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

Marcus D. Leech patchvonbraun at gmail.com
Tue Mar 5 11:19:28 EST 2019


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
>
>
>
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> *From:* USRP-users <usrp-users-bounces at lists.ettus.com> on behalf of 
> Marcus D. Leech via USRP-users <usrp-users at lists.ettus.com>
> *Sent:* Tuesday, March 5, 2019 7:03:42 PM
> *To:* 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
>
>
>
>
>
>>
>> /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!/
>>
>> 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 
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>>
>

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