Different FFT window effect on Amplitude at peak

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hashemi7102
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Different FFT window effect on Amplitude at peak

Post by hashemi7102 » Fri Dec 25, 2009 2:37 pm

Hi
by selecting different FFT windows, Amplitude at peak will differ.
Then by which window the measure is correct?
And why you don't normalize signal after windowing to get peak
in all windows like rectangular window?
with regards

PeterF
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Re: Different FFT window effect on Amplitude at peak

Post by PeterF » Sun Dec 27, 2009 1:36 pm

I am afraid that different types of spectrum plot will affect the amplitude at peak. That is normal by my understanding. If you disagree, then I will check with the designers when we are open again on the 4th January.
Regards,
PeterF.

hashemi7102
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Re: Different FFT window effect on Amplitude at peak

Post by hashemi7102 » Wed Dec 30, 2009 9:48 am

Hi
Thanx for reply.
I don't Have access to any other product to compare the peaks
but i have found this article:
http://www.tek.com/Measurement/App_Note ... 8815-2.pdf (i also atached it)
This is an aplication note for Tektronix TDS1000 oscilloscopes.
it's told in section 1.23 page 22 that "the TDS
oscilloscopes correct the FFT magnitude output data by a factor of 1/CG, where CG is the coherent gain
of the window"

Also i have another question:
The FFT size can be changed, if size is bigger or less than
scope memory , which part of data is choosed for FFT?
Attachments
55W-8815-2.pdf
(384.45 KiB) Downloaded 230 times

PeterF
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Re: Different FFT window effect on Amplitude at peak

Post by PeterF » Fri Jan 15, 2010 8:54 am

Hi,
The FFT is carried out by the PicoScope6 program, on a live signal, using the PC resources and memory. It is not dependant on the scope buffer memory.
Regards,
PeterF.

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