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

WB6BNQ wb6bnq at cox.net
Tue Dec 11 04:55:40 UTC 2012

Hi Charles,

Well, perhaps you are not looking close enough.  That is you need to be observing
at a finer level of comparison.  The changes, observed here and at another
location, are in parts in 10-10 to 10-11 range, sometimes larger.  At one of the
locations there was a direct correlation to the air conditioning cycle.


"Charles P. Steinmetz" wrote:

> >That temperature sensor does have an effect on the final outcome as
> >it is part of
> >the internal equation.  So buffering the ambient temperature is important.
> I've heard this before, but the evidence I have seen does not seem to
> support the proposition.
> While switching the Dallas chip in one, I used the opportunity to
> bring the chip temporarily outside of the Tbolt housing on a cable to
> investigate whether the Tbolt makes any internal use of the
> temperature data.  Neither freeze spray nor bringing a soldering iron
> near the chip, when it was outside of the Tbolt housing and the Tbolt
> housing was well insulated from the changes in chip temperature,
> seemed to have any effect on the operation of the Tbolt, either
> normal or in holdover.
> I have also run Tbolts with the newer ("wrong") temperature chips for
> long periods, and have not observed any systematic differences in
> performance between them and units with the older chips, either in
> normal operation or in holdover.  In Tbolts with the newer chips, the
> reported temperature often has little connection with the actual
> temperature and, at times, jumps abruptly, yet the Thunderbolts
> operate normally with no corresponding jumps in operating parameters.
> My supposition/conclusion is that the temperature sensor was provided
> so telcom operators could get a rough idea of the temperature in
> remote cell-site transmitter shacks, not for internal use by the Tbolt.
> As long as the Tbolt is housed so that its reported temperature does
> not change too rapidly, the oven control loop will keep the crystal
> very close to its set temperature over a wide range of ambient
> temperatures.  I have used this approach and have also actively
> controlled the housing temperature, and have not observed any
> material difference in frequency or timing stability between the two
> approaches.
> Best regards,
> Charles
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