[time-nuts] PPS phase between two GPS units.

[Graham / KE9H]

Are they running off the same power supply?
If so, I would run them from different power supplies as an experiment.
--- Graham

==

On Tue, Dec 22, 2015 at 6:19 AM, Attila Kinali <attila at kinali.ch> wrote:

> On Tue, 22 Dec 2015 11:57:55 +0100
> Mike Cook <michael.cook at sfr.fr> wrote:
>
> > > A sampling difference of 1 cycle with 48Mhz clocks would give you ~21ns
> > offset if not using sawtooth correction. Can you do the sawtooth
> correction
> > and see if the offset is reduced?
>
> This is the most likely explanation. The LEA-6 modules use a 24MHz
> oscillator
> which is doubled for the processor, leading to the 48MHz clock.
>
> >   Good thinking Brian. But I would expect the difference to wander from
> 21s
> > UNLESS the the two receivers clocks are lock stepping. Injection locking
> > might do this if the two module are physically close enough.
>
> Injection locking wont work by simply playing the modules close to
> eachother.
> The oscillators are shielded well enough that quite some injection energy
> would
> be needed. Unless the TIMEPULSE2 output of one module is used to generate a
> 8MHz signal which is directly injected into the power suplly of the other,
> i
> don't see how injection locking would work. And even then, I wouldn't be
> sure
> if injection locking could be acheived.
>
> What could be done, though, is to lift the shield over the cpu side of the
> LEA-6, unsolder the oscillator and use an external 24MHz oscillator to
> supply both LEA-6 modules.
>
> If you do this, you could even go as far as to use the sawtooth correction
> message to stear the reference oscillator. That way you wouldn't need to
> measure the PPS output and could to a "fully" digital control system
> instead.
>
>                         Attila Kinali
>
> --
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