So the SBX daughter board has a phase resync feature, which I think would alleviate my problem. For other boards it is noted in [1] that :
"Most daughterboards use a fractional-N synthesizer ... Generally, these fractional- N synthesizers introduce a random phase offset after each retune ..., this random phase offset will need to be measured and compensated for in software." I'd appreciate pointers on how to do this. Thank you, AB [1] https://kb.ettus.com/Synchronization_and_MIMO_Capability_with_USRP_Devices ________________________________ From: Bakshi, Arjun Sent: Friday, September 1, 2017 6:29:49 PM To: Edwin Li; [email protected] Subject: Re: [USRP-users] Changes in wired channel after restarting flowgraph The only solution I've found is picking a center frequency that is a multiple of 64MHz based on this reply by Matt http://lists.gnu.org/archive/html/discuss-gnuradio/2008-06/msg00017.html Regards, AB ________________________________ From: Edwin Li <[email protected]> Sent: Friday, September 1, 2017 6:13:03 PM To: Bakshi, Arjun; [email protected] Subject: Re: [USRP-users] Changes in wired channel after restarting flowgraph Looks like there is a random phase. Every time you start, the phase of the clock maybe different. Hence when you plot the signal, it's going to be different. I can observe the same random phase in my BPSK program. Bakshi, Arjun via USRP-users <[email protected]<mailto:[email protected]>>于2017年9月1日周五 下午2:48写道： Hi all, Had posted about this before, but focusing on 1 simple case here. I'm observing a change in a wired channel every time I restart my flow graph. I'm using 1 USRP + WBX board, i.e. tx and rx on the same USRP. So time/frequency sync should not be a factor, I believe. I simply do: start-> sleep(2)-> stop->wait->start->sleep(2).... looped 10 times, and record the rxed signal. I see that during the 2 seconds the channel remains constant, however after the restart the channel changes. Any ideas on why this is happening? I was expecting to see the same channel no matter how many times I restart the flow or even power cycle the USRP. Figures attached: Real and imaginary part of rxed signal, subsampled ~110 to fit it all in. Thank you, Arjun _______________________________________________ USRP-users mailing list [email protected]<mailto:[email protected]> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
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