# Analog and Digital Communication Dec 2006

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

Note: Attempt any five questions.

All question carry equal marks.

1. (a)  State and prove time shifting and time differentiation property of Fourier transform

(b) Find Fourier transform of the following.

(i)  Sgn (t)

(ii) Cos ω0t  u(t)

2. (a)    A multiple tone modulating signal f(t) consisting of three frequency is given by :

f (t) = E1 cos ω1t + E2 cos ω2t + E3 cos ω3t

Where   ω3 > ω2 > ω1 > and E1>E2>E3. The signal F (t) modulates a carrier ec = Ec dos wc t.

(i)  Derive an expression for AM wave.

(ii) Draw a signal-sided spectrum and find the bandwidth.

(b)     What is synchronous detection? Explain phase and frequency errors in synchronous detection of

AM-SC signal.

3. (a)    Find the expression for FM wave and define modulation index. Draw the spectrum and explaion

how modulation index affects bandwidth.

(b)     How FM signal can be generated with PM signal? Discuss in detail

4. (a)    Draw the block diagram of superhetrodyne receiver and explain each block in detail.

(b)      Explain quantization of signal. What is signal to Quantization noise ratio for PCM system? How

it can be improved effectively?

5. (a)    Explain PCM technique . Explain Why PCM is noice resistant than other form of pulse

Modulation.

(b)   Draw the schematic diagram of a delta modulation system and explain its working. What is its

Limitation and how are they overcome?

6. (a)      Explain the generation  and reception of BSPK scheme

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

7. (a)    Show that the entropy is maximum when all the message are equiproble.

(b)    Apply Shannon-fano coding producer to find the coding efficiency for the following message

ensemble:

[X] = [ X1 X2 X3 X4  X5 X6 X7  ]

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

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

(i)  Envelope detector

(ii) Companding.

(iii) Comparison of AM and FM system

(iv) SNR in SSB system

(v) DPCM

(Vi) Pre-emphasis and De-emphasis.