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ECE :: Communication Systems

  1. In telephone systems the relation between load r, number of calls initiated during a specified interval λ and average duration of a call (h) is

  2. A.
    r = λh
    B.
    r = λh2
    C.
    λ = rh
    D.
    h = λr

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  3. In a Vidicon camera tube

  4. A.
    grid G1 accelerates electrons
    B.
    grid G2 accelerates electrons and grid G3, slows down electrons
    C.
    grid G3 accelerates electrons and grid G2 slows down electrons
    D.
    both grids G2 and G3 accelerate electrons

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  5. In a CD the sampling frequency is nearly

  6. A.
    half the highest frequency in audio signal
    B.
    equal to highest frequency in audio signal
    C.
    double the highest frequency in audio signal
    D.
    four times the highest frequency in audio signal

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  7. Consider the following statements about loop antenna

    1. It is suitable for direction finding application
    2. It is a single turn or multiturn coil carrying RF current
    3. The loop is surrounded by a magnetic field everywhere perpendicular to the loop
    Which of the above statements are correct?

  8. A.
    1 and 2 only
    B.
    1 only
    C.
    1, 2, 3
    D.
    2 and 3 only

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  9. Which of the following is present in both TRF receiver and superheterodyne receiver?

  10. A.
    Detector
    B.
    Mixer
    C.
    IF amplifier
    D.
    Local oscillator

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  11. The number of channels in a stereophonic system is

  12. A.
    8
    B.
    4
    C.
    2
    D.
    1

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  13. When the carrier is unmodulated, a certain transmitter radiates 9 kW when the carrier is sinusoidally modulated the transmitter radiates 10.125 kW. The modulation index will be

  14. A.
    0.1
    B.
    10.15
    C.
    0.4
    D.
    0.5

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  15. A signal x(t) = 100 cos (24p x 103t) is ideally sampled with a sampling period of 50 μ sec and then passed through an ideal low pass filter with cut off frequency of 15 kHz Which of the following frequencies are present at the filter output?

  16. A.
    12 kHz only
    B.
    8 kHz only
    C.
    12 kHz and 9 kHz
    D.
    12 kHz and 8 kHz

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  17. A sinusoidal voltage of 2 kV peak value is amplitude modulated to give 20% modulation. The peak value of each side band term is

  18. A.
    400 V
    B.
    200 V
    C.
    100 V
    D.
    800 V

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  19. Consider the following reasons for using antenna coupler

    1. To prevent illegal radiation of spurious frequencies
    2. To tune out reactive components of antenna impedance
    3. To have correct value of load impedance for transmitter.
    Which of the above are correct?

  20. A.
    1, 2, 3
    B.
    1, 2
    C.
    1 only
    D.
    2, 3

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