[time-nuts] OCXO aging behavior

Rick Karlquist richard at karlquist.com
Wed Sep 2 17:25:33 UTC 2009

Alan Melia wrote:
> Maybe this is not "aging" you are looking at...parts in 10^9 over a few
> days

I agree.  Aging is the forest and you are watching the trees.
The adjustment pot could also have some mechanical relaxation
issues that work like delayed hysteresis.  The 10811 designers
had fits getting the piston trimmer capacitor to behave.
Originally, you would adjust the frequency and then it would
walk off.  Turned out to be the lubricant in the cap was
migrating around.

>>> I had always thought that crystals changed frequency consistently in one
>> direction as they age. That is until recently. I was trying to get the

This is not always true any more than the idea that aging always
keeps getting better and better with time.  It is probably more valid
for low performance crystals that have substantial contamination
that is trying to reach equilibrium.  High quality crystals are so
clean that this mechanism is negligible.  Instead, the built in
stress of the crystal is being relieved, but cracks can propagate
like a cracked windshield.  Thus nothing is particularly predictable.
(Any predictable aging mechanism will be identified and eliminated
in a good fab).

Rick Karlquist N6RK

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