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
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