[ntp:questions] like a kid with a new toy (PPS jitter)

Dave Hart davehart at gmail.com
Thu Feb 5 07:58:42 UTC 2009


After close to a week of calibration, I fudged then flipped off
noselect on my GPS+PPS refclock in the early minutes of the UTC day.

It looks to me (from my limited perspective of no other local
refclocks) that I've gone from single-digit milliseconds to double-
digit microseconds accuracy.

Looking at the last 800 loopstats lines for the refclock, representing
a bit more than 3 hours of 16s polls, the offsets in microseconds look
like

-79.497	min
-26.961	mean
20.565	max
17.381	stddev

The jitter (us)

1.907	min
7.974	mean
35.64	max
4.651	stddev

How does that look to more jaded PPS eyes?

The refclock is a Garmin GPS 18x LVC connected to a dual PII 400 via
serial with PPS wired to the carrier detect pin.

Cheers,
Dave Hart




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