[time-nuts] GPSDO recovery from holdover
magnus at rubidium.dyndns.org
Sat Dec 1 22:39:24 UTC 2012
On 12/01/2012 06:28 PM, Said Jackson wrote:
> Hello Azelio,
> We added a user adjustable jam-sync threshold some time ago for European
> DVB-T applications for that reason. The customer can now decide the phase
> window in which the frequency is drifted slowly without a phase jump.
Interesting to hear that others have done the same thing. It seemed like
a decent way of dealing with it.
> But I think your math may be off, with default settings we typically do
> phase adjustments with about 2E-011 (0.02ppb, 0.0002Hz at 10MHz,
> 0.02Hz at 1GHz carrier) frequency offsets. To correct 1000ns offset from
> your example, it would take about 50K seconds, or a bit more than a half
> a day with those settings.
One can also wonder if the limit is relevant, as you are about to
resolve a rather catastrophic situation where you already cause
interference, so moving out of it quickly should be first priority and
only when back to reasonable time-error would it be relevant to obey
frequency error limits.
The transmitters and the recievers would be able to follow, as they have
large enough bandwidth for it.
> But if you set the loop parameters more aggressively to 1ns/s as in your
> example, it would take less than 20 minutes to correct 1us.. Not 12hrs.
> Unless you meant to say ms?
What's a off by one prefix among friends?
But still, one has to be careful.
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