[USRP-users] Problem of SBX board to support full-duplex communications.

Josh Blum josh at ettus.com
Thu Jun 21 03:44:04 EDT 2012

On 06/20/2012 11:30 PM, Alex Zhang wrote:
> Hi,
> As declared by SBX applications nodes, it supports full-duplex, which means
> the transceiver can perform transmission and receiving at the same time.
> However, within my application, I found the SBX is working as half-duplex,
> even I set the antenna as RX2 for receiver, and TX/RX for transmitter.
> In my case, I am setting up a point to point link and try the double-way
> communcations, i.e, A send a request to B, and B should send a reply back
> to B.
> The observed behavior is: B can only send the reply by a delay to ensure
> the A receive this reply correctly. I am suspecting this is due to the
> half-duplex
> switching time at A. My test result shows that the B should delay 9ms after
> it gets request from A and then the reply can be delivered to A safely.
> Otherwise,
> A can not receive this reply or the received packet fails in CRC check.
> In GNURadio community, many guys complains the PING test fails, due to the
> ARP query failure. I add the delay to the ARP reply and this PING test
> passed.

We had a similar discussion in April. It was working, no?

> So I believe there is some problem in duplex, either caused by incorrect
> setting or board issue.
> Is there anything I missed, to get the SBX board supporting full-duplex?

Well, the tunnel.py is gnuradio's most infamous example...

You might consider debugging the setup at a lower level. A simple flow
graph in gnuradio-companion perhaps? Antennas are connected, power
levels expected, frequencies expected etc.


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