Hi all, I'm currently using a USRP N310 for an application that requires coherent 4 channel RX w/ the ability to TX on 1 channel as well. In the past, I've used USRP X310s to do 4 channel coherent RX and found the calibration process for that to be relatively straight forward using the TwinRX cards. It was simply phase aligned input signals into each RX port and computing the constant phase offset between channels and just adjusting for that factor in my processing digitally.
My understanding is that this is more complicated w/ the N310. The procedure as I understand is that during initialization the N310 external LO needs to be set at 5 GHz. After initialization, the external LO can be set to 2 times the desired center freq, but that there is still a 180 deg ambiguity between channels which would need to be figured out via calibration w/ a phase aligned input signal. Is this correct? Is there some way to shorten or optimize this procedure? Second question would be if the process is simpler on different USRP models akin to how the X310 w/ TwinRX cards work where you just need to compute some calibration values once at powerup and afterwards those values hold pretty true for a long time as long as your gain/center freq don't change. Having the requirement of being able to TX on at least 1 channel prevents me from using an X310 w/ TwinRX cards. Thanks, -David
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