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ECE :: Communication Systems

  1. For an antenna of height ht metres, the radio horizon is equal to

  2. A.
    4ht metres
    B.
    4ht km
    C.
    2.5ht km
    D.
    2.5ht metres

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  3. If in a radio receiver, RF signal has a frequency of 800 kHz and local oscillator that of 1000 kHz, then at the output of the mixer, the frequencies found would be __________ kHz.

  4. A.
    800 to 1000
    B.
    200, 800, 1000, 1800
    C.
    only 200
    D.
    only 1800

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  5. In the stabilized reactance modulator AFC system

  6. A.
    phase modulation is converted into amplitude modulation by the equalizer circuit
    B.
    the discriminator frequency must not be too low or the system will fail
    C.
    the discriminator must have a fast time constant to prevent demodulation
    D.
    the higher discriminator frequency, better the oscillator frequency stability

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  7. In AM, the modulation envelope has a peak value double the unmodulated carrier level, when the modulation is

  8. A.
    25%
    B.
    33%
    C.
    50%
    D.
    100%

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  9. Which of the following is correct (FDM means Frequency Division Multiplexing and TDM means Time Division Multiplexing)?

  10. A.
    FDM requires lower bandwidth but TDM has more noise immunity
    B.
    FDM has more noise immunity and requires lower bandwidth than TDM
    C.
    FDM requires channel synchronization while TDM has more noise immunity
    D.
    FDM requires more multiplexing while TDM requires band pass filter

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  11. Consider the following applications/ advantages of radar beacons

    1. navigation
    2. target identification
    3. accurate tracking of enemy targets
    4. large increase in maximum range
    Which of the above are correct?

  12. A.
    1, 2, 3, 4
    B.
    1, 2, 4
    C.
    1, 2
    D.
    2, 3, 4

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  13. The signal plate of vidicon tube is coated with tin oxide.

  14. A.
    True
    B.
    False

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  15. The maximum permissible distance between two samples of a 10 kHz signal

  16. A.
    100 μ sec
    B.
    50 μ sec
    C.
    10 μ sec
    D.
    none

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  17. In telephone systems, load is expressed in the unit of

  18. A.
    erlangs
    B.
    decibels
    C.
    bells
    D.
    watts

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