# Mumbai University Previous year question papers

## Principles of Communication

N.S. : (1) Question NO.1 is compulsory.

(2) Attempt anyfour questions out of remaining six questions.

1. (a) Derive an expression for noise voltage.

(b) What is companding?

(c) Compare ground wave propagation with space wave propagation.

(d) Define Nyqujst Rate. What is th~ standard sampling frequency for speech signals?

2. (a) An AM transmitter developes an unmodulated power output of 100 watts across a 10n load. The carrier is modulated by a sinusoidal signal with a modulation index of 0,5. ,Assuming fm= 5 KHz and fc = 2 MHz:

(i) Write the equation of AM.

(ii) Find the total power of the modulated output.

(iii) Draw the spectrum.

(b) Differentiate low level modulation from high level modulation. collector modulated class C amplifier for AM generation.Explain the working of 10

3. (a) Draw the block diagram of a phase cancellation SSB generation and explain how the carrier and unwanted side band are suppressed. What change is necessary to supress the other side band?

(b) Draw the block diagram ofAM superhetrodyne receiver and explain its working. 10

4. (a) What are the different methods of FM generation? Explain the working of reactancemodulator.

(b) A FM signal is given by V = 5 sin [6 x 106t + 2 sin 1000 t].

Find:

(i) Carrier and modulating frequencies.

(ii) Modulation index and maximum deviation.

(iii) The power dissipated by this FM wave in a 5Q resistor.

5. (a) Stateand prove samplingtheorem for low pass band limited signal. Explain aliasing error. 10

(b) Draw neat block diagram of Delta modulator and explain its working. What are tne drawbacks of Delta modulator and how are they overcome by ADM?

6. (a) Describe the following terms:

(i) Skip distance

(ii) Critical frequency

(iii) Virtual Height

(iv) Maximum usable frequency.

(b) What is multiplexing in Communication System? Draw the block diagram ofTDM-PCM system and explain.

7. Write short notes on any two :-

(a) Automatic Gain Control

(b) FM Ratio Detector

(c) Ring Modulator

(d) Pre-emphasis and De-emphasis.