Hi Rob, One other thing, if you're not on UHD v3.15.0.0, I'd recommend to update to it. There was some phase reset and accumulator fixes with 3.15.0.0.
https://github.com/EttusResearch/uhd/blob/UHD-3.15.LTS/CHANGELOG#L44 Regards, Nate Temple On Mon, Jan 27, 2020 at 11:17 AM Nate Temple <nate.tem...@ettus.com> wrote: > Hi Rob, > > You should always use a tune request with a timed command when you want to > align channels. > > One thing you could test is to try using the internal LO and see if you > get different results. > > Also you could try using the integer N tuning mode, but I don't think it > will make any difference for this issue. Checkout this great blog post on > USRP tuning if you haven't seen it before that covers a few more tips on > USRP tuning: > http://www.radio-science.net/2017/12/adventures-in-usrp-tuning.html > > Regards, > Nate Temple > > On Mon, Jan 27, 2020 at 9:33 AM Rob Kossler <rkoss...@nd.edu> wrote: > >> Hi Nate, >> I changed the subject as to not further hijack the other thread. Of the >> 16 captures I collected, some of them included a tuning command (but using >> the same timed commands I use for other devices such as TwinRx). But, >> others did not. For example, for the first two data points below (with >> measured phase difference of -77 and -19 respectively). I simply issued >> two consecutive timed streaming commands. So, I was very perplexed by the >> results. >> >> In any event, I plan to re-take the data today both with and without a >> DDC. Hopefully, if I get rid of the DDC, I will see consistent phase >> results, but we'll see. Let me know if you have other ideas. >> Rob >> >> On Mon, Jan 27, 2020 at 12:04 PM Nate Temple <nate.tem...@ettus.com> >> wrote: >> >>> >>> @Rob: With the current init process of the N310, yes it is required to >>> first set the external LO to 5 GHz. >>> >>> With regards to the offsets you're seeing, I believe you should only see >>> a possible phase difference of 180* within the two channels on the same DB. >>> Are you issuing a tune request at the start of streaming? >>> >>> Regards, >>> Nate Temple >>> >>> On Mon, Jan 27, 2020 at 8:20 AM Rob Kossler via USRP-users < >>> usrp-users@lists.ettus.com> wrote: >>> >>>> Robert, Sammy, >>>> I am presently running some tests which compare the X310/TwinRx and the >>>> N310 with regard to channel-to-channel phase. In my setup, I have a signal >>>> source that is split 8 ways (1:8 splitter) to feed the 4 channels of my >>>> TwinRx and 4 channels of my N310. I have seen some strange behavior of the >>>> N310 that perhaps Robert has experienced? Take a look: >>>> >>>> - For the TwinRx (for which I am a more experienced user with LO >>>> sharing), I get consistent channel-to-channel phase difference among all >>>> channels. This is true regardless of power cycles, re-starts of UHD, >>>> etc. >>>> - For the N310 (for which I am a beginner when it comes to external >>>> LO operation) >>>> - it seems more complex to run in this mode (as compared to >>>> TwinRx). In order to get it to work, I have had to disable startup >>>> QEC >>>> calibration because it seems that the N310 initial cal occurs at >>>> 2500 MHz >>>> RF such that I would need to have my external LO at 5000 MHz for >>>> startup >>>> (during the UHD deveice 'make') and then later switch my external LO >>>> to the >>>> desired RF*2. Is this true? >>>> - when I run with either external LO or internal LO, I see >>>> inconsistent channel-to-channel phase results even between the two >>>> channels >>>> of a given daughterboard that share the same LO. I do not >>>> understand how >>>> this is possible. My results over 16 captures (with some re-starts >>>> of UHD, >>>> device reboots, and switching between internal/external LO) show the >>>> following channel-to-channel phase difference between channels 0 and >>>> 1 >>>> which share the same LO: (values in degrees) -77, -19, -77, -19, >>>> -77, -19, >>>> -19, 39, -19, -19, -77, -19, -77, 39, -19, -19. Note that there are >>>> only 3 >>>> unique values and the delta happens to be 58 deg, but I don't know >>>> what >>>> that implies... >>>> >>>> Rob >>>> >>>> >>>>
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