[time-nuts] Maser manual

[Bruce Griffiths]

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:
http://tf.nist.gov/general/pdf/156.pdf

Again the dielectric constant tempco is a significant issue.



> Cheers,
> Magnus

Bruce