[USRP-users] phase-aligning two USRPs without Octoclock

Marcus D. Leech patchvonbraun at gmail.com
Tue Jan 28 12:35:58 EST 2020

On 01/28/2020 05:53 AM, Sourin Mondal (Vehere) wrote:
> Hi Marcus,
> I think my previous email is not sent properly so sending again. 
> Thanks for the information you provided. This 5 degrees is for what 
> frequency? Are you sure its 5 degrees or less? What is the precision?
> Regards,
> Sourin
The component of phase offset from the synthesizers should be small, 
after a phase-reset using timed-command tuning, irrespective of
   frequency.  Other components of phase offset, such as differential 
heating effects, wiring-length differences, etc, will have a
   frequency-sensitive component.

> ------------------------------------------------------------------------
> *From:* Marcus D. Leech <patchvonbraun at gmail.com>
> *Sent:* Monday, January 27, 2020 11:54 AM
> *To:* Sourin Mondal (Vehere) <sourin.mondal at vehere.com>
> *Cc:* usrp-users at lists.ettus.com <usrp-users at lists.ettus.com>
> *Subject:* Re: [USRP-users] phase-aligning two USRPs without Octoclock
> On 01/27/2020 01:00 AM, Sourin Mondal (Vehere) wrote:
>> Hi Marcus,
>> Thanks for the information. Could you please also tell what is the 
>> accuracy with which the phases are aligned between USRP channels, 
>> when we use 10 MHz reference to align, in pico-seconds or nano-seconds?
>> Regards,
>> Sourin
> The answer to that question depends very much on the hardware involved.
> In general, two synthesizers locked to the same clock won't have a 
> zero phase *offset* from one another, but will be phase-coherent
>   on an ongoing basis.
> Now, for *some* types of Ettus hardware, there is special hardware 
> that can arrange to phase-reset during tuning, so that all the 
> participating
>   synthesizers will have small phase-offsets with respect to one another.
> We generally talk in terms of degrees, rather than picoseconds or 
> nanoseconds.  Residual phase offsets will typically be under 5 degrees.
> But keep in mind that things like differential heating of cables, and 
> internal circuit in ANY coherent radio can case the phase relationships
>   to drift slightly.
>> ------------------------------------------------------------------------
>> *From:* Marcus D. Leech <patchvonbraun at gmail.com> 
>> <mailto:patchvonbraun at gmail.com>
>> *Sent:* Thursday, January 23, 2020 12:48 PM
>> *To:* Sourin Mondal (Vehere) <sourin.mondal at vehere.com> 
>> <mailto:sourin.mondal at vehere.com>
>> *Subject:* Re: [USRP-users] phase-aligning two USRPs without Octoclock
>> On 01/22/2020 11:53 PM, Sourin Mondal (Vehere) wrote:
>>> Hi Marcus,
>>> Do I need to use 1 PPS also along with 10 MHz reference? And are 
>>> there any software commands to be used along with these hardware 
>>> configuration for synchronizing multiple USRPs without octoclock? If 
>>> so what are those commands?
>>> Regards,
>>> Sourin
>> You would do well to spend some time with this app-note:
>> https://kb.ettus.com/Synchronization_and_MIMO_Capability_with_USRP_Devices
>> Indeed, there are many app-notes that might be relevant for you.
>> Along with:
>> http://files.ettus.com/manual/

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