**B.E. (fourth semester) EXAMINATION, JUNE, 2005**

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

**ANALOG AND DIGITAL COMMUNICATION**

Note: Attempt any five questions. All question carry equal marks. Missing data, if any can be assumed.

1. (a) Find Fourier transform of the given signal s(t) = 2t + t^{2 }.

(b) Find magnitude and phase spectrum of the given fig.

© Find spectrum of ω (t) = sin 2 π f_{1}t. sin 2 π f_{2}t.

2. (a) If a squaring circuit followed by a low pass filter of cut-off frequency 2B. This is followed by a

square rooter. Determine an expression for the output of the square rooter when the input is an

AM signal.

(a) A carrier V_{c} cos ω_{c }t is modulated by a signal tone modulating signal:

F (t) = V_{m} cos ω_{m }t. Find:

(i) Total modulated power

(ii) R.M.S. Value of the modulated signal

(iii) Transmission efficiency for 100% modulation

3. (a) What do you mean by narrowband and wideband FM?

(b) What is the importance of the parameter modulation index in AM and FM. If a carrier 20 cos 5

π 10^{6 }t is modulated by signal:

F(t) = 2cos 10^{4} 2π t + 6cos 10^{3} 2π t + 5cos 10^{5} 2π t

Find the bandwidth of the FM signal and FM signal assume

K_{f} =10^{3} × 15 Hz per volt.

4. (a) What are the limitation of delta modulation system and how they can be overcome ?

(b) Explain the PSK (phase shift keying) systems. The bandwidth requirement in QSPK reduces to half

as compared to BPSK justify it.

5. (a) Calculate the information rate of a binary symmetric system in which the possible symbols A and

B were transmitted at the rate of 1000 symbols per second, if the system noise cause 1% of the

Symbols to be received incorrectly.

(b) State source coding and channel coding theorems. Define efficiency and redundancy of a code.

6. (a) Calculate the overall noise figure of four amplifiers stage cascaded.

(b) Why and where we use pre emphasis and de-emphasis circuits?

(c) An amplifier operating over the frequency range of 500 to 900 kHz has a 200kΩ input of this

Amplifier if the amplifier temperature is 20^{0}c.

7. (a) What do you understand by low level and high level modulation ? Draw the block diagram for

High level modulation and explain.

(b) Explain function of superhetrodyne receiver.

(c) Draw pharos diagram of AM and FM signal and compare them.

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

(a) Optimum filter

(b) Persevall’s theorem

(c) Convolution code

(d) Poisson and gaussion distribution