[time-nuts] 10811 crystal orientation

Tom Van Baak tvb at LeapSecond.com
Fri Jul 10 22:51:12 UTC 2009


> One is do crystal oscillators change frequency when they
> are turned. The answer to that is yes. This gravitational
> acceleration effect is rather huge, parts in ten to the 9th
> or so, and anyone can see this. This is why you never
> touch, bump, or move, or rotate a laboratory frequency
> standard (this includes GPSDO and cesium standards).

And to give you a *picture* instead of just numbers... Here is
a plot showing frequency changes in an OCXO (this from a
free-running Thunderbolt GPSDO) over the span of one hour.
Every 5 minutes or so I rotated the rectangular box on some
axis by 90 degrees.

<http://www.leapsecond.com/pages/ocxo-2g/TBolt-2g-6axis.gif>

You can see that the sudden frequency jumps due to change
in g-force on the crystal are about -0.5e-9 to +1.5 e-9, which
is 100x the normal frequency noise for this oscillator (about
2e-11 pk-pk or about 2e-12 adev).

Hopefully this result won't come as a big surprise to anyone; the
so-called "2g turn-over" spec is common for quality oscillators.
Again, this is why when you enter the world of precision timing
at 1e-10 and below you tend not to ever touch your standards.

Now if one of you happened to have a fully-programmable 3-axis
turntable and a couple of hours you could slowly create a most
beautiful high-resolution 3D color plot showing the precise shift
in frequency as a function of axis.

/tvb




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