# RGTU Exam Question Papers – CS, IT, EE, EI, IT & BM – IV SEM – Analog and Digital Communication

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 + t2 .

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

©      Find spectrum of ω (t) = sin 2 π f1t. sin 2 π f2t.

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 Vc cos ωc t is modulated by a signal tone modulating signal:

F (t) = Vm cos ωm 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 106 t is modulated by signal:

F(t) = 2cos 104 2π t + 6cos 103 2π t + 5cos 105 2π t

Find the bandwidth of the FM signal and FM signal assume

Kf =103 × 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

(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 200c.

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