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Q.1
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.2
For telegraphy the most commonly used modulation system is
FSK
Two tone modulation
PCM
Single tone modulation
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
Under ordinary circumstances, impulse noise can be reduced in
FM only
AM only
Both AM and FM
None of the above
Q.5
Which of the following is used to generate PDM?
Free running multi-vibrator
Monostable multi-vibrator
JK flip-flop
Schmitt trigger
Q.6
In case of frequency modulation, modulating voltage remains constant if the modulating frequency is lowered, then
Amplitude of distant sidebands decreases
Amplitude of distant sidebands increases
Amplitude of distant sidebands remains constant
Amplitude of distant sidebands first increases, then decreases
Q.7
Full duplex operation permits transmission in both directions at the same time.
True
False
Q.8
A zero mean white Gaussian noise is passed through an ideal low pass filter of bandwidth 10 kHz. The output of the samples so obtained would be
Correlated
Statistically independent
Uncorrelated
Orthogonal
Q.9
A three stage telephone switching structure is to have 128 input and 128 output terminals. There are 16 first stage and 16 third stage matrices. To avoid blocking the number of intermediate paths required is
16
15
8
1
Q.10
For a low level AM system, the amplifiers modulated stage must be
Linear devices
Harmonic devices
Class C amplifiers
Non-linear devices
Q.11
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.12
The colour of an object is decided by
The reflected colour
The wavelength transmitted through it
Reflected colour for opaque object and wavelength transmitted through it for transparent objects
None of the above
Q.13
Commercial Frequency deviation of FM is
70 kHz
75 kHz
80 kHz
65 kHz
Q.14
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.15
A cordless telephone using separate frequencies for transmission in base and portable units is known as
Duplex arrangement
Half duplex arrangement
Either A or B
Neither A nor B
Q.16
In TV systems, equalising pulses are sent during
Horizontal blanking
Vertical blanking
Serrations
Horizontal retrace
Q.17
For a given carrier wave, maximum undistorted power is transmitted when value of modulation is
1
0.8
0.5
0
Q.18
The modulation index of an FM is changed from 0 to 1. How does the transmitted power change?
Gets halved
Gets doubled
Gets increased by 50 percent
Remains unchanged
Q.19
To eliminate ghosts in the picture
Use a longer transmission line
Connect a booster
Change the antenna orientation of location
Twist the transmission line
Q.20
Circular polarization
Is useful in reducing depolarization effect on received wave
Involves critical alignment of transmitting and receiving antenna
Is useful in discrimination between reception of adjacent beams
None of the above
Q.21
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.22
VSB modulation is preferred in TV because
It reduces the bandwidth requirement to half
It avoids phase distortion at low frequencies
It results in better reception
None of the above
Q.23
Which of the following is a digital modulation technique?
PCM
PSK
DM
All
Q.24
Assertion (A): In FM the frequency of the carrier is varied by the modulating voltage
Reason (R): FM and PM are two forms of angle modulation.
Both A and R are correct and R is correct explanation of A
Both A and R are correct but R is not correct explanation of A
A is correct but R is wrong
A is wrong but R is correct
Q.25
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.26
If in a broadcasting studio, a 1000 kHz carrier is modulated by an audio signal of frequency range 100-5000 kHz, the width of channel is __________ kHz.
5
4.9
995
10
Q.27
In Modulation, “carrier” is
Resultant wave
Speech voltage to be transmitted
Voltage with constant frequency, phase or amplitude
Voltage for which frequency, phase or amplitude is varied
Q.28
Which one of the following is analog?
PCM
PWM
Delta modulation
Differential PCM
Q.29
PAM stands for
Pulse Analogue Modulation
Phase Analogue Modulation
Pulse Amplitude Modulation
Phase Amplitude Modulation
Q.30
A telephone channel requires a bandwidth of about
1 kHz
3 kHz
10 kHz
50 kHz
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