[time-nuts] Thunderbolt oven / non-stable operating temperature
Charles P. Steinmetz
charles_steinmetz at lavabit.com
Wed Dec 12 03:33:48 UTC 2012
>Although the Trimble oscillator has superb phase noise
>performance, it has TERRIBLE temperature sensitivity.
It appears that most do but some don't. Between the results I have
seen posted on the list (Lady Heather screen shots) and my own data,
they seem to fall into two groups. I have two with excellent
oscillator tempcos, but a third unit I have is about 100x worse and
the sign of its tempco is reversed compared to the first two. That
one appears to consume approximately the same oven power as the other
two, and heats the housing approximately equally, so the oven does
not appear to have a gross failure. All three have Trimble 37265 OCXOs.
I initially thought the third unit's oven controller was broken (low
gain). Then I noticed that the great majority of posted Lady Heather
plots appear to be from units similar to that one, with the much
higher tempco and reversed tempco sign compared to my two low-tempco
units. But I have seen a few other plots that appear to be from
units similar to my first two. The two with the low tempcos do not
appear to be inferior to other Tbolts with respect to stability, PN, or aging.
I'm inclined to think that all 37265 OCXOs are supposed to work like
my first two, and that the ones with large tempcos are the result of
a supply or manufacturing error (most likely, a mismatch between the
oven set point and the crystal). But who knows? There do seem to be
many more of the ones with large tempcos around. It would be
interesting to take a few 37265s apart to see if there are any
obvious differences between the high- and low-tempco units, and if
tweaking the oven set points would reduce the tempcos of the high-tempco units.
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