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Q.1
In Pulse Code Modulation system
Large bandwidth is required
Quantising noise can be overcome by companding
Quantising noise can be reduced by decreasing the number of standard levels
Suffers from the disadvantage of its incompatibly with TDM
Q.2
A modem is classified as low speed if data rate handled is
Upto 100 bps
Upto 250 bps
Upto 400 bps
Upto 600 bps
Q.3
The main function of a balanced modulator is to
Produce balanced modulation of a carrier wave
Produce 100% modulation
Suppress carrier signal in order to create a single-sideband or double sideband
Limit noise picked by a receiver
Q.4
Which of the following does not cause losses in optical fibre cables?
Stepped index operation
Impurities
Microbending
Attenuation in glass
Q.5
A buffer amplifier is
A double-tuned amplifier
A high gain amplifier
A cathode follower stage
None of the above
Q.6
Commercial Frequency deviation of FM is
70 kHz
75 kHz
80 kHz
65 kHz
Q.7
If output power of a radio receiver is doubled, its volume is increased by __________ dB.
2
3
1
-3
Q.8
Which of the following is used to generate PDM?
Free running multi-vibrator
Monostable multi-vibrator
JK flip-flop
Schmitt trigger
Q.9
When the length of antenna is a whole wavelength
The radiation at right angles is zero
The radiation at right angles is maximum
The radiation is zero in all directions
The radiation is maximum in all directions
Q.10
Which of the following is a digital modulation technique?
PCM
PSK
DM
All
Q.11
For telegraphy the most commonly used modulation system is
FSK
Two tone modulation
PCM
Single tone modulation
Q.12
The disadvantage of FM over AM is that
High output power is needed
High modulating power is needed
Noise is very high for high frequency
Large bandwidth is required
Q.13
A telephone channel requires a bandwidth of about
1 kHz
3 kHz
10 kHz
50 kHz
Q.14
Which of the following is an indirect way of generating FM?
Armstrong modulator
Varactor diode modulator
Reactance FET modulator
Reactance bipolar transistor
Q.15
One of the advantages of base modulation over collector modulation of a transistor class C amplifier is
Improved efficiency
Better linearity
High power output per transistor
The lower modulating power requirement
Q.16
The maximum power output of a standard A earth station over the total band allocated to satellite communication is about
0.5 kW
8 kW
20 kW
50 kW
Q.17
As per Shannon-Hartley theorem, a noise less Gaussian channel has
Zero capacity
Infinite capacity
Small capacity
None of the above
Q.18
An audio signal (say fromHz toHz) is frequency translated by a carrier having a frequency ofHz. The values of initial (without frequency translation) and final (after frequency translation) fractional change in frequency from one band edge to the other are
200 and 1.01
200 and 10.01
200 and 100.1
200 and 200
Q.19
Skip distance depends on time of day and angle of incidence.
True
False
Q.20
In practical commercial FM system, channel bandwidth is
150 kHz
100 kHz
88 MHz
108 MHz
Q.21
If sampling is done at the rate ofkHz. The bandwidth required is
35 kHz
70 kHz
10 kHz
1280 kHz
Q.22
In EM waves, polarization
Is always vertical in an isotropic medium
Is caused by reflection
Is due to transverse nature of waves
Results from longitudinal nature of waves
Q.23
It is found that a ship to ship communication suffers from fading. This can be avoided by using
Space diversity
Frequency diversity
Broad band antenna
Directional antenna
Q.24
An FM radio receiver which is tuned to a 91.6 MHz broadcast station may receive an image frequency of __________ MHz.
102.3
113
70.2
80.9
Q.25
In case of low level amplitude modulation system, the amplifiers following the modulated stage must be
Class C amplifiers
Linear devices
Non-linear devices
Harmonic devices
Q.26
For a low level AM system, the amplifiers modulated stage must be
Linear devices
Harmonic devices
Class C amplifiers
Non-linear devices
Q.27
A three stage telephone switching structure is to haveinput andoutput terminals. There arefirst stage andthird stage matrices. To avoid blocking the number of intermediate paths required is
16
15
8
1
Q.28
A zero mean white Gaussian noise is passed through an ideal low pass filter of bandwidthkHz. The output of the samples so obtained would be
Correlated
Statistically independent
Uncorrelated
Orthogonal
Q.29
Under ordinary circumstances, impulse noise can be reduced in
FM only
AM only
Both AM and FM
None of the above
Q.30
In a FM receiver, amplitude limiter
Amplifiers low frequency signals
Reduces the amplitude of signals
Eliminates any change in amplitude of received FM signals
None of the above
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