[time-nuts] GPSDO time constant
phk at phk.freebsd.dk
Thu Jan 8 08:57:26 UTC 2009
In message <B6F04190894A41EEAAE0305A898A548E at pc52>, "Tom Van Baak" writes:
>Here are ADEV plots and interesting results from a recent
>experiment on varying the time-constant of a GPSDO:
Tom, part of the reason for the sub-optimally short default time
constant is to be able to cope with worst-case specs of the
Even though they are pretty good, shifts in voltage, temperature
and orientation does affect them.
A very good example of this effect is the NTPD PLL, which
uncritically belives otherwise unplausible good news, and
lengthens the poll-period to 20 minutes and then refuses
to accept that it did it wrong, until i thas seen three
or four (= one hour) samples saying so, after which it
breaks lock and starts over.
In a lab setting, it makes sense to increase over the default
time-constant, just remember that it impacts your loops ability
to cope with for instance a 2g turnover.
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
More information about the time-nuts