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ECE :: Communication Systems

  1. A pre-emphasis circuit provides extra noise immunity by

  2. A.
    converting the phase modulation of FM
    B.
    preamplifying the whole audio band
    C.
    amplifying the higher audio frequencies
    D.
    boosting the pass frequencies

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  3. The ratio for 100% amplitude modulation with identical total transmitted power (mf is modulation index of FM) is

  4. A.
    mf2
    B.
    m2f
    C.
    mf3
    D.
    m3f

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  5. The function of a modulator is to

  6. A.
    separate two frequencies
    B.
    extract information from the carrier
    C.
    amplify the audio frequency signal
    D.
    impress the information on to a RF carrier

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  7. Which of the following radio waves are not reflected by ionosphere?

  8. A.
    Waves above 1 kHz
    B.
    Waves above 1 MHz
    C.
    Waves above 10 MHz
    D.
    Waves above 30 MHz

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  9. Square law modulators utilise

  10. A.
    linear range of V-I characteristics of a diode
    B.
    linear range of V-I characteristics of a triode
    C.
    non-linear region of V-I dynamic characteristics of a diode
    D.
    non-linear region of V-I dynamic characteristics of a triode

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  11. Which of the following is a disadvantage of Vestigial Sideband (VSB) system?

  12. A.
    Low video frequencies are attenuated
    B.
    Bandwidth is conserved resulting in a saving of 2 MHz per channel over DSB system
    C.
    It results in a power boost of two video frequencies
    D.
    It possess the advantages of both DSB and SSB system

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  13. The maximum permissible distance between two samples of a 2 kHz signal is

  14. A.
    1000 μ sec
    B.
    500 μ sec
    C.
    250 μ sec
    D.
    2000 sec

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  15. When the video signal is applied to the picture tube in a TV receiver, the strength of video signal is about

  16. A.
    1000 V
    B.
    200 V
    C.
    50 V
    D.
    1 V

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  17. In the above case if the modulating frequency is increased to 20 kHz the bandwidth will be

  18. A.
    0.05 MHz
    B.
    1 MHz
    C.
    2 MHz
    D.
    4 MHz

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  19. Assertion (A): In FM all power amplifiers can be operated in class C

    Reason (R): FM is a constant amplitude modulation system.

  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

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