[time-nuts] What interrupts aging?
kb8tq at n1k.org
Sun Feb 5 18:31:00 EST 2017
Aging can be caused by many things. Stress on the blank (and can and leads and plating and …) is one
source. There are good reasons to believe that quartz vs metal stress can take > 1 month to settle out
to the 90% level. Particle (think borders down to atoms) equilibrium inside the can is another source.
Adsorption / desorption rates on many of the likely candidates also run out into the > 1 month range.
More or less — you can adsorb stuff in a few seconds that takes many weeks to desorb. Yes this is
only the start of a very long list ….
How long an interruption to stir things up? Does the oven go to full power after your interruption? If it
does, things are likely to get tossed around and aging (or retrace or warmup or whatever you want to
call it) is going to get going.
Pile on top of this the fact that crystals are not the only thing that does aging like things. Capacitors
have a fun characteristic known as dielectric absorption. Some (tantalums) have leakage that drops
a LOT with time spent at temperature and voltage. Either way, bump the voltage and things move around
for a while. Use the wrong caps and it can be quite a while.
Next layer is keeping the OCXO at the same temperature. When a “normal” OCXO is sitting there on
the bench, it’s in it’s own very specific temperate zone. Convection (and maybe other things) have acted
over quite a while to set up that zone. Touch it / bump it / move it / blow on it …. you will change the
temperature. Most likely you will change the gradient across the package. Rick wrote some papers
back in the 90’s about why this really messes things up…. ( Again this is the start of a very long list …).
It’s even longer if you have DAC’s and voltage references external to the OCXO.
So yes, you can get aging a lot of ways. Knowing what is and what is not aging can get a bit complicated.
> On Feb 5, 2017, at 3:11 PM, John Ackermann N8UR <jra at febo.com> wrote:
> We know of OCXO that have been continuously running for years and have exceptional aging, supposedly as a result.
> What does it take to interrupt that? A momentary loss of power? The oven cooling down? Some long period of off-time? Or, once the oscillator has baked in will it return to that low aging once it has been powered up and thermally stabilized?
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