[time-nuts] Re: Realtime comparing PPS of 3 GPS

[Bob kb8tq]

Hi

The variation you see is dependent on a number of things. One of them is space 
weather. If you do your run during a very active period ( typically peak sun spots)
you may see some very dramatic swings on a single band device. 

Bob

> On May 30, 2022, at 3:00 AM, Erik Kaashoek via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> Further evaluation did shown the time differences between the 3 GPS modules was due to difference in the trigger level setting of the timer/counter and difference in length of GPS antenna cables.
> After removal of the phase drift due to Rb frequency offset the attached image shows the phase differences of the 3 modules versus a Rb reference.
> The two ATGM modules are very consistent over a 2.8 hours period. The NEO-7M varies wildly  with phase errors above 100 ns. Possibly due to a somewhat less optimal antenna position.
> It seems phase variations over time in the order of 10-20 ns are indeed unavoidable, even with a good antenna.
> Erik.
> <3GPS_phase_difference.png>_______________________________________________
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