DBSRx capturing image spectrum

GNU Radio
1

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?

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

2

On Fri, 2010-11-12 at 19:56 +0200, john kimionis wrote:

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.

–n