[time-nuts] Re: Rubidium oscillator : pack it in styrofoam or attach it to a heath-sink?

[Bob kb8tq]

Hi

There are notes here and there talking about MTBF vs temp on this or that
Rb. 

One simple answer is a servo fan based approach and a target around 45C.

Bob

> On Oct 5, 2021, at 11:55 AM, Dana Whitlow <k8yumdoober at gmail.com> wrote:
> 
> I wonder what the detailed thermal model of telecom Rb's looks like.  I
> cool my PRS-10's
> hear sink surface to ~55C with a heatsink, but parts of some other surfaces
> of the package
> run several degrees hotter.  This rather puzzles me, and worries me.
> 
> Dana
> 
> 
> On Tue, Oct 5, 2021 at 10:46 AM Bob kb8tq <kb8tq at n1k.org> wrote:
> 
>> Hi
>> 
>> Rubidiums are somewhat unusual beasts. They typically have two heated
>> zones ( = two ovens) in
>> them. One is a bit hotter than the other. Because of the basic physics,
>> those ovens are right next
>> to each other / in contact with each other.
>> 
>> If you go to crazy with the insulation, the “colder” oven will heat up due
>> to heat leakage from the
>> “hotter” oven.  You need a certain amount of heat coming off the package
>> to allow this to happen.
>> 
>> The bigger issue is that there is a pretty big batch of electronics near
>> the ovens in the typical telecom
>> Rb. Unless you heatsink things pretty well these parts heat up. When they
>> do their MTBF drops
>> quite a bit. You save a couple of watts of heat (maybe) and loose the Rb
>> after a year or two. Not
>> a great tradeoff.
>> 
>> Yes, there are a lot of different designs for lab grade Rb’s. There are
>> also some really tiny little
>> guys running around. Neither category is all that easy to get on the
>> surplus market. If you want
>> to dive into either of those categories, there are issues, they just may
>> not be quite the same.
>> 
>> Bob
>> 
>>> On Oct 4, 2021, at 1:39 PM, Wim Peeters <peeters_w at scarlet.be> wrote:
>>> 
>>> Insulation decreases the power consumption.  But it will also increase
>> the temperature of the electronics.
>>> 
>>> A heath-sink will cool the electronics but will increase the power
>> consumption.
>>> 
>>> Or maybe insulate the  part of the case that gets hot, and put a
>> heat-sink on the other parts?
>>> 
>>> Wim Peeters
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