# Mumbai University Previous year question papers

## Principles of Communication

N.B.: (1) Question No.1 is compulsory.

(2) Attemptany four from remainingquestions.

(3) Assumesuitable additional data if necessary and state them clearly.

1.

(a) Explain frequency spectrum of the AM wave.

(b) ~xplain FM noise triangle.

(c) What is meant by Nyquist rate in sampling, what is standard samPlingfrequency for speech signal?

(d) What is companding? .

(e) Describe the space wave propagation.

2.

(a) The AM transmitter developes an unmodulated power output of 400 watts, across a 50 Q load. The carrier is modulated by a sinusoidal signal with a modulation index 0.8.

Assuming FM = 5 KHz and Fc = 1 MHz

(I) Find the Vand write equation of AM

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

(b) In FM explain:

(i) Maximum Frequency Deviation

(ii) Modulation Index

(iii) Pre-emphasis

(iv) De-emphasis

(v) Frequency spectrum and bandwidth.

3.

(a) Find the mathematical expression of FM signal. 10

(b) Explain slope overload error ~nd hunting error in Delta modulation. Find the condition to avoid slope overload ern;>r. .

4.

(a) A FM signal is given by :

V = 10 sin [5 x 10~ e + 4 sin 1250 e].

Find: (i) Carrier and Modulating Frequencies.

(ii) Modulation Index and Maximum deviation.

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

(b) What is multiplexing in communication system? Draw the block diagram of TDM-PCM system. Also calculate the bit rate at the output of this system.

5.

(a) (i) State advantage of digital communication over analog communication. Justify each point. List some digital communication techniques.

(ii) Explain what is meant by quantization noise. ‘ 4

(b) A receiver is tuned to 3-30 MHz frequency range of 40.525 MHz: 10

(i) Find the range of local oscillator frequency and image frequency. It is an AM receiver with’ each channel occupying 10KHz bandwidth.

(ii) Draw Frequency response of IF and AF amplifiers.

6.

(a) Draw the block diagram of phase cancellation SSB generator and explain how the carrier and unwanted sidebands are supressed. What changes i~ necessary to supress the other sideband?

(b) (i) Compare Wideband and Narrowband FM 5

(ii) Compare FDM and TDM. 5

7.

(a) Describe the following terms in relation with skywave propagation?

(i) Skip Distance

(ii) Critical Frequency

(iii) Virtual Height

(iv) Maximum Usable Frequency.

(b) Write short notes on the following (any two) :-

(i) Automatic Gain Control (AGC)

(ii) Ground Wave Propagation

(iii) Direct Method 6f FM Generation.