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 »

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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Joined: Thu Jun 07, 2007 10:53 am
Location: Cambridgeshire

Re: Different FFT window effect on Amplitude at peak

Post by PeterF »

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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Joined: Fri Dec 25, 2009 2:25 pm

Re: Different FFT window effect on Amplitude at peak

Post by hashemi7102 »

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 510 times

PeterF
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Location: Cambridgeshire

Re: Different FFT window effect on Amplitude at peak

Post by PeterF »

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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