Hi there, We have a simple set up where we collect iq snippets from 3 usrp's at the same rx-times via timed commands. We introduce delays between the usrp's via a reference delay box and try to recover the introduced delays via cross-correlation.
Things work great when all the rx's belong to the same USRP family. For instance we have been able to recover the correct delay for all B210 (with GPSDO/TCXO) or all E310 (with GPS antenna) scenarios. However, when we mix different USRP's, the delays computed via cross-correlation no longer make sense. For instance, when we use 1 B210 and 2 E310's the delays between B210 and E310's just oscillate wildly but the relative difference between E310 remains relatively stable. We tested 2 B210's with a single X310 (with GPSDO/OCXO) as well and we see the same problem as well. The interesting thing is though visualizing the spectrum of collected snippets from different USRPs show pretty much the spectrum of the known applied signal. Is there some fundamental discrepancy between different USRP families? Or maybe UHD somehow interprets samples differently for different USRP's (flipping i and.q, different rx-time, pps implementations, some precision issues maybe)? In any case I would be grateful if anyone can shed some light onto this behavior. Best, John
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