[time-nuts] PPS offset between GPS receivers

Bob Camp lists at rtty.us
Wed Dec 5 00:39:49 UTC 2012


Hi

Based on a quick look, the SkyNav does not appear to be a timing specific part. A 2 us error in a navigation part would come as a big surprise.

Bob



On Dec 3, 2012, at 11:12 PM, Gabs Ricalde <gsricalde at gmail.com> wrote:

> 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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