[time-nuts] PPS offset between GPS receivers

Gabs Ricalde gsricalde at gmail.com
Tue Dec 4 04:12:53 UTC 2012

I'm using a Symmetricom 58534A GPS timing receiver and a GPS board with a
SkyNav SKG25A1 module driving stratum 1 NTP servers.

On one of the servers, the ppstest output while the 58534A is connected
looks like:
source 0 - assert 1354495734.000000102
source 0 - assert 1354495735.000000040

When I switch the PPS source to the SKG25A1, the ppstest output
indicates the PPS of that receiver is about 2 us early compared to the 58534A:
source 0 - assert 1354495740.999997923
source 0 - assert 1354495741.999997905

The setup looks like this:
58534A GPS -> 10 m CAT5 cable -> MC3486 RS422 receiver -> GPIO
active antenna -> 3 m cable -> SKG25A1 GPS -> GPIO

Both receivers were factory reset before the test.
I'm planning on getting another GPS receiver to check which receiver
is at fault. Has anyone found timing differences this large with their
GPS receivers?

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