URSP noise

hi everyone. i was working with the USRP1. I’m testing a MOD/DEMOD
DBPSK. I
have only one USRP, so, i connected TX_A( from daughterboard LFTX-LF)
to
RX_A ( from daughterborad LFRX-LF) with a coaxil. All system works
well
without URSP but when i taste with the USRP i get so much noise and the
SNR
give me -infinite. I checked the problem comes from “uhd ursp sourse”
block, that make me think the problem is the noise from URSP. some
suggestions?
Regards.
Lucas.

Hi Lucas,

You say you connected TXA to RXA directly via a cox cable? Did you put
an
attenuator inline? I am afraid you may have damaged your RX side by
transmitting directly into it without protection. Most USRPs can be
damaged with input power greater than -10 dBm. Disconnect that cable
immediately and try testing the RX side alone to make sure that it is
not
damaged. Then, if you want to go back to a looback test, make sure that
you put about 60 dB of attenuation between the RX and TX ports.

The noise you were seeing was almost certainly not a problem with your
source block, but your RX being over-driven (dying).

Good luck.

Very Respectfully,

Dan CaJacob

Dan:

That’s generally good advice, with the single exception of the BASIC/LF
card family–they don’t have any gain–they’re just ADC/DAC buffers, so
it’s generally safe to loop them directly.

On 2014-11-11 11:27, Dan CaJacob wrote:

Dan CaJacob


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Thanks, Marcus. You’re absolutely right. I didn’t read carefully
enough.

Very Respectfully,

Dan CaJacob