Electronics HandBook

One mark Questions

1. What is meant by dc load line?

Ans: DC load line is a straight line drawn on the output characteristics representing output

DC voltage and corresponding direct current under no signal conditions.

2. What is thermal runaway?

Ans: The self destruction of an unbiased transistor due to increase in temperature and hence

increase in leakage current is called thermal runaway.

3. What is leakage current?

Ans: Leakage current is the current through a device due to the motion of minority charge

carriers under reverse biased condition.

4. Draw the circuit symbol of Op-amp?

5. List out any two characteristics of an ideal op-amp?

Ans: 1. Infinite input impedance

2. Infinite open loop gain.

6. List out any two characteristics of practical op-amp?

Ans: 1. Input impedance is few MΩ

2. Open loop gain is 105.

7. Define input off set voltage?

Ans: Input offset voltage is the small voltage that should be applied between two input

terminals to make output voltage zero.

8. Define CMRR of an op-amp?

Ans: CMRR is defined as the ratio of differential mode gain to common mode gain.

9. What is logarithmic amplifier?

Ans: Logarithmic amplifier is a circuit whose output is proportional to natural logarithm of

the input voltage.

10. What is carrier wave?

Ans: Carrier wave is the high frequency wave on which audio signal is superimposed to

transmit to large distances.

11. What is modulation?

Ans: Modulation is the process by which one of the characteristics of a high frequency carrier

wave is changed in accordance with the instantaneous value of a low frequency information

signal.

12. How is the length of antenna related to frequency of the signal?

Ans: The length of the antenna required for transmission id inversely proportional to the

frequency of the signal.

L = 𝐶

4𝑓

13. Define amplitude modulation?

Ans: Amplitude modulation is the process in which amplitude of the carrier wave is varied in

accordance with instantaneous value of the modulating signal.

14. Write the expression for instantaneous voltage of an AM wave?

Ans: 𝑉𝐴𝑀= 𝑉𝐶(1+𝑚𝑎 𝑠𝑖𝑛𝑤𝑚 𝑡). 𝑠𝑖𝑛𝑤𝑐 𝑡

15. Define modulation index of an AM wave?

Ans: modulation index of an AM wave is the ratio of amplitude of modulating signal ( 𝑉𝑚 ) to

the amplitude of the carrier wave signal (𝑉𝐶).

16. How many side bands are present in AM?

Ans: Two.

17. Mention the expression for the modulation index in terms of 𝑉𝑚𝑎𝑥 and 𝑉𝑚𝑖𝑛 .

Ans: 𝑚𝑎 = 𝑉𝑚𝑎𝑥 −𝑉𝑚𝑖𝑛

𝑉𝑚𝑎𝑥 +𝑉𝑚𝑖𝑛

18. Why is transmission of side bands important?

Ans: As the side bands contain the required signal, their transmission is important.

m = 𝑚12 +𝑚2

2 +𝑚32 +⋯…… .𝑚𝑛2

19. What is SSB-SC?

Ans: Single side band suppressed carrier.

20. Define frequency modulation?

Ans: Frequency modulation is the process of varying frequency of carrier wave in accordance

with the instantaneous value of modulating signal.

21. Write the expression for instantaneous voltage of frequency modulated wave?

Ans: 𝑉𝐴𝑀= 𝑉𝐶𝑠𝑖𝑛(𝑤𝑐 𝑡 +𝑚𝑓 𝑠𝑖𝑛𝑤𝑚 𝑡).

22. Define carrier swing?

Ans: Carrier swing is the total variation in frequency from minimum to maximum value.

23. What is pre-emphasis?

Ans: Pre-emphasis is the process of boosting relative amplitudes of high frequency

components of the modulating signal to improve signal to noise ratio.

24. Define heterodyning?

Ans: Heterodyning is the process of mixing or beating together two signals of different

frequencies to produce a set of new frequenices.

25. Mention the value of IF for AM reception?

Ans: 455khz

26. Mention the value of IF for FM reception?

Ans: 10.7Mhz

27. Draw the circuit symbol of a power diode?

28. Give the expansion of PBJT?

Ans: Power bipolar junction transistor.

29. Draw the circuit symbol of npn PBJT?

30. What is the other name for SCR?

Ans: Thyristor.

31. How many PN junctions are there in SCR?

Ans: Two.

