[time-nuts] GPSDO time constant

[Magnus Danielson]

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:
>>
>> http://www.leapsecond.com/pages/tbolt-tc/
> 
> 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
> oscillator.
> 
> 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.

Cheers,
Magnus