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

Marcus D. Leech patchvonbraun at gmail.com
Mon Jan 27 01:24:00 EST 2020

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>
> *Sent:* Thursday, January 23, 2020 12:48 PM
> *To:* Sourin Mondal (Vehere) <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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