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vrf transfer function scope

Question asked by VRFuser on Jul 17, 2003
Hello Bern,

I am not sure if this will answer your question fully, but may provide some food for thought.  Most modern scopes have an inherent FFT function.  However, if you want more flexibility, pull the time domain trace data back into VEE and do your FFTs in VEE.  If you are running VEE 6 or greater you can take advantage of the Matlab FFT (main difference compared to VEE's in-built FFT is that Matlab FFT is complex i.e. does not assume real data).  The advantage of doing your FFT in the PC is 1) greater flexibility in choice of windowing function - most windows trade off mainlobe width against sidelobe level: choose your window according to your requirements 2) flexibility to zero-pad/re-sample.

If you have the time data, then you can also calulcate the coherence function in VEE.  I am not sure what you are referring to with the transfer function - stimulus on Ch.1 and response on Ch.2  If so, then you could calculate the transfer response as the ratio of the two in the frequency domain.  Things to look out for on the scope will be the dynamic range (number of bits for the A/D) and memory depth (number of points in the capture is going to translate to frequency resolution in the FFT for a given sample rate).

Best Regards

Andy
--------------------
Andy Street
Technical Consultant
Agilent Technologies
Tel: +44-1189-275395
Mob: +44-7765-897003
Fax: +44-1189-276862


-----Original Message-----
From: bern muller [mailto:bernhard.muller@dlcdesignaudio.com]
Sent: 17 July 2003 23:12
To: VEE vrf
Subject: [vrf] transfer function scope


A tad off  topic, but we are in need of an oscilloscope that will do not
only FFT, but also transfer function and coherence. Bandwidth is not
critical, but a wide variety of sampling rates is desireable (thus ruling
out sound card based solutions). A scope that sends raw data to VEE for
processing would be perfectly acceptable. Anybody know of such  a thing?


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