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DESIGN AND CONSTRUCTION OF AN HF/VHF/UHF 3-3000MHz ACTIVE ANTENNA
NAME/INDEX
SUBMITTED IN PARTIAL FULFILMENT FOR THE AWARD OF HIGHER NATIONAL DIPLOMA IN ELECTRICAL/ELECTRONICS
ENGINEERING
DEPARTMENT OF ELECRICAL/ELECTRONICS ENGINEERING ACCRA POLYTECHNIC
SEPTEMBER 2008
CERTIFICATION BY SUPERVISOR
I hereby certify that this project work was carried out under my
supervision. I therefore approve that the work is adequate in scope
and quality for the partial fulfillment of the requirement for the award
of a Higher National Diploma (HND) in Electrical/Electronics
Engineering.
SUPERVISOR:
SIGN…………………………….
DATE……………………………
I
DEDICATION
This project is dedicated to
II
DECLARATION
I ………………………………………………….. Declares that the work
was undertaken whilst in Accra Polytechnic.
I further affirm that, this work so far as I know has not been
submitted to any institution for the award of any certificate and the
source of information has been fully acknowledged
NAME………………………………………..
SIGN…………………………….
DATE……………………………
III
ACKNOWLEDGEMENT
IV
ABSTRACT
The project in question is an Active Antenna which is used to
amplify radio signals received by a passive antenna.
When connected to a passive antenna with resistance ranging from
75 to 300Ω the active antenna boosts the signals to a higher and
strong signal to be fed to a television or a radio receiver.
The Active Antenna amplifies signals with frequencies between 3 to
3000MHz.
V
TABLE OF CONTENTS
CONTENT PAGE
CHAPTER ONE
1.1 INTRODUCTION 1
1.2 BACKGROUND 2
1.3 DEFINATION 3
1.4 OBJECTIVES 4
1.5 SIGNIFICANCE OF STUDY 5
1.6 METHOLOGY 6
CHAPTER TWO
2.1
VI
CHAPTER THREE
3.1 COMPONENT LIST
3.2 CABLE
CHAPTER FOUR
4.1 GENERAL MODE OF OPERATION
4.2 IMPORTANT
4.3 PRECAUTIONS
4.4 SUMMARY
4.5 RECORMENDATIONS
REFERNCE
VII
CHAPTER ONE
1.1 INTRODUCTION
If you have a shortwave or high-frequency receiver or scanner that
is struggling to capture signals with a short, whip antenna, and you'd
like the kind of performance that a 60-foot long wire antenna can
provide but lack the space to put one up, consider using the AA-7 HF/VHF/UHF Active Antenna described in this article. The AA-7 is
a relatively simple antenna that is designed to amplify signals from 3
to 3000 Megahertz, including three recognized ranges: 3-30 MHz
high-frequency (HF) signals; 3-300 MHz very-high frequency (VHF)
signals; 300-3000MHz ultra-high (UHF) frequency signals. Those
bands are typically occupied by shortwave, television stations,
government, and commercial radio signals.
1
1.2 BACKGROUND
In many of our urban cities it is rear to see people mounting tall
poles to fix an antenna. They may want to but are reluctant because
of the amount of work they’ll have to do before receiving a signal
from a radio of television station which is only a few kilometers from
them.
How much more someone in a distant place, say in about hundreds
of miles away from that station. No wonder there are a lot of tall
bamboo pole in this remote places.
It is to this effect that this project was designed to amplifier the little
signals received by the existing passive antennas.
2
1.3 DEFINITION
The project 3-3000MHz active antenna is named AA7 as
abbreviation of Active Antenna and the seven stands for the variety
of frequencies.
It can be powered by a 9v small size battery when used outdoors or
a place where there’s no electricity or powered by the mains.
It is convenient to carry and portable.
Also comes with easy to connect terminals and a gain control.
3
1.4 OBJECTIVES
The main objective of this project is to help increase weak signals
received by radio devices and amplify them into strong and better
signals.
Another objective is to create alternative power for it to make is easy
to use at places where there’s no electricity.
The project is also designed aid people at places where transmitted
signals between 3-3000 MHz received have strength or weak. It is
our aim that every person irrespective of their location to enjoy good
reception of radio and TV transmission.
