[oc] New! FFT core, transform gain issue

[h.larsen@risoe.dk]

Hi,

I have tested the cfft core, but found that the gain is 29.4 both in N=1024
FFT and IFFT, whereas the documentation says it should be 0.0287 in FFT
mode, and 29.4 in IFFT mode. 

I simply supply a real ampliude of a sine wave to the input of the
cfft1024X12: Something like->
Iin=A*sin(2pi*F*t) + DC; 
Qin=0; 

and measure the output amplitude (FFT or IFFT, no difference, except to
phase of output). It gives a peak at bin 0 of DC*29.4 and two peaks at the
proper bins with an amplitude of 14.7*A each, which makes sense only if the
gain is 29.4=14.7*2 (two bins).

Anybody who have tried similar things? 

In particular a comment from the briliant designer ZHAO Ming would be very
welcome.

regards
henning larsen
Electronics des. engineer
Risoe national laboratory
Denmark
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