Hi Etienne, I didn't see anything about "timed commands" in your email. These are needed in order to get phase synchronization. In particular, the "set_time_now" function is a red flag because you should be using instead "set_time_next_pps". See this <http://lists.ettus.com/pipermail/usrp-users_lists.ettus.com/2019-December/061112.html> topic regarding use of timed commands. Rob
On Mon, Feb 24, 2020 at 1:43 PM Marcus D. Leech via USRP-users < usrp-users@lists.ettus.com> wrote: > 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 > > _______________________________________________ > USRP-users mailing list > USRP-users@lists.ettus.com > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >
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