[time-nuts] FA2 internal reference oscillator test

[Mark Sims]

I did a test of the FA2 internal OCXO oscillator.  The FA2 uses this as the reference if you don't connect an external reference.  You can adjust the oscillator frequency with a small pot on the back panel.  As shipped the oscillator was 0.10 Hz off.  I adjusted to be within 0.003 Hz (I didn't try to fiddle it to be spot on).

I did the oscillator test by having it measure an HP-5071A cesium oscillator (10 MHz) which is assumed to be (and is) spot on and very high quality.  Any deviations from the noise floor test that I did earlier are mostly due to the FA2 internal oscillator.

The wobbles in the frequency plot are due to air conditioning.  The oscillator changes freq by around 0.00025 Hz / degree C.  The oscillator drifted at the rate of 0.00635 Hz / day, but the drift rate is slowing down (it's now around 0.005 Hz / day).   It will be interesting to see how it ages in over the next few weeks.
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