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

[Magnus Danielson]

Hi,

It's a complex picture as depending on temperature of the components, 
and other aspects such as RF intensity, sensitivity to this or that 
changes, line with changes etc. It also depends on the actual buffert 
gas mix, which by the way changes over time due to leakage.

There is really three parts, the lamp, the filter and the detector cell. 
Turns out that  the filter and cell temperatures end up in about 65 
degrees C. For some I've seen 73 degrees C. For the lamp, you end up 
with something in 110-120 degrees C. Physically these two temperatures 
is just next to each other, as the lamp needs to shine straight into the 
microwave cavity of the cell but the filter cell needs the same 
temperature as the cell.

One can optimize the temperatures for strongest signal, which sounds 
like a good thing for S/N, one can optimize them for minimal sensitivity 
for lamp or RF intensity or you can optimize it for low line width. 
Depending on the conditions, you end up with a bit different settings. 
If it is easy to stabilize RF intensity for instance, then one can relax 
that optimization, similarly for lamp intensity. Then you can push it 
for a balance between line-width (Q) and S/N. For others, this is not 
feasible, for instance for simplicity/cost and/or size.

Regardless, temperatures of rubidiums is quite a different mess to that 
of cesiums or hydrogen masers, and let me tell you that temperature of 
the later is a mess I look at quite a bit at the moment.

Cheers,
Magnus

On 2021-10-05 17:45, Bob kb8tq 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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