[time-nuts] HP 5345A

[Rick Karlquist]

Hal Murray wrote:
> I thought aging was generally uni-directional and reasonably predictable
> if
> you had enough data.
>
> Does it wander in both directions?

This is probably on the list of the "10 greatest myths about
crystal oscillators".  Many decades ago, there were systematic
aging effects such as you speak of.  I remember learning as
a youth that glass crystals age up and metal crystals age down.
Over the years, any such systematic effects have been analyzed
one by one to understand the root cause, and then the process
has been fixed to get rid of that aging effect.  What we are
now left with are tiny cracks and crevasses that grow sporadically
like a crack in an auto windshield.  At least that is what we
think is going on.  The process people, like my friends Charles
Adams and Jack Kusters, have worked themselves out of a job
had taken retirement, because, like the "efficient stock market"
theory, there is no predictability to the aging data.  It is truly
a "random walk down Wall Street" or in this case a random walk
in time.  Oscillators will age in one direction for a while but
may then age in the opposite direction for while for no particular
reason.  Not only that, but crystals will jump a part in 1E^9
or so every so often.  I've never seen a 10811 crystal without
jumps if you wait long enough.  I don't know of any other crystal
makers who claim to not have jumps.

Rick Karlquist N6RK