Article View: comp.dsp
Article #582FFT S/N replies
From: Mike Chin
Date: Fri, 19 Jan 1990 01:48
Date: Fri, 19 Jan 1990 01:48
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1406 bytes
The problem with my trying to find S/N from an FFT was
that I was doing something like:
sum(bins due to noise)
----------------------------
sum(bins due to fundamental)
I should have been doing:
sqrt{sum((bins due to noise)^2)}
----------------------------
sqrt{sum((bins due to fundamental)^2)}
Thanks to oakhill!radio!charlie@cs.utexas.edu (Charlie Thompson)
for this.
Also, Steve Omner (steveno@tekigm2.men.tek.com) reminded me to
look at the effects of my windowing. My blackmann-harris used
a0-a3 coefficients that has sidelobes at the level I'm trying
to resolve. The ADC manafacturer is sending me their new window
set; we'll see if it makes any difference.
Bob Jewett <jewett%hpl-opus@hplabs.hp.com> advocates using a direct
sine fitting, and sent me a nice program that crunched my simulated
data very well.
Thanks also to the others who gave hints.
Mike Chin
Lawrence Berkeley Labs
MJChin@lbl.gov
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Path: arc1-ca.pugleaf.net!utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!uwm.edu!uakari.primate.wisc.edu!brutus.cs.uiuc.edu!usc!ucsd!helios.ee.lbl.gov!ux1.lbl.gov!mikec From: mikec@ux1.lbl.gov (Mike Chin) Newsgroups: comp.dsp Subject: FFT S/N replies Message-ID: <4648@helios.ee.lbl.gov> Date: 19 Jan 90 01:48:03 GMT Sender: usenet@helios.ee.lbl.gov Distribution: usa Organization: Lawrence Berkeley Laboratory, Berkeley Lines: 28 X-Local-Date: 18 Jan 90 17:48:03 PST