32. Draw the schematic diagram of SCR?

33. Draw the circuit symbol of thyristor?

34. Write an expression for SCR anode current when positive gate current is applied?

Ans: 𝐼𝐴 =∞2𝐼𝐺+𝐼𝐶0

1−(∞1+∞2)

35. Draw the circuit symbol of TRIAC?

36. Expand IGBT?

Ans: Insulated gate bipolar transistor.

37. Draw the circuit symbol of IGBT?

38. How many two input NAND gates are required to produce two input OR function?

Ans: Three.

39. How many two input NOR gates must be used to produce two input OR function?

Ans: Two.

40. Expand ASCII?

Ans: American standard code for information interchange.

41. Expand EBCDIC?

Ans: Extended binary coded decimal interchange code.

42. Define MAX terms?

Ans: Max term is a special case sum (OR) term containing all the input variables that make

up a Boolean expression.

43. What is k maps?

Ans: A cell in a k map is a box which represents a particular combination of variables in its

product form.

44. What is a don’t care condition?

Ans: An output condition that may be either 1 or 0 without affecting the operation of the

system is called don’t care condition.

45. Define a clock pulse?

Ans: A clock is a periodic train of pulses or square waves which acts as a control signal. The

output changes state only when clock makes transition.

46. Write the direct address of the accumulator?

Ans: OE0.

47. Expand EEPROM?

Ans: Electrical Erasable programmable read only memory.

48. Expand PIC?

Ans: Peripheral interface controller.

49.What is run time error?

Ans: Run time error occur when the user tries to run ambiguous instructions(like infinite

loop, divided by 0).

50. What is cell splitting?

Ans: Dividing the entire geographical area into hexagonal shaped cells that fit together to

form a honey comb pattern.

51. What is piconet?

Ans: Linking of one Bluetooth device that serves as a master controller to a maximum of

seven other Bluetooth slave devices.

Two Mark Questions

1. Draw the symbols of n channel and p channel JFET?

2. Write any 2 difference between JFET and BJT?

JFET BJT

Voltage controlled device Current controlled device

Unipolar device Bipolar device

3. What is pinch off voltage, what is the value of drain current at pinch off?

Ans: Pinch off voltage is the gate source voltage at which the drain current is zero.

4. Write the steps involved in drawing DC equivalent circuit of an amplifier?

Ans:

Reduce all the AC sources to zero.

Open all the capacitor.

5. Write any 2 application of CC amplifier?

Ans: Buffer amplifier to reduce the maximum power delivered to the load,

Also called current amplifier and unity gain amplifier.

6. What are the advantages of negative feedback?

Stabilization of the gain

Increase in input impedance

Decrease in output impedance

Increase in bandwidth

Reduction in noise and distortion

7. Draw the block diagram of current shunt and voltage series negative feedback?

(i) Current shunt negative feedback

(ii) Voltage series negative feedback

8. Explain virtual ground concept with respect to op-amp?

Ans: If 𝑉𝐴 and 𝑉𝐵 are the voltages at inverting and non-inverting terminals then open loop

gain

A = 𝑉𝑜

𝑉𝐴−𝑉𝐵 = ∞

𝑉𝐴 − 𝑉𝐵 = 0

𝑉𝐴 = 𝑉𝐵

9. Distinguish between damped and un-damped oscillations?

Ans: Damped oscillations are those oscillations whose amplitude goes on decreasing with

respect to time.

Un-damped oscillation are those oscillations whose amplitude remains constant with respect

to change in time.

10. Explain the condition for Barkhaussian criteria?

The total phase shift around the closed loop should be equal to 0° or 360°.

The product of open loop gain and feedback ratio is always unity.

11. Mention the limitations of LC oscillators?

Ans: Value of inductors and resistors change due to changes in temperature hence the

frequency of RC and LC oscillators don’t remain constant.

