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[Discuss-gnuradio] offset at input of LF_RX

From: ematlis
Subject: [Discuss-gnuradio] offset at input of LF_RX
Date: Thu, 21 Jun 2007 17:22:26 -0400 (EDT)

Hi all-

can anybody explain why the USRP/ LF_RX would seem to introduce a DC bias or offset to a signal generated by a function generator? I have a function generator configured to produce a 1 kHz .1 V P-P signal into a 50 Ohm load. I have a Lecroy digital oscilloscope configured with the input at high-impedance to monitor the signal. When I connect the signal to the USRP, I see the trace on the Lecroy gets shifted UP by about .06 volts, ie I have to add a -0.06 V offset at the function generator to zero the bias.

Oddly enough, usrp_oscope.py doesn't show any DC bias whatsoever, regardless of what offset I put into the function generator. Maybe it's removed inside the flow-graph?

Any thoughts on either of these questions?



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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