Communications Systems

15 Questions

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Communications Systems

Time: 30 Minute


Questions and Answers
  • 1. 
    The audio frequencies range from:
    • A. 

      20 Hz to 20,000 kHz

    • B. 

      20 Hz to 20 kHz

    • C. 

      20 kHz to 20,.000 kHz

    • D. 

      None of these

  • 2. 
    The length of a half wave dipole at 30 mega-hertz is:
    • A. 

      5 m

    • B. 

      10 m

    • C. 

      25 m

    • D. 

      80 m

  • 3. 
    A TV station transmits signals of 500 MHz. What is the wavelength used by the TV station?
    • A. 

      0.3 m

    • B. 

      0.6 m

    • C. 

      0.6 km

    • D. 

      None of these

  • 4. 
    A radio can tune to any station in the frequency range of7.5 MHz to 12 MHz band. The corresponding wavelength band is:
    • A. 

      40 m to 20 m

    • B. 

      80 m to 40 m

    • C. 

      40 m to 25 m

    • D. 

      80 m to 60 m

  • 5. 
    Calculate the phase velocity of electromagnetic wave having electron density and frequency for D layer, N = 40 electron/cc, v = 300 kHz:
    • A. 
    • B. 
    • C. 
    • D. 
  • 6. 
    When radio waves passes through ionosphere, phase difference between space current and capacitive displacement current is:
    • A. 

      0 rad

    • B. 

      (3π/2) rad

    • C. 

      (π/2) rad

    • D. 

      π rad

  • 7. 
    Which of the following frequencies will be suitable far beyond the horizon communication?
    • A. 

      10 kHz

    • B. 

      10 MHz

    • C. 

      1 GHz

    • D. 

      1000 GHz

  • 8. 
    Ozone layer above Earth’s atmosphere will:
    • A. 

      Prevent infrared radiations from sun reaching Earth.

    • B. 

      Prevent infrared rays reflected from Earth from escaping Earth’s atmosphere.

    • C. 

      Prevent ultraviolet rays from sun.

    • D. 

      Reflect back radio-waves.

  • 9. 
    Arrange the following communication frequency bands in the increasing order of frequencies: 1. AM Broadcast 2. Cellular mobile radio 3. FM Broadcast 4. Television UHF 5. Satellite communication
    • A. 

      1, 3, 4, 2, 5

    • B. 

      1, 2, 3, 4, 5

    • C. 

      5, 2, 4, 3, 1

    • D. 

      1, 3, 2, 4, 5

  • 10. 
    A radio-station has two channels. One is AM at 1020 kHz and other FM at 89.5 MHz. For good results you will use:
    • A. 

      Longer antenna for the AM channel and shorter for the FM

    • B. 

      Shorter antenna for the AM channel and longer for the FM

    • C. 

      Same length antenna will work for both

    • D. 

      Information given is not enough to say which one to use for which

  • 11. 
    The sky wve propagation is suitable for radio-waves of frequency:
    • A. 

      Upto 2 MHz

    • B. 

      From 2 MHz to 20 MHz

    • C. 

      From 2 MHz to 30 MHz

    • D. 

      From 2 MHz to 50 MHz

  • 12. 
    Given below is the circuit diagram of an AM demodulator. For good demodulation of AM signal of carrier frequency f, the value of RC should be:
    • A. 

      RC = 1/f

    • B. 

      RC < 1/f

    • C. 

      RC ≤ 1/f

    • D. 

      RC >> 1/f

  • 13. 
    A transparent solid cylindrical rod has a refractive index of  . It is surrounded by air. A light ray is incident at the mid–point of one end of the rod as shown in the figure. The incident angle θ for which the light ray grazes along the wall of the rod is:
    • A. 
    • B. 
    • C. 
    • D. 
  • 14. 
    If both the lens of an antenna and the wavelength of the signal to be transmitted are doubled, the power radiated by the antenna:
    • A. 

      Is doubled

    • B. 

      Is halved

    • C. 

      Increases 16 times

    • D. 

      Remains constant

  • 15. 
    A radar has a power of 1KW and is operating at a frequency of 10 GHz. It is located on a mountain top of height 500 m. The maximum distance upto which it can detect object located on the surface of the earth (Radius of the Earth = 6.4 X 106 m) is:
    • A. 

      80 km

    • B. 

      64 km

    • C. 

      40 km

    • D. 

      16 km