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ECE :: Communication Systems

  1. Human ear can detect sound intensities of the order of

  2. A.
    10-4 W/m2
    B.
    10-8 W/m2
    C.
    10-13 W/m2
    D.
    10-18 W/m2

  3. If output power of a radio receiver is doubled, its volume is increased by __________ dB.

  4. A.
    2
    B.
    3
    C.
    1
    D.
    -3

  5. Which of the following statements is correct?

  6. A.
    Convex lens has positive focal power and concave lens have negative focal power
    B.
    Convex lens has negative focal power and concave lens have positive focal power
    C.
    All lens have positive focal power
    D.
    All lens have negative focal power

  7. In Modulation, "carrier" is

  8. A.
    resultant wave
    B.
    speech voltage to be transmitted
    C.
    voltage with constant frequency, phase or amplitude
    D.
    voltage for which frequency, phase or amplitude is varied

  9. To eliminate ghosts in the picture

  10. A.
    use a longer transmission line
    B.
    connect a booster
    C.
    change the antenna orientation of location
    D.
    twist the transmission line

  11. Consider a sampled signal y(t) = 5 x 10-6 x(t) where x(t) = 10 cos (8p x 103)t and ts = 100 μ sec. when y(t) is passed through an ideal low-pass filter with a cut off frequency of 5 kHz, the output of the filter is

  12. A.
    5 x 10-6 cos (8p x 103)t
    B.
    5 x 10-5 cos (8p x 103)t
    C.
    5 x 10-1 cos(8p x 103)t
    D.
    10 cos(8p x 103)t

  13. The frequency range of 300 kHz to 3000 kHz is known as

  14. A.
    low frequency
    B.
    medium frequency
    C.
    high frequency
    D.
    very high frequency

  15. Which of the following does not cause losses in optical fibre cables?

  16. A.
    Stepped index operation
    B.
    Impurities
    C.
    Microbending
    D.
    Attenuation in glass

  17. For a low level AM system, the amplifiers modulated stage must be

  18. A.
    linear devices
    B.
    harmonic devices
    C.
    class C amplifiers
    D.
    non-linear devices

  19. Assertion (A): In FM the frequency of the carrier is varied by the modulating voltage

    Reason (R): FM and PM are two forms of angle modulation.

  20. 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