[USRP-users] Phase drift issue of N310

Marcus D. Leech patchvonbraun at gmail.com
Thu Mar 14 17:14:22 EDT 2019


On 03/14/2019 05:07 PM, Ali Dormiani via USRP-users wrote:
> Hello all,
>
> Sorry for spreading misinformation. I frequently conflate clock and LO 
> incorrectly. Additionally the results I posted are for an array of 
> multiple N310's which definitely have different clocks.
>
> I was taught in class that carrier frequency offset happens when an 
> access point (AP) and client have imperfect LO's. (EX. wifi router at 
> 2.41 GHz and laptop at 2.39 Ghz).
>
> Looking at the block diagram, could separate LO's for each AD9361 be 
> the source of this phase behavior?
>
Independent N310s that aren't sharing a reference clock cannot be relied 
upon to have consistent phase and frequency.  This is normal and
   expected.  No two oscillators will operate at precisely the same 
frequency.  The more $$$ you spent on an oscillator, the higher the quality,
   with a non-linear $$$ vs quality curve.

But expecting two independent radios to be on exactly the same frequency 
and phase without an external, common, reference, is not
   realistic at all.


>
>
>
>
>
> On Thu, Mar 14, 2019 at 1:39 PM Damon via USRP-users 
> <usrp-users at lists.ettus.com <mailto:usrp-users at lists.ettus.com>> wrote:
>
>     Hi Marcus,
>
>     The UHD Version is v3.14.0.0-rc1.
>
>     Best regards,
>
>     Damon
>
>     >> Hi Ali,
>     >>
>     >> The daughterboards have their own clock generators, but they
>     are not
>     >> exactly 'independent'. At least they don't have to be, as they
>     share the
>     >> same reference clock. Look at the block diagram:
>     >>
>     >> https://kb.ettus.com/images/9/9d/USRP_N310_N300_DB_Schematic.pdf
>     >>
>     >> and "Ref Clock" block. I don't have N310 and I know that
>     reality can be
>     >> a bit far from expectations (i.e. look at my "What makes sense
>     and what
>     >> doesn't in the way carrier frequency is set for TwinRX
>     currently?" post).
>     >>
>     >> But maybe the daughterboards can be configured to use that
>     reference clock.
>     >>
>     >>
>     >> Best Regards,
>     >> Piotr Krysik
>     > The LMK clock generator uses the reference clock from the
>     mainboard, so
>     > there should not be any mutual phase-jitter/drift issues.  I can
>     test this
>     >     on my N310 in the coming day or two.
>     >
>     > What version of UHD is in use?
>
>
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>
>
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