On 6/7/17 7:35 PM, Bob kb8tq wrote:
Hi
Metal actually makes things a bit worse since it has a lower thermal resistance
than glass.
This is also why a high performance dewar is made from glass rather than metal.
Yes, you
can go to weird stuff like titanium (it has been done). You can’t afford that ….
If you fill the entire dewar with a heat conductor you make things worse still.
The idea is to
*block* heat flow out of the heated area. Even without fill, the wall of the
dewar goes from the outside
world to the heart of the heated area. It is the perfect “sneak" path into the
oven. Actually
it’s not that much of a sneak path since it’s a well known effect :)
Again, none of this is particularly original. Take a hammer to any dewar based
OCXO and
the details are going to be similar.
And the wires provide a thermal path - you've got to get power to it and
the oscillator signal out.
In dewar OCXOs (like the USOs made by APL), the leads are essentially
the only thermal path in/out.
BTW, you don't want to do oil filled. All oil filled electronics (unless
welded closed) inevitably leaks, oozes, or otherwise puts oil on the
outside. If you *must* have oil, then use solid, uninsulated wires to
penetrate the surface of the oil. Otherwise you'll gain new appreciation
for what capillary action is.
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