# Analog and Digital Communication June 2002

(ElectronicsElectronics & Telecom. Engg.)

ANALOG AND DIGITAL COMMUNICATION

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

1. (a)      Find the Fourier transform of sin Ω0t. Compare with the transform of cos Ω0t.

(b)     Show that the power spectral density and the correlation function of a periodic wave forms are a Fourier transform pair.

2. (a)     Derive PSD of a rectangular pulse train with pulse with ‘to’ repeating at interval ‘to’ with Arbitrary amplitudes.

(b)     Discuss the detection method used for amplitude modulated signals. Draw circuit diagram and waveforms.

3. (a)     How the FM signal can be generated with PM signal? Discuss one technique in detail.

(b)     Draw the block diagram of a superhetrodyne receiver. Explain each block in brief.

(4)     Two signals m1(t) and m2(t) Each band limited to 4kHz are sample at Nyquist rate , PCM encoded and then time multiplexed .Draw the scheme to transmit the signals and find out the rate of transmission if 8bit PCM is used.

(b      Why companding is needed? Discuss the law of companding.

5. (a)     What are the techniques used for digital modulation ? Discuss any one in detail.

(b)      Discuss the properties of the matched filter. What is the need of using the same?

6. (a)      Show that the entropy is maximum , when all the message are equiprobable.

(b)     State the Shannon’s Theorem regarding channel capacity. Explain the Significance of same.

7. (a)      What is line coding ? Give some example of line codes and explain in brief.

(b)      Find out the (7,4) cyclic code for the Given word A =1011.

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

(a)      Time shifting and frequency shifting property of Fourier transform.

(b)          Comparasion of various AM systems.

(c)          Delta modulator

(d)         Random signal and variable