4
1.5 SIGNIFICANCE OF STUDY
The main objective of this project is
To help increase our knowledge of study on the existing Active
antennas and to improve on them.
To replace the existing ones with a more accessible and user
friendly type.
To help prevent the hazards of tuning you antenna every time
one changes the TV or Radio channel.
This project is versatile making it easy to be applied either a
Television or radio set.
To make an active antenna that is transferable and applicable
any where.
5
1.6 METHODOLOGY
In its simplest form, an active antenna uses a small whip antenna
that feeds incoming RF to a pre-amplifier, whose output is then
connected to the antenna input of a receiver. Unless specifically
designed otherwise, all active antennas are intended for receive-
only operation, and thus should not be used with transceivers;
transmitting into an active antenna will probably destroy its active
components. A well designed broadband active antenna consider
field strength of the desired signal (measured in micro volts per
meter of antenna length), atmospheric and other noise, diameter of
the antenna, radiation resistance, and antenna reactance at various
frequencies, plus the efficiency and noise figure of the amplifier
circuit itself.
All important information needed for this project to takeoff was
acquired form two main source namely primary and secondary
sources.
Primary source were sources were the personal interactions with my
supervisor and workers of a well equipped and well knowledgeable
on this project.
Secondary sources were the research at the library and the internet.
6
CHAPTER TWO2.1 Terminology
The words antenna (plural: antennas[) and "aerial" are used
interchangeably; but usually a rigid metallic structure is termed an
antenna and a wire format is called an aerial. In the United Kingdom
and other British English speaking areas the term aerial is more
common, even for rigid types. The noun aerial is occasionally written
with a diaresis mark — aërial — in recognition of the original spelling
of the adjective aërial from which the noun is derived.
The origin of the word antenna relative to wireless apparatus is
attributed to Guglielmo Marconi. In 1895, while testing early radio
apparatus in the Swiss Alps at Salvan, Switzerland in the Mont
Blanc region, Marconi experimented with early wireless equipment.
A 2.5 meter long pole, along which was carried a wire, was used as
a radiating and receiving aerial element. In Italian a tent pole is
known as l'antenna centrale, and the pole with a wire alongside it
used as an aerial was simply called l'antenna. Until then wireless
radiating transmitting and receiving elements were known simply as
aerials or terminals. Marconi's use of the word antenna (Italian for
pole) would become a popular term for what today is uniformly
known as the antenna.
7
A Hertzian antenna is a set of terminals that does not require the
presence of a ground for its operation (versus a Tesla antenna
which is grounded.) A loaded antenna is an active antenna having
an elongated portion of appreciable electrical length and having
additional inductance or capacitance directly in series or shunt with
the elongated portion so as to modify the standing wave pattern
existing along the portion or to change the effective electrical length
of the portion. An antenna grounding structure is a structure for
establishing a reference potential level for operating the active
antenna. It can be any structure closely associated with (or acting
as) the ground which is connected to the terminal of the signal
receiver or source opposing the active antenna terminal, (i.e., the
signal receiver or source is interposed between the active antenna
and this structure.
2.2 OverviewAntennas have practical uses for the transmission and reception of
radio frequency signals (radio, TV, etc.). In air, those signals travel
close to the speed of light in vacuum and with a very low
transmission loss. The signals are absorbed when propagating
through more conducting materials, such as concrete walls, rock,
etc. When encountering an interface, the waves are partially
reflected and partially transmitted through.
8
2.3 ParametersThere are several critical parameters that affect an antenna's
performance and can be adjusted during the design process. These
are resonant frequency, impedance, gain, aperture or radiation
pattern, polarization, efficiency and bandwidth. Transmit antennas
may also have a maximum power rating, and receive antennas differ
in their noise rejection properties. All of these parameters can be
measured through various means.
2.4 Resonant frequency
The "resonant frequency" and "electrical resonance" is related to the
electrical length of the antenna. The electrical length is usually the
physical length of the wire divided by its velocity factor (the ratio of
the speed of wave propagation in the wire to c0, the speed of light in
a vacuum). Typically an antenna is tuned for a specific frequency,
and is effective for a range of frequencies usually centered on that
resonant frequency. However, the other properties of the antenna
(especially radiation pattern and impedance) change with frequency,
so the antenna's resonant frequency may merely be close to the
center frequency of these other more important properties.
