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Sqaure Wave Fourier Transform question

  1. Nov 23, 2009 #1
    1. The problem statement, all variables and given/known data

    This is a question from a Physics Lab i recently completed. We used a function generator to provide a signal to a spectrum analyzer that performed a Fourier transform on the signal. In this case the signal was a square wave. When viewing the Fourier transform on a log scale, smaller peaks were being produced of a constant magnitude compared to the main Fourier peaks that incrementally dropped in magnitude. What do these smaller peaks correspond to?

    2. Relevant equations



    3. The attempt at a solution

    The only thing i can come up with is that the signal was not totally pure? I really dont understand Fourier transforms all that well.
     
  2. jcsd
  3. Nov 23, 2009 #2

    berkeman

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    Staff: Mentor

    Can you post shots of the square wave and the spectrum analyzer screen?

    (BTW, I may move this to Intro Physics; I'm not sure yet.)
     
  4. Nov 23, 2009 #3
    Cant post a picture unfortunately.

    I apologize if its in the wrong forum again, i didnt think Fourier transforms were introductory physics. I ran a search on Fourier and saw mostly advanced physics and calculus and beyond, so i thought this forum was acceptable.

    The base frequency was 100mhz, so the standard scale showed increasingly smaller peaks every 100mhz. The log scale showed more or less the same thing with the magnitude of the peaks decreasing but a different scale obviously, as well as peaks that remained at a constant magnitude, maybe 2/3 the magnitude of the largest main peak.
     
  5. Nov 23, 2009 #4

    berkeman

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    Staff: Mentor

    No worries about the forum. Could you maybe sketch the spectrum analyzer display and scan/post it? It's hard to speculate on the source of the other spectrum spikes without seeing their spacing, frequencies, etc.
     
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