[time-nuts] Maser manual

Bruce Griffiths bruce.griffiths at xtra.co.nz
Wed Sep 1 20:19:00 UTC 2010

Magnus Danielson wrote:
> On 09/01/2010 09:39 PM, Poul-Henning Kamp wrote:
>> In message<24C547B54EA34A69BACC4F823BB4036F at pc52>, "Tom Van Baak" 
>> writes:
>>> I found the original copies of both EFOS manuals, along with
>>> a few photos. See:
>>>     http://www.leapsecond.com/museum/efos/
>> Interesting.
>> Page 4/3 in the service manual states:
>>     For the Hydrogen Maser, this unperturbed frequency
>>     is
>>         f(H) = 1 420 405 751.768 +/- 0.002 Hz
>>     In practice, this frequency is perturbed by
>>     interaction of the hydrogen atoms with the walls
>>     of the interaction volume container, doppler
>>     effects, interactions between the atoms themsel-
>>     ves, etc.  The resulting frequency for the EFOS
>>     Maser is taken to be
>>         F(o) = 1 420 405 751.689 Hz
>> I have no idea where the EFOS was produced, but somebody should try
>> to calculate the relativistic correction for their height above the
>> geoid, and see how much of the systematic 0.079Hz frequency difference
>> that explains...
> Neuchatel, which still leaves a bit of unspecified height.
> However, this effect would be cancelled as their cesium clocks would 
> be on the same height above the geoid (give or take a few meters).
> So, their indication is correct. The C-field also pulls the atoms of 
> course, which they failed to point out in the cited text.
>> If I were to build a maser myself, I would probably not attempt
>> to copy the EFOS, as the large mechanical dimensions add significant
>> cost in materials and machining.
>> I would be much more tempted by a sapphire loaded cavity design like
>> this one:
>> http://www.nict.go.jp/publication/shuppan/kihou-journal/journal-vol50no1.2/0304.pdf) 
>> As that brings the mechanics inside the work envelope of main-stream
>> CNC machines with the required tolerances.
> Yes, but what is the issues relating to sapphire loading? What's the 
> cost of the sapphire block and having it machined?
The tempco of the dielectric constant of sapphire is quite large so the 
cavity resonance tempco is somewhat larger than that of an unloaded 
copper or aluminium cavity.

There is a NIST paper detailing a somewhat earlier attempt to use a 
dielectric cavity:

Again the dielectric constant tempco is a significant issue.

> Cheers,
> Magnus


More information about the time-nuts mailing list