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List: usrp-users
Subject: Re: [USRP-users] about phase and time reference feedback issue
From: Marcus_Müller via USRP-users <usrp-users () lists ! ettus ! com>
Date: 2016-10-27 9:44:46
Message-ID: 09fb81da-31a5-36ff-f348-bfc64b7eff5a () ettus ! com
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Dear Sanjok,
as explained, you can't use an internal and an external reference at the
same time; there's a causality problem there...
What you should do is just take the GPSDO from the first USRP and
installl it in the Octoclock.
Alternatively, you can also just use the first USRP (with the GPSDO
installed) as "master" and don't make a connection from the octoclock to
that USRP, but then you'll have to measure and calibrate the delay
between that USRP and the others.
Best regards,
Marcus
On 27.10.2016 11:31, Sanjoy Basak wrote:
> Hi Marcus,
> I actually have 4 X310s in total. With these I am trying to make a
> MIMO receive array, with as many rx elements as possible. My
> application is to implement DoA estimation of incoming signal with
> Music/digital beamforming (test both actually). Now if I am not
> including one X310 (the reference feeding USRP) then I am losing rx
> elements. I also want a complete coherent system.
>
> My boss wanted me to make sure if buying one Octoclock without gpsdo
> is enough.
> So I am looking at the possibilities.
> If its not possible then we will go for the Octoclock-G.
>
> Best regards
> Sanjoy
>
>
>
> On Thu, Oct 27, 2016 at 10:43 AM, Marcus Müller
> <marcus.mueller@ettus.com <mailto:marcus.mueller@ettus.com>> wrote:
>
> Hi Sanjoy,
>
> if you have an octoclock, you don't need the connection from the
> first X310 to the octoclock. And you *must* set all USRPs to
> external, if you want to use the external clock for all USRPs.
>
> So, your diagram is still impossible, because it includes a
> loopback on the leftmost X310. I don't understand why you think
> you need to make the connection from the left USRP to the
> Octoclock, could you explain?
>
>
> Best regards,
> Marcus
>
>
> On 27.10.2016 10:32, Sanjoy Basak wrote:
>> Hi Marcus,
>> Thanks for the explanation. Now I understand.
>> We have 4 X310s and one equipped with GPSDO. We are trying to
>> make time and phase synchronized MIMO operation. So the final
>> goal is to make this configuration work.
>> Inline image 1
>>
>> As we already have one GPSDO module, we are willing to buy one
>> Octoclock without GPSDO. It would also save some money.
>> But if I want to make this configuration work, I will have to put
>> all the USRPs on external. If I put one on internal and others on
>> external, then it would be the same as daisy chained.
>>
>> Could you please tell me if this configuration is anyhow possible
>> with Octoclock (without GPSDO), by modifying UHD code or using
>> any patch.
>> Or we must buy Octoclock-G.
>>
>> Best regards
>> Sanjoy
>>
>>
>>
>> On Wed, Oct 26, 2016 at 4:50 PM, Marcus Müller via USRP-users
>> <usrp-users@lists.ettus.com <mailto:usrp-users@lists.ettus.com>>
>> wrote:
>>
>> Hi Sanjoy,
>>
>> you've got a misunderstanding there.
>>
>> If you set the reference input to external, the USRP stops
>> using its own reference oscillator, but uses what you feed in
>> externally.
>>
>> So, the USRP used to generate the reference for the other one
>> must be set to use its internal oscillator, or else there's
>> no active 10MHz reference in your overall system.
>>
>> Best regards,
>>
>> Marcus
>>
>>
>> On 10/26/2016 04:43 PM, Sanjoy Basak via USRP-users wrote:
>>> Hello everyone,
>>> I am planning to make the following configuration to test
>>> the phase and time coherence between 2 X310s. One X310 is
>>> with GPSDO. I am taking 10 MHz reference and 1 pps signal
>>> from that usrp and then feed both USRPs with the same signal
>>> distributed from a T connector.
>>>
>>>
>>> Inline image 3
>>>
>>> However, it did not work.
>>>
>>> Afterwards I found out that the problem is in this
>>> configuration. If I take the 10 MHz signal and 1 pps signal
>>> from ref_out and pps_out and feed that USRP with the same
>>> signal (with time and clock reference External), it does not
>>> work.
