Hal Murray wrote:
A couple of graphs in case anybody is looking for examples...
This is a 3 MHz OCXO from Telco surplus.
The can says EROS-800-M45, 94-12. I haven't found a data sheet but it's
supposed to be equivalent to Isotemp 127-10.
It's got a mechanical adjustment, no electrical adjustment. (I haven't
touched the adjustment.)
The can is 2.5 x 2.75 x 1.75 inches. I'd call it medium quality. Nothing
fancy, but probably better than most of the small ovens. When I was playing
a while ago, I could see changes when I grabbed the can with my fingers.
It was powered off for at least 6 months before I started this run.
I'm collecting samples every 5 minutes. I discarded the first 3 samples
after power on. The first was way low. (It's so far off that the rest of
any graph gets compressed into a flat line.) The next two overshot.
When I run out of other things to do, I'll make another run with samples
closer together for the first few hours. But first I want to watch the drift
some more.
So far, the drift has generally been in one direction. That's when averaged
over several days. There is enough noise on the hour scale that I wouldn't
want to try to predict anything to get better holdover.
Your holdover properties should be evaluated after running for say 30
days. A frequency compensation get you a first degree correction which
together with TDEV measures give you an indication of aggregated
holdover properties.
To my eye, there is a bend in the drift curve at 4 days. I can't think of
any environmental change that happened then. I might have bumped it.
Considering the wobble on day 8, I'd say the day 4 shift is within what
environmental shifts do to you, where as on day 4 the curvature is still
steep so the added effects fools the eye.
Cheers,
Magnus
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