# RGPV Question Papers -BE IV SEM – Analog and Digital Communication – Common for All – 2002

B.E. (fourth semester) EXAMINATION, Dec, 2002

(Common for EE,ELET,IT & CS)

ANALOG AND DIGITAL COMMUNICATION

(CS-4503)

Note:   Attempt any five questions. Answer to all part of a question should be attempted together.

Assume suitable value for missing data if any.

(a)        Define the Fourier transfourm of a time dependent signal x(t) and how will you find the inverse

Fourier transform of the function X(w) ?

(b)        Determine the Fourier transform of the following function:

(i)     x(t)= a  for  -T2 <= t <= T2

=0 for all other value of t.

(ii)    x(t)= sin Ωmt.

2.(a)      If g(t) is obtained by involving by x(t) and h(t) i.e., g(t) =*n(t) and G(Ω),X(Ω) and H(Ω) be

The Fourier transfourm of the function g(t) and h(t) respectively . The prove that:

G(Ω) = H(Ω). X(Ω)

(b)          What is Dirac delta function? What is its Fourier transform?

3.(a)       For a modulating signal band limited to 8kHz What is the tramission band width of a narrow

Band FM signal ? For the same modulating signal, what will be the transmissions band width of

a band FM signal with a modulating  index of 4 ?

(b)          Consider an FM  system where the modulating signal is a sinusoid of ±2 volts peak to peak at

a frequency of 20 kHz . The modulator has a frequency sensitivity of 50kHz volt. Determine the

Significant band width of the FM signal using crayon’s rule. is thr MBFM or WFBM.

4.(a)        Why band pass limiter is frequency in FM discriminator (demodulator)?

(b)           Explain the use of “pre-emphases” and “De –emphases” circuits in a FM system.

5.(a)        What are the process involved in PCM ? State advantages and disadvantages when compared

With other pulse modulation system.

6.(a)        Let x be a random variable with uniform probability density function in the interval (-1,1.)

Determine the variable of x.if y=x2 , Determine the wheater x and y are uncorrelated.

(b)           Write down the expression for FSK, PSK and QPSK  signals.

7.(a)        Explain the terms (i) entropy of a discrete information (ii) Redundancy (iii) Coding efficiency.

(b)           State and prove Shannon’s theorem for channel capacity. What do you understand by Binary

Symmetric Channel (BSC) ?

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

(a)            Error correcting codes.

(b)            Poisson’s Distribution