# RGPV Previous Question Papers BE 4th Semester

# Analog and Digital Communication Dec 2005

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

**Note: Attempt any five questions. **

**All question carry equal marks.**

** Assume any missing data.**

1. (a) Define the following :

(i) Modulation

(ii) Various modulation techniques

(iii) Modulation index for AM and FM

(iv) Amplitude modulation

(b) Explain generation method of AM using square law modulator with a suitable figure.

2. (a) Derive an expression to show that for every modulating frequency component the amplitude modulated wave contains two sides band frequency in addition to the carrier and also that of the amplitude.

(b) Write ten properties of Fourier transform with mathematical description.

3. (a) Draw the block diagram of superhetrodyne AM receiver and explain each section.

(b) Explain any two terms from the following:

(i) Delta modulation

(ii) VSB

(iii) Quantization

4. (a) Write about the following

(i) ASK (ii) FSK (iii) QPSK

(B) Define the matched filter. Describe the matched filter with expression.

5. (a) Find the channel capacity of the BSC shown in fig. 1.

(b) Explain the linear block code with encoder; decoder

6. (a) Draw the basic block diagram of producing FM from PM and explain each block in short.

(b) Compare the AfC and AGC. Justify that which is better for receiver and why?

7. (a) The joint probability density of the random variable X and Y is expressed as

F(x,y) = ¼ e ^{-x-y},for -∞< x<∞

-∞< y<∞

(i) Are x and y statically independent random variable?

(ii) Determine the probability that x ≤ 1 y = 0

(b) Explain DPSK transmitter with a block diagram.

8. Write short notes on any two of the following:

(a) Spectrum and tramission BW of FM signals

(b) SNR, SSB and DSB

(C) BFSK

(d) Poisson distribution