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Re: [Discuss-gnuradio] DBSRx capturing image spectrum

From: Nick Foster
Subject: Re: [Discuss-gnuradio] DBSRx capturing image spectrum
Date: Fri, 12 Nov 2010 10:45:20 -0800

On Fri, 2010-11-12 at 19:56 +0200, john kimionis wrote:
> Hi,
> I am trying to capture a RFID Reader-Tag Conversation at 866.3MHz. I'm
> testing 2 cards: A FLEX 900 and a DBSRx rev2.2. With the FLEX900 i'm
> able to clearly see the Reader signals and the tag replies, but with
> the DBSRx the signals showed distorted by some higher frequency
> signals. 
> Using usrp_fft.py with the same settings and USRP/Antennas at the same
> exact position what I surprisingly saw was that the DBSRx is capturing
> an image of the RFID spectrum 400 kHz away!
> What could this mean? Is something on the front-end damaged?

It's possible. If you're using a USRP1, try swapping daughterboard sides
to make sure the problem follows the daughterboard. It looks as though
either the I or Q channels are not operating.


> Here are the two screenshots of usrp_fft.py. one for FLEX 900 (good
> one) and one for the DBSRx (problematic)
> http://twitshoot.com/1f
> http://twitshoot.com/1g
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