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

[Bob kb8tq]

Hi

The whole device is magnetic shielded. If you mess with the “where things go
you need to come up with new magnetic shields. 

Since you are dealing with microwave this and microwave that, stretching out
the distance from the physics package to the “other stuff” is going to involve
some redesign of this or that. Even the VHF stuff that fires up the bulb probably
isn’t going to be “happy” with the leads moved here or there. 

As you move this or that, you change the heat sinking on this or that oven. That
will get you into a bit of re-optimization and (possibly) re-heat sinking of things. 

So: can you do it? Sure you can. The 5065 has some (but not all) of the electronics
pretty far away from the physics package. With enough effort and redesign you 
could do the same thing. 

My guess: It’s quicker / easier / cheaper / better results to find a 5065 that needs
a lot of TLC ….

Bob

> On Oct 5, 2021, at 4:17 PM, paul swed <paulswedb at gmail.com> wrote:
> 
> This is a good discussion and has my brain cell working.
> Totally agree on te temperatures in the filter and such.
> But I have always disliked the temperature everything is running at in the
> telco RB's.
> So would it make sense to actually seperate the boards and get them away
> from the heat while leaving the hot items as is? The leads can be
> lengthened, even the RF.
> Regards
> Paul
> WB8TSL
> 
> On Tue, Oct 5, 2021 at 4:09 PM Magnus Danielson via time-nuts <
> time-nuts at lists.febo.com> wrote:
> 
>> 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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