[time-nuts] Improving the stability of crystal oscillators

[Richard (Rick) Karlquist]

Don Collie wrote:

>     Yes, you can cut a crystal to have an inversion temp at 25Deg C. [well 
> certainly with an AT cut - I`m not sure about the SC cut.]
> Cheers,............................................Don C.

The AT cut has an inflection point at 25 degrees C.  You cannot
get a "turnover" (which is what I think you mean an "inversion")
at the inflection point.

As SC cut inventor Jack Kusters explained to me, the "true" SC cut
has an inflection point temperature of around 85 degrees C.  You can get