[time-nuts] OCXO startup transient
hmurray at megapathdsl.net
Sat Jun 27 19:22:51 EDT 2009
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
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.
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.
For my purposes, it takes a few hours to a few days to settle down, depending
upon how stable you want it.
Watch for scale changes.
First 3 hours:
First 3 days:
First 10 days:
These are my opinions, not necessarily my employer's. I hate spam.
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