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Frequency Modulation Help

  1. May 10, 2016 #1
    1. The problem statement, all variables and given/known data

    A pure tone (sine) carrier signal of 440 Hz is frequency modulated by another sine wave of frequency 440Hz with an amplitude of 1760.
    (a) For the steady-state portion of the output signal generated by synthesis above, calculate: i) the deviation and ii) the Index of modulation.

    (b) For the steady-state portion of the output signal generated by synthesis above, calculate the frequency of the carrier and sideband partials.

    (c) For the steady-state portion of the output signal generated by synthesis above, and using the Bessel functions represented below, calculate relative amplitude of the carrier and sideband partials, allowing for aliasing.

    Could someone please advise me as to how I would go about working through this question?

    Thanks in advance
     
  2. jcsd
  3. May 10, 2016 #2

    BvU

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    Hello Mymla, :welcome:

    Please read the guidelines; we aren't supposed/allowed to help if no effort is made by the poster.

    In the mean time: check the numbers: modulating 440 Hz with 440 Hz ? 1760 whatkindathings ?
     
  4. May 10, 2016 #3
    1. The problem statement, all variables and given/known data
    A pure tone (sine) carrier signal of 440 Hz is frequency modulated by another sine wave with a frequency of also 440Hz. The amplitude of the modulating wave (The deviation) is 1760. The amplitude of the carrier is 1.
    (a) For the steady-state portion of the output signal generated by synthesis above, calculate: i) the deviation and ii) the Index of modulation.

    (b) For the steady-state portion of the output signal generated by synthesis above, calculate the frequency of the carrier and sideband partials.

    (c) For the steady-state portion of the output signal generated by synthesis above, and using the Bessel functions represented below, calculate relative amplitude of the carrier and sideband partials, allowing for aliasing.

    2. Relevant equations


    3. The attempt at a solution
    The deviation is 1760 as this is the amplitude of the modulator
    The index of modulation is the deviation/mod frequency = 1760/440 = 4


    Side bands = 440+fm, 440-fm, 440+2fm, 440-2fm, 440+3fm, 440-3fm……. As far as the deviation. (1760 above and below 440)
    So:
    First pair: 440+440 and 440-440
    Second Pair: 440+880 and 440-880
    Third pair: 440+1320 and 440-1320
    Forth pair: 440+1760 and 440-1760
    So we have side bands at: 880, 0, 1320, -440, 1760, -880, 2200, -1320

    This is where I get stuck. How do I work out the amplitudes of these. How does aliasing effect them?
     
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