Re: [Discuss-gnuradio] set_auto_tr(), gr_stall, and PTT

[Michael Dickens]

On Dec 29, 2007, at 4:03 PM, Matt Ettus wrote:
> Your message stated you wanted to do "simultaneous TX/RX".  If you  
> want to switch back and forth, then you do not want simultaneous,  
> which is a good thing.  You want to use the auto t/r switching mode.


Just to clarify, and IIRC so please correct:

The "auto_tr()" mode works as follows: If -nothing- is on the TX  
stream on the USRP hardware (e.g. data is stalled, by whatever  
means), then RX will happen.  If -anything- is going across USRP TX  
hardware (e.g. all 0's, your desired signal, whatever), then TX will  
happen.

The best way to make use of "auto_tr()" is via packets, not  
streams ... thus my comment about not yet trying out a "gr_stall"  
block for streaming, since I haven't really tried "packets" yet.

Given my PPT example, it makes more sense to use half-duplex on 1  
antenna (not auto_tr), or full-duplex on 2 antennas (not auto_tr),  
rather than try to packetize the data stream to make use of auto_tr.

Thus, if your application can be easily packetized, then the use of  
"auto_tr" is warranted.  Otherwise, either use different antennas or  
manually switch the USRP_TX object on and off.