Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Phase Spectrum

  1. Aug 12, 2010 #1

    I'm trying to understand how do i get the phase spectrum from a Fourier Transform. From this site


    this statement

    "The phase spectrum is usually calculated by taking the arctangent of the ratio of imaginary to real parts of the Fourier transform."

    Yeah, right. So, when i have a sum of functions that are Fourier Transforms, how do i know which is the real part and the imaginary part of the entire sum??????
  2. jcsd
  3. Aug 13, 2010 #2

    and the same with imaginary part. Does this answer the question, or I misunderstood something?
  4. Aug 13, 2010 #3
    it answer half of the things i asked. The unanswered part is how do i get the imaginary and the real parts of any fourier transform???
  5. Aug 13, 2010 #4
    I think I'm missing something. Ther real and imaginary part of a complex function are taken the same way you do for numbers... try giving an example so we can see where's the problem...
  6. Aug 13, 2010 #5
    i have this function

    [PLAIN]http://j.imagehost.org/0556/fun_ao_pre_trans_fourier.png [Broken]

    the fourier transform is

    [PLAIN]http://j.imagehost.org/0286/fun_ao_trans_fourier.png [Broken]

    now, how do i get the real and the imaginary parts??
    Last edited by a moderator: May 4, 2017
  7. Aug 13, 2010 #6
    Ah ok, the problem is then more about complex numbers than with Fourier transforms. You have to put the Fourier transform in the form a + jb, with a and b real numbers. Then a will be the real part and b the imaginary part. You go by steps:

    1) The exponential decomposes like


    2) The inverse of a complex number is


    3) Oh and finally recall that [tex]j^2=-1[/tex] !!!!!!!

    Using these 3 rules, you can, with a bit of patience, write your expression like a + jb. Try it yourself, if you don't get it we'll see.
  8. Aug 24, 2010 #7
    ok, but how do i do with the dirac function????
  9. Aug 25, 2010 #8
    Treat the delta function just like an ordinary real function.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: Phase Spectrum