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 <[email protected]> > 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 <[email protected]> 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 <[email protected]> wrote: >>>> >>>>>> I spent a lot of years buying Rbs 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 temps 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 -- [email protected] >>>>> To unsubscribe, go to >>>>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >>>>> and follow the instructions there. >>>>> >>>> _______________________________________________ >>>> time-nuts mailing list -- [email protected] >>>> To unsubscribe, go to >>>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >>>> and follow the instructions there. >>> >>> >>> _______________________________________________ >>> time-nuts mailing list -- [email protected] >>> To unsubscribe, go to >>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >>> and follow the instructions there. >> >> >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to >> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >> and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
