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NI USRP 2922 Full Duplex?

Hello!

 

We are trying to develope simple PW radar with NI USRP-2922 and LabVIEW. We have done it with 2 USRPs (NI USRP-2920, NI USRP-2922) - one for Tx and one for Rx. And now we want to build PW radar only with NI USRP 2922. In datasheet for NI USRP-29xx series we found, that some hardware configuration is capable of full duplex operation. But we were not sure if NI USRP-2922 is!

 

So we tried little something to make sure it works in full duplex mode. We tried testing it with NI USRP EX Tx Continuous Async.vi and NI USRP EX Rx Continuous Async.vi. We connected Tx/Rx to Rx with SMA/SMA cable and 30 dB attenuator. The problem is, that even when there is no connection beetwen Tx/Rx and Rx, Rx is receiving transmitted signal.

 

We found this VI online. The result is the same. When there is no connection beetwen Tx/Rx and Rx, Rx is receiving. 

 

Does NI USRP-2922 supports full duplex operations? If it does, what is wrong with it? What to do to solve this problem?

 

Regards,

Blaz

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Dear blpongrac,

 

First of all, let me welcome you to the NI Forums. I am looking forward to help you solving your issue.

 

I reproduced the issue what you mentioned, and I saw a little unwired crosstalk between the RX1/TX1 channel and the RX2 channel but that had really low amplitude (about 5000 times lower then the wired way), when I tried your VI with the wire, it had about 20% amplitude loss of the signal (probably caused by the wire), which is not so much. I think your in your VI the "Receive I/Q Graph" had the "Autoscale Y axis" turned on, it can confuse anybody who does not read the exact amplitude next to it. Anyway this device is able to work in full duplex, so your idea is good to use one instead of two devices.

 

You can read about customization of Graphs and Charts in LabVIEW here:

http://zone.ni.com/reference/en-XX/help/371361J-01/lvconcepts/customizing_graphs_and_charts/

 

Best regards,

Tamas

Tamas Benics
Application Engineer
National Instruments
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I actually did not thought of that! Thank you Tamas for your help!

 

Regards

Blaz

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There's about 30dB of isolation between the Tx and Rx paths (i.e. - a tone on the Tx path will show up about 30dB down on the Rx path).  In some applications, 30dB is great so it's not an issue.  However, if you're interested in utilizing all 80-ish dB of receiver dynamic range, I've found your best bet is to just use two radios.  

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