Thanks for the prompt response Marcus. Should the discrepancies express themselves as a constant offset in cross-correlation or can the delay measurements also oscillate in a volatile fashion? For B210-E310 we see a more constant looking offset whereas B210-X310 is just wild.
Also I remembered this discussion <https://lists.ettus.com/empathy/thread/2H5WCI2MEWWJKXHXGPMK5UWQXETQ4JRW?hash=L7PPGLOU2FJDCA4ELC2TXJZW75WJQX4C#L7PPGLOU2FJDCA4ELC2TXJZW75WJQX4C> from sometime ago where rising vs falling edges were used for different USRPs. Given your answer, can we say that for timed commands it is not a good idea to mix and match different USRP series? Best, John On Thu, Feb 3, 2022 at 11:27 PM Marcus D. Leech <patchvonbr...@gmail.com> wrote: > On 2022-02-03 15:17, John Hodgins wrote: > > 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 > > > > _______________________________________________ > > USRP-users mailing list -- usrp-users@lists.ettus.com > > To unsubscribe send an email to usrp-users-le...@lists.ettus.com > The group delays between USRP families will be different due to > different FPGA implementations, the exact "placement" of time-of-day > registers, etc. > > It would be very difficult to guarantee phase-coherence across different > USRP device types, because the implementations are different--not just > the FPGA bits and > pieces (DUCs, DDCs, etc), but also the analog stages will be different. > > _______________________________________________ > USRP-users mailing list -- usrp-users@lists.ettus.com > To unsubscribe send an email to usrp-users-le...@lists.ettus.com >
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