[USRP-users] different phase difference using splitter on each run

Koyel Das (Vehere) koyel.das at vehere.com
Tue Mar 5 22:41:00 EST 2019


The timed commands are as follows in rx_multisamples.cpp


if(sync=="now"){
        //This is not a true time lock, the devices will be off by a few RTT.
        //Rather, this is just to allow for demonstration of the code below.
        usrp->set_time_now(uhd::time_spec_t(0.0));
        }
        else if (sync == "pps"){
        usrp->set_time_source("external");
        usrp->set_time_unknown_pps(uhd::time_spec_t(0.0));
        boost::this_thread::sleep(boost::posix_time::seconds(1)); //wait for pps sync pulse
        }
        else if (sync == "mimo"){
        UHD_ASSERT_THROW(usrp->get_num_mboards() == 2);

        //make mboard 1 a slave over the MIMO Cable
        usrp->set_clock_source("mimo", 1);
        usrp->set_time_source("mimo", 1);

        //set time on the master (mboard 0)
        usrp->set_time_now(uhd::time_spec_t(0.0), 0);

        //sleep a bit while the slave locks its time to the master
        boost::this_thread::sleep(boost::posix_time::milliseconds(100));
        }

1. "now", 2 ."pps" and 3. "mimo"

I was using "now" but still I don't get same phase difference in each run. Is there any other time command that I have to use or what do I have to set?

Regards,


Koyel Das
Senior – Product Engineer

Vehere | Proactive Communications Intelligence & Cyber Defence
M: +919051132173 | T: +91 33 40545454 | F: +91 33 40545455 | W: www.vehere.com<http://www.vehere.com/>

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________________________________
From: Marcus D. Leech <patchvonbraun at gmail.com>
Sent: Wednesday, March 6, 2019 9:06:24 AM
To: Koyel Das (Vehere); 'USRP-users at lists.ettus.com'
Subject: Re: [USRP-users] different phase difference using splitter on each run

On 03/05/2019 10:28 PM, Koyel Das (Vehere) wrote:

"I'm not familiar with the 2964R, so can't personally comment on it."


Sorry I meant 2954 R. Does it also have LO sharing or that is not required in that?


Regards,

That model is based on the UBX transceiver card, which doesn't have LO sharing, but using timed commands can cause the two
  synthesizers to come into phase alignment.




Koyel Das
Senior – Product Engineer

Vehere | Proactive Communications Intelligence & Cyber Defence
M: +919051132173 | T: +91 33 40545454 | F: +91 33 40545455 | W: www.vehere.com<http://www.vehere.com/>

[unnamed]<https://www.linkedin.com/company/vehere-interactive-p-ltd> [unnamed (1)] <https://twitter.com/VehereIndia>  [unnamed (2)] <https://www.facebook.com/VehereIndia/>

Vehere is the proud recipient of the Fastest Growing Technology Company Awards in India & Asia since 2012!

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________________________________
From: Marcus D. Leech <patchvonbraun at gmail.com><mailto:patchvonbraun at gmail.com>
Sent: Tuesday, March 5, 2019 9:57 PM
To: Koyel Das (Vehere); 'USRP-users at lists.ettus.com<mailto:USRP-users at lists.ettus.com>'
Subject: Re: [USRP-users] different phase difference using splitter on each run

On 03/05/2019 11:21 AM, Koyel Das (Vehere) wrote:
So they don’t share same master oscillator? Is this true for 2964R as well?
Do you mean the reference clock on the board?  They all share that, but each channel has its own LO synthesizer.

I'm not familiar with the 2964R, so can't personally comment on it.

You can achieve 4-channel phase coherence with the TwinRx--see the APP Note here:

https://kb.ettus.com/Direction_Finding_with_the_USRP%E2%84%A2_X-Series_and_TwinRX%E2%84%A2


Koyel Das
Senior – Product Engineer
Vehere | Proactive Communications Intelligence & Cyber Defence
M: +919051132173 | T: +91 33 40545454 | F: +91 33 40545455 | W: www.vehere.com<http://www.vehere.com>



Vehere is the proud recipient of the Fastest Growing Technology Company Awards in India & Asia since 2012!

The content of this e-mail is confidential and intended solely for the use of the addressee. The text of this email (including any attachments) may contain information, which is proprietary and/or confidential or privileged in nature belonging to Vehere Interactive Pvt Ltd and/or its associates/ group companies/ subsidiaries. If you are not the addressee, or the person responsible for delivering it to the addressee, any disclosure, copying, distribution or any action taken or omitted to be taken in reliance on it is prohibited and may be unlawful. If you have received this e-mail in error, please notify the sender and remove this communication entirely from your system. The recipient acknowledges that no guarantee or any warranty is given as to completeness and accuracy of the content of the email. The recipient further acknowledges that the views contained in the email message are those of the sender and may not necessarily reflect those of Vehere Interactive Pvt Ltd. Before opening and accessing the attachment please check and scan for virus. WARNING: Computer viruses can be transmitted via email. The recipient should check this email and any attachments for the presence of viruses. The company accepts no liability for any damage caused by any virus transmitted by this email.
________________________________
From: Marcus D. Leech <patchvonbraun at gmail.com><mailto:patchvonbraun at gmail.com>
Sent: Tuesday, March 5, 2019 9:49:28 PM
To: Koyel Das (Vehere); 'USRP-users at lists.ettus.com<mailto:USRP-users at lists.ettus.com>'
Subject: Re: [USRP-users] different phase difference using splitter on each run

On 03/05/2019 11:10 AM, Koyel Das (Vehere) wrote:
Are RX1 and RX2 of RF0 controlled by same master oscillator? Will connecting two antennas to RX1 and RX2 of RF0, rather than to RX1 of RF0 and to RX1 of RF1, give same phase difference between these two channels at every run?
All channels have their own LO.

