[ntp:questions] GPS Offset problems
utahcbs at gmail.com
utahcbs at gmail.com
Sat Jan 31 01:09:27 UTC 2015
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.
remote refid st t when poll reach delay offset jitter
188.8.131.52 10.20.229.51 2 u 33 64 7 33.777 10.353 5.371
time.utah.edu 184.108.40.206 3 u 35 64 7 0.880 1.186 0.182
utcnist2.colora .ACTS. 1 u 31 64 7 13.350 1.439 0.042
220.127.116.11 .ACTS. 1 u 32 64 7 31.841 5.743 1.930
freiburg .GPS. 1 u 31 64 7 5.336 -999.51 40.219
shaun .GPS. 1 u 31 64 7 5.072 -999.65 1.103
augsburg .3801. 1 u 32 64 7 4.599 970.238 2.261
This is obviously right after starting NTP, but this is the trend that stays
even after NTP is locked on.
Any idea what I am doing wrong?
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