12. Write any 2 advantages of RC oscillators over LC oscillators?

RC oscillators provide constant output and good stability

RC oscillators don’t require any inductor and hence size and cost get reduced

13. Draw the block diagram of general electronic communication system?

14. Mention different types of modulation?

Ans: Amplitude modulation

Frequency modulation

Phase modulation

15. Draw frequency spectrum of FM wave?

16. Write the advantages of FM over AM?

All transmitted power is useful

Signal to noise ratio is very high

Fidelity is very high

Noise can be completely eliminated

17. What are primary constants of transmission lines?

Series resistance (R)

Series inductance (L)

Shunt capacitance (C)

Shunt conductance (G)

18. Draw the equivalent circuit of transmission lines for radio frequency?

19. Mention any two types of antenna?

Yagi antenna

Helical antenna

20. Draw the forward and reverse characteristics of power diode?

21. Write the expression for current through power diode and explain its terminology?

22. Draw V-I characteristics of SCR?

23. Mention the types of power MOSFET?

Depletion type power MOSFET

Enhancement power MOSFET

24. Draw the pin details of IC7402?

25. What is addressing mode, why is it necessary?

Ans: CPU can store data in registers, memory or external source. These data source address

are specified using addressing modes. The data can be accessed using any one of the modes.

26. Explain briefly data transfer instruction?

Ans: If the data is moved from source to destination using the instruction are called data

transfer instruction example: MOV, PUSH, POP and XCH.

27. Briefly explain syntax error?

Ans: Syntax error is the result of violating the grammar of C programming language. When

these errors occur, computer display an error message specifying the line number where the

error has occurred.

inta,b,c

a=20, b=c; computer will indicate semicolon is missing.

28. Mention the steps involved in running the program?

Understand the instruction

Store data and instructions

Perform computation

29. For what purpose if-statement and if-else statement are used?

Ans: If-statement is used to execute a set of instructions conditionally, it is also called one

way branching.

If-else is used when there are 2 statements which are to be executed alternatively, it is also

called two way branching.

30. Write the syntax of do-while statement?

Ans: do

Statement;

while(condition);

31. What is the use of break statement?

Ans: Break statement is used to terminate the loop and exit from a particular and exit from a

particular switch case label.

Syntax for break,

------------------------------

------------------------------

Break;

------------------------------

32. What is ISP, Mention its role in computer networking?

Ans: ISP is internet service provider, it provides the software for communication over

internet. ISP has one more towers to which thousands of cables, modems are connected for

the use of subscribers.

33. Mention few applications of communication satellites?

Voice communication

TV and radio broadcasting

Teleconferencing

Mobile communication

34. Define critical angle and critical frequency?

Ans: Critical angle for a given layer is the maximum angle of incidence of a radio wave

under ionospheric propagation that gets returned to the earth.

Critical frequency for a given layer is the highest frequency of beamed radio wave that will

be returned to the earth.

35. Explain the condition of Barkhaussan criterion?

Ans: 1. The total phase shift around the closed loop should be 0° to 360°.

2. The magnitude of product of the open loop gain of the amplifier (A) and feedback

ratio(β) is unity, |Aβ| = 1.

Three Mark Questions.

1. With circuit diagram, explain the working of CE amplifier?

The AC signal is applied between base and emitter terminals and output is taken at the

collector. R1, R2 provide biasing to the transistor. 𝑅𝐸provides stabilisation and 𝐶𝐸 provides

easy alternate path for the ac to flow, coupling capacitors 𝐶1and 𝐶2 block DC and allow ac

signals.

During the positive half cycle of input signal, forward bias emitter base junction increases.

Hence base current 𝐼𝐵 , 𝐼𝐸 𝑎𝑛𝑑 𝐼𝑐 increase. This makes 𝐼𝑐𝑅𝑐 increase.

During the negative half cycle of ac input signal, forward bias on emitter base junction

decreases. Hence 𝐼𝐵 , 𝐼𝐶 , 𝐼𝐸 decrease, decreasing 𝐼𝑐𝑅𝑐 .

2. Write frequency allocation table for different communication systems?

Frequency Name of frequency band Uses

3-30kHz (VLF) very low frequency Long distance communication

30kHz-300kHz Low frequency (LF) Navigation services

300kHz-3MHz Medium frequency (MF) Radio broadcasting

3Mhz-30Mhz High frequency (HF) Telephone, aviation

30Mhz-300Mhz Very high frequency(VHF) Radar, TV

300Mhz-3Ghz Ultra high frequency (UHF) TV, Radar

3Ghz-30Ghz Super high frequency(SHF) Satellite communication

30Ghz- 300Ghz Extreme high frequency(EHF) Special purpose

communication

3. What is modulation? Briefly explain the reasons which make modulation an essential step

in communication system?

