[time-nuts] SMPS or conventional?

[Bob kb8tq]

Hi

The magnetic field sensitivity is dependent on a lot of things. 
Strangely enough, the higher the C field, the more sensitive 
the physics package is ( yes, that’s weird …). All Rb’s incorporate
shielding to reduce the external field impact. Since the shielding
is rarely perfect, there are asymmetries in the response. 

All that turns this into a “field from here at level X” matters on this
Rb and not on that one sort of thing. 

=======

The “easy” way to get a feel for what’s what is to rotate the device 
in the horizontal plane. The earth’s mag field (unless you are close
to the magnetic poles) will change in a predictable manner. If you see
a measurable frequency change … you have an answer.

The more complicated approach uses Helmholtz coils. It’s more complicated
mainly because they take time to fab …..

Both approaches are only approximate unless you go a bit crazy on 
a bunch of minor details. 

Bob

> On Oct 22, 2020, at 6:17 AM, Angus via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> Hi,
> 
>   The magnetic field issue has bothered me a little too, but I don't
> know whether it has a practical effect. Maybe putting a fan in a
> plastic or aluminium box close to the Rb might show something - unless
> someone already knows the effects.
> 
>   I have a compass on the bench beside the LPRO, and it does drift a
> bit. What surprised me most was how much the field around the mains
> transformers changed each time they are switched on or off.
> 
> Angus.
> 
> On Wed, 21 Oct 2020 10:04:11 -0400, you wrote:
> 
>> Hi
>> 
>> The only issue with the “controlled fan” approach is that you
>> have a variable magnetic field as a result. That and the vibration
>> both can impact the stability of the Rb. Some means of isolating
>> the fan from the immediate vicinity of the Rb sounds like a good idea. 
>> 
>> Bob
>> 
>>> On Oct 21, 2020, at 9:31 AM, Luiz Alberto Saba <las at intercat.com.br> wrote:
>>> 
>>> I am thinking in an black aluminium finned heatsink, the size of the base plate, and a fan, controlled by an electronic thermostat (sensor direct coupled to the heatsink). Is that ok?
>>> 
>>> Em 21/10/2020 09:40, Wannes Sels escreveu:
>>>> There are conflicting requirements regarding temperature in Rb's:
>>>> 
>>>> - For best performance, the rubidium and quartz oscillators must be kept at
>>>> a high and stable temperature.
>>>> - For reliability, the supporting electronics must be kept at a lower
>>>> temperature.
>>>> 
>>>> The heater takes care of the high temperature. The stability of the
>>>> temperature can be improved by increasing the thermal mass, i.e. adding a
>>>> block of aluminium or copper.
>>>> The electronics can be kept cooler with a heatsink, and forced ventilation
>>>> if needed.
>>>> 
>>>> When you stick both the electronics and physics in a small package, this
>>>> becomes more difficult. For the PRS-10 some form of heatsink is pretty much
>>>> required to keep the electronics cool enough. Although I seem to remember
>>>> reading somewhere that the "benchtop" heatsink they offer now is lighter
>>>> than older units.
>>>> 
>>>> If the room temperature is not stable enough, you might want to increase
>>>> the size of the heatsink and add a fan. This reduces the temperature swing
>>>> inside the unit, while still cooling the electronics, at the cost of
>>>> increased power draw for the heater.
>>>> 
>>>> 
>>>> 
>>>> 
>>>> On Wed, Oct 21, 2020 at 5:38 AM Hal Murray <hmurray at megapathdsl.net> wrote:
>>>> 
>>>>>> I spent a lot of years buying Rb’s and putting them on small heatsinks.
>>>>> I
>>>>>> always was disappointed in their reliability. That continued to be the
>>>>> case
>>>>>> up to the point that the baseplate temp’s got into the 40C region.  In my
>>>>>> case, that took a fan 
> .
>>>>> How well did it work if the heat sink wasn't small?  What is your version
>>>>> of
>>>>> small?
>>>>> 
>>>>> Do you have any data (or vague memories) of how much it helps to orient
>>>>> the
>>>>> heat sink so the fins are vertical so they encourage warm air to flow up
>>>>> past
>>>>> the fins?
>>>>> 
>>>>> --
>>>>> These are my opinions.  I hate spam.
>>>>> 
>>>>> 
>>>>> 
>>>>> 
>>>>> _______________________________________________
>>>>> time-nuts mailing list -- time-nuts at lists.febo.com
>>>>> To unsubscribe, go to
>>>>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
>>>>> and follow the instructions there.
>>>>> 
>>>> _______________________________________________
>>>> time-nuts mailing list -- time-nuts at lists.febo.com
>>>> To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
>>>> and follow the instructions there.
>>> 
>>> 
>>> _______________________________________________
>>> time-nuts mailing list -- time-nuts at lists.febo.com
>>> To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
>>> and follow the instructions there.
>> 
>> 
>> _______________________________________________
>> time-nuts mailing list -- time-nuts at lists.febo.com
>> To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
>> and follow the instructions there.
> 
> _______________________________________________
> time-nuts mailing list -- time-nuts at lists.febo.com
> To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> and follow the instructions there.