>>> Inline image 4
>>>
>>> Could anyone tell me how to make it work. I am using uhd 3.9.2
>>>
>>> Best regards
>>> Sanjoy
>>>
>>>
>>>
>>>
>>> _______________________________________________
>>> USRP-users mailing list
>>> USRP-users@lists.ettus.com <mailto:USRP-users@lists.ettus.com>
>>> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
>>> <http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com>
>> _______________________________________________ USRP-users
>> mailing list USRP-users@lists.ettus.com
>> <mailto:USRP-users@lists.ettus.com>
>> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
>> <http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com>
>>
>>
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<p>Dear Sanjok,</p>
<p>as explained, you can't use an internal and an external reference
at the same time; there's a causality problem there...</p>
<p>What you should do is just take the GPSDO from the first USRP and
installl it in the Octoclock.</p>
<p>Alternatively, you can also just use the first USRP (with the
GPSDO installed) as "master" and don't make a connection from the
octoclock to that USRP, but then you'll have to measure and
calibrate the delay between that USRP and the others. <br>
</p>
<p>Best regards,</p>
<p>Marcus<br>
</p>
<br>
<div class="moz-cite-prefix">On 27.10.2016 11:31, Sanjoy Basak
wrote:<br>
</div>
<blockquote
cite="mid:CAJPQ1a2G3GwgFGDbqzj=eWC1i23DpEi2hb7hZFKD8mR7Xm_5Bw@mail.gmail.com"
type="cite">
<div dir="ltr">Hi Marcus,
<div>I actually have 4 X310s in total. With these I am trying to
make a MIMO receive array, with as many rx elements as
possible. My application is to implement DoA estimation of
incoming signal with Music/digital beamforming (test both
actually). Now if I am not including one X310 (the reference
feeding USRP) then I am losing rx elements. I also want a
complete coherent system.</div>
<div><br>
</div>
<div>My boss wanted me to make sure if buying one Octoclock
without gpsdo is enough.</div>
<div>So I am looking at the possibilities. <br>
If its not possible then we will go for the Octoclock-G.</div>
<div><br>
</div>
<div>Best regards</div>
<div>Sanjoy<br>
<br>
</div>
<br>
<img moz-do-not-send="true" class="mailtrack-img"
src="https://mailtrack.io/trace/mail/92727d5624ed7307d7a5564c445ae442d9c3cbb6.png?u=588056"
height="0" width="0"></div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Thu, Oct 27, 2016 at 10:43 AM,
Marcus Müller <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:marcus.mueller@ettus.com" \
target="_blank">marcus.mueller@ettus.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div bgcolor="#FFFFFF" text="#000000"> Hi Sanjoy,<br>
<br>
if you have an octoclock, you don't need the connection
from the first X310 to the octoclock. And you <b>must</b>
set all USRPs to external, if you want to use the external
clock for all USRPs.<br>
<br>
So, your diagram is still impossible, because it includes
a loopback on the leftmost X310. I don't understand why
you think you need to make the connection from the left
USRP to the Octoclock, could you explain?<br>
<br>
<br>
Best regards,<br>
Marcus
<div>
<div class="h5"><br>
<br>
<div class="m_8983338922032068770moz-cite-prefix">On
27.10.2016 10:32, Sanjoy Basak wrote:<br>
</div>
<blockquote type="cite">
<div dir="ltr">Hi Marcus,
<div>Thanks for the explanation. Now I
understand. </div>
<div>We have 4 X310s and one equipped with GPSDO.
We are trying to make time and phase
synchronized MIMO operation. So the final goal
is to make this configuration work.<br>
<img src="cid:part3.F8A27E80.475133E9@ettus.com"
alt="Inline image 1" height="198" width="410"></div>
<div><br>
</div>
<div>As we already have one GPSDO module, we are
willing to buy one Octoclock without GPSDO. It
would also save some money. </div>
<div>But if I want to make this configuration
work, I will have to put all the USRPs on
external. If I put one on internal and others on
external, then it would be the same as daisy
chained. </div>
<div><br>
</div>
<div>Could you please tell me if this
configuration is anyhow possible with Octoclock
(without GPSDO), by modifying UHD code or using
any patch. </div>
<div>Or we must buy Octoclock-G.</div>
<div><br>
</div>
<div>Best regards</div>
<div>Sanjoy<br>
<br>
<br>
</div>
<img moz-do-not-send="true"
class="m_8983338922032068770mailtrack-img"
src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7"
height="0" width="0"></div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Wed, Oct 26, 2016 at
4:50 PM, Marcus Müller via USRP-users <span
dir="ltr"><<a moz-do-not-send="true"
href="mailto:usrp-users@lists.ettus.com"
target="_blank">usrp-users@lists.ettus.com</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0
0 0 .8ex;border-left:1px #ccc
solid;padding-left:1ex">
<div bgcolor="#FFFFFF" text="#000000">
<p>Hi Sanjoy,</p>
<p>you've got a misunderstanding there.</p>
<p>If you set the reference input to
external, the USRP stops using its own
reference oscillator, but uses what you
feed in externally.</p>
<p>So, the USRP used to generate the
reference for the other one must be set to
use its internal oscillator, or else
there's no active 10MHz reference in your
overall system.<br>
</p>
<p>Best regards,</p>
<p>Marcus<br>
</p>
<div>
<div class="m_8983338922032068770h5"> <br>
<div
\
class="m_8983338922032068770m_2221750532959179453moz-cite-prefix">On 10/26/2016 \
04:43 PM, Sanjoy Basak via USRP-users wrote:<br>
</div>
</div>
</div>
<blockquote type="cite">
<div>
<div class="m_8983338922032068770h5">
<div dir="ltr">
<div>Hello everyone,</div>
<div>I am planning to make the
following configuration to test
the phase and time coherence
between 2 X310s. One X310 is with
GPSDO. I am taking 10 MHz
reference and 1 pps signal from
that usrp and then feed both USRPs
with the same signal distributed
from a T connector. </div>
<div><br>
</div>
<div><br>
</div>
<div><img
src="cid:part6.6B1F90F1.F1F8E102@ettus.com"
alt="Inline image 3"
style="margin-right:0px"
height="177" width="304"><br>
</div>
<div><br>
</div>
<div>However, it did not work.</div>
<div><br>
</div>
<div>Afterwards I found out that the
problem is in this configuration.
If I take the 10 MHz signal and 1
pps signal from ref_out and
pps_out and feed that USRP with
the same signal (with time and
clock reference External), it does
not work.</div>
<div><img
src="cid:part7.42299FEA.CBD7824F@ettus.com"
alt="Inline image 4"
style="margin-right:0px"
height="157" width="271"></div>
<div><br>
</div>
<div>Could anyone tell me how to
make it work. I am using uhd 3.9.2<br>
</div>
<div><br>
</div>
<div>Best regards</div>
<div>Sanjoy</div>
<br>
<br>
<img moz-do-not-send="true"
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class="m_8983338922032068770m_2221750532959179453mailtrack-img" height="0" \
width="0"></div> <br>
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