# Mumbai University Previous year question papers

Table of Contents

## IV Sem IT Examination Dec 2012

## Principles of Communication

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

(2) Solve any three from the remaining.

(4) Assume suitable data * whereever *required.

(3) Illustrate your answers with neat diagrams.

1. (a) Find Fourier transform of unit impulse signal o(t). 5

(b) Draw and explain the basic block diagram of Communication system.

(c) Explain A-law and W1awcompanding.

(d) Comp-are Frequency modulation and Phase modulation. 5

2.(a) De~ineAmplitude Modulation. * Derive *the equation of AM

*Draw*

*wave.**of AM for m*

*envelope*

(b) A 400 W carrier is modulated to depth of 75% . Calculate total power in,followirig forms of AM : .

(i) DSB – Fe

(ii) DSB – SC

(iii) SSB – FC

(iv) SSB – SC.

3.a) Explain working of Foster Seely discriminator with phasor diagram. 10

(b) In an FM syster:n,when the Audio Frequency (AF) is 500 Hz and the At:

* voltage *is 2·4 V, the deviation is 4·8 kHz. If the AF,

*is now increased to 7·2 V, what is new deviation ? If the AF*

*voltage**is raised to 10V while the AF is dropped to 200 Hz, what is new deviation? Find modulation index in each case.*

*voltage*

4. (a) Explain the sideband generation in SSB using phase shift method. 10

(b) Explain satellite communication system. List applications in * various *fields.

5.

(a) Draw and explain block diagram of four channel FDM system. 10

(b) Explain double * conversion *superhetrodyne receiver with neat block diagram. 10

6.(a) Explain the terms sensitivity, image frequency, double spotting, automatic gain control and three point tracking in radio *receivers.*

(b) How * adaptive *DM is improvement of linear DM ? Draw block diagram of adaptive DM and explain its working.

7. (a) State sampling theorem for low pass signals. What in Nyquist rate?

(b) Explain working of balanced modulator.

(c) Define Noise temperature and Noise Bandwidt.h.

(d) Find Fourier transform of x(t) = e-