AM modulation: f<B

Discussion in 'The Projects Forum' started by antennaboy, Feb 26, 2012.

  1. antennaboy

    Thread Starter Active Member

    Jan 31, 2008
    45
    0
    Hello Forum,
    In AM modulation the carrier frequency f>>B where B is the bandwidth of the transmitted message signal m(t)....

    What would happen if f<B?

    AM modulation simply translates the spectrum B to f in frequency domain...

    thanks
    antennaboy
     
  2. MrChips

    Moderator

    Oct 2, 2009
    12,440
    3,361
    For any x and y,

    sin(x) sin(y) = ( cos(x-y) - cos(x+y) )/2.
     
  3. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
    782
    I've attached images of a normal AM signal [fc=1000Hz, fm=100Hz, 0.5 modulation index] with its FFT plot and the same for an abnormal signal in which the original carrier and modulation frequencies are simply swapped.

    As Mr Chips' comments suggest the sidebands are the same but the carrier is shifted down in the latter case - as you would likely expect. One would never consider transmitting a signal of the second type.
     
    Last edited: Feb 28, 2012
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