Hi Rob. You are specifying use of the RX external LO correctly via device arguments. Each of the daughtercards on the N310 contains a single Analog Device AD9371 2 TX x 2 Rx RF integrated transceiver. The two Tx channels share an LO and the 2 Rx channels share an LO. Consequently, the TX or RX frequency of RF channel 0 and RF channel 1 are constrained by the RFIC to be the same and the TX or RF frequency of RF channel 2 and RF channel 3 must be the same. The AD9371 is capable of FDD operation, so the TX frequency does not need to be equal to the RX frequency.
The LO tuning code for the N310 daughterboard in UHD is (not obviously) located here and, as you correctly point out, is handled differently from previous USRPs: https://github.com/EttusResearch/uhd/tree/maint/host/lib/usrp/dboard/magnesium Magnesium is the internal code Ettus Research name for the N310 daughterboard. We will make this obscure fact more obvious in the documentation. -Robin On Sun, Apr 8, 2018 at 2:31 AM, Marcus D. Leech via USRP-users < usrp-users@lists.ettus.com> wrote: > On 04/07/2018 10:39 AM, Rob Kossler wrote: > > Hi Marcus, > No, I haven't fooled with LO level adjustments. I set the LO at about 3 > dBm and did not change it. The LO freq is indeed 2x (LO at 4884MHz with > center freq at 2442MHz). I suspect that my custom software, which was > developed for first B210 and then X310 with several daughterboard variants, > may be sending tune commands in a way that is not ideal for an external LO > configuration. There was a similar issue when I first started using TwinRx > with "companion" or "external" LO and UHD would issue warnings about tuning > one channel first and then the other when both channels had to be at the > same freq because they shared an LO. So, my request for examples was to > help me see if I am issuing the tuning requests correctly for this external > LO config. > > Rob > > Understood. > > Hopefully, one of the R&D folks will chime in here. I don't currently > have one in my inventory, so running a bit blind. > > > > On Fri, Apr 6, 2018 at 7:32 PM, Marcus D. Leech via USRP-users < > usrp-users@lists.ettus.com> wrote: > >> On 04/06/2018 05:14 PM, Rob Kossler via USRP-users wrote: >> >>> Hi, >>> Are there any examples for using the N310 with external LO? I have >>> gotten some strange results (strange spectral mirror-ing) when using as >>> just a 4 channel receiver. I am using the "args" argument to set >>> rx_lo_source, but my code is setting the individual channel frequencies as >>> I do for other USRPs and I noticed various warnings in the terminal window >>> for each channel that I tune. >>> >>> On a separate note, I get some strange results if I set the clock_source >>> to external in the args (using with OctoClock). If I leave it internal, no >>> problem. For now, I am leaving it internal until I can solve the problem >>> above with LO source. >>> >>> Rob >>> >>> >>> Rob, just shooting from the hip here, since I haven't "lived" with an >> N310 yet... >> >> Have you tried adjusting the LO levels let's say 2dB in either direction >> to see if that changes the imaging behavior? Also, remember that the >> external LO input >> on the N310 must be a 2XLO -- at twice the desired Fc, and only up to >> 8GHz (giving a 4GHz antenna frequency). >> >> >> >> >> _______________________________________________ >> USRP-users mailing list >> USRP-users@lists.ettus.com >> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >> > > > > _______________________________________________ > USRP-users mailing list > USRP-users@lists.ettus.com > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com > >
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