[time-nuts] GPS Disciplined Oscillators
SAIDJACK at aol.com
SAIDJACK at aol.com
Wed Apr 25 14:18:23 EDT 2007
In a message dated 4/25/2007 09:50:38 Pacific Daylight Time,
mfeher at eozinc.com writes:
>So, to
>reiterate the question, if I was clear enough, what kind of frequency
>excursions should I anticipate to see amongst my three disciplined
>oscillators in lets say 24 hours, or in a month. Assume GPS disciplining was
>working all of that time (can I even assume that with aging?). BTW, how is
>my assumption regarding the oscillators aging?
Hello Mike,
from my experience, good oscillators will age parts in 1E-08 per day or
less. Bad ones can age much faster, some parts in 1E-06 in the first days even.
That's a pretty significant variation in EFC voltage required to compensate
that.
We have seen units that age significantly in the first 2 - 3 days, then slow
down, and after 6 months or so almost have no aging. We have seen units
where the aging actually accelerates over time.
Aging is a very slow changing process after the crystal has run some days
(second derivative is small), so GPS locking will usually easily compensate this
error.
There are oscillators that have popcorn noise (frequency jumps) that can be
really annoying, and this effect is similar to rapid aging (from one second to
another): almost sudden the phase/frequency of the OCXO changes radically
from one second to another. This is usually caused by either dust particles
leaving, or landing on the crystal, the crystal "cracking" in it's holders, or
radioactive particles hitting the crystal.
Also, thermal effects will usually require much larger shifts in EFC voltage
than aging, unless you are using a double-oven high quality OCXO. Thermal
effects on the required EFC voltage usually swamp aging effects and are harder
to deal with because they are more or less random, and not a nice (almost)
straight line on the EFC voltage.
bye,
Said
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