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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