# Mumbai University Previous year question papers

## Basic of Analog & Digital Communication System

N.H. (1) Question No.1 is compulsory.

(2) Answer any four questions out of remaining six questions.

(3) Figures to the right indicate full marks.

I. Answer any four of the following :- 20

(a) Compare and contrast between AM and FM.

(b) In a broadcast superheterodyne receiver having no RF amplifier, the loaded Q of the antenna coupling circuit is 150. If the IF is 455 kHz, calculate the  image frequency and its rejection ratio at 1400 kHz.

(c) Explain noise triangle in FM.

(d) Explain the-following terms :-

(i) Signal-to-noise ratio

(ii) Noise fi”gure

(iii) Noise factor

(iv) Equivalent noise temperature.

(e) Explain frequency division multiplexing.

2. (a) When the modulation percentage is 75 an AM transmitter produces 10k W. How much of this is carrier power? What would be the percentage power saving if the carrier and one of its sidebands were suppressed before transmission took place?

(b) Explain VSB transmission. _ 8

(c) Explain the phase shift method for SSB generation giving voltage equations at each stage.

3.(a) Compare FM and PM. 4

(b) Explain Armstrong method ofFM generation with the help of a neat block diagram and phasor diagrams.

(c) In an FM system, when the audio frequency is 1000 Hz and AF voltage is 2 V, the frequency deviation is 4·8 kHz. If the AF voltage is raised to 10 V while the AF is dropped to 500 Hz, find the modulation index in each case.

4. (a) With the help of a neat block diagra~ and waveforms explain super~eterodyne AM radio receiver.

(b) Explain the working of a phase descrimininator FM detector with the help of a neat circuit diagram and phasor diagrams.

5.(a) State sampling theorem. Explain flat-top sampling. Draw its spectrum and explain aperture effect.

(b) Explain generation and delnodulation of PAM, PPM and PWM with waveforms. 10

6. (a) Explain delta modulation with a neat block diagram and waveforms. Also explain slope overload error and granular noise. Suggest the remedy for both.

(b) Draw the following line codes for 11010 :- 5

(i) Unipolar NRZ

(ii) Polar NRZ

(Hi) Polar RZ

(iv) Unipolar RZ

(v) AMI.

(c) Draw and explain the block diagrams of PCM transmitter and receiver. 5

7. Write short notes on :–

(a) Companding in PCM