# RTU Previous Exam Papers BE CSE Fourth Semester

# Analog and Digital Communication July 2011

**UNIT-I**

1 (a) How to demodulate of AM waves by square law detector ? Explain it with suitable circuit diagram.

(b) The total power circuit of AM signal is 1000 W. Determine the power being transmitted at carrier frequency and at each of sideband when the modulation is 100%.

**OR**

1(a) Explain the generator and demodulation of PAM signal.

(b) Determine the Nequest rate and Nequest interval for given signal :

x (/) = 6 cos 50;r/ + 20 sin 300#/ -10 cos 100;r/

**UNIT-II**

2 (a) What is the signal to quantization noise ratio for linear quantization and explain it mathematically.

(b) Define the compacting. Explain the /i-law and A-law compading.

**OR**

(a) Explain the delta modulation is detail with suitable diagram.

(b) A television signal having a bandwidth of 4.2 MHz is transmitted using binary PCM system, given that the number of quantization level is 512. Determine :

(i) Code word length

(ii) Final bit rate.

**UNIT-III**

3 (a) Derive the expression for spectrum of BISK and sketch the same.

(b) Explain the generator and detector of MSK signal.

**OR**

(a) Draw the block diagram of QPSK and explain it working.

(b) Explain the generator of ASK signal.

**UNIT-IV**

4(a) Derive the general transmission line equation.

(b) Explain the working of public switch telephone network system.

**OR**

(a) Explain the salient features of optical fiber communication system in communication application.

(b) A step index multimode fiber with a numerical aperture 0.20 support approximate 1000 modes at a 850 nm wavelength, determine :

(i) What is diameter of its core

(ii) How many modes does the fiber supports at 1320 nm.

**UNIT-V**

(a) Explain the following terms :

(i) Channel capacity

(ii) Average information

(iii) Shanon’s theorem.

(a) Explain the operation of syndrome calculator for cyclic codes with suitable block diagram.

**OR**

(a) Let C be a (7, 4) cyclic code with g(x) = l + x+x^{3}, find a generator matrix G for C. Find the code word for d = (1010).

(b) Explain the linear block code.