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ECE :: Communication Systems

  1. In AM receiver the oscillator frequency is

  2. A.
    always equal to signal frequency
    B.
    always equal to 455 kHz
    C.
    always higher than signal frequency
    D.
    always lower than signal frequency

  3. The modulation index of an AM wave is measured using a CRO. The waveform is as shown in figure, the modulation index is nearly

  4. A.
    43%
    B.
    30%
    C.
    23%
    D.
    17%

  5. A photo diode converts light signals to binary.

  6. A.
    True
    B.
    False

  7. A three stage telephone switching structure is to have 128 input and 128 output terminals. It has been found that at peak time the utilization probability is 0.1. The number of intermediate links required for non-blocking configuration is 15. If the actual number of intermediate links is 5, the probability of blocking of call is

  8. A.
    1%
    B.
    0.5%
    C.
    0.2%
    D.
    0.1%

  9. In pulse code modulation, if the signal is sampled at the rate of f and the number of pulses in one code group is p, then the number of pulses per second will be

  10. A.
    p/f
    B.
    f/p
    C.
    1/pf
    D.
    pf

  11. A narrow band FM does not have the following feature

  12. A.
    it has two sidebands
    B.
    both sideband equal in magnitude
    C.
    both sideband have same Phase Difference
    D.
    it does not show Amplitude variation

  13. When number of quantization levels are two, then the average transmission power in NRZ polar signalling is __________ that of NIRZ unipolar signalling.

  14. A.
    B.
    C.
    D.
    None

  15. In telecast

  16. A.
    video and audio signals are frequency modulated
    B.
    video signals are frequency modulated but audio signals are amplitude modulated
    C.
    both audio and video signals are amplitude modulated
    D.
    video signals are amplitude modulated and audio signals are frequency modulated

  17. A pulse width signal can be governed by

  18. A.
    free running multi-vibrator
    B.
    monostable multi-vibrator
    C.
    Schmitt trigger
    D.
    JK flip-flop

  19. In MTI radar, clutter means

  20. A.
    echos from moving targets
    B.
    echos from stationary targets
    C.
    atmospheric noise
    D.
    thermal noise