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Trying a MATLAB program for AM transmission, depth issues.

  1. Feb 20, 2013 #1
    Hi there;
    I am trying to make a MATLAB program to do an amplitude modulation on a biphasic pulse.

    The equation I am using is the following:

    Vout2(i)= (Vc/1000)*(1+(depth.*cos(2*pi*Fm*(i/carrier_freq)))).

    Where Fm is the modulating frequency,
    carrier_freq is the frequency of the carrier signal
    Vc is the carrier signal voltage

    There is a loop of 100 times around it.
    As you can see I am trying to save the voltage values in an array and I am trying to get
    the maximum and minimum values of the array.

    Then using the depth equation (Vmax-Vmin)/(Vmax+Vmin), I am trying to get the depth back to make sure that the equation is working properly.

    However, what I have noticed is that for different combination of Fm and carrier_freq, the depth is changing as well. For instance, if Fm is 200Hz and carrier_freq is 1200Hz @ a depth of 30%, I am getting 25.98% back from the program instead of 30% and from the oscilloscope, the depth is approximately 25%.
    But for values such as 100Hz Fm and 1200Hz carrier_freq, I am getting the 30% depth back both from the program and the oscilloscope.

    Why am I loosing the depth? I should be getting the 30% back right?

    I really appreciate your help.
  2. jcsd
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