Communication miscellaneous

Communication miscellaneous

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Communication

Communication miscellaneous
  1. Figure shows the Fourier spectra of signal x(t) the Nyquist sampling rate for the given function x(t) is—










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    The bandwidth of X(t) is 105 Hz = 100 kHz
    Nyquist sampling rate = 2fm = 200 kHz

    Correct Option: B

    The bandwidth of X(t) is 105 Hz = 100 kHz
    Nyquist sampling rate = 2fm = 200 kHz

  1. In respect of the block diagram shown in the figure below, the input power is 1 mW. The output power PO will be—










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    Here, decibel gain of a system consists of several subsystems in cascade. And the resultant gain will be the sum of decibel given of all the constituent sub systems.
    i.e. 10 – 6 + 2 – 6 = 0 dB
    It means the input and output power levels would be same since.
    given in

    dB = 10log10
    P0
    Pi

    or
    0 = 10log10
    P0
    Pi

    or
    100=
    P0
    Pi

    or
    or P0 = Pi = 1 mW
    Hence alternative (B) is the correct choice.

    Correct Option: B

    Here, decibel gain of a system consists of several subsystems in cascade. And the resultant gain will be the sum of decibel given of all the constituent sub systems.
    i.e. 10 – 6 + 2 – 6 = 0 dB
    It means the input and output power levels would be same since.
    given in

    dB = 10log10
    P0
    Pi

    or
    0 = 10log10
    P0
    Pi

    or
    100=
    P0
    Pi

    or
    or P0 = Pi = 1 mW
    Hence alternative (B) is the correct choice.

  1. One of the main functions of R.F. amplifier in a superheterodyne receiver is to—








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    The main function of R.F. amplifier in a superheterodyne receiver is to improve image frequency rejection.

    Correct Option: C

    The main function of R.F. amplifier in a superheterodyne receiver is to improve image frequency rejection.

  1. Six independent low pass signals of bandwidth 3ω, ω, ω, 2ω, 3ω, and 2ω Hz are to be time division multiplexed on a common channel using PAM. To achieve time, the minimum transmission bandwidth of the channel should be kHz—








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    The commutator in TDM (Time Division multiplication) has to be rotated a speed twice that of highest bandwidth i.e. 3ω × 2 = 6ω
    channel capacity = 2 x highest Bandwidth
    = 2 × 6ω Hz = 12ω Hz

    Correct Option: C

    The commutator in TDM (Time Division multiplication) has to be rotated a speed twice that of highest bandwidth i.e. 3ω × 2 = 6ω
    channel capacity = 2 x highest Bandwidth
    = 2 × 6ω Hz = 12ω Hz

  1. In a low-level AM system, the amplifier which follows the modulated stage must be the—








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    In a low-level AM system, the amplifier which follows the modulated stage must be the linear device.

    Correct Option: A

    In a low-level AM system, the amplifier which follows the modulated stage must be the linear device.