[time-nuts] Improving the stability of crystal oscillators

[Bruce Griffiths]

Brooke Clarke wrote:
> Hi Bruce:
>
> I've also looked into drilling a hole (garden hose, 90 deg fitting & pipe with 
> end smashed flat to make a nozzle will easily drill as deep as the pipe is 
> long).  Then using a short length of capped copper pipe at the bottom and the 
> rest PVC.
>
> Like I think here in California wine country 4 feet would be plenty deep.  But 
> this method only works at your home location.  Not too good for a clock that 
> will be sent to someone else.
>
> I think the long time constant method can be done in a few cubic inches.
>
> Have Fun,
>
> Brooke Clarke
>   
Brooke

The required depth depends on the soil diffusivity and the temperature
stability required.
It is instructive to install thermometers at depth intervals of a foot
or so and record the temperature fluctuations experienced by each
thermometer.
This was first done around 1860 by Forbes.
I repeated the experiment in 1966.

Bruce