9
Antennas can be made resonant on harmonic frequencies with
lengths that are fractions of the target wavelength. Some antenna
designs have multiple resonant frequencies, and some are relatively
effective over a very broad range of frequencies. The most
commonly known type of wide band aerial is the logarithmic or log
periodic, but its gain is usually much lower than that of a specific or
narrower band aerial.
2.5 Gain
Gain as a parameter measures the directionality of a given antenna.
An antenna with a low gain emits radiation with about the same
power in all directions, whereas a high-gain antenna will
preferentially radiate in particular directions. Specifically, the Gain,
Directive gain or Power gain of an antenna is defined as the ratio
of the intensity (power per unit surface) radiated by the antenna in a
given direction at an arbitrary distance divided by the intensity
radiated at the same distance by an hypothetical isotropic antenna.
The gain of an antenna is a passive phenomenon - power is not
added by the antenna, but simply redistributed to provide more
radiated power in a certain direction than would be transmitted by an
isotropic antenna. If an antenna has a greater than one gain in some
directions, it must have a less than one gain in other directions since
energy is conserved by the antenna.
10
An antenna designer must take into account the application for the
antenna when determining the gain. High-gain antennas have the
advantage of longer range and better signal quality, but must be
aimed carefully in a particular direction. Low-gain antennas have
shorter range, but the orientation of the antenna is inconsequential.
For example, a dish antenna on a spacecraft is a high-gain device
(must be pointed at the planet to be effective), while a typical WiFi
antenna in a laptop computer is low-gain (as long as the base
station is within range, the antenna can be in an any orientation in
space). It makes sense to improve horizontal range at the expense
of reception above or below the antenna. Thus most antennas
labeled "omnidirectional" really have some gain Sometimes, the
half-wave dipole is taken as a reference instead of the isotropic
radiator. The gain is then given in dBd (decibels over dipole):
0 dBd = 2.15 dBi
2.6 Radiation pattern
The radiation pattern of an antenna is the geometric pattern of the
relative field strengths of the field emitted by the antenna. For the
ideal isotropic antenna, this would be a sphere. For a typical dipole,
this would be a toroid. The radiation pattern of an antenna is
typically represented by a three dimensional graph, or polar plots of
the horizontal and vertical cross sections.
11
2.7 Impedance
As an electro-magnetic wave travels through the different parts of
the antenna system (radio, feed line, antenna, free space) it may
encounter differences in impedance (E/H, V/I, etc). At each
interface, depending on the impedance match, some fraction of the
wave's energy will reflect back to the source[5], forming a standing
wave in the feed line. The ratio of maximum power to minimum
power in the wave can be measured and is called the standing wave
ratio (SWR). A SWR of 1:1 is ideal. A SWR of 1.5:1 is considered to
be marginally acceptable in low power applications where power
loss is more critical, although an SWR as high as 6:1 may still be
usable with the right equipment. Minimizing impedance differences
at each interface (impedance matching) will reduce SWR and
maximize power transfer through each part of the antenna system.
Complex impedance of an antenna is related to the electrical length
of the antenna at the wavelength in use. The impedance of an
antenna can be matched to the feed line and radio by adjusting the
impedance of the feed line, using the feed line as an impedance
transformer. More commonly, the impedance is adjusted at the load
(see below) with an antenna tuner, a balun, a matching transformer,
matching networks composed of inductors and capacitors, or
matching sections such as the gamma match.
12
2.8 Bandwidth
The "bandwidth" of an antenna is the range of frequencies over
which it is effective, usually centered on the resonant frequency.
The bandwidth of an antenna may be increased by several
techniques, including using thicker wires, replacing wires with cages
to simulate a thicker wire, tapering antenna components (like in a
feed horn), and combining multiple antennas into a single assembly
and allowing the natural impedance to select the correct antenna.
Small antennas are usually preferred for convenience, but there is a
fundamental limit relating bandwidth, size and efficiency.
Polarization
The "polarization" of an antenna is the orientation of the electric field
(E-plane) of the radio wave with respect to the Earth's surface and is
determined by the physical structure of the antenna and by its
orientation. It has nothing in common with antenna directionality
terms: "horizontal", "vertical" and "circular". Thus, a simple straight
wire antenna will have one polarization when mounted vertically,
and a different polarization when mounted horizontally.
