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List: usrp-users
Subject: Re: [USRP-users] Issues using TwinRX and x310 (phase shift)
From: Rob Kossler via USRP-users <usrp-users () lists ! ettus ! com>
Date: 2020-02-25 18:00:08
Message-ID: CAB__hTRZAMF3A3UPU-VKF2F+fHTw1EkA0u+NvKnFAcW1=3CqkQ () mail ! gmail ! com
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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
>
[Attachment #5 (text/html)]
<div dir="ltr"><div>Hi Etienne,</div><div>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 <a \
href="http://lists.ettus.com/pipermail/usrp-users_lists.ettus.com/2019-December/061112.html">this</a> \
topic regarding use of timed commands.</div><div>Rob</div><div><br></div><br><div \
class="gmail_quote"><div dir="ltr" class="gmail_attr">On Mon, Feb 24, 2020 at 1:43 PM \
Marcus D. Leech via USRP-users <<a href="mailto:usrp-users@lists.ettus.com" \
target="_blank">usrp-users@lists.ettus.com</a>> wrote:<br></div><blockquote \
class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid \
rgb(204,204,204);padding-left:1ex">
<div bgcolor="#FFFFFF">
<div>On 02/24/2020 05:06 AM,
VAILLANT.Etienne via USRP-users wrote:<br>
</div>
<blockquote type="cite">
<div>
<p class="MsoNormal"><span lang="EN-GB">Hi all,<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB">I would like to perform
DOA measurements and I am using a USRP x310 with two \
TwinRX.<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB">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).<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB">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 <i>Save</i> QT GUI Check Box in GRC many times
which triggers a
<i>File Sink</i> block and thus generates as many \
files.<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB">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 <i>Save</i>). 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).<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB">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
<i>set_time_now()</i> but I don't really know how to deal
with it.<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB">To acquire the signal I
am using either <i>
UHD: USRP Source</i> block with 4 channels or the <i>TwinRX
USRP Source</i> block. In the first case, LO parameters
are the following:<u></u><u></u></span></p>
<p><span lang="EN-GB"><span>-<span style="font:7pt "Times New \
Roman""> </span></span></span><span lang="EN-GB">Ch0
Source Internal / export True<u></u><u></u></span></p>
<p><span lang="EN-GB"><span>-<span style="font:7pt "Times New \
Roman""> </span></span></span><span lang="EN-GB">Ch1
Source Companion / export False<u></u><u></u></span></p>
<p><span lang="EN-GB"><span>-<span style="font:7pt "Times New \
Roman""> </span></span></span><span lang="EN-GB">Ch2
Source External / export False<u></u><u></u></span></p>
<p><span lang="EN-GB"><span>-<span style="font:7pt "Times New \
Roman""> </span></span></span><span lang="EN-GB">Ch3
Source External / export False<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB">I work on <i>Ubuntu</i>
18.04 (I can't change since some other activities rely on
this computer).<u></u><u></u></span></p>
<p><span lang="EN-GB"><span>-<span style="font:7pt "Times New \
Roman"">
</span></span></span><i><span lang="EN-GB">GRC</span></i><span \
lang="EN-GB"> 3.7.10.1 (minimum version required for <i>gr-doa</i> \
application)<u></u><u></u></span></p>
<p><span lang="EN-GB"><span>-<span style="font:7pt "Times New \
Roman"">
</span></span></span><i><span lang="EN-GB">UHD</span></i><span \
lang="EN-GB"> 3.10.3.0 (with the v3.10.1.0 recommended for
<i>gr-doa </i>application, my TwinRX were not detected (<i>Unknown</i>)
via <i>uhd_usrp_probe</i>)<u></u><u></u></span></p>
<p><span lang="EN-GB"><span>-<span style="font:7pt "Times New \
Roman"">
</span></span></span><i><span lang="EN-GB">gr-doa</span></i><span \
lang="EN-GB"> installed from source but all the make test have failed (I guess this \
is another topic since I don't use <i>gr-doa</i> functions in my basic test \
presented above?). <u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB">I am quite a new comer
to this SDR world, thus any help would be much appreciated,
thanks very much in advance!<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB">Kind \
regards,<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB"><u></u> <u></u></span></p>
<p class="MsoNormal"><b><span>Etienne
VAILLANT<u></u><u></u></span></b></p>
<p class="MsoNormal"><u></u> <u></u></p>
</div>
<br>
</blockquote>
Perhaps you could share your GRC flow-graph with us?<br>
<br>
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,<br>
which is where having the GRC flow-graph to look at would be
useful.<br>
<br>
Cheers </div></blockquote><blockquote class="gmail_quote" style="margin:0px 0px \
0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div \
bgcolor="#FFFFFF"> <br>
</div>
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rel="noreferrer" target="_blank">http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com</a><br>
</blockquote></div></div>
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