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ECE :: Communication Systems

  1. Consider the following statements as regards DPSK and DEPSK

    1. DPSK demodulator requires a device which operates at carrier frequency and provides a delay of bit time Tb
    2. In DPSK, synchronous demodulation recovers the signal b(t) and the decoding of b(t) to generate d(t) is done at base band
    3. In both DPSK and DEPSK errors always occur in pairs
    Which of the above statements are correct?

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

  3. An audio frequency of 5 kHz is translated to a radio frequency carrier of frequency 1 MHz and transmitted it to space through an antenna. The required height of antenna is

  4. A.
    150 m
    B.
    300 m
    C.
    75 m
    D.
    600 m

  5. Pre-emphasis circuit is used

  6. A.
    after modulation
    B.
    before modulation
    C.
    before detection
    D.
    after detection

  7. In which frequency range is the noise figure in a transistor minimum

  8. A.
    intermediate frequencies
    B.
    low frequencies
    C.
    high frequencies
    D.
    very high frequencies

  9. In commercial FM Broadcasting, A radio station transmitting the signal at 98.3 MHz, it is

  10. A.
    carrier frequency
    B.
    modulation frequency
    C.
    message frequency
    D.
    channel frequency

  11. The message carrying efficiency is best in

  12. A.
    AM
    B.
    FM
    C.
    AM-SC
    D.
    Phase modulation

  13. An SSB-AM signal cannot be demodulated by

  14. A.
    Balanced modulator
    B.
    Complete phase shift generator
    C.
    Diode balanced modulator
    D.
    Product detector

  15. Which of the following could be the equation for non-linear resistor shown in figure?

  16. A.
    a + be + ce2 + de3
    B.
    a - be - ce2 - de3
    C.
    a + be + ce2 - de3
    D.
    a + be - ce2 - de3

  17. The pre-emphasis circuit is used

  18. A.
    prior to modulation
    B.
    after demodulation
    C.
    for low frequency components of the signal
    D.
    none of the above

  19. The modulation index of wideband FM signal is

  20. A.
    less than unity
    B.
    unity
    C.
    greater than unity
    D.
    nearly 0.67