[time-nuts] Continously drifting HP 10811...

[Charles Steinmetz]

Ulf wrote:

> the oscillators exhibit a monotonus EFC voltage drift towards 0 volts.  About + 1 mV in 3 minutes.
>    *   *   *
> Test time has been 3 Days, and I beleive thata 10811 should have been able to reach thermal equilibrium during this time.

There is much more than thermal equilibrium goijng on.  Any oscillator 
that has been disturbed in any manner [meaning, disturbed from a normal 
state of being powered up and running 24/7/365 in a nice, quiet 
location] will need more time to settle in.

A disturbance can be most anything -- mechanical shock, humidity change, 
temperature change, adjusting the frequency, being powered off and back 
on, etc., etc.

Each oscillator is unique about dealing with disturbances.  Some go 
crazy, wandering around in both directions for weeks or months until 
they settle and changing the direction of their aging drift.  Some 
settle to a different frequency than they were on before, and need to be 
adjusted (which is its own disturbance, so it may need to be done a few 
times over the course of a month or more).

Where being powered down is the disturbance, how badly an oscillator 
behaves when it is powered back on often depends on how long it has been 
off.  If it has been off for a week or more, you could well be starting 
all over again, just like with a new oscillator.  Also, oscillators that 
have been off for a long time have often been disturbed in other ways 
while they were off -- jostling, removal from equipment, being tossed 
across the room (you'd be horrified at how salvage folks treat 
oscillators and other delicate instruments, if you knew), being shipped 
across the country (or around the world), exposed to temperature 
extremes, etc., etc., etc.

Bottom line -- if a quartz oscillator has been powered off for weeks or 
more, expect it to take at the very least a week, and in my experience 
usually considerably longer -- a month, or even a year -- to settle to a 
drift rate that a time-nut would consider acceptable.

My best 10811-class oscillator is a Symmetricom that looks and works 
just like a double-oven 10811, which came as original equipment in an HP 
GPSDO.  I thought it would never settle, and it took more than six 
months to reach a "time-nuts-acceptable" drift rate.  It continued to 
improve for another six months, until it finally settled in as my best 
10811-class oscillator.  It has been powered up continuously for over 
twelve years now, and it still is.

Be patient.

Charles