Ans: Modulation is the process by which some characteristics of a high frequency carrier

wave is varied in accordance with instantaneous value of another signal called modulating

signal.

Modulation is required due to the following reasons:

To reduce length of antenna.

To increase operating range.

For wireless communication.

To avoid mixing signals.

To reduce noise and interference.

4. Derive an expression for AM wave?

Ans:

5. Derive an expression for modulation index in terms of 𝑉𝑚𝑎𝑥 and 𝑉𝑚𝑖𝑛 ?

Ans: If 𝑉𝑚𝑎𝑥 and 𝑉𝑚𝑖𝑛 represent maximum and minimum values of amplitude of modulated

carrier voltage, then

6. Explain with circuit diagram the pre-emphasis and de-emphasis processes?

Ans: Pre-emphasis is the process of boosting the relative amplitude of high frequency

components of modulating signal.

It is done at the transmitter to boost modulating frequencies above 1KHz. RC high pass filter

or differentiator is used as pre-emphasis circuit.

This circuit increases amplitude of modulating signal with increase in frequency.

De-emphasis: It is the process of attenuating relative amplitudes of high frequency

components of the modulating signal.

It is done at the receiver. It is a low pass filter or an integrator. It produces lower output at the

higher frequencies because the capacitive reactance of capacitance decreases as frequency

increases.

7. Explain the following characteristics of a radio receiver?

Ans: Sensitivity: sensitivity of a radio receiver is its ability to respond to weak signal and is

expressed as the minimum signal input voltage or power required to produce required output.

Selectivity:is theability of the radio receiver to distinguish between required signal to which

receiver is turned and the other signal frequencies.

Fidelity: of a radio receiver is its ability to reproduce the signal that appears in its input

faithfully to its output.

8. Obtain the expression for the anode current of SCR when the gate current is zero?

Ans:

9. List the different types of flip flops?

Ans: SR flip flop

D flip flop

JK flip flop

Master-Slave JK flip flop

10. Draw the logic symbol, truth table and timing diagram of D flip-flop?

11. Mention the different types of addressing modes?

Ans: Immediate addressing mode

Register addressing mode

Direct addressing mode

Indirect addressing mode

12. Briefly explain the different bits of binary memories of different registers?

13. Write the format of simple C program?

Ans: Format of simple C program is

main()

----------------

Statement;

-----------------

14. Mention the different relational operators and their meaning?

15. Explain call hand-off and frequency reuse used in cell phone system?

Ans: Call hand-off is the process in which a call in progress is transferred from a radio

channel of a cell site to a radio channel of another cell as a mobile phone user moves from

one cell to another.

Frequency reuse is the process in which the same set of carrier frequencies are used in

different cells that are geographically separated.

16. Draw a labelled diagram of Bluetooth system?

17. Compare Wi-Fi and Bluetooth?

Ans:

Wi-Fi Bluetooth

Access is point centered Symmetrical between two Bluetooth devices

Serves well in high speed application Serves well in simple application

18. With a diagram, explain the operation of a communication satellite system?

Ans: Satellite acts as a relay station for earth sources. A transmission station sends the

information to the satellite, which in turn retransmits to the receiving stations.

The original signal being transmitted from the earth station to the satellite is called uplink of

6GHz. The retransmitted signal from the satellite to the receiving station is called downlink

of 4GHz.

19. Give a classification of RADAR systems?

Ans: RADAR (Radio Detection and Ranging)

Doppler wave radar

Doppler radar

FM radar

Phased array radar

Planar array radar

2 Pulsed Radar

Moving target indicator (MTI) radar

Radar beacons

Five Mark Question.

1.Explain the steps required to draw the DC load line for voltage divider bias?

DC load line is drawn from the end points and is plotted as shown below:

2. Classify the amplifiers on different criteria?

Ans:

Criteria Classification

Input signal Small signal amplifier, large signal amplifier

Nature of output Voltage amplifier, power amplifier

Frequency range AF, RF, IF, VHF, UHF & SHF amplifier

Operating point Class A, Class B, Class C & Class AB

amplifier

Configuration CB, CE, CC amplifier

Coupling RC, direct, transformer coupled amplifier

Stages Single and multi-stage

Bandwidth Wide band and narrow band amplifier

3. Compare CE, CB, CC amplifiers?

Ans:

Parameter Types of amplifiers

CE CB CC

Current gain High (β) Less than 1 Highest (1+β)

Voltage gain High Moderate Low

Power gain Highest Moderate Moderate

Phase shift 180° 0° 0°

Input impedance Moderate Low High

Output impedance Moderate High Low

Bandwidth Narrow Wide Wide

Applications AF amplifier RF amplifier Impedance matching

4. Explain the circuit diagram and the working of RC coupled amplifier explain the frequency

response curve and mention advantages, disadvantages and application?

