[time-nuts] OCXO Retrace
Charles Steinmetz
csteinmetz at yandex.com
Thu Feb 11 11:11:59 EST 2016
Bob wrote:
>The Trimble TBolts were made over a long period of time. If you
>compare "early" (90's) units to the "late" (~2005) units there are
>differences in performance.
If I'm not mistaken, that is largely because they used several
different (part number) OCXOs. I'm not sure it's so much a
progression over time as it is evidence of "special" models built to
user specifications. The ones I've seen with any specific OCXO seem
to perform similarly to others with that same OCXO. [1]
[1] Except that, as I've noted before, there seem to be two distinct
groups of the P/N 37265 OCXOs, one group with tempco about 100x
better than the other, larger group. Other than the tempcos, these
two groups seem to perform similarly. My working hypothesis is that
all 37265s are supposed to perform like the low-tempco units, but
that the ovens in the high-tempco units are not adjusted correctly to
the turnover temperature of the crystals. I did hack into one of the
high-tempco units and, after some experimentation, was able to get
its tempco down into the ballpark of the low-tempco units by
adjusting the oven temperature (but an anecdotal result for one unit
doesn't prove anything). I have not been able to discern any pattern
WRT date codes or serial numbers between these two groups, but my
sample size is probably too small to reveal one even if it were there.
Best regards,
Charles
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