Communication Systems MCQ

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• Commercial Frequency deviation of FM is
  ক

  70 kHz

  খ

  75 kHz

  গ

  80 kHz

  ঘ

  65 kHz
• In case of low level amplitude modulation system, the amplifiers following the modulated stage must be
  ক

  Class C amplifiers

  খ

  Linear devices

  গ

  Non-linear devices

  ঘ

  Harmonic devices
• For a low level AM system, the amplifiers modulated stage must be
  ক

  Linear devices

  খ

  Harmonic devices

  গ

  Class C amplifiers

  ঘ

  Non-linear devices
• Under ordinary circumstances, impulse noise can be reduced in
  ক

  FM only

  খ

  AM only

  গ

  Both AM and FM

  ঘ

  None of the above
• When the length of antenna is a whole wavelength
  ক

  The radiation at right angles is zero

  খ

  The radiation at right angles is maximum

  গ

  The radiation is zero in all directions

  ঘ

  The radiation is maximum in all directions
• In a FM receiver, amplitude limiter
  ক

  Amplifiers low frequency signals

  খ

  Reduces the amplitude of signals

  গ

  Eliminates any change in amplitude of received FM signals

  ঘ

  None of the above
• PAM stands for
  ক

  Pulse Analogue Modulation

  খ

  Phase Analogue Modulation

  গ

  Pulse Amplitude Modulation

  ঘ

  Phase Amplitude Modulation
• Which of the following is a digital modulation technique?
  ক

  PCM

  খ

  PSK

  গ

  DM

  ঘ

  All
• The colour of an object is decided by
  ক

  The reflected colour

  খ

  The wavelength transmitted through it

  গ

  Reflected colour for opaque object and wavelength transmitted through it for transparent objects

  ঘ

  None of the above
• Full duplex operation permits transmission in both directions at the same time.
  ক

  True

  খ

  False
• In case of frequency modulation, modulating voltage remains constant if the modulating frequency is lowered, then
  ক

  Amplitude of distant sidebands decreases

  খ

  Amplitude of distant sidebands increases

  গ

  Amplitude of distant sidebands remains constant

  ঘ

  Amplitude of distant sidebands first increases, then decreases
• The main function of a balanced modulator is to
  ক

  Produce balanced modulation of a carrier wave

  খ

  Produce 100% modulation

  গ

  Suppress carrier signal in order to create a single-sideband or double sideband

  ঘ

  Limit noise picked by a receiver
• For telegraphy the most commonly used modulation system is
  ক

  FSK

  খ

  Two tone modulation

  গ

  PCM

  ঘ

  Single tone modulation
• The maximum power output of a standard A earth station over the total band allocated to satellite communication is about
  ক

  0.5 kW

  খ

  8 kW

  গ

  20 kW

  ঘ

  50 kW
• For a given carrier wave, maximum undistorted power is transmitted when value of modulation is
  ক

  1

  খ

  0.8

  গ

  0.5

  ঘ

  0
• In TV systems, equalising pulses are sent during
  ক

  Horizontal blanking

  খ

  Vertical blanking

  গ

  Serrations

  ঘ

  Horizontal retrace
• A cordless telephone using separate frequencies for transmission in base and portable units is known as
  ক

  Duplex arrangement

  খ

  Half duplex arrangement

  গ

  Either A or B

  ঘ

  Neither A nor B
• For a plate-modulated class C amplifier the plate supply voltage is E. The maximum plate cathode voltage could be almost high as
  ক

  2E

  খ

  3E

  গ

  4E

  ঘ

  6E
• In Modulation, “carrier” is
  ক

  Resultant wave

  খ

  Speech voltage to be transmitted

  গ

  Voltage with constant frequency, phase or amplitude

  ঘ

  Voltage for which frequency, phase or amplitude is varied
• Circular polarization
  ক

  Is useful in reducing depolarization effect on received wave

  খ

  Involves critical alignment of transmitting and receiving antenna

  গ

  Is useful in discrimination between reception of adjacent beams

  ঘ

  None of the above
• To eliminate ghosts in the picture
  ক

  Use a longer transmission line

  খ

  Connect a booster

  গ

  Change the antenna orientation of location

  ঘ

  Twist the transmission line
• In a TV receiver antenna the length of reflector rod
  ক

  Is the same as that of dipole

  খ

  Is less than that of dipole

  গ

  Is more than that of dipole

  ঘ

  May be equal, more or less than that of dipole
• As per Shannon-Hartley theorem, a noise less Gaussian channel has
  ক

  Zero capacity

  খ

  Infinite capacity

  গ

  Small capacity

  ঘ

  None of the above
• VSB modulation is preferred in TV because
  ক

  It reduces the bandwidth requirement to half

  খ

  It avoids phase distortion at low frequencies

  গ

  It results in better reception

  ঘ

  None of the above
• The disadvantage of FM over AM is that
  ক

  High output power is needed

  খ

  High modulating power is needed

  গ

  Noise is very high for high frequency

  ঘ

  Large bandwidth is required
• For attenuation of high frequencies we should use
  ক

  Shunt capacitance

  খ

  Series capacitance

  গ

  Inductance

  ঘ

  Resistance
• If output power of a radio receiver is doubled, its volume is increased by __________ dB.
  ক

  2

  খ

  3

  গ

  1

  ঘ

  -3
• DVD uses
  ক

  Laser beam for both recording and playback

  খ

  Laser beam for recording and video head for playback

  গ

  Video head for recording and laser beam for playback

  ঘ

  None of the above
• In Pulse Code Modulation system
  ক

  Large bandwidth is required

  খ

  Quantising noise can be overcome by companding

  গ

  Quantising noise can be reduced by decreasing the number of standard levels

  ঘ

  Suffers from the disadvantage of its incompatibly with TDM
• A modem is classified as low speed if data rate handled is
  ক

  Upto 100 bps

  খ

  Upto 250 bps

  গ

  Upto 400 bps

  ঘ

  Upto 600 bps