The circuit diagram shows the 2 stage RC coupled transistor amplifier using voltage divider

bias in CE configuration. The connection to the second stage from the first stage is done

through coupling capacitor 𝐶𝑐 . Cin couples input signal to first stage and 𝐶𝑐 couples the

signal from first stage to second stage. R1, R2 provide the required biasing and 𝑅𝐸 provides

the stabilisation. 𝐶𝐸 bypasses AC across the resistor 𝑅𝐸 . The AC input signal is applied to the

input of the first stage, it gets amplified and appears at its output with a phase difference of

180°. This amplified signal is feed to the input of the second stage through the coupling

capacitor 𝐶𝐶 . The second stage further amplifies the signal and produces a phase reversal of

180° with repect to input signal. The signal is inverted twice and the input and output of 2

stage CE amplifier are in phase.

Frequency response curve.

At low frequency the coupling capacitor offers high reactance and hence it allows only a

small part of the signal to pass from one stage to the next stage therefore the gain is less at

low frequency. At high frequency the coupling capacitor offers a low reactance and acts like

a switch. Hence due to loading effect of the next stage increases and the gain decreases. In

mid frequency range the effect of coupling capacitor is such that it maintains a constant

voltage gain.

Advantages:

1. It is the most convenient and least expensive multistage amplifier.

2. It has a wide frequency response i e its gain versus frequency curve remain constant for a

wide frequency range.

3. It gives less frequency distortion.

Disadvantages:

1. Th& overall gain of the amplifier is comparatively small because of the loading effect of

number of stages.

2. itbcomes noisy wth the passage of long time

3. It provides poor impedance matching between the stages

Applications

R-C coupled amplifiers provide excellent audio-fidelity over a wide range of frequencies.

Therefore they are widely used as voltage amplifiers e g in the initial

stages of Public Address System.

5. With the circuit diagram explain the working of class B push pull amplifier?

Ans: Class B push pull amplifier is as shown in the diagram. T1 and T2 are 2 centre tap

transformer and Q1 and Q2 are 2 identical transistors. Transformer T1 produces signal

voltages V1 and V2 which are 180° out of phase with each other. These 2 signals are applied

to the 2 transistors. Transformer T2 couples AC output signal from collector to loudspeaker.

The 2 emitter are connected to centre tap of transformer secondary. During positive half cycle

of input voltage secondary winding of T1 has voltages V1 and V2 transistor Q1 conducts and

Q2 is cut off. The collector current through Q1 produces amplified and inverted voltage

which applied to loudspeaker through a transformer.

6. Explain with circuit diagram the action of class C collector tunned power amplifier?

It has parallel tunned circuit as collector load. The value of capacitance and inductance of

tunned collector are selected such that it resonant with the same frequency which is equal to

frequency to be amplified. The high frequency signal to be amplified is given to the input of

the amplifier. The resonant frequency of parallel tunned circuit is made equal to frequency of

signal by changing the value of capacitor. If the input signal has several frequency amplifier

will select and amplify those frequency which are close to resonant frequency in this way the

amplifier selects and amplifies the desired frequency.

7. What are the different types of negative feedback? Explain each with block and diagram?

Ans: Different types of negative feedback are

1. Voltage feedback

2. Current feedback

The combination of both may also be present in a circuit. At the same, time, both voltage

current can be feedback to the input either in series or parallel, then they named as:

1. Series — Voltage feedback

2. Series — Current feedback

3. Shunt — Voltage feedback

4. Shunt — Current feedback

Inthiscircuitvoltage isfeedbacktotheinputinseriesThisemployedhigh inputimpedance

andlowoutputimpedanceandinvanablyemployedin negativefeedbackamplifies.

In this circuit current is feedback in series to the input.It provide high input impedance and

output.

In this circuit voltage is feedbackin shunt to the input. It provides low output impedance input

and high.

