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ECE :: Communication Systems

  1. Which is most important subsystem for recovering and reconstructing signal in a TDM system?

  2. A.
    Envelope detector followed by a low pass filter
    B.
    Synchronization ckt for proper timing
    C.
    Bandpass filter to segregate channels
    D.
    Coherent detector to ensure frequency and phase connection

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  3. Which one of the following is an indirect way of generating FM?

  4. A.
    Armstrong modulator
    B.
    Varactor diode modulator
    C.
    Reactance FET modulator
    D.
    Reactance bipolar transistor modulator

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  5. Companding is used in PCM to

  6. A.
    reduce bandwidth
    B.
    increasing S/N ratio
    C.
    get almost uniform S/N ratio
    D.
    increase bandwidth

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  7. Assertion (A): In AM the amplitude of carrier is made proportional to the instantaneous amplitude of modulating wave

    Reason (R): In AM, frequency of side band = frequency carrier ± frequency of modulating wave.

  8. A.
    Both A and R are correct and R is correct explanation of A
    B.
    Both A and R are correct but R is not correct explanation of A
    C.
    A is correct but R is wrong
    D.
    A is wrong but R is correct

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  9. Pressing a key on telephone set generates two frequencies. The basis for selection of these frequencies is

  10. A.
    the harmonics of one frequency should not be mistaken for the other frequency
    B.
    the audio input to the handset transmitter should not be mistaken for a key pressing
    C.
    both (a) and (b)
    D.
    neither (a) nor (b)

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  11. The orbital period of a geostationary communication satellite is

  12. A.
    12 hours
    B.
    24 hours
    C.
    36 hours
    D.
    48 hours

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  13. Which of the following is not true as regards communication receiver?

  14. A.
    It is exactly same as radio receiver used in households
    B.
    It can be used, besides communication, for detection in high frequency bridges
    C.
    It is designed to perform the task of low and high frequency reception better than in household receiver
    D.
    Its tuning and operation are more complicated than those in household receiver

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  15. Which of the following is the disadvantage of PDM and PPM?

  16. A.
    It requires pulses of larger widths
    B.
    More samples are needed per second
    C.
    More powerful transmitter is required
    D.
    None of the above

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  17. Frequency frogging is used in a carrier system to

  18. A.
    conserve frequencies
    B.
    reduce distortion
    C.
    reduce cross talk
    D.
    none of the above

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  19. TDM

  20. A.
    can be used with PCM only
    B.
    interleaves pulses belonging to different transmissions
    C.
    combines five groups into a super group
    D.
    stacks 24 channels in adjacent frequency slots

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