[time-nuts] GPSDO time constant
magnus at rubidium.dyndns.org
Thu Jan 8 10:58:42 UTC 2009
Poul-Henning Kamp skrev:
> 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.
Isn't this more due to surrounding (obviously flawed) heuristics rather
than the PLL?
Interesting never the less.
> 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.
Most labs would have issues with a 2g turnover. :)
Flipping oscillators that runs is evil and should be avoided at all
times. Should be in the rulebook for time-nuts.
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