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

Tom Miller tmiller at skylinenet.net
Mon Dec 10 22:29:32 UTC 2012

Hi Sarah,

The temperature you are seeing is that of a Dallas IC mounted on the main PC 
board. You are seeing the ambient temp of the board, not inside the OCXO 


----- Original Message ----- 
From: "Sarah White" <kuzetsa at gmail.com>
To: "Discussion of precise time and frequency measurement" 
<time-nuts at febo.com>
Sent: Monday, December 10, 2012 5:15 PM
Subject: [time-nuts] Thunderbolt oven / non-stable operating temperature

Ended up with a gently used trimble thunderbolt a few months ago, and
been trying to figure out the best settings to use (time constant,
damping, etc.) for best performance.

I got distracted though. There is something which I find rather
annoying, and I'm spending more time messing with this factor than
actually observing the performance at different damping / time constant
/ etc...

The temperature seems to be aprox 20C above ambient temperature rather
than a steady 40C. I thought the purpose of the oven was to keep the
temperature stable. When I adjust the thermostat because I'm chilly, the
thunderbolt gets warmer too (but not by as much)

I've tried (seemingly, to me) everything:

light insulation

putting the unit in a spot away from drafts

putting the unit in a place away from drafts in a shoebox with light
insulation with a fan blowing in it (currently in a cupboard in this
state, and the temp seems to fluctuate the least, but still by more than
1-2 degrees centigrade)

I feel like shouldn't need to fuss with ambient conditions this heavily
for an OCXO, and find myself researching construction / design for a DIY
outer-oven to wrap the thunderbolt in.

Anyone have experience with non-stable temperature on a trimble thunderbolt?

I've also noticed (monitoring with Lady Heather's Disciplined Oscillator
Control Program v3.10 by John Miles aka KE5FX) the thunderbolt unit
sometimes flags an alarm briefly (and I rarely ever manage to write it
down before the screen updates or the alarm goes away) and the last one
I was able to "catch" before it went away was related to temperature.

Should I be getting a steady / non-flucturating 40C or something if the
oven is working normally?

Thanks in advance,

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