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Fourier spectrum problem

  1. Jun 30, 2013 #1
    1. The problem statement, all variables and given/known data

    I am trying to figure out how to graph the signal spectra of an AM signal where the message m(t) is multiplied by the carrier, which is sin^3 (wt) instead of cos (wt). I can do the FT but I do not know how to graph this since there are imaginary numbers as coefficients

    Also, I do not know how to do the fourier transform of say sin(3x). You get to this point:

    kj/8 ∫m(t) e^-j6pi(f-f0)t dt what do I do with the 6pi???

    2. Relevant equations

    Euler's identity for sin(x), sin^3(x) = (3/4)sin(x) - (1/4)sin(3x)

    y(t), the output, = km(t)sin^3(ωt)

    3. The attempt at a solution

    Using these two equations I have found the FT of the signal to be as follows:

    Y(f) = -[((3kj)/8)F(f-f0) + ((3kj)/8)F(f+f0)] + F{ the sin(3x) function, which IDK how to do!}

    Just dont know how to graph that or get the second portion of the answer. Thanks
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Jul 1, 2013 #2

    rude man

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    Gold Member

    I don't see how you can graph anything if you're not given what m(t) is. Such as m(t) = m0 sin(w0t)?
     
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