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

[Alexander Pummer]

swap the two receivers and see which one is leading, if leading is 
changing the delay difference is with the antenna signal distribution
73
KJ6UHN
Alex
On 12/21/2015 8:03 PM, paul swed wrote:
> 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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