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

[ematlis]

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:

www.nd.edu/~ematlis/z.gnuradio/multi_scope.jpg
www.nd.edu/~ematlis/z.gnuradio/multi_fft.jpg


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

Any suggestions?

thanks,
eric

************************************
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