Sunday, 27 April 2014

Analog Communication Important Questions For External Exams And Easy Units

Analog Communication Important Questions For External Exams And Easy Units


1.Define Noise, Figure of Merit, and Signal to Noise ratio. List out the assumptions of Noise calculation
in communication system.

2.Give the general representation of noise in communication system and Calculate the power spectral density of it.

3.Calculate the power spectral density of Noise in case of DSB-SC and also calculate Figure of merit.

4.Calculate the power spectral density of Noise in case of SSB-SC and also calculate Figure of merit.

5.Calculate Figure of merit in case of Amplitude modulated wave.

6.Prove that for very low noise case Envelope detection method is identical to synchronous detection.

7.Explain Envelop detection method for high Noisy case.

8.Calculate Figure of merit in case of Non linear demodulation.

9.Compare Non linear demodulation and Synchronous detection with the help of equations.

10.Give the block diagram of Frequency demodulation and calculate Figure of merit for it.

11.Bring out the relationship between AM and FM Noise performance.

12. Explain the phasor diagram of FM Noise.

13.What is threshold effect in FM? What is the technique to improve the threshold of FM wave.

14.Discuss in brief about Pre-emphasis.

15.Discuss in brief about De-emphasis.

16.Explain Noise in phase modulation and derive the expression to calculate the Figure of Merit.

17.Compare AM and PM on the basis of Noise performance.

18.The received signal power in an AM signal with a modulating signal of frequency 5 KHz is 10-12? and
receiver input noise PSD is 10-20?/Hz. Assuming the noise power to be restricted to the message signal band width.
Find input signal to noise ratio at the input receiver.

19.In a DSB-SC system, the signal is extending from 97 KHz to 103 KHz with a carrier frequency of 100 KHz.
If the received signal power is 80 P?, and the noise PSD at the receiver input is 10-14 ?/Hz,
find the output signal to noise ratio.

20.Calculate the transmission bandwidth and the required transmitter power of DSB-SC,
SSB-SC and AM-DSB with carrier systems for transmitting an audio signal,
which has a Bandwidth of 15 KHz with an So/No of 50 db.
The channel introduces a 40 db power loss and the channel noise is PSD ?/2= 10-9 ?/Hz.
Assume m2. X2 (t) = 0.5.

21.Prove that narrow band FM offers no improvement in SNR over AM

22.It is given the threshold level for AM is equivalent to the input (SNR)I = 10.
Assume this conclusion is also valid for FM.
Find the (SNR)o at the threshold level for FM and also find the modulation index ß that produces (SNR)o = 30 dB at
the threshold.

23.An AM receiver, operating with a sinusoidal modulating signal and 30% modulation,
has output SNR of 30dB. Find the corresponding carrier-to-noise ratio.
By how many dB can we decrease the carrier-to-noise ratio so that the system is operating just above threshold?

24.Given an FM broadcast system with parameter ?f = 75 kHz and B =15 kHz. Assuming Sx
= ½, find the output SNR and calculate the improvement (in dB) over the base band system.

25.Prove that the performance of an SSB modulation system using synchronous detection is equivalent to the performance
of both DSB and base band system.


1.Name the constituent stages of A.M. radio transmitter and briefly give the function of each stage.

2.What are the main requirements of a radio transmitter regarding the carrier frequency? Briefly discuss
these requirements.

3.Enumerate the precautions necessary in the design and operation of an L-C oscillator for use as a Master
oscillator in a radio transmitter.

4.Draw the block diagram of SSB transmitter using filters for side band suppression and explain its working.

5.Give the block diagram of radio telegraph transmitter using on-off keying.

6.Describe the principle methods of on-off keying.

7.Give the block diagram and describe the working of FSK transmitter.

8.Give the reason for keying transients due to amplitude on-off keying. How can these keying transients be kept below?

9.Draw the block diagram and describe the working of a simple FM transmitter using reactance modulator.

10.What are the principle of sources of frequency drift in reactance modulator FM transmitter and how
can such a drift be reduced.

11.Draw the circuit and explain the working of reactance modulator FM transmitter using AFC frequency stabilization.

12.Give the principle of Armstrong method of frequency modulation.

13.What are the Sources of distortion in Armstrong method and how to reduce it

14.Draw the block diagram of Armstrong FM transmitter and describe its working

15.Classify Radio transmitters in detail

16.What is class C Amplifier? Explain its use in radio transmitters

17.Distinguish between AM and Fm Radio. List out their applications

18.Explain the necessity of buffer and driver amplifiers in radio transmitters

19.Draw the block diagram of an SSB-SC transmitter employing side band suppression filter and explain.

20.Explain what happens to the carrier and side bands when passing the AM or FM signal through a mixer
as compared to a frequency multiplier

21.A transmitter has carrier output power 100w and an efficiency of 75%. How much power is
supplied by the modulating amplifier for 100% modulation and 50 % modulation

22.A collector modulated class-C amplifier has output power of 1000w and an efficiency of 80%.
Determine the dc supply power and power dissipation for 100% modulation

23.An SSB transmitter with carrier amplitude of 10 v is being tested using triangular modulating
signal with peak voltage of 0.5v. The transmitter is connected to a dummy load of 50 O. Calculate the actual
power dissipated into load

24.A direct FM transmitter has reactance modulator with frequency sensitivity Kf = 2 KHz/v and a peak deviation of 500 Hz.
This modulator is followed by a buffer and doubler, Tripler followed by a power amplifier.
Find the Oscillator frequency if the transmitter is to operate at a carrier frequency of 150 MHz

25.A carrier wave of frequency 1 MHz is modulated 50% by a sine wave of 5 KHz.
The resulting AM signal is passed through a parallel resonant circuit (RLC) tuned to carrier frequency and has
Q = 175.Determine the percentage modulation of the output signal.

