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

Dana Whitlow k8yumdoober at gmail.com
Tue Nov 21 09:34:44 EST 2017

Hi Ole,

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

I think I've heard the one-second lifetime figure before.

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

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.


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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