In this circuit current is feedback in shunt t6 the input. It provicies high input and low output

impedance.

8. Draw the circuit diagram of voltage series feedback amplifier and derive the expressions

for input and output impedances?

9. What is differential amplifier, Draw four modes of differential amplifier?

Ans: Differential amplifier is a circuit which amplifies the difference of input applied to it.

Dual Input and unbalanced output differential amplifier.

Single input balanced output differential amplifier.

Single input unbalanced output differential amplifier.

10. What is operational amplifier write the properties of ideal op-amp and also draw its AC

equivalent circuit?

Ans: It’s a direct coupled high gain high bandwidth amplifier.

Characteristics Ideal Op-amp

Open loop gain ∞

Input impedance ∞

Output impedance 0

Bandwidth ∞

CMRR ∞

Slew rate ∞

Input offset voltage 0

11. Explain virtual ground concept and also derive an expression for the ouput of an inverting

adder?

Even though the inverting terminal is not grounded, there exists zero voltage at A. Hence A is

called virtual ground.

The output is negative sum of input voltages.

12. With circuit diagram, show how to obtain an expression for the output which is logarithm

of input?

The output voltage is proportional to natural logarithm of input voltage.

13. With the circuit diagram, show how to obtain an output which is anti-logarithm of input?

Substituting eq(1) and (2) in eq (3)

14. Derive an expression for voltage gain of an inverting amplifier?

Ans:

15. Draw the block diagram of an electronic communication system and explain the function

of each block in brief?

Source: It generates message which is called information, signal or data.

Transmitter: It is a circuit which processes the information and transmits effectively in all

the directions in the space.

Channel or Medium: Medium is that in which the information propagates.

Receiver: It receives the signal from the space and processes the information to make it

suitable for the destination.

Destination: It is the end user of the information.

Noise: It is unwanted electrical disturbance added to the message in the communication

channel.

16. Explain the circuit diagram, the working of collector modulated class C amplifier?

The modulating signal is applied to the collector of the transistor and hence this circuit is

called collector modulator. It has RF amplifier in class C mode, in which the amplifier

conducts only for a portion of positive half cycle of input signal. LC tank circuit is tuned to

resonate at carrier frequency. The signal to be modulated is connected to the class C amplifier

through the transformer 𝑇1. The secondary winding of transformer 𝑇1connects the modulating

signal in series with collector supply 𝑉𝑐𝑐 . Thus amplitude of collector current varies with

amplitude of modulating signal.

17. Draw the block diagram and explain the various stages of an AM transmitter?

The transmitter performs modulation and raises the power level of a modulated wave to

required level for effective radiation. The microphone converts the audio signal into an

equivalent audio electrical signal. The output is filtered to have a bandwidth of 10KHz.

The pre amplifier provides the required voltage amplification. The driver amplifier increases

the power level of the signal as required by the high power modulation amplifier.

The high frequency carrier wave is generated by a crystal oscillator which has highest

frequency stability. The carrier signal is fed to a buffer amplifier which is low gain, high

input impedance amplifier which isolates crystal oscillator and the power level of the carrier

signal to drive the modulated class C amplifier.

18. Derive an expression for the instantaneous value of a FM wave?

Ans: Let the modulating signal be given by 𝑣𝑚 = 𝑣𝑚 cos𝑤𝑡. Where w is angular frequency, 𝑣𝑚 is the peak amplitude.

Let the carrier voltage be given by the equation 𝑣𝑐 = 𝑣𝑐 sin(𝑤𝑐 𝑡 + Ø). Where 𝑤𝑐 is the angular frequency of the carrier and 𝑣𝑐 is the peak amplitude of the carrier

phase angle Ø = 𝑤𝑐 𝑡 + Ø

19. With a block diagram, explain the various stages of FM transmitter?

The modulating signal is applied to the pre-emphasis circuit, which improves signal to noise

ratio. AF amplifier amplifies output of pre-emphasis. The processed signal is fed to reactance

modulator. The reactance modulator uses a transistor or FET connected across tank circuit of

carrier oscillator.

The oscillator frequency depends on the tank reactance which in turn depends on the

instantaneous amplitude of modulating signal. Thus, output of reactance modulator will be a

frequency modulated wave.

