[ntp:questions] GPS Offset problems

Brian Inglis Brian.Inglis at SystematicSw.ab.ca
Sat Jan 31 04:17:46 UTC 2015

On 2015-01-30 18:09, utahcbs at gmail.com wrote:
> I built a GPS (HP 58503) based NTP server about 10 years ago.  It worked fine but eventually died, and I built a replacement.  But I am having no end of problems with long offsets.
> The new machine is Linux-based with a Z3801 and PPS.  It consistently shows an offset as compared to other NTP clocks.
> After about a week of trying to figure it out, I got desperate and bought a used Datum Tymserv 2100 as a stopgap until I could figure out the problem.  It worked great until recently, and now it has a 1-second offset as compared to the world.
> Both servers share a common antenna (Symmetricom GPS LT) on a HP/Symmetricom splitter.  Obviously I make certain that I have good GPS signal and everything is locked.
> I recently purchased a SECOND Datum 2100 and it had the exact same offset.  So I ran a new wire and hooked it to a different antenna of the same model, same offset.
> So I changed to a different antenna, same offset -1 second as compared with known good network servers.
> Here is what I have running in this example:
> Freiburg = Datum 2100
> Augsburg = Linux server with HP Z3801, shared with Freiburg's antenna
> Shaun = Datum 2100 on different antenna
> When I go into Augsburg, all seems good (PPS currently disabled), but it is off by nearly a second in the other direction, +1 second from known-good servers so +2 seconds from my other servers.
> Clearly I am doing something wrong.  I've been beating my head against a wall for quite a while trying to figure it out.  I have another system with a Z3805 that has an offset of 16000 with a good lock.

See recent posts on timenuts archives about Datum Tymserve 2100 et al early leap second, checks, and fixes.

Take care. Thanks, Brian Inglis

More information about the questions mailing list