[USRP-users] Phase Synchronization of two usrp b210's
Marcus D. Leech
patchvonbraun at gmail.com
Mon Feb 11 18:55:57 EST 2019
On 02/11/2019 06:34 PM, Aravind Dhulipalla via USRP-users wrote:
> Hi Marcus,
> Yes, I am following the link and using an external 10MHz and 1pps
> reference signals. The way I am trying to synchronize is to have two
> usrp's transmit different sine waves one with constant phase and the
> other with a varying phase from 0 to 360degrees. I am calculating the
> sum of amplitudes of the received signals and the phase at which the
> amplitude sum is maximum will be the phase offset. By following this
> approach I am getting a phase offset between 0 to 3 degrees. But when
> I issue the next stream command with sine wave of calculated phase
> offset I am seeing a huge phase difference between them anywhere
> between 0 to 180 degrees for each run. I am not sure if my approach is
> a correct one.
I cannot quite parse what you're doing.
Are you saying the *mutual phase* offset changes between runs, or that
the phase measured *between runs* changes?
I would totally expect some phase-offset unpredictability between two
B210s. They aren't designed to have a predictable phase in that sense,
of the way the synthesizers work. They have no phase-resynch, and
since a fractional-N PLL synthesizer "naturally" doesn't lock at any
particular phase-angle relative to the reference, no two PLL
synthesizers, even if seeing EXACTLY THE SAME REFERENCE FREQUENCY, can
be guaranteed to have a predictable-and-low phase-offset after tuning,
even if tuned at "exactly" the same time.
> On Sun, Feb 10, 2019 at 12:59 AM Marcus Müller
> <marcus.mueller at ettus.com <mailto:marcus.mueller at ettus.com>> wrote:
> Hi Aravind,
> first of all, have you seen
> http://files.ettus.com/manual/page_sync.html ?
> You'll find in the last paragraph that after each tuning, your phase
> relationship between different B210s will be random, but constant for
> the run (aside from minor PLL drift).
> So, you need to tune, and then calibrate; how that can be done depends
> on the system you're building.
> Best regards,
> On Fri, 2019-02-08 at 17:03 -0800, Aravind Dhulipalla via USRP-users
> > Hi,
> > Has anyone achieved phase synchronizing between two usrp b210's
> > external reference and pps? If yes I would appreciate any help
> that I
> > can get.
> > Thanks
> > Aravind.
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