# URSP noise

**URL:** <https://www.ruby-forum.com/t/ursp-noise/233014>\
**Category:** GNU Radio\
**Created:** [November 11, 2014, 5:08pm UTC](https://www.ruby-forum.com/t/ursp-noise/233014 "2014-11-11T17:08:48Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![addis\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c4cdca/32.png) [@addis\_a](https://www.ruby-forum.com/u/addis_a)\
**Post date:** [November 11, 2014, 5:08pm UTC](https://www.ruby-forum.com/t/ursp-noise/233014/1 "2014-11-11T17:08:48Z")

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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.

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**Author:** ![Lucas\_Lopez](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/e36b37/32.png) [@Lucas\_Lopez](https://www.ruby-forum.com/u/Lucas_Lopez)\
**Post date:** [November 11, 2014, 5:32pm UTC](https://www.ruby-forum.com/t/ursp-noise/233014/2 "2014-11-11T17:32:05Z")

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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

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**Author:** ![Lucas\_Lopez](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/e36b37/32.png) [@Lucas\_Lopez](https://www.ruby-forum.com/u/Lucas_Lopez)\
**Post date:** [November 11, 2014, 5:35pm UTC](https://www.ruby-forum.com/t/ursp-noise/233014/3 "2014-11-11T17:35:40Z")

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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
> 
> * * *
> 
> Discuss-gnuradio mailing list  
> [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)  
> [Discuss-gnuradio Info Page](https://lists.gnu.org/mailman/listinfo/discuss-gnuradio) [1]

Links:

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**Author:** ![Lucas\_Lopez](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/e36b37/32.png) [@Lucas\_Lopez](https://www.ruby-forum.com/u/Lucas_Lopez)\
**Post date:** [November 11, 2014, 5:39pm UTC](https://www.ruby-forum.com/t/ursp-noise/233014/4 "2014-11-11T17:39:15Z")

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

Very Respectfully,

Dan CaJacob