"Electromagnetic wave polarization filters" are structures which can
be employed to act directly on the electromagnetic wave to filter out
wave energy of an undesired polarization and to pass wave energy
of a desired polarization.
13
Reflections generally affect polarization. For radio waves the most
important reflector is the ionosphere - signals which reflect from it
will have their polarization changed unpredictably. For signals which
are reflected by the ionosphere, polarization cannot be relied upon.
For line-of-sight communications for which polarization can be relied
upon, it can make a large difference in signal quality to have the
transmitter and receiver using the same polarization; many tens of
dB difference are commonly seen and this is more than enough to
make the difference between reasonable communication and a
broken link.
Polarization is largely predictable from antenna construction but,
especially in directional antennas, the polarization of side lobes can
be quite different from that of the main propagation lobe. For radio
antennas, polarization corresponds to the orientation of the radiating
element in an antenna. A vertical omnidirectional WiFi antenna will
have vertical polarization (the most common type). An exception is a
class of elongated waveguide antennas in which vertically placed
antennas are horizontally polarized. Many commercial antennas are
marked as to the polarization of their emitted signals.
Polarization is the sum of the E-plane orientations over time
projected onto an imaginary plane perpendicular to the direction of
motion of the radio wave.
14
In the most general case, polarization is elliptical (the projection is
oblong),meaning that the antenna varies over time in the
polarization of the radio waves it is emitting. Two special cases are
linear polarization (the ellipse collapses into a line) and circular
polarization (in which the ellipse varies maximally). In linear
polarization the antenna compels the electric field of the emitted
radio wave to a particular orientation. Depending on the orientation
of the antenna mounting, the usual linear cases are horizontal and
vertical polarization. In circular polarization, the antenna
continuously varies the electric field of the radio wave through all
possible values of its orientation with regard to the Earth's surface.
Circular polarizations, like elliptical ones, are classified as right-hand
polarized or left-hand polarized using a "thumb in the direction of the
propagation" rule. Optical researchers use the same rule of thumb,
but pointing it in the direction of the emitter, not in the direction of
propagation, and so are opposite to radio engineers' use.
In practice, regardless of confusing terminology, it is important that
linearly polarized antennas be matched, lest the received signal
strength be greatly reduced. So horizontal should be used with
horizontal and vertical with vertical. Intermediate matchings will lose
some signal strength, but not as much as a complete mismatch.
15
Transmitters mounted on vehicles with large motional freedom
commonly use circularly polarized antennas so that there will never
be a complete mismatch with signals from other sources. In the case
of radar, this is often reflections from rain drops.
2.9 Transmission and reception
All of the antenna parameters are expressed in terms of a
transmission antenna, but are identically applicable to a receiving
antenna, due to reciprocity. Impedance, however, is not applied in
an obvious way; for impedance, the impedance at the load (where
the power is consumed) is most critical. For a transmitting antenna,
this is the antenna itself. For a receiving antenna, this is at the
(radio) receiver rather than at the antenna. Tuning is done by
adjusting the length of an electrically long linear antenna to alter the
electrical resonance of the antenna.
16
CHAPTER THREE
3.1 Active AntennasIn its simplest form, an active antenna uses a small whip antenna
that feeds incoming RF to a pre-amplifier, whose output is then
connected to the antenna input of a receiver. Unless specifically
designed otherwise, all active antennas are intended for receive-
only operation, and thus should not be used with transceivers;
transmitting into an active antenna will probably destroy its active
components. A well designed broadband active antenna consider
field strength of the desired signal (measured in microvolts per
meter of antenna length), atmospheric and other noise, diameter of
the antenna, radiation resistance, and antenna reactance at various
frequencies, plus the efficiency and noise figure of the amplifier
circuit itself.
