[time-nuts] H-Maser drift (was: Why discipline Rubidium oscillator?)

Ole Petter Rønningen opronningen at gmail.com
Tue Nov 21 10:45:15 EST 2017

Hi, Dana.

> What does 'EFOS' mean?  I hadn't heard the term before.

EFOS was a series of masers made by Oscilloquartz in Switzerland, there is a little information on my website www.efos3.com under «about».

The manuals for those masers are also available, lots of good info for the interested: 

> I do hear mixed reports about where the conversion to atomic H
> occurs, and consider the jury to still be out on that question.

Well, I think that jury is in.. :) plenty of information in old papers on that part.


> I had thought that the volume of the storage bulb was much
> smaller in out maser, perhaps in the pint to quart range.  For a
> frequency of ~1420 MHz, I guess it would take a cavity that is
> operating in a somewhat higher than fundamental mode if the
> volume is in the gallon regime as you suggest.  But with the
> narrow gain profile width of this transition, I supposed there'd
> be no risk of the thing running in the wrong mode.
> Dana
> On Tue, Nov 21, 2017 at 8:14 AM, Ole Petter Ronningen <opronningen at gmail.com
>> wrote:
>>> On Tue, Nov 21, 2017 at 2:50 PM, Attila Kinali <attila at kinali.ch> wrote:
>>> [...] The advantage of the platinum valve
>>> system is that it "generates" single atom Hydrogen, as required
>>> by the maser.
>> Picking nits here.. It was my understanding that the splitting of molecular
>> hydrogen into atomic hydrogen happens using RF in the dissociator - not in
>> the platinum leak valve. Is my understanding incorrect?
>>> Within the cavity there is a small glass bulb that keeps the atoms
>>> in the right position of the cavity field.
>> 4.5 liters in EFOS type masers - so not *that* small. I believe other
>> masers are the same order of magnitude.
>>> Yes, IIRC normal numbers are several 10s to 100s of wall collisions
>>> before the atom loses its state due to wall colisions and without
>>> contributing to the signal.
>> Lifetime ~1 second I think
>>>> I've long wondered what causes the slow frequency drift, typically
>>> amounting
>>>> to about 3E-14 over a time span of several months.
>>> Mostly changes in the wall coating leading to a different wall collision
>>> shift and mechanical changes of the cavity dimension (think air pressure
>>> and creep) leading to a different cavity pulling. To a lesser extend
>>> it's the changes in the quality of the vacuum and number of Hydrogen
>> atoms
>>> in the cavity.
>> Also aging of electronic components - coarse tuning of the cavity is done
>> by temperature, and any drift if the temperature-sensor/amplifiers etc will
>> result in drift. At least for EFOS type masers.
>> Ole
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