On 10/11/2014 05:38 PM, k1...@comcast.net wrote:
I can't wrap my head around why fft transform of complex signal produces a
complex output. After all the output reflects the amount of energy per
frequency bin and frequency bins and energy are both real numbers, no?
I'm trying to write a python script to analyze the energy across frequency
bins but I don't know where to insert a complex to mag block. I think if I can
understand the fft I will know to put the complex to mag.
The output of an FFT is complex because it contains magnitude _and_ phase. If
the output is I,Q (cartesian coordinates) then the magnitude is the length of
the vector from 0,0 to I,Q or sqrt(i^2 + q^2). The phase of the signal is
atan2(Q,I).
Note that the FFT transforms Voltage samples into Voltages per frequency bin.
When you say "energy" you may mean power which is the magnitude squared or (i^2
+ q^2).
jeff, wa1hco
Thanks
Brad.
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