# Analog and Digital Communication June 2003

(Common for EE, EC, IT & CS Engg.)

ANALOG AND DIGITAL COMMUNICATION

Note:   Attempt any five questions. All question carry equal marks. Assume any missing Data.

1. (a)    Define convolution . State and prove time the frequency convolution.

(b)    Find the Fourier transforms of eternal sinusoids

(i)        Cos Ωc t and (ii) sin Ωc t. sketch the frequency spectrum also.

2.(a)   With the of circuit diagram explained the working of balanced modulator for DSB –SC generation

The output current of a 60 percent modulated AM generator is 1.5 a. to what value will this

Current rise if the generator is additionally modulated by another audio wave, whose modulation

Index is 0.? What will be the percentage saving if the carrier and one of the side bands are now

Suppressed.

3. (a)  Explain various types of frequency modulation also discuss the spectrum the and transmission

BW of FM signals

(b)  A 20 MHz 5 v carrier is modulated by a 500 Hz sine wave the maximum frequency deviation is 15

KHz and the same modulation index is obtained four both FM and PM. Write expression for the

Modulate wave for (i) FM. Next if modulating frequency is increased to 3 kHz other things

Remaining the same Write new expression for (iii) and (IV) PM.

4. (a)   Draw the schematic diagram of a delta modulator and explain its working what is granular noise?

Give a method to reduce the noise.

5. (a)    Draw the explain the block diagram of OPSK transmitter.

(b)   Compare various digital carrier modulation schemes.

6.(a)    Find the channel capacity in the channel shown in figure. 1. (b)       Use Huffman coding to find the coding efficiency for the following, message ensemble –

[x]  = [x1  x2 X3 X4 X5 X6 X7 ]

[p] = [.4 .2 .12. .08 .08 .04 ]

7. (a)   Draw the block diagram of super heterodyne receiver and explain the function of each stage .

(b)   Draw the block diagram of PCM system and explain its working.

8.         Write short notes on any two of following.

(i)     Synchronous detection for SSB-SC signals

(ii)     Parameter variation method FM generation

(iii)     Companding

(iv)     Quantization

(v)      SN Performance of PCM