[time-nuts] Thunderbolt oven / non-stable operating temperature
shalimr9 at gmail.com
shalimr9 at gmail.com
Tue Dec 11 13:56:31 UTC 2012
These may have been due to improper oven operation in the OCXO. To make sure, you have to bring out the temp sensing chip like Charles has done.
Sent from my Droid Razr 4G LTE wireless tracker.
From: WB6BNQ <wb6bnq at cox.net>
To: Discussion of precise time and frequency measurement <time-nuts at febo.com>
Sent: Mon, 10 Dec 2012 10:55 PM
Subject: Re: [time-nuts] Thunderbolt oven / non-stable operating temperature
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
> Best regards,
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