Mark wrote:
For the first 6 hours PU stayed at 432us, then it dropped sharply to
5.6us and then slowly climbed to 18us.
Doesn't seem right to me.
Nothing it does in the first 6 hours has anything to do with
anything. (1) The oscillator will be swinging around wildly
(comparatively speaking, relative to its stability after it has been
running unmolested for months). (2) Further, 6 hours is almost
certainly a shorter period than it normally uses to forecast PU, so a
forecast after ANY six-hour period of data collection (even when
fully warm and stable) will not be its best estimate.
I do not know HP's algorithm, but it sounds like it didn't seriously
try to compute PU until after 6 hours, then it started trying with
(1) too little data and (2) data from an unstable oscillator, so it's
no surprise it is wandering around. I'll be very surprised if it
settles down near its long-term stability in less than a month of
continuous, undisturbed running (continuous meaning don't turn it
off, undisturbed meaning don't move it or bump it very hard -- if you
do either of these, start counting from zero again).
Be patient. OCXOs need time to reach stability when re-started in a
new environment (particularly if they have been off for more than a
few days and/or bumped around, both of which are probably true of
yours). Some are better about this than others, but what I've said
is pretty typical of the 10811-and-better class of OCXOs, IME.
Best regards,
Charles
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