17
3.2 Circuit DescriptionThe schematic diagram of the AA-7, contains only two active
elements; Q1 (an MFE201 N-Channel dual-gate MOSFET) and Q2
(a 2SC2570 NPN VHF silicon transistor). Those transistors provide
the basis of two independent, switchable RF pre-amplifiers. Two
double-pole double-throw (DPDT) switches play a major role in this
operation of the AA-7. Switch S1 is used to select one of the two
pre-amplifier circuits (either HF or VHF/UHF). Switch 2 is used to
turn off the power to the circuit, while coupling the incoming RF
directly to the input of the receiver. That gives the receiver non-
amplified access to the auxiliary antenna jack, at J1, as well as the
on-board telescoping whip antenna. With switch S2 in its power-on
position, the input and output jacks are disconnected and B1 (a 9
volt battery) is connected to the circuit. With switch S1 in the
position shown in the schematic, incoming RF is directed to the HF
pre-amp circuit built around Q1 (an MFE201 N-Channel dual-gate
MOSFET). The HF pre-amp operates with an exceptionally low
noise level, and is ideal for copying weak CW and singe-side band
signals. When S1 is switched to the other position, the captured
signal is coupled to the VHF/UHF pre-amp built around Q2 (a
2SC2570 NPN VHF silicon transistor), which has excellent VHF
through microwave characteristics.
18
With the on-board whip antenna adjustable to resonance through
much of the VHF-UHF region (length in feet = 234 divide by the
frequency in MHz), the VHF/UHF mode is ideal for indoor and
portable use with VHF scanners and other receivers. Either mode
can be used when tuning 3-30 MHz HF signals. The VHF/UHF pre-
amp offers higher gain than the HF pre-amp, but also has a higher
noise level. You can easily choose either amplifier for copying any
signal; of interest--just try both positions. The RF gain control (R5)
can be used to trim the output of either amplifier.
Caution: The AA-7 is not intended for transmitting operation (be it
Ham, Maritime, or CB); if it is used with a transceiver of any kind,
make sure it is not possible to transmit by accidentally pressing a
mike button or CW key. Transmitting RF into the AA-7 is likely to
ruin one of both of the transistors in the circuit.
19
3.3 CIRCUIT CONSTRUCTIONThe AA-7, which can be built from scratch or purchased in kit
form from the supplier listed in the Parts List, was assembled on
a printed circuit board, measuring 4 by 4-11/16 inches. A
template for the PCB board is shown in fig. 2. You can either
etch your own board from that template, or purchase the circuit
board or the complete kit of parts (which includes the pcb and
all parts, but not the enclosure). The kit comes with a 16-page
kit instruction manual that gives step-by-step assembly
instructions and contains additional information not covered in
this article. Kit assembly time, working slowly and carefully,
should take less than an hour. Most of the parts specified in the
Parts list are standard components and can be procured
through conventional hobby electronics suppliers. However,
some parts--J1, J2, S1, S2, and R5-- have particular physical
mounting dimensions; the Printed Circuit Board is designed to
accept these particular parts. In addition, Q1 and Q2 can be
hard to find; however, it is possible to make substitutions
provided that you can find a supplier. Suitable replacements for
Q1 and Q2 are given in the Parts List.
The telescoping whips antenna screw-mounts to the board; the
screw provides contact between the printed circuit board traces
and the antenna.
20
To save time and trouble locating and ordering hard-to-find
parts, a Special Parts Kit is also offered by the supplier listed in
the Parts List.
A parts placement (layout) diagram for the AA-7's printed circuit
board is shown in figure 3. When assembling the circuit, be
especially careful that transistors Q1 and Q2, and the
electrolytic capacitor C4, are oriented as shown.
Although not shown in the schematic (Fig. 1) or the layout (Fig.
3) diagrams, an optional led power indicator can be added to
the circuit. Adding a power indicator to the circuit allows you to
tell at a glance if the circuit is on; leaving the circuit on, even
though the AA-7 draws only about 0.7 mA, will eventually
discharge the battery. Of course, adding an led will increase the
current drain to by about 7 mA, but the red glow makes it
obvious when the unit is on.
If you decide to include the LED indicator in your project, power
for the indicator can be easily taken from the switched 9-volt DC
terminal of S2 (center terminal, right side, looking at the top of
S2). Simply connect the positive voltage to the anode (longer
wire) of the led and connect her cathode lead through a current
limiting resistor of about 1000 ohm to a ground point on the
printed circuit board, or as the author did from the frame of R5.
Mount the led at any convenient point near the switch.
