Hi Paul,
So, sure, most of the electronics is actually better served away from
the heat, but that is the compromise of the cheap telco rubidiums that
need things fit into a small space. Another aspect is that isolating
them as you suggest can help reduce the amount of heat we need to
produce, and with that the current through transistors to burn energy
for heating, which is another source of failure, a strain on MTBF in
itself. At the same time, as you isolate, you need to leak more heat
from the colder filter/cell so that it can dump heat from the lamp side
and still have a regulating heating to maintain the temperature you
want. So you need to understand the balances and keep everything there.
Chopping up an LPRO like this is possible for sure. The LPRO also uses
the temperature of the filter/Cell block to stabilize the crystal, and
the oscillator part needs to be more or less straight there or you end
up in trouble. If you have a couple, you can let most of the electronics
be dead but at high temperature and another bord cold to do what can be
done at a bit of distance, if that is what makes you go. I have enough
LPROs not to care, I have spares.
Hope it helps.
Cheers,
Magnus
On 2021-10-05 22:17, paul swed 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
<[email protected] <mailto:[email protected]>> 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 <[email protected]
<mailto:[email protected]>> 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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