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vrf fft

Question asked by VRFuser on May 10, 2006
Latest reply on May 10, 2006 by VRFuser
Hello,
 
As others have said:
1) If your scope has native fft functionality (in other words you can tell the scope to perform the fft), then you will need to find the command syntax to tell the scope to do this and then pull the fft trace back.
 
However, it may well be easier to:
a) Set up the scope for a time domain measurement - voltage scaling, timebase, number of points, trigger etc
b) Trigger a measurement
c) Transfer the captured trace over to the PC
d) Perform an fft using either the native VEE command, or the Matlab version
 
There are some additional advantages to using the second approach.  Firstly, unless you data is self windowed (tends to zero at its end points) you should apply a window, e.g. hanning, blackman etc.  There are a large number of choices available in VEE/Matlab.  Secondly, you have complete control over the signal processing - imagine if you have to move to another scope at some stage that maybe does not have the same functionality or has slightly different fft functionality.  By processing on the PC you control the routine and can ensure consistent processing.  Thirdly, you get the complex fft - magnitude and phase - whereas many scopes will only return you the magnitude.
 
The difference between VEE's native fft and Matlab's fft is that VEE assumes a real valued waveform and returns the first half of the fft (for a real valued waveform the second half is the complex conjugate of the first half), whilst Matlab's fft gives you both halves (if that makes sense).  Take a look in the Matlab documentation that ships with VEE as there is some excellent material on fft's, windowing etc
 
Good luck,
 
Andy
 
  _____  

From: LOW,POH-CHUAN (Non-A-Malaysia,ex1) [mailto:poh-chuan_low@non.agilent.com]
Sent: Tuesday, May 09, 2006 10:04 PM
To: VRF
Subject: [vrf] fft



Hi, I’m a beginner. Do any one know how to get the fast Fourier transform fft() from scope?


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