M.Sc. (Semester (CBCS) Examination Nov/Dec-2018
Electronics Science
COMMUNICATION SYSTEMS
Time: 2½ Hours Max. Marks: 70
Instructions: All questions are compulsory.
All questions carry equal marks.
Q.1 Multiple choice questions. 14
The bandwidth of AM system
fm 0.5 fm
2 fm 4 fm
If the carrier of a 100 percent modulated AM wave is suppressed, the
percentage power saving will be
50 150
100 66.66
The carrier is simultaneously modulated by two sine wave with the modulation
indices of 0.3 and 0.4; the total modulation index
is 1 is 0.4
is 0.5 is 0.7
One of the following cannot be used to remove unwanted sideband in SSB.
This is the
Filter system Phase shift method
Third method Balance modulator
An FM signal with a modulation index mf is passed through the frequency
tripler. The wave in the output of the Tripler will have a modulation index of
mf/3 mf
3mf 9mf
Indicate the false statement.
Modulation is used to
reduce the bandwidth used
separate the differing transmissions
ensure that intelligence may be transmitted over long distances
allow the use of practicable antennas
In the spectrum of a frequency modulated wave
the carrier frequency disappears when the modulation index is large
the amplitude of any sideband depends on the modulation index
the total number of sidebands depend on the modulation index
the carrier frequency cannot disappear
The most common modulation system used for telegraphy is
frequency shift keying two tone modulation
pulse code modulation single tone modulation
Indicate which of the following system is digital
Pulse position modulation Pulse code modulation
Pulse width modulation Pulse frequency modulation
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10) Quantizing noise occurs in
time division multiplex frequency division multiplex
pulse code modulation pulse width modulation
11) Scheme in which several channels are interleaved and then transmitted
together is known as
Frequency division multiplex Time division multiplex
A group A super group
12) Which of the following encoding methods does not provide for
synchronization?
RZ NRZ-L
NRZ-I Manchester
13) The minimum bandwidth of Manchester and differential Manchester is
that of NRZ.
the same as twice
thrice None of the above
14) Unipolar, bipolar, and polar encoding are types of
line block
NRZ Manchester
Q.2 Attempt the following (any Four) 08
Define sampling theorem.
Explain the need of modulation in communication system.
Explain the concept of modulation index and bandwidth in an FM system.
What is the significance of guard-time in multiplexing of PAM signals?
Explain Half Duplex System.
Write note on (Any Two) 06
What are the applications of spread spectrum? Explain any one briefly.
An amplitude modulated amplifier provides an output 106W at 100%
modulation. The internal loss in 20 W
What is the unmodulated carrier power?
What is sideband power?
Explain pre-emphasis and de-emphasis.
Q.3 Answer the following (Any Two) 08
Explain the diode detector for AM detection.
Explain the effect of random noise on the output of an FM receiver fitted
with an amplitude limiter.
Explain frequency shift keying.
Answer the following (Any One) 06
Draw and explain the high level modulated AM transmitter.
Draw and explain dual slope FM detector.
Q.4 Answer the following (Any Two) 10
Define multiplexing. Why it is necessary? Explain frequency division
multiplexing.
Explain BPSK and DPSK.
Explain the working of frequency hopping spread spectrum.
Answer the following (Any One) 04
Explain the CDMA technique.
Draw and explain the generation of PTM.
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Q.5 Answer the following (Any Two) 14
Calculate the percentage power saving when the carrier and one of the
sidebands are suppressed in an AM wave modulated to a depth of
100 percent and
50 percent
Find the carrier and modulating frequencies, the modulation index, and the
maximum deviation of the FM wave represented by the voltage equation
12 5 sin 1250 What power will this FM wave dissipate in a
10Ω resistor?
Explain synchronous and asynchronous time division multiplexing of PCM
signal.