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

[Magnus Danielson]

Hi,

I agree with Bob, get a 5065 or similar. Another approach is just to 
realize how cheap telco rubidiums are and have a stockpile of 
replacements. Testing them through is fairly straight-forward.

Cheers,
Magnus

On 2021-10-06 00:10, Bob kb8tq wrote:
> 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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