Re: [Discuss-gnuradio] if uhd_transmitter instantiated after receiver, TX works, otherwise RX works

[Josh Blum]

On 06/18/2012 05:21 AM, King Qiu wrote:
> hi George,
> I noticed theses odd things several months ago. I am using USRP2s with
> XCVR2450. Since my UHD was upgraded to 003.004.000 or newer version, my
> USRP2s can't work in half duplex mode. When uhd_transmitter is
> instantiated later than uhd_receiver, tx works well but rx can't receive
> packets. When uhd_receiver is instantiated later than uhd_transmitter,
> rx could receive packets, but tx works with abnormal spectrum.
> 
> Now I have to use an old version (003.003.002) UHD. With this version,
> both tx and rx work well. So I doubt that there is a bug in version
> 003.004.xxx. Maybe Ettus can help us fix it.
> King Qiu
> 
> 
> 

Thanks for the tip. I think I figured it out.

The property to use an LO offset was true for TX and not RX. This would
mean that tuning an individual chain and using it would be fine; but
since there is a shared LO, the offset would not be compensated for by
the DSP on the chain in the other direction, hence, it not working.

If you dont mind trying, here is a simple 1 liner patch:
http://pastebin.com/KiR3e6j0

-josh

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