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
0 h : 0 m : 1 s