USRP-2943 sync daughter boards on a single device

[amir13]

I am interested in getting phase aligned input from RX1 of channel 0 and 1 (two daughter boards), but unfortunately they are time but not phase aligned. Can both be aligned to have a zero phase difference on acqusition?

[Air_Frantz]

Hello,

Due to their design, the LOs on the USRP are synthesized using the 10MHz reference clock.  According the document below in the 'Phase coherency vs. phase alignment' section, "During synthesis, as the reference is divided, the phase may lock on either rising or falling edges producing a constant but arbitrary phase offset on each channel"

http://www.ni.com/example/14311/en/

So we can only guarantee that after tuning to a specific LO frequency(on multiple channels or devices sharing the same ref clock) we have LOs that have a constant phase relationship to one another during the run.  This phase offset will change every time you retune the LOs.

For MIMO or related applications that require phase alignment, a training sequence is necessary.  You would tune to a frequency, send a signal to all channels, record phase offsets for the channels, and apply a phase correction to the IQ data.