[time-nuts] Rb cooling

[Poul-Henning Kamp]

Cooling Rb's is a much misunderstood discipline.

Most Rb's have a specified "base plate temperature range".

For instance the PRS10 specifies -20..+65°C

Cooling Rb's should happen only through the base-plate.

Cooling other surfaces creates unwanted temperature gradients inside
the Rb unit.

The colder you run a Rb, the more power it uses to keep important
bits inside warm.

Running it near the top end of the range wears out the electronics
in it faster.

No matter what kind of cooling, it is important that it offers
sufficient cooling capacity for the internal ovens to have a
margin to work with.

For frequency stability, you should strive to have a constant
baseplate temperature.

Putting a fan on anything, will generally speed up and amplify the
effects of any ambient temperature changes.

For optimal frequency stability, you want to do is mount
your Rb on a huge lump of iron which you can keep at a
constant temperature around 35-40°C by natural convection.

Iron is better than Cu/brass/Al because it conducts heat slower and
less eagerly, thus attenuating ambient temperature fluctuations.

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.