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ECE :: Communication Systems

  1. Fields are said to be circularly polarised if their magnitudes are

  2. A.
    equal and they are in phase
    B.
    equal but they differ in phase by ± 90°
    C.
    unequal and differ in phase by ± 90°
    D.
    unequal but are in phase

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  3. Three analog signals, having bandwidths 1200 Hz, 600 Hz, 600 Hz are sampled at their Nyquist rates, encoded with 12 bit words, and time division multiplexed. The bit rate for the multiplexed signal is

  4. A.
    115.2 kbps
    B.
    28.8 kbps
    C.
    57.6 kbps
    D.
    38.4 kbps

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  5. In a CD player the speed of CD is

  6. A.
    constant at 500 rpm
    B.
    constant at 200 rpm
    C.
    varies from 200 to 500 rpm
    D.
    none of the above

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  7. In the output of a DM speech encoder, the consecutive pulses are of opposite polarity during time interval t1 < t < t2. This indicates that during this interval

  8. A.
    the input to the modulator is essentially constant
    B.
    the modulator is going through slope overload
    C.
    the accumulator is in saturation
    D.
    the speech signal is being sampled at the Nyquist rate

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  9. A fascimile reproduction has a specification of 200 lines per frame, progressive scanning and 5 frames per second. The time to scan one line is

  10. A.
    5 ms
    B.
    2.5 ms
    C.
    1 ms
    D.
    0.1 ms

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  11. Consider the following features of monochrome TV

    1. Number of lines per picture 625
    2. Interlace ratio 2 : 1
    3. Aspect ratio 4 : 3
    4. Channel bandwidth 8 MHz
    As regards CCIR system B, which of the above are correct?

  12. A.
    1, 2, 3, 4
    B.
    1, 2, 3
    C.
    1, 2, 4
    D.
    2, 3, 4

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  13. In the absence of noise, if C is channel capacity in bits/s, δf is channel bandwidth in Hz and N is number of coding levels. Then

  14. A.
    C = log2 N
    B.
    C = (δf) log2 N
    C.
    C = 2 (δf) log2 N
    D.
    C = 0.5 (δf) log2 N

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  15. The open loop gain of an amplifier is 50 but is likely to change by 20%. If negative feedback with β = 0.1 is used, the change in gain will be about

  16. A.
    20%
    B.
    10%
    C.
    4%
    D.
    0.05%

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  17. Audio amplifiers need

  18. A.
    Bass control
    B.
    Treble control
    C.
    Both Bass and Treble control
    D.
    Either Bass or Treble control

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  19. The open loop gain of an amplifier is 200. If negative feedback with β = 0.2 is used, the closed loop gain will be

  20. A.
    200
    B.
    40
    C.
    4.878
    D.
    1.212

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