Hi Erik,
have you tried running all receivers off the same antenna via a power
splitter (make sure to dc block all but one receiver)? That should
remove the uncertainty due to antenna differences (location, RF
characteristics, etc.).
Also, are you using ground planes for your puck antennas? These types of
antennas typically require a ground plane for optimal performance [1].
Best regards,
Carsten
[1]
https://content.u-blox.com/sites/default/files/products/documents/GNSS-Antennas_AppNote_(UBX-15030289).pdf#page=16
On 30.05.22 13:00, Erik Kaashoek via time-nuts 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.
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