[time-nuts] Does adjusting ocxo's degrade adev / madev ?

Don Latham djl at montana.com
Thu Nov 27 20:58:48 UTC 2014


Just replaced an ocxo in my ST620 with a Moron ocxo, which had been unpowered for a few years in all probability. It took several days to come to a reasonable equilibrium. In a system with as many components as an ocxo, I suspect that seeking a new equilibrium will take an appreciable time well beyond design criteria, as Charles expresses. Hunting time constants may indeed be quite long.
Don

> On Nov 27, 2014, at 1:48 PM, Charles Steinmetz <csteinmetz at yandex.com> wrote:
> 
> Mark wrote:
> 
>> I've long had a nagging suspicion that OCXO's that are not adjusted will in practice have lower ADEV than ones that are tweaked regularly.   Several days ago I noticed that one of my 10811's was performing quite well (I believe this is the first time any of 10811's have delivered adev / madev numbers in the 13's) and this was sustained for approx 2 days.   After trimming the frequency and letting it sit for a number of hours  I noticed the adev was notably worse.
> 
> Every time a quartz oscillator is disturbed in any way, its stability is very likely to go down for a time until it settles back in.  The disturbance could be adjusting its frequency (either mechanically or via EFC), interrupting the power, changing the crystal temperature, physically bumping the unit, or anything else that changes its operation.  How long it takes to settle back into "normally stable" operation depends on the crystal itself and on how violent the disturbance was.  I would never expect a quartz oscillator to be back to normal stability for at least some days after a macro frequency adjustment.  [Tiny, tiny adjustments such as done by ongoing GPS discipline do not seem to have a large effect on the stability of quartz oscillators.]
> 
> But I note that you say an oscillator that had never delivered stability in the e-13's had a couple of very good days, and then didn't go back to the e-13's in a number of hours.  First, you probably shouldn't expect it to go back to the "couple of good days" level -- it's likely to go back to its "normal" level.  And second, you shouldn't expect it to get there for at least a few days.
> 
> Best regards,
> 
> Charles
> 
> 
> 
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