26.In the transmitter reactance modulator, the input resistance of transistor is 500 ohms with ß = 100.
What is the equivalent capacitance? If ß swings from 50 to 120, what are the values of minimum and maximum values of
capacitance? The circuit has R2 = 10 KO, C2 = 1000 pf.

27.A given AM broadcast station transmits a total power of 50 kw for single tone modulation with m=0.7071.
Find Carrier power and transmission efficiency

28.Compare low level modulation and high level modulation of radio transmitters

29.What is electromagnetic spectrum? List out the frequency bands, their channel characteristics,
frequencies and applications.

30.Why are limiters and Pre emphasis filters used in FM radio transmitters


1. Draw the block diagram and explain the working of a TRF receiver. List out its advantages and disadvantages.

2. Explain the working principle of a super heterodyne receiver with the help of neat block diagram

3. Explain the necessity of a mixer in a receiver. Give a circuit schematic and explain

4. Draw the block diagram and explain the operation of an ISB receiver.

5. Draw the block diagram of Super heterodyne receiver designed to receive FM signals and explain its working

6. Discuss the need for limiter and de-emphasis circuit in FM receivers

7. Illustrate the FM detection by a PLL with the help of its Schematic

8. With a neat sketch, explain the working of a communication receiver

9. What are the special features of communications receiver? Brief them

10. Draw the squelch circuit and explain its operation

11. Explain the operation of a noise limiter in FM receivers?

12. Describe the fading phenomenon and its types in detail.

13. What is meant by diversity reception? Explain different techniques

14. Discuss the capture effect in detail. List out its advantages and disadvantages

15. Explain the differences between AM and FM receivers

16. Explain the IF amplifier circuit and its purpose in the receiver

17. Draw the two stage IF amplifier and explain its operation

18. Explain about spurious responses in radio receivers and how they can be reduced

19.When a super heterodyne receiver is tuned to 555KHz, its local oscillator provides the mixer
with an input at 1010KHz, what is the image frequency? The antenna at receiver is connected to mixer
via a tuned circuit whose loaded Q is 40. What will be rejection ratio for the calculated image frequency?

20. Calculate the image rejection of a receiver having an RF amplifier,
and a 455 KHz IF with Q’s of relevant coils as 65 at an incoming frequency of 120 KHz and 20 MHz.

21. Calculate the image rejection of a double conversion receiver,
which has a first IF of 2 MHz and a Second IF of 200 KHz,
an RF amplifier whose tuned circuit has a Q of 75and which is tuned to a 30 MHZ signal.

22. Bring out the advantages of a dual gate MOSFET over BJT for use in radio circuits

23. List out the consequences of choosing the IF very high and very low

24. Write a short notes on Notch filters

25. Explain the procedure for LO Tuned circuit alignment

26. Explain the importance of AVC and explain its operation

27. Explain various types of Tone control circuits

28. What are the special features of DAGC

29. Explain the advantages of RF stage and explain the action of RF amplifier

30. Explain the purpose and working of Tracking Circuits


1. What is Time Division Multiplexing? Explain in detail
2. What is meant by Pulse Amplitude Modulation and explain any one-modulation technique in detail
3. What is meant by Pulse Width Modulation Explain the generation of Pulse width modulation?
4. What is meant by Pulse Width Modulation Explain the demodulation of Pulse width modulation?
5. What is meant by Pulse Positon Modulation Explain the generation of Pulse Position modulation?
6. What is meant by Pulse Position Modulation Explain the demodulation of Pulse Position modulation?
7. Compare the performance of PAM, PWM, and PPM
8. What is Pulse modulation? Explain in brief various types of pulse modulation with neat sketches.
9. Explain in brief about Bit interleaving in TDM.
10. What is Multiplexing? Compare FDM and TDM.
11.Explain the PAM Noise performance
12. What is Sampling. Derive Sampling Theorem for Band pass Signals.
13. Explain the generation of PAM Signal using Diode Bridge Modulator.
14. Explain the generation of PAM Signal using Sample and Hold Circuit
15. Explain the generation of PAM Signal using transistor Modulator
16. Explain how to demodulate PAM Signal using Equalizer
17. Explain how to demodulate PAM Signal using a Holding circuit
18. Explain the generation of PWM Signal using Monostable Multivibrator.
19.Compare Analog Modulation and Pulse modulation.
20. Explain Natural Sampling with neat sketches
21. Explain Flat Top Sampling with neat sketches.
22. Derive the equation to calculate the Channel bandwidth for a PAM Signal.
23. Explain Single polarity and Double Polarity PAM techniques

24. Consider a signal m(t) = 10 Cos1000pt. Cos 4000pt.
Find the minimum sampling rate based on sampling theorem for low pass and band pass signals.


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