[time-nuts] Holdover recovery

[Bob Camp]

Hi

On a surplus cell phone GPSDO it’s going to be:

1) System has been down for a while (= something failed) 
2) System is now working ( = something was fixed)
3) The primary system spec must now be met (+/- 100 ns time alignment).
4) The secondary system spec should be met (+/- 5x10^-8 frequency) 
5) Get it done now.

Both the time alignment and frequency specs are highly system dependent. The time
offset is likely to be aligned in a modulo 100 ns step. It then is fine tuned over some 
time period to take out the rest of the error. If it’s done over a 50 second period, they
can do it at a 1x10^-9 frequency offset (but probably don’t …. more likely it’s a higher 
offset at the start of the period).

Bob


> On Apr 3, 2016, at 11:39 PM, Hal Murray <hmurray at megapathdsl.net> wrote:
> 
> 
> Has anybody studied what happens when a GPSDO comes out of holdover?  Has 
> anybody seen any specs?  I don't think I have.
> 
> I think you have a choice of quick recovery for time or frequency, but you 
> can't get both.
> 
> Suppose your setup has been in holdover for a while.  The frequency is 
> slightly off.  The time offset of the PPS pulse will be the integral of the 
> frequency offset.
> 
> What happens when you come out of holdover?  If you fix the frequency, the 
> PPS will stay off.
> 
> Suppose the PPS has drifted by 1 ns.  If you correct that in 1 second, the 
> frequency will need to be off by 1E9 during that second.
> 
> 
> -- 
> These are my opinions.  I hate spam.
> 
> 
> 
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