# Mumbai University Previous year question papers

## Basic of Analog & Digital Communication System

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

(2) Attempt any four questionsout of remainingsix questions.

(3) Assume suitable data wherever required and state clearly.

(4) Figures to the right indicate full marks.

(5) Illustrate answers with sketches wherever required.

(a) Define (i) Noise (ii) Signal to noise ratio (iii) Noise Factor (iv) Noise figure

(v) Noise temperature.

(b) State and explain sampling theorem.

(c) Distinguish between: Narrow band and wide band F.M.

(d) Write a note on vestigial \$ide band transmission.

(e) What is companding 7 Explain with typical companding curves.

2~ (a) What are sources of noise 7 Explain in detail. 8

(b) Explain with the help of neat circuit diagram and waveforms A.M. generation using plate modulator.Whpt are the advantages of plate modulator over Grid modulator 7

3. (a) An Amplitude modulated waveform has the form VAM = [ 10+5 cos 6000 nt + 4 cos 8000 nt.]. cos 50,000nt.

(i) Sketch the amplitude spectrum of VAM’

(ii) What is the modulation index and Bandwidth of A.M. Signal 7

(iii) Find the power content of each spectral component including the carrier

(Assume R = 50 Q).

(iv) Find the total power and side band power.

(b) What are the methods of SSB generation 7 Explain anyone of them.

4.(a) A 20MHz carrier is modulated by a 400 Hz modulating signal. The carrier voltage is 5V and maximum deviation is 10KHz. Write down the mathematical expression for EM. and P.M.waves. If the modulating frequency is increased to 2 KHz keeping everything else constant write down the expression for the EM. and P.M.waves.

(b) Explain Indirect method [ Armstrong Method] of EM. generation with the help of block diagram and phasor diagram.

(b) Sketch the circuit and phasor diagram of a phase discriminator and prove that it works as a EM. demodulator.

6. (a) Explain PAMand PWM generation with the help of block diagram and waveforms. 10

How is PWM demodulated 7.

(b) Draw the block diagram and waveforms of Adeptive delta modulator and explain in detail. What are the advantages of this modulator over delta modulator.

(i) Sensitivity (ii) Selectivity (iii) Double spotting

(iv) Image frequency & its rejection.

(b) Explain PCM with the help of block diagram & waveforms.

(c) Write a note on TOM and FDM.

(d) In respect to the sky wave propagation explain the following terms :-

(i) Virtual height (iii) Skip distance

(ii) MUF (iv) Critical frequency.