# Dealing with TX/RX cross-talk on USRP **URL:** \ **Category:** GNU Radio\ **Created:** [April 5, 2014, 10:02pm UTC](https://www.ruby-forum.com/t/dealing-with-tx-rx-cross-talk-on-usrp/240281 "2014-04-05T22:02:53Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![musicdenotation](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/ea666f/32.png) [@musicdenotation](https://www.ruby-forum.com/u/musicdenotation)\ **Post date:** [April 5, 2014, 10:02pm UTC](https://www.ruby-forum.com/t/dealing-with-tx-rx-cross-talk-on-usrp/240281/1 "2014-04-05T22:02:53Z")
I’m looking for tips on how to deal with the USRP TX/RX leakage. I’m transmitting with 30db (max) gain while trying to measure RSSI on the RX2 channel and experiencing about 40db of energy leakage from the TX/RX. My TX and RX chains are separated by 50MHz. Not sure how I can filter it out. I’m thinking an antenna amp would work, so I could turn down the gain on the USRP; however, I want to try and avoid this. Is there a fast way to switch between RX/TX channels? I did some quick tests with just turning off the TX channel flow graph, but the leakage takes a long time to dissipate. ---
**Author:** ![kena](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/e9bcb4/32.png) [@kena](https://www.ruby-forum.com/u/kena)\ **Post date:** [April 5, 2014, 10:32pm UTC](https://www.ruby-forum.com/t/dealing-with-tx-rx-cross-talk-on-usrp/240281/2 "2014-04-05T22:32:06Z")
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Hi Ken, first question: Which USRP/Daughterboard? Maybe you should be asking this question on the [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) mailing list; I’m going to go ahead and CC: that list in my reply. Basically, limited crosstalk is very hard to avoid; especially when trying to deal with a weak RX while TX’ing high power you’ll run into problems you can’t really circumvent due to the fact that RF signals on the same PCB inevitable leak. An RX LNA close to the antenna is usually the way to go here, or even separating RX and TX. You could try turning off the TX amp (gain to 0 and transmit complex(0,0)), maybe that might help more than shutting down the flow graph. If you manage to get success using that way, I’d greatly appreciate you notifying the list. Greetings, Marcus On 05.04.2014 22:01, Ken A. wrote: > quick tests with just turning off the TX channel flow graph, but > the leakage takes a long time to dissipate. > > \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ 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) -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 Comment: Using GnuPG with Thunderbird - [http://www.enigmail.net/](http://www.enigmail.net/) iQEcBAEBAgAGBQJTQGf+AAoJEBQ6EdjyzlHtWEoIAJgEUUrRXo4GSArtMYzZt/FY PJKJeCKZQaYT3XUD+eWLCYOr5p67pMzPChuRJYjyZlzSNVafgHlUIhoX0YALC+4R 6Q9Cxh1C0DFEEcwQW5cfrCi0w1rIAtLZ00NrDQGAOl8mfO2wkJXElpXF4I7k64ac /fONTbSWrnYQWjUXNijSJxw+W+x3F8tz4aR7erN2U7uW+kMco8JcrbikJvMYGr3b L5fvkv8H45B9YoprbMiG/IA5M1UJlThUcs5fQq47dG5JAq1Mx0W18ki06CjTCX1l wtoFwL3tmTNNrMR+X6SibzonUXy+/iLkk0G1NUXXF+PL4QoBhmZumU5SyZddWMg= =PIsR -----END PGP SIGNATURE----- ---
**Author:** ![kena](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/e9bcb4/32.png) [@kena](https://www.ruby-forum.com/u/kena)\ **Post date:** [April 6, 2014, 1:14am UTC](https://www.ruby-forum.com/t/dealing-with-tx-rx-cross-talk-on-usrp/240281/3 "2014-04-06T01:14:27Z")
Hi Ken, > I’m looking for tips on how to deal with the USRP TX/RX leakage. I’m > transmitting with 30db (max) gain while trying to measure RSSI on the RX2 > channel and experiencing about 40db of energy leakage from the TX/RX. My TX > and RX chains are separated by 50MHz. Not sure how I can filter it out. I’m going to assume WBX/SBX/RFX DB here (which have pretty much the same TX/RX + RX2 path switching). 40 dB seems a bit low for the isolation, usually I’d expect 50-60 dB. But then, the baseband filter should help you gain more. If you’re not already doing it, you can offset tune so that the carrier you’re transmitting/receiving is more “on the edge” of the baseband low pass. You need to plan this depending on the daughter card bandwith. If you need more, there is some hw mod you can do on the board. Removing the cap between RX and TX switch and connecting both end to ground is the easiest fix to increase isolation. One guy even went as far as sawing a RFX board in two to increase isolation (yeah, I know that sounds crazy but both half are pretty much independent … it probably voids your warranty though, you’ll have to check with ettus 😛 ) Cheers, ``` Sylvain ```