# Analog and Digital Communication 2007

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

Note: Attempt any five questions.

All question carry equal marks.

All parts of the question should be attempted at the one place.

1.(a)    Show that a normalized Gaussian pulse is its own Fourier transforms.

(b)      Prove that a Dirac comb is its own Fourier transforms.

2.(a)   with the help of block diagram explain the phase discrimination method of VSB generation. Also

Discuss VSB is better then SSB.

(b)      An amplitude modulated signal is given by:

ФAM (+) =10 cos (2π × 2 106 t) 4 cos (2π × 2 106 t). cos

(2π ×103 t)+ 5 cos (2π × 2 106 t). cos (4π ×106 t) volts

(i)      Find the various frequency components and the corresponding modulates indices.

(ii)     Draw the line spectrum

(iii)    Determine the carrier power and the sideband power.

(iv)    Efficiency of AM signal

3. (a)  Determine the expression of wide band FM . Show that if the modulation index is less than 0.6

Than wave generated is a narrow band FM wave. Also calculate the power of the FM signal.

Discuss by the efficiency of the FM signal is 100 % when   mg = 2.4,  5.52.

(b )    A modulate signal 5 cos 2π 15× 103 t, angle modulates a carrier A cos ωct. Find the modulation

Index and the bandwidth for FM and PM system. Assume kp = kg =15 kHzvolt.

4. (a)   Discuss flat top sampling What is aperture effect and how it could be overcome.

(b)      Explain the principle of delta modulation. Discuss why Delta modulation is not a practical

Alternative to PCM.

5. (a)   A continuous signal is band limited to 5kHz . The signal is quantized in level of a PCM system with

The probabilities 0.25, 0.2, 0.2, 0.1, 0.1, 0.05, 0.05, and 0.05, calculate the rate of information.

(b)    Find the mutual information for the channel shown in below figure. ©     What is the difference between mutual information and channel capacity? What is the redundancy

of the channel?

6. (a)   Explain the generation and detection of BPSK signal . Discuss why interchannel and intersymbol

Inferences are pronoused in BPSK.

7. (a)  Apply Shannon fano coding procedure for the following message ensemble . Also determine the

efficiency

[X] = [ X1, X2, X3, X4,  X5, X6, X7  ]

[P] = [0.4 0.20 .12 0.08 0.08 0.08 0.04]

Take M = 2.

(b)  Consider a(7,4) block code generated by :

1 0 0 0     :    110

G=    0  1 0 0     :    011

0  0 1 0     :   101

0  0  0 1   :     111

Explain how the error syndrome is help in correcting a single error.

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

(i)  Matched filter

(ii) Difference between AM and PM signal

(iii)  SRN in SSB signal.