Etienne VAILLANT, It's also worth noting that you need to do some work on the generated python flowgraph outside of GRC to ensure a consistent phase relationship between channels. Namely, you need to make sure the following criteria are met on a TwinRX system:
1. All USRPs share a common reference clock (10MHz Ref) 2. All USRPs share a common sense of time (PPS) 3. LOs are shared 4. DSP tuning is synchronous 5. Streaming is started synchronously If it's a single X310, don't worry about 1 and 2 - the internal reference and PPS are fine. Sounds like you're sharing LOs correctly for number 3. For number 5 I believe you can set a stream start time in your USRP source block, and number 4 requires you implement timed commands in the generated python code (all cordics in the FPGA need to be synchronously reset within the DDC). We've actually been discussing something really similar in the thread [[Re: [USRP-users] USRP X310 ignored DSP retuning on TX when using a timed command]]. This is dealing with some TX nuances which shouldn't be an issue for you if you're just doing RX. Sam Reiter On Thu, Feb 27, 2020 at 7:03 AM VAILLANT.Etienne via USRP-users < usrp-users@lists.ettus.com> wrote: > Hi Marcus, > > > > Thank you for your answer. > > I have upgrade my system to UHD 3.13.0.2 and GRC 3.7.13.4 and I still have > those random phase shifts. > > > > Please find attached my flow-graph and some screenshots of what I get when > I start the acquisition (before and after manually shifting the phase > between channels). > > I have also added the warnings I got when I click on play in GRC, plus the > results of 12 identical acquisitions as an example (12 successive clicks on > SAVE). > > > > Thanks very much for your support. > > > > Best regards, > > Etienne. > > > > *De :* USRP-users <usrp-users-boun...@lists.ettus.com> *De la part de* > Marcus D. Leech via USRP-users > *Envoyé :* lundi 24 février 2020 19:43 > *À :* usrp-users@lists.ettus.com > *Objet :* *** BULK *** Re: [USRP-users] Issues using TwinRX and x310 > (phase shift) > > > > > -------------------------------------------------------------------------------------------------------------------------------------- > Attention, ce courriel provient d Internet. L emetteur n est peut-etre pas > celui que vous pensez. > Merci de considerer ce point en lisant ce courriel, en y repondant, ou en > cliquant sur les liens. > > -------------------------------------------------------------------------------------------------------------------------------------- > > On 02/24/2020 05:06 AM, VAILLANT.Etienne via USRP-users wrote: > > Hi all, > > > > I would like to perform DOA measurements and I am using a USRP x310 with > two TwinRX. > > > > First I am trying to perform some very basic tests in order to understand > what I am doing: I generate a CW at 1850 MHz, going through a power > splitter (4-ways 0°), feeding the 4 inputs of the two TwinRX (A:0, A:1 and > B:0, B:1). > > I save the raw IQ data via Gnuradio Companion in a file and I repeat the > procedure several times, generating several files. All the files are saved > with the same USRP tuning (I don’t stop or retune the signal/USRP between > two acquisitions). Basically I just click on a *Save* QT GUI Check Box in > GRC many times which triggers a *File Sink* block and thus generates as > many files. > > > > Then I want to re-plot the signals from the IQ data via Matlab, and my > problem is that I get some different phase shift between the signals. > Please find attached a screenshot of 12 identical acquisitions (12 > successive clicks on *Save*). What is important to me is the phase shift > between the two signals, and I expected it to be identical in all cases > (since all the acquisitions are identical). It seems to be OK for almost > all the acquisitions, except for the 8, 9 and 10, where the phase shift is > different from all the others (and the three of them look identical…). I > have perform this test several times and every time some random > acquisitions are shifted from the others (sometimes there are 2 or 3 > different values of phase shift, it is not always 90° or else). > > > > There is something I misunderstood or I do wrong but I can’t find what. I > have read some people with a similar issue discussing about the function > *set_time_now()* but I don’t really know how to deal with it. > > > > To acquire the signal I am using either * UHD: USRP Source* block with 4 > channels or the *TwinRX USRP Source* block. In the first case, LO > parameters are the following: > > - Ch0 Source Internal / export True > > - Ch1 Source Companion / export False > > - Ch2 Source External / export False > > - Ch3 Source External / export False > > > > I work on *Ubuntu* 18.04 (I can’t change since some other activities rely > on this computer). > > - *GRC* 3.7.10.1 (minimum version required for *gr-doa* > application) > > - *UHD* 3.10.3.0 (with the v3.10.1.0 recommended for *gr-doa > *application, > my TwinRX were not detected (*Unknown*) via *uhd_usrp_probe*) > > - *gr-doa* installed from source but all the make test have > failed (I guess this is another topic since I don’t use *gr-doa* > functions in my basic test presented above?). > > > > I am quite a new comer to this SDR world, thus any help would be much > appreciated, thanks very much in advance! > > > > Kind regards, > > > > *Etienne VAILLANT* > > > > > > Perhaps you could share your GRC flow-graph with us? > > Also, there have been some phase-offset fixes in later versions of UHD, > but it's not clear at this point whether that applies in your case or not, > which is where having the GRC flow-graph to look at would be useful. > > Cheers > > ___________________________________________________________________________________________________________________________________ > > This email and any attachments are confidential to the intended recipient and > may also be privileged. > If you are not the intended recipient please delete it from your system and > notify the sender. > You should not copy it or use it for any purpose nor disclose or distribute > its contents to any other person. > > > Ce courriel et ses pieces-jointes sont envoyes de maniere confidentielle et > doivent etre traites avec attention. > Si vous n'etes pas le destinataire, merci de le detruire et d'en informer son > auteur. > Vous ne devez pas copier, utiliser, reveler ou diffuser son contenu a > quiconque. > > _______________________________________________ > USRP-users mailing list > USRP-users@lists.ettus.com > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >
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