, 111, 114, 143-149, 156, 232-233speech, 2, 5, 11, 23, 52, 85, 99-100, 104, 112, 117, 205, 216-217speed, 27-28, 92, 97, 145, 178, 222, 224, 235, 244-245, 254-255, 258

xii

Index

splitter, 192, 194Splitting, 228-229SSB, 15-16, 25, 34, 91, 99-102, 104-116SSBFC, 109SSBRC, 109, 112-113SSBSC, 107, 109-112, 114stereo, 118, 167storage, 93, 257STP, 92strength, 52, 106, 119, 167, 186, 194-196strip, 64, 162Strowger, 202-203, 205-206, 211subcarrier, 139, 141-144, 152-153, 156, 158subscriber, 91, 199-200, 203-211, 213, 215, 221, 231, 239subscribers, 199-201, 204, 206, 209-211, 214, 239subsystems, 2, 99, 221subtracting, 34superhet, 62, 69, 72, 76-77, 99superheterodyne, 62-63, 66-67, 72, 79, 99, 105superposition, 26Supervision, 217, 221supervisory, 200suppressed, 15, 34-35, 48, 107-109, 112, 143, 156switch, 4, 25, 27-28, 91, 106, 165, 186, 203, 213-215, 217, 220, 229, 234, 237, 239-240, 250switchboard, 199, 222switches, 26, 28, 186, 202, 220-221switching, 5-6, 26-28, 198-199, 201-203, 205, 208, 213-214, 216, 219, 221, 229-231, 233, 239, 253SWR, 179symmetrical, 14, 30, 33sync, 121, 127, 129-137, 139-142, 151-153, 156, 159-160, 258synchronisation, 136, 141, 156, 244synchronization, 7-8, 123, 129-131, 136-137synchronizing, 127, 129-130, 132-133, 161, 168synchronous, 7-8, 245, 255, 258synthesizers, 109, 112systems, 2, 4, 7, 16, 36, 97, 112, 123, 128-131, 138, 140, 143, 150, 154, 156, 166, 169, 176, 198-201, 205, 219, 221-223, 225-227, 230-231, 233, 235-236

TTACS, 227talkie, 8, 36, 96Tandem, 214-215, 219TDD, 236

TDMA, 233techniques, 9, 12, 16, 74, 109, 114, 122, 236, 257TELCO, 212-213, 221Telegrams, 206Telegrapgh, 253telegraph, 3-4, 114, 242, 250, 252-254Telegraphy, 241, 253telephone, 3-5, 16, 84, 91-92, 96, 109, 114, 119, 198-202, 205-206, 208, 212-214, 216-219, 221-223, 225-226, 229-234, 236-239, 253, 256-258telephones, 3, 97, 207, 209, 216, 219, 224-228telephony, 112-113, 199, 225, 234-235teleprinter, 251-253telescene, 140teletypewriter, 52, 251television, 117-118, 120, 127-132, 134, 136, 140, 146, 148-150, 152-155, 160-165, 169, 178, 182-183, 185, 188, 193, 195Telex, 253terminals, 41-43, 81, 84, 87, 194termination, 221-222Terrestrial, 92, 234THD, 103TIA, 222, 224-225, 233timebase, 141-142tip, 98, 216, 222-224Token, 222traffic, 6, 94, 113-114, 199, 209, 220, 236-240transceiver, 91, 93-98, 101, 104, 231transceivers, 91, 93-99, 103transconductance, 41-42transducer, 2-3, 170transformer, 29, 62, 74, 215transistor, 26-27, 29-33, 37, 41, 74, 98transistors, 10, 26-28, 52, 63transmission, 1-3, 5-9, 11, 16, 19-20, 22, 25-26, 36, 47, 76, 89, 91-94, 96-98, 104-107, 109, 112-114, 117, 121, 129, 143, 169-170, 175, 185, 192-193, 202, 216, 219, 221, 223, 227-228, 233-235, 237, 241, 244, 250-251, 254-255, 257transmitter, 1-4, 7-8, 11, 18, 25-26, 28, 35-37, 41, 45-48, 50, 83, 91, 94-96, 98-99, 101-102, 104, 106-107, 112-113, 117, 119, 129, 136, 138, 152-153, 159-160, 175, 177, 179, 181-184, 192-193, 198-199, 216-217, 226, 228, 250, 252-255transmitters, 16, 36, 46, 48, 97-99, 109, 143, 181-182, 227-229transponder, 92TRF, 61-62, 76-77, 79trunk, 206, 213, 215, 219-221, 237-239trunks, 219-221, 237-238, 240TTY, 251tuner, 96, 99, 117, 160-161, 167

