[time-nuts] Double ovened 10811-60158 on ebay

Neville Michie namichie at gmail.com
Sun Jul 20 18:58:46 EDT 2008

If it is only the rapidity of humidity transients that concern you ,  
it is possible
to "insulate" the HP10811 against humidity fluctuations.
0.25 inch of wool felt all around the unit will provide a hygral buffer
with a time constant, probably as long as 8 hours.
Wool has an equilibrium moisture content of 15% moisture at 65%RH,
and with fibres of about 20 microns diameter it responds in seconds to
any increase or decrease of humidity by absorbing or desorbing
moisture from the air.
Wool is quite stable up to 100*C and so could be used as the insulation
in a double oven system.
The hygral sensitivity of wool has a temperature consequence, and  
latent heat and
heat of hydration are released as moisture is absorbed. This usually  
adds to the thermal stability of the insulated item, which is why  
wool is
comfortable to wear.
Just in case you were interested,
Neville Michie

On 21/07/2008, at 5:45 AM, Rick Karlquist wrote:

> A non sealed 10811 responds to humidity in a few minutes.
> The speed is nearly limited by the rate of change achievable
> in the environmental chamber.
> Rick Ksrlquist N6RK
> Tom Van Baak wrote:
>> It would seem to me that a perfectly hermetically sealed oscillator
>> is not a requirement for a typical GPSDO. Environmental effects
>> to the oscillator that work slowly will be absorbed by the GPSDO
>> tracking algorithm.
>> If someone wants a fun project -- measure a 10811-60158 while
>> changing the humidity from 10% to 90% and see if the oscillator
>> drifts faster or a lot slower than the GPSDO time constant of the
>> Z3801A.
>> /tvb
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