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[Discuss-gnuradio] multi scope/fft not working right?

From: ematlis
Subject: [Discuss-gnuradio] multi scope/fft not working right?
Date: Wed, 20 Jun 2007 15:29:20 -0400 (EDT)

Hi all-

I'm trying to build a multi-reciever program modelled on the stuff in the multi_antenna directory, however there seems to be a problem with the multi_fft and multi_scope programs. I have 2 LF daughterboards, and I'm using a function generator to send a 1 kHz sine wave with .1 V p-p levels. I start either the _fft or _scope program with the arguments -d 250 -f 0.

What I'm observing is a very distorted signal; the distortion appears to be due to the presence of significant energy in some harmonics away from 0 Hz. I can remove them if I sharpen the default filter, but I have to have a cuttoff very close to my 1 khz to clean it up. What is going on? I have two images, one for the scope and one for the fft at:


The standard usrp_oscope.py and usrp_fft.py do not show these harmonics and the signal is very clean.

Any suggestions?


Eric H. Matlis, Ph.D.
Aerospace & Mechanical Engineering Dept.
120 Hessert Center for Aerospace Research
University of Notre Dame
Notre Dame, IN 46556-5684
Phone: (574) 631-6054
Fax:   (574) 631-8355

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