[time-nuts] Thunderbolt oven / non-stable operating temperature

Charles P. Steinmetz charles_steinmetz at lavabit.com
Wed Dec 12 03:33:48 UTC 2012

Mark wrote:

>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.

Best regards,


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