21
3.4 SCHEMATIC DIAGRAM
223.5 COMPONENT LIST
COMPONENT DESCRIPTION QUANTITY
Q1 AF239S (DUAL-GATE MOSFET) 1
Q2 2SC2570 (NPN VHF/UHF SILICON
TRANSISTOR)
1
R1 1MΩ (MEGA OHM RESISTOR) 1
R2 220KΩ (RESISTOR) 1
R3,R6 100KΩ (RESISTOR) 2
R4 100Ω (RESISTOR) 1
R5 10K Ω POTENTIOMETER 1
C1,C2,C5,C6 0.01uF, CERAMIC DISC 4
C3 100pF CERAMIC DISC 1
C4 4.7 to 10Uf/16VDC,
ELECTROLYTIC CAPACITOR
1
S1,S2 DPDT SWITCH 2
MISC PCB BOARD, WIRE, SOLDER
23
CHAPTER FOUR
4.1 GENERAL MODE OF OPERATIONThe RF preamplifier section of an active antenna may be of several
different styles. A fixed-tuned preamp has the greatest gain for the
specific frequency of the operation, but is limited to only that
frequency. A variable-turned amplifier can be peaked within a range
of frequencies, but the circuitry is more complex and expensive and
tuning requires constant resetting whenever the receiver frequency
is changed. A broadband preamplifier doesn’t require any tuning,
Making it very versatile and easy to use, but has less gain at any
specific frequency. The AA-7 described here. For simplicity and low
cost, is of a dual broadband design.
24
4.2 LIMITATIONS
The difficulties involved in getting the major component from a class
A source was very difficult because all the companies who
manufactures these components do not sell components in small
quantities and it was very hectic getting all these components.
Some of the components were imported from Singapore and that
took a lot of time to arrive making it difficult to compile study and the
construction of the project together.
Researches, typing and printing is very difficult to complete because
of the frequent power outages and time constrains.
25
4.3 PRECAUTIONS In other to arrive at a good and a successful project, the following
precautions were taken into consideration:
1. The circuit was built under supervision to ensure accuracy.
2. The circuit diagram was first tested with schematic circuit
stimulator software and then mounted on a Vero board and
then rechecked for accuracy to prevent damage of any
component.
3. The entire component were thoroughly checked and tested for
consistency and efficiency.
4. Correct soldering techniques were ensured as well as the
usage of a correct solder.
5. The right tools and equipment were used for this project.
6. Suitable equivalent replacement of components was ensured
at places where the original components were not available.
26
4.8 CONCLUSION The entire project was finally concluded that; this lighting system
and computers would no more loose data or be interfered with
power outage to reduce productivity.
The use of highly inflammable fuels to produce power for lighting
would now be a thing of the past.
The system can be run for a long period of time since it can be
hooked on an external battery.
This project could go a long way to help reduce data loss and the
number of houses brought down by fire due to the use of candles
and other sources of lighting which uses highly inflammable fuel,
and it will help in creating employment for the youth if encouraged in
the country.
57SUMMARY
From the above project it was realized that, this UPS(uninterrupted
Power Supply) system could go a long way to help manage the
power problem since some amount of energy could be stored for
future use, and in this direction help reduce the burden on the
government.
58
RECOMMENDATIONS
My recommendations were based on research made and are as
follows:
1. Firstly, it is highly recommended for health centers such as
clinics, hospitals and maternity homes.
2. Secondly it is recommended for schools.
3. For any one who uses a computer of a system that has a
volatile memory.
4. Thirdly for places where electricity source is not consistent.
5. Furthermore it is recommended for domestic use.
6. Last but not the least; government must encourage such
projects to generate employment for the youth at large.
59
REFERENCES
1. Carols Advance Electronics and Training Centre.
2. www.wikipedia.com/english
Page Copyright © 1995 - Tony van Roon
Project Copyright © 1994, by Fred Blechman
Copyright and Credits:
"Electronics Hobbyist Handbook", Spring 1994. Copyright © Fred
Blechman and Gernsback Publications, Inc. 1994. Published with
permission from Gernsback. (Gernsback Publishing no longer
exists).
Document updates & modifications, all diagrams, PCB/Layout drawn
by Tony van Roon.
Re-posting or taking graphics in any way or form of this project
is expressly prohibited by international copyright laws.