The Analog Devices AD9361 RF integrated transceiver in the B205mini has a divide-by-2 PLL inside when using an external reference input, so there will always be a 180 degree phase ambiguity.
See this post from my former colleague (also named Robin) at ADI: https://ez.analog.com/thread/73543 -Robin > > On Tue, Feb 20, 2018 at 8:53 AM, Francois Quitin via USRP-users < > usrp-users@lists.ettus.com> wrote: > >> Dear all, >> >> >> >> I’m having a problem synchronizing two USRP-B205 mini. >> >> >> >> The setup is as follows: I use one USRP as a transmitter, the other as a >> receiver, and they are connected by cable. The “ref” input of both USRPs is >> connected to a 10MHz output (also tried with PPS output) of an Octoclock. >> In GNURadio, the “Clock source” (“Time source” when using PPS) is set to >> “external”. >> >> >> >> I then transmit a signal with one USRP (constant source, real sine >> source, BPSK sequence) with one USRP and receive it with the other USRP. >> The received signal is rotating in the IQ-plane, as if there were some LO >> frequency offset remaining. >> >> >> >> In principle, if both USRPs are connected to the same reference, there >> should be no frequency offset. Any ideas where this is coming from? >> >> >> >> Cheers, >> >> François >> >> >> >> >> >> _______________________________________________ >> USRP-users mailing list >> USRP-users@lists.ettus.com >> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >> >> >
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