[time-nuts] OCXO Retrace

Chuck Harris cfharris at erols.com
Thu Feb 11 11:59:26 EST 2016

I would venture that your unit has a broken SMD part, or a bad
solder joint.

Try using a wooden chopstick, and lightly pressing here and there,
and touching various parts to see what happens.

-Chuck Harris

Artek Manuals wrote:
> 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.
> Dave
> 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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