[time-nuts] SMPS or conventional?

[Angus]

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.
>>>> 
>>>> 
>>>> 
>>>> 
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