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

[paul swed]

I think you are doing the right test to see if the splitter delay is the
issue 21 ns is mighty small and a real possibility.
Regards
Paul
WB8TSL

On Mon, Dec 21, 2015 at 8:24 PM, <dan at irtelemetrics.com> wrote:

> Hi All,
>
> So I've been playing with some timing hardware here, and have noticed
> something rather curious. I have two otherwise identical Lea-6T GPS
> modules, configured exactly the same. These units are tied to the same
> antenna, with a splitter with the same length cables running to each unit.
> They were given the same survey coordinates. Initially there was not any
> appreciable difference between the PPS outputs. The outputs were on average
> within about one nS of each other. However after a day or two they started
> to display a difference of about 21nS between the PPS outputs. This is also
> evident in the GPSDO output, as the phase of the 10Mhz is also skewed by
> 21nS or so.
>
> A few days ago I started a 48 hour survey. The came up virtually identical
> coordinates at the end of that survey. After the survey the phase is still
> 21nS different.
>
> At this point, my only thought is the GPS splitter. It's DC coupled to one
> unit, and AC coupled to the other. It is possible there are some delays on
> one output vs. the other due to the blocking caps and bypass inductor in
> the splitter. I've tried swapping the GPSDO units on the splitter, so we'll
> see what happens there.
> Can anyone offer any insight as to why the two units may have a different
> PPS output timing? It's not really a problem, more of a curiosity and
> mildly academic exercise.
> Thanks,
> Dan
>
>
>
>
>
>
>
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