Author Topic: FFT Function on oscilloscope -> basic spectrum analysis?  (Read 1212 times)

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chromesphere

FFT Function on oscilloscope -> basic spectrum analysis?
« on: March 05, 2013, 02:26:08 PM »
Once i get onto something, i wont let go :)

So i'm researching oscilloscopes and i saw on afrotechmods youtube video of an oscillocope it showed his oscilloscope could do a basic frequency analysis (is that what FFT means?).

(Skip to 4:15)


Do you have this function on your oscilloscope / do you use it?  I know its not going to be a replacement for a spectrum analyser, but i thought it might be ok for audio / guitar pedal stuff?  Also i know there are other options out there, pc software, pc oscilloscopes with built in spectrum analysers etc but im specifically interested in the frequency analysis feature of an oscilloscope.

EDIT: Just to clarify, the question is 'is FFT a basic sort of spectrum analyser?' and if so 'is it useful / do you use it?'.  Sorry my question wasnt clear.

Thanks for any help as always,
Paul
« Last Edit: March 05, 2013, 02:30:59 PM by chromesphere »
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amptramp

Re: FFT Function on oscilloscope -> basic spectrum analysis?
« Reply #1 on: March 05, 2013, 04:49:16 PM »
Yes, it is a form of frequency analysis.  FFT stands for Fast Fourier Transform which is a mathematical means of deriving frequencies from time-based waveforms.  The Fourier Transform has some symmetries that can be exploited to speed up processing and that is why it is called FAST Fourier Transform.

chromesphere

Re: FFT Function on oscilloscope -> basic spectrum analysis?
« Reply #2 on: March 05, 2013, 10:10:08 PM »
It will be interesting to see how useful it is when analysing a signal through a circuit.  Hopefully you can see the bandwidth in some detail.
Paul
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Seljer

Re: FFT Function on oscilloscope -> basic spectrum analysis?
« Reply #3 on: March 05, 2013, 11:18:37 PM »
Its also useful for spotting noise, particulary power supply noise where its at a constant frequency.

Another fun thing to do is to put white noise through a phaser and watch the notches move around.

Paul Marossy

Re: FFT Function on oscilloscope -> basic spectrum analysis?
« Reply #4 on: March 06, 2013, 10:09:38 AM »
I need to get a modern scope that will do these sorts of things. My o'scope is ancient.  :icon_redface:
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pickdropper

Re: FFT Function on oscilloscope -> basic spectrum analysis?
« Reply #5 on: March 06, 2013, 11:31:16 AM »
Try downloading the trial version of Spectra Plus.  You can do it on your computer with a sound card.

merlinb

Re: FFT Function on oscilloscope -> basic spectrum analysis?
« Reply #6 on: March 07, 2013, 01:48:32 AM »
One problem with the FFT display on most scopes is that the frequency axis is linear, not logarithmic, which makes frequency response plots look weird. The FFT function is mainly useful for examining the harmonic signature of waveforms, rather than frequency response.