M.Sc. (Electronic Science) (Semester
(CBCS) Examination, 2017
COMMUNICATION SYSTEM
Day Date: Saturday, 22-04-2017 Max. Marks: 70
Time: 10.30 AM to 01.00 PM
N.B. Attempt five questions.
Q and are compulsory.
Attempt any three from Q.3 to Q.7.
Use of non programmable calculator.
Q.1 Choose the most correct alternative: 08
The most suitable method for detecting a modulated signal
to cos 2Xfmt) cos 2Xfct is
Envelope detector Synchronous detector
Ratio detector Both a and b
When the number of quantising levels is 16 in PCM, the
number of pulses in a code group will be
3 4 8 16
24 telephone channels are frequency division multiplexed
using an SSB modulation. Assuming 3 kHz frequency per
channel, the required band width is ………….
8 kHz 27 KHz 21 KHz 72 KHz.
A 1000 kHz carrier is simultaneously modulated by 300 Hz and
2 kHz audio sine wave. Which of the following frequency will
not be present in the output?
998 kHz 999.7 kHz 1000.3 kHz 700 kHz
In an FM signal, the modulating frequency is 2KHz and
maximum deviation is 10KHz. The bandwidth requirement is

2 kHz 10 kHz 5 kHz 32 kHz
Noise can be measured by
D.C. voltmeter A.C. voltmeter
Either of the above None of the above
In TV transmitter, the function of duplexer is
To amplify video signal
To remove distortions in audio signal
To combine outputs of visual and audio transmitters
To amplify audio signal
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A 400 w carrier amplitude modulated with m=0.75. The total
power in AM is
400 W 512W 588W 650W
Q.1 State Truth/False 06
To separate channels in FDM receiver we have to use Band
pass filter.
An angle modulated signal is given by cos x 106t
30 sin 150t 40 cos 150t). The maximum frequency and
phase deviation of are 7.5 KHz and 100 p rad.
In a 100% amplitude modulated signal, the power in the upper
sideband when carrier power is to be 100 W and modulation
system SSBSC. is 50W.
For attenuation of low frequencies we should use series
capacitance.
The simplest method of suppression of unwanted side band in
AM is filter method.
24 telephone channels are frequency division multiplexed
using an SSB modulation. Assuming 3 kHz per channel, the
required band width is 21 KHz.
Q.2 Attempt the following: 14
Discuss the operation of Class B power amplifier. 05
Differentiate between TDM and FDM 05
Explain about RZ and NRZ codes. 04
Q.3 Explain the block diagram of low level modulated AM transmitter. 08
Draw the block diagram of AM receiver and explain each block. 06
Q.4 Explain the demodulation of an FM signal using dual slope
detector.
08
Explain the block diagram of PLL. 06
Q.5 Explain how cross talk can be eliminated in TDM. 08
Differentiate between PAM, PWM and PPM. 06
Q.6 Explain the modulation technique of BPSK signal. 08
Discuss in brief the various transmission modes. 06
Q.7 Explain the acquisition of a DS signal. 08
What is CDMA? Explain in detail.