[time-nuts] OCXO Retrace

Artek Manuals Manuals at ArtekManuals.com
Thu Feb 11 06:05:47 EST 2016

To further underscore Charles point and to add another dimension to the 
discussion.,The Z3801A that I have been working to bring back from 
intensive care in the last two weeks is sensitive to a very slight 
mechanical shock.

The unit was laying open on the bench with all kinds of test clips 
hanging out of it (power IN and monitor of the various DC supply 
busses). At one point I slightly repositioned the Z3801 and in doing so 
"dropped" (front edge only ) about 1/4". Nothing scary but a noticeable 
THUMP. Less than a minute later I noticed that the PPS error began 
drifting lower and over the next 30 minutes stabilized almost 200ns low. 
At that point I powered it down for 5 minutes and then ran a survey 
again and it was fine . I repeated the little experiment a couple off 
times and each time it received a "thump" it started drifting low. 
Simply left alone over a period of several hours it would return to 
center around 0 pps on its own. The moral I took away from the little 
experiment was to make sure the Z3801A's final resting place on the 
bench when it gets out of the hospital and returns to work was in a low 
traffic - "quiet" location where it would not get bumped.


On 2/11/2016 12:16 AM, Charles Steinmetz wrote:
> Bob wrote:
>> I'll see if I can figure out which of these is retracing the "wrong"
>> way and put it in a unit.  I'll let it cook for a couple of days and
>> then post a plot.  Like I said, these are all Trimble 34310-T, though
>> I know that there were at least two manufacturers for that part
>> number.  They were all positive EFC devices with more or less the same
>> frequency range.
> I would expect all OCXOs with the same part number to have the same type
> of crystal (though maybe not from the same manufacturer), so they should
> all be the same (within some distribution around nominal) WRT the
> *warmup* drift.  As to the actual (post-warmup) *retrace* drift, there
> is no right or wrong direction.  If you let an OCXO go cold 100 times,
> wait a day or more (each time), and then power it up, it will likely
> retrace up sometimes and down other times.  One of my 10811s pretty much
> alternates from one cold start to the next (but I very rarely power it
> down).
> Once again, crystals are very individual devices with very individual
> personalities, and they are often unpredictable.  They are made to be
> powered up and left undisturbed for months/years/decades.  Use them that
> way, evaluate them that way, and don't waste time puzzling about what
> they do for the first month after you power them up.  It does not make
> any sense to power them on and off "rapidly" (off for less than a week,
> on for less than a week) and try to draw conclusions about anything that
> matters with respect to their performance.
> Best regards,
> Charles
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