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Need clarification about FM demodulation

  1. Sep 19, 2009 #1
    For the Frequency modulation the carrier frequency will change with respect to data. but i need to transmit the modulated carrier at 93.5MHz means what i need to do.
  2. jcsd
  3. Sep 19, 2009 #2
    The carrier frequency can be generated by a VCO (voltage controlled oscillator), all you have to do is to vary its tuning voltage very slightly.
  4. Sep 19, 2009 #3


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    93.5 MHz is the "quiet" frequency of the carrier without any modulation on it.

    When there is speech or music, this frequency varies but only over a very small percentage of the carrier frequency.

    It may vary up to 100 KHz which is only 0.1% of the carrier frequency.

    The frequency variation with modulation is centred about the carrier frequency so it swings up and down by equal shifts.
  5. Sep 20, 2009 #4
    From the fig the data 01010 is modulated in a carrier ( carrier frequency is X MHz).Based on the data '1' the carrier frequency changed to Y MHz. Then how it is possible to transmitte the modulated carrier in a single frequency.

    Attached Files:

    Last edited: Sep 20, 2009
  6. Sep 20, 2009 #5


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    The frequency does move, but only by a small amount.

    A data "0" may be 93.500 MHz while a data "1" may be 93.501 MHz.

    This is called Frequency Shift Keying (FSK). In this case, the shift would be 1 KHz.

    It could be shifted further, but there might be other signals nearby and if less shift is used, then there can be more signals in the same spectrum portion.
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