mikec@ux1.lbl.gov (Mike Chin) (01/19/90)
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