Re: [Discuss-gnuradio] Dealing with TX/RX cross-talk on USRP

[Sylvain Munaut]

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
:p )


Cheers,

    Sylvain