[USRP-users] Does each antenna of USRP N210 can both transmit and receive?

Ian Buckley ianb at ionconcepts.com
Tue Jun 26 14:02:43 EDT 2012


Alex,
First off, safety talk; the only way you can use any (single) URSP radio in a full duplex application is to use both the RX2 SMA (for receive) and the TX/RX SMA (for transmit). It is unsafe to directly connect the TX port of the (any!) radio to the RX port of the radio without appropriate bandpass filters that are specific to the frequencies in use in the specific application. If un-attenuated TX signal energy reaches the RX portion of the radio, it will certainly be damaged.

Thus to use a single antenna you must construct from filters an appropriate diplexer that prevents any significant TX signal energy from reaching the RX port. A more simple approach appropriate for uses on a typical USRP budget is to connect 2 separate antenna's one to TX and RX...but, even in this case external filters are appropriate since TX signal energy that radiates into the RX antenna will either de-sensitize or saturate the RX input circuitry, even if it is outside the band of interest selected by downstream tuning and digital filtering. In short the local TX signal is loud, the received signal from the remote USRP is quiet, you must do everything possible to stop one interfering with the other in a full-duplex application.

Another way you can achieve an "ideal" RF environment for conducting basic full duplex testing is to directly connect the 2 USRP's with 2 coax's, one for each direction WITH INLINE ATTENUATION. This would isolate any of the effects I just described above. Again it's vital to use appropriate attenuation in the scenario, do not just rely on turning the TX power down, it's too easy to make a mistake and destroy a radio.

If you wish to debug and understand the issues involved in operating full duplex I strongly suggest you write you own GRC based basic radio's and examine and experiment with the produced spectrum's to understand what I've described better. 


-Ian


On Jun 26, 2012, at 9:23 AM, Alex Zhang wrote:

> Hi Nick,
> 
> Do you have any comments on my problem?
> 
> Thanks.
> 
> On Mon, Jun 25, 2012 at 3:33 PM, Alex Zhang <cingular.alex at gmail.com> wrote:
> Maybe I did not use the SBX correctly.
> What I observed is that the if the my USRP tries to receive something right after it just complete a packet transmission, it always fails in receiving the correct data, even the repsonder sends out the reply correctly. Thus I add delay at the responder before each reply is transmitting, as the other side is still in TX/RX switching. 
> 
> Please see this link for my problem description.  http://comments.gmane.org/gmane.comp.hardware.usrp.e100/3964 
> 
> I have tried to set the TX and RX at different antennas, like the RX is RX2, TX is at TX/RX. But the problem still there, more like as working in half-duplex mode.
> 
> 
> On Mon, Jun 25, 2012 at 3:04 PM, Nick Foster <nick at ettus.com> wrote:
> On Mon, Jun 25, 2012 at 12:58 PM, Alex Zhang <cingular.alex at gmail.com> wrote:
> SBX board claims to support full-duplex. 
> However, I still have problem in using SBX board to carry out the full-duplex communication.
> 
> Alex,
> 
> SBX is by design full duplex. XCVR2450 is half-duplex by nature and was not designed for simultaneous TX/RX. Could you please elaborate on how SBX is not functioning in full duplex mode in your application?
> 
> --n
>  
> 
> On Mon, Jun 25, 2012 at 1:39 PM, <mleech at ripnet.com> wrote:
> On 25 Jun 2012 14:33, Weixian Zhou wrote:
> 
>> I am using USRP N210 and the daughter boards are XCVR2450. Does each antenna can both transmit and receive, or one antenna can only transmit and another can only receive?
>> 
>>  
>> -- 
>> Regards,
>> Weixian Zhou
>> 
>> 
> 
> http://files.ettus.com/uhd_docs/manual/html/dboards.html#xcvr-2450
> 
> Either port can perform either function.  But it's a half-duplex device, so you can't TX and RX at the same time.
> 
>  
>  
>  
> 
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> 
> 
> 
> -- 
> 
> Alex,
> Dreams can come true – just believe.
> 
> 
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> 
> 
> 
> 
> -- 
> 
> Alex,
> Dreams can come true – just believe.
> 
> 
> 
> 
> -- 
> 
> Alex,
> Dreams can come true – just believe.
> 
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