The oscillator is followed by a buffer amplifier which isolates oscillator from subsequent

stages. The limiter maintains the amplitude constant. Class C power amplifier amplifies

modulated wave to required power levels. The FM signal is then fed to the transmitting

antenna.

20. Explain the basic principle of superheterodyne AM receiver and explain the function of

each block?

RF section:It is tuned filter that receive the requiredstations by tuning the filter to right

frequency band. The output o RF stage is fed to mixer stage.

Mixer: Its is a kHz device that converts carrier frequency 𝑓𝑐 to a fixed IF of 455kHz. The

oscillator is made to generate a frequency exactly 455kHz above the incoming carrier

frequency 𝑓𝑐 thus, a constant frequency difference is maintained between local oscillator

frequency and incoming RF signal.

Local Oscillator:Its is a colpitts oscillator which generates a sine wave.

IF amplifier:Its has two or more stage of 455kHz frequency tuned voltage amplifiers for

giving better selectively and stability.

Detector: It separates modulating signal from the AM signal.

AF amplifier: Audio signal is first amplified using RC coupled voltage amplifier to raise its

level to drive a power amplifier.

Power amplifier: The audio power amplifier output is fed to loud speaker through

impedance transformer. The loud speaker reproduces the original information.

21. Draw the equivalent circuit of transmission line. Explain the primary and secondary

constants?

Primary constants:

The series resistance per unit length R is proportional to the square root of frequency.

The inductance L per unit length for a 2 wire T-line is

D is the distance between 2 wires and d is diameter of each wire.

The capacitance C per unit length for 2 wire system is

Where is the permittivity of free space, D is the distance between 2 wires and d is the

distance between the plates of capocator.

Secondary constants:

The series impedance of T-line is Z=R+jwL

The shunt admittance of T-line is y=G+JWC are the two secondary constants.

22. What is an antenna? Briefly explain any four types of antenna?

Ans: An antenna is a device that radiates and receives electromagnetic waves.

Helical antenna: Its has a conducting wire wound in the form of a helix. They are mounted

over ground place and are used at earth base stations in satellite communication system.

Yagi antenna:Its is an array of parallel, straight antenna elements one or more driven and

one or more parasitic.

Loop antenna:It receivesradio signal more efficiently. The loop is wound on an form, which

may be box or spiral wound.

Horn antenna:It hasa flaring metal wave guide shaped like a horn to direct radio waves in a

beam. These are used at UHF and microwave frequencies above 300Mhz.

23. Distinguish between analog and digital communication?

Ans:

Analog Communication Digital communication

Has infinite number of values Finite set of discrete values

AM, FM, PWM types of modulation Uses PCM

Needs simple circuitry Needs complex circuitry

Low transmission speed and noise level High transmission speed and low noise

Bandwidth is less Bandwidth is high

Signal transmitted is analog Digital signal is 1 or 0

24. Draw the block diagram of digital communication and explain the function of each block?

Channel Encoder: Generates channel code word from the source code words.

Modulator: Modulates the channel code words into a continuous wave.

Low pass filter: Allows only lower frequencies and blocks the other frequencies.

Synchronisation: Is required to demodulate a carrier modulated wave.

Demodulator: Converts continuous waveform into ordinary signal.

Channel decoder: Decodes the channel code word.

Source decoder: Converts channel decoder code word into information signal.

25. Explain the universal property of NAND gate and realize AND, OR, NOT and XOR gates

with their respective truth tables?

Ans: NAND is called universal gate because other logic gates can be realised using NAND

gates.

(1) AND gate from NAND gates:

(2) OR gate from NAND gates:

(3) NOT gate from NAND gates:

(4) XOR gate from NAND gates:

26. What is half subtractor? Explain its working with a truth table, logic diagram and timing

diagram?

Ans: Half subtractor is a logic circuit which subtracts two bits and gives difference and

borrow.

27. Explain the working of clocked JK flip flop with its logic diagram, truth table and timing

diagram?

Ans: When J=0 & K=0 the S and R inputs are both at 0 and hence the output is in the hold

state.

When J=0 & K=1, S input is at 0 while R can be either 0 or 1, but output is always in the

reset state.

When J=1 & K=0, S input can be 0 or 1 but R input is always at logic 0 and hence the output

remains at a stable SET state.

When J=1 & K=1 the flip flop goes to complementary state of previous output ie, flip flop

toggles

28. Explain the working of SISO shift register with relevant diagram?

With four SR flip flop it can store upto 4 bits of data. Serial data is applied to S input of the

first flip flop.