The TwinRx has LO sharing mode.



Koyel Das
Senior – Product Engineer
Vehere | Proactive Communications Intelligence & Cyber Defence
M: +919051132173 | T: +91 33 40545454 | F: +91 33 40545455 | W: www.vehere.com<http://www.vehere.com>



Vehere is the proud recipient of the Fastest Growing Technology Company Awards in India & Asia since 2012!

The content of this e-mail is confidential and intended solely for the use of the addressee. The text of this email (including any attachments) may contain information, which is proprietary and/or confidential or privileged in nature belonging to Vehere Interactive Pvt Ltd and/or its associates/ group companies/ subsidiaries. If you are not the addressee, or the person responsible for delivering it to the addressee, any disclosure, copying, distribution or any action taken or omitted to be taken in reliance on it is prohibited and may be unlawful. If you have received this e-mail in error, please notify the sender and remove this communication entirely from your system. The recipient acknowledges that no guarantee or any warranty is given as to completeness and accuracy of the content of the email. The recipient further acknowledges that the views contained in the email message are those of the sender and may not necessarily reflect those of Vehere Interactive Pvt Ltd. Before opening and accessing the attachment please check and scan for virus. WARNING: Computer viruses can be transmitted via email. The recipient should check this email and any attachments for the presence of viruses. The company accepts no liability for any damage caused by any virus transmitted by this email.
________________________________
From: USRP-users <usrp-users-bounces at lists.ettus.com><mailto:usrp-users-bounces at lists.ettus.com> on behalf of Marcus D. Leech via USRP-users <usrp-users at lists.ettus.com><mailto:usrp-users at lists.ettus.com>
Sent: Tuesday, March 5, 2019 7:03:42 PM
To: usrp-users at lists.ettus.com<mailto:usrp-users at lists.ettus.com>
Subject: Re: [USRP-users] different phase difference using splitter on each run

On 03/05/2019 06:01 AM, Koyel Das (Vehere) via USRP-users wrote:

Hi,


I am using USRP 2955 R and I have connected an antenna to one end of a two channel splitter and connected the other two ports of the splitter to the two RX1 pors of USRP. I am getting different phase difference in each run of USRP though in one particular run the phase difference is constant for all channels. The tuned frequency is 2.4 GHz and sampling rate is 1 MSps so as expected that channel phase differences are almost same. But when I stop acquiring data and restart it using gnuradio or the API, then I am getting again a new value of phase difference across all channels, which is again same across channels. Is USRP so unstable that it gives different value of phase difference for each run for the same frequency, and sampling rate? The setup in the runs are also the same.


Regards,

Koyel


Koyel Das
Senior – Product Engineer

Vehere | Proactive Communications Intelligence & Cyber Defence
M: +919051132173 | T: +91 33 40545454 | F: +91 33 40545455 | W: www.vehere.com<http://www.vehere.com/>

This isn't about "instability".  It's about the way PLL synthesizers work, and the fact that by default each channel is using its own synthesizer.

There are a few things that need to happen:

   All the channels you're receiving need to be in the same multi_usrp block, which, among other things, is a conceptual "synchronization domain".

   Use timed-commands for tuning (which is a bit awkward to arrange in Gnu Radio, you'll have to modify the generated code).  This will arrange
   for the synthesizers to be given a "resynch" signal at exactly the same time.

   OR

   Use the "shared LO" features of the TwinRX cards that are on the 2955.

See the knowledge-base document on the TwinRX and phase-synchronization here:

https://kb.ettus.com/TwinRX






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The content of this e-mail is confidential and intended solely for the use of the addressee. The text of this email (including any attachments) may contain information, which is proprietary and/or confidential or privileged in nature belonging to Vehere Interactive Pvt Ltd and/or its associates/ group companies/ subsidiaries. If you are not the addressee, or the person responsible for delivering it to the addressee, any disclosure, copying, distribution or any action taken or omitted to be taken in reliance on it is prohibited and may be unlawful. If you have received this e-mail in error, please notify the sender and remove this communication entirely from your system. The recipient acknowledges that no guarantee or any warranty is given as to completeness and accuracy of the content of the email. The recipient further acknowledges that the views contained in the email message are those of the sender and may not necessarily reflect those of Vehere Interactive Pvt Ltd. Before opening and accessing the attachment please check and scan for virus. WARNING: Computer viruses can be transmitted via email. The recipient should check this email and any attachments for the presence of viruses. The company accepts no liability for any damage caused by any virus transmitted by this email.





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