The HP 10811A (generally regarded as a pretty good oscillator) has a spec of
4.5E-9 over 70C which is 6.4E-11/C. If I'm reading my notes correctly, that
tbolt oscillator measured at 1.4732E-10 parts/C... about 2.3 times worse than
a 10811A.
Generally Thunderbolt oscillators have rather crappy tempcos. There has been
a lot of talk about them being double oven units, but I seriously doubt that.
They make pretty good T to F converters...
Note that some of the tempco could be due to the power supply, it is outside
of the temperature controlled box. A previous test indicated that about 1/3 of
the tempco was due to power supply variations)
Those temperature cycles in the graph are +/- 10 millidegrees... the
oscillator should be moving 3 parts/trillion over the cycle (assuming no
thermal lag). Such a small change shows up very clearly in the self-reported
OSC error data from the Thunderbolt.
------------------
The oscillator tempco shown on the screen is -1.6 ppb per degree C. 1/10 of
that would be 0.16 ppb/C. I would hope that the oscillator in your Thunderbolt
is much better than that.
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