When serial data is transferred into the register, each new bit is clocked into first flop at the

positive edge of each clock pulse. The bit that was stored by first flip flop is transferred to

second flip flop and so on.

The shifting out of stored data 0101serially from the register requires four clock pulses.

29. Simplify the Boolean equation Y=∑m(4,5,7,9,11,12,13,15)+∑d(1,3,8) using k-map. Draw

the NAND gate equivalent circuit to realise the simplified equation?

Y=∑m(4,5,7,9,11,12,13,15)+∑d(1,3,8)

Y= 𝐵𝐶 + 𝐷

30. Compare a microprocessor with a microcontroller?

Ans:

Microprocessor Microcontroller

uP have many operational codes for moving

data and performing operations, but it has

only few bit handling instructions.

uC have one or two operational codes for

moving data from and performing operations,

but it has many bit-handling instructions.

uP is concerned with rapid movement of

code and data from external addresses to the

chip

uC is concerned with rapid movement of bits

withtin the chip

uP need external digital parts to perform its

tasks as computer

uC can function as computer without addition

of external digital parts

uP are used in general purpose computing

devices, supports wide range of applications

with general hardware

uC are used in embedded systems and

supports only dedicated applications with

customized hardware

31. Mention the features of 8051?

Ans:

8- bit CPU with registers A (accumulator) and B

16-bit program counter (PC) and data pointer(DPTR)

8-bit program status word(PSW)

8-bit stack pointer(SP)

Internal ROM or EPROM of 4k bytes

Internal RAM of 128bytes

Four 8-bit I/O ports(P0-P3)

Two 16-bit timer/counter T0 and T1

Full duplex serial data receiver /transmitter

2 external and 2 internal interrupts

Oscillator and clock circuits

32. Draw the pin details of 8051?

33. Write 10 basic structure of C programming?

Ans: Overview of a C program

Documentation Section

Link Section

Definition Section

Global declaration section

main() function section

Declaration part

Executable part

Subprogram Section

Function 1

Function 2

Function 3

--- (user defined functions)

Function n

34. Briefly explain the format of a simple C program?

Ans: Pre-processor directives

main()

A pair of flower brackets

Declaration and statements

User created sub-program or functions

The above described components are organised as follows:

Pre-processor directives

main()

Declaration and statements

Pre-processor directives

C program contains one or more functions or sub programs. Many functions are already

written and complied in the library so we can tell the compiler to use these standard

functions. Eg: #include<stdio.h>, #include <math.h>

main()

C program must have a main function which is identification for the start of the main part of

the program.

A pair of flower brackets

An opening brace “” must appear immediately after the word main() and closing brace””

must follow the last instruction.

Declaration and statements

Part of the program were all the variables, arrays and functions and so on are identified with

their data types. Statements can also include C commands or names of functions in the

library.

35. Draw the flowchart to show the process of compiling and running C program?

36. List the advantages and applications of Wi-Fi?

Ans:

Wi-Fi is used to access the internet via hotspots with a laptop computer.

It is one of the most reliable, flexible and affordable wireless networking technology.

Wi-Fi allows cheaper deployment of local area network in outdoor areas like

historical buildings.

The price of chipsets for Wi-Fi continues to drop, making it an economical

networking operation.

The standard Wi-Fi device will work anywhere in the world.

37. With a neat block diagram, explain the operation of fibre optic communication?

The information signal to be transmitted is first converted to digital format using analog to

digital converter, which is compatible with the communication medium.

These digital pulses are then fed to a optical fibre cable which can transmit them over long

distances. At the receiving end, a light sensitive devices like a photocell is used to detect light

pulses. It converts light into an electrical signal.

The receiver circuit processes the electrical signal to recover the original information.

38. Draw the block diagram of a radar system and explain the function of each block?

Transmitter: The radar transmitter produces high frequency RF pulses and its transmitted

into space by the antenna.

Duplexer: It switches the antenna between transmitter and receiver alternately. This is

required because high power pulses of transmitter will destroy the receiver if energy were

allowed to enter the receiver.

Receiver:It amplifies and demodulates the received RF signals. It provides video signals on

the output.

Radar antenna:The antenna transfers the transmitting signal to space with the required

distribution and efficiency.