xiii

Index

tuning, 43, 64, 70, 74, 99, 106, 112, 142, 165turnstile, 179-182TV, 8-9, 63, 69, 114, 117, 119-124, 126-127, 130, 134, 138, 147, 149, 151, 154, 157-160, 166-168, 177, 183, 185-186, 188-190, 193-195Twist, 223twisted, 1, 91-92, 215, 223TX, 98-99, 101-102, 222

UUART, 9Uda, 175, 183-184UHF, 18, 94-95, 97, 159, 169, 182, 185, 188-189, 192-195ULWA, 172UMTS, 234Uniselector, 204, 209units, 36, 93, 96, 121, 169, 227, 231, 238, 241universal, 186, 233, 242unmodulated, 13-14, 16, 18-19, 39, 41, 73, 82uplink, 91, 94, 234, 236USB, 13-15, 25, 100-101, 106, 108, 110-111, 113-115UTP, 92, 215, 222, 224UWC, 233

Vvaractor, 41, 43-44VBS, 137VCO, 1, 45, 47VCR, 132, 167, 195vestige, 114Vestigial, 109, 114VFO, 99-100VGA, 1, 157VHF, 18, 93-95, 97, 114, 159, 169, 182, 185, 187, 189-195Video, 115, 120-121, 131-132, 136-138, 145, 149, 151, 153, 157, 161-162vidicon, 124, 149violet, 145, 147-148virtual, 6VLSI, 257-258

voice, 1, 4-7, 9, 11, 16, 23, 95-97, 104, 114, 159, 198, 209, 219, 221, 223, 225, 231, 234-237, 241voltage, 2, 11-12, 14, 18-19, 23, 25, 29-30, 36, 40-45, 48, 53-54, 56, 59, 61, 74, 83, 85-90, 98, 108, 123-125, 128, 131, 134-135, 138, 151, 199, 218, 221, 223voltages, 89, 125, 163, 221voltmeter, 81Volts, 13, 38, 51, 78, 80VSAT, 92VSB, 114-115, 157-159VSBFC, 109

Wwalkietalkie, 95WAN, 5watts, 10, 106wave, 2-3, 5, 11-15, 17-18, 25, 31, 33, 35, 39, 45, 52, 62-63, 81-82, 85, 92-93, 97, 104, 108, 115, 167-172, 174, 181-183, 186-187, 189, 191, 198, 254, 257waveform, 12, 30, 44, 46, 81-83, 129-131waveguide, 169, 172wavelength, 94-95, 145, 148, 170, 173, 178, 183, 185, 187waves, 2-3, 5, 63, 82, 91-92, 117, 127, 167, 169-171, 178, 183, 188-189, 255WCDMA, 234Web, 225why, 147, 227wideband, 39-40, 190, 235wire, 2, 4, 74, 91-92, 170, 187, 189, 191, 193, 196, 199, 215, 217, 219, 221, 223-225wireless, 1, 3, 5, 36, 91, 97, 225, 234-235, 253wiring, 192, 222-225WMSC, 234Wpm, 244

YYagi, 175, 183-185YagiUda, 183yellow, 145, 147-148, 154, 168, 186YIQ, 154-155, 158-159

xiv

Index

yoke, 162-164, 168, 196YUV, 154-155

Documents

Affiah Telecommunication Systems I