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vrf NTP from VEE

Question asked by g.nied on May 23, 2004
Hello All,

With regard to the 'zoom FFT', I am not sure what NI are referring to exactly.  There are many different forms of the Fourier Transform in wide use (discrete Fourier transform, chirp-Z transform and of course the FFT).  In VEE-land, the FFT is relatively simple in that it takes real-valued 'time' data and its implementation of the FFT produces complex valued frequency domain data.  VEE's native Fourier Transform does not allow you to input complex time domain data into the transform.  However, the Matlab implementation of the FFT can employ real or complex valued time domain data.  It may be that what NI are referring to is something similar to the Matlab FFT implementation. 

In several HP/Agilent Signal Analyzer products, we have signal analysis (FFT) modes called 'baseband' and 'zoom'.  In baseband mode, the frequency analysis region is from DC to some upper frequency.  The sampled input time domain data is real.  In zoom mode, an IQ demodulator is used to resolve a signal centred at some frequency Fo, into I and Q components.  The FFT operates using I[n]+jQ[n], where n is the nth sample i.e. complex data into the FFT.  The frequency domain analysis region then exists over some finite span about Fo, (span determined by the sampling rate).

Thus, if this is the type of capability you are looking for, then you can simply use Matlab's FFT with complex input data.  Alternatively, Matlab also implements the Chirp-Z transform, which essentially allows you to analyzer specific regions in the frequency domain (within the sampling criteria established by Nyquist et al), with a user defined frequency increment.

If you can supply more info on exactly what you mean with zoom FFT, then it may be possible to identify either a native VEE function or Matlab function that will fulfil the requirement.

Hope this helps

Andy


-----Original Message-----
From: FUKUI Yutaka [mailto:fukui.yutaka@jp.fujitsu.com]
Sent: 24 May 2004 07:20
To: PDL-LISTS,VRF (A-Lists,unix1)
Subject: [vrf] Re:Zoom FFT


Hi,


I heared about it at the seminar on the FFT held by the

National Instrument and feel a litle interest in it.

However, I have neither documentations nor examples (in VEE or C/C++)
about

the zoom FFT algorithm.


Regards,
FUKUI Yutaka


> Hello,

> Has anybody documentation or examples (in VEE or C/C++) about the zoom FFT algorithm implementation?
> I can't get enough information about it on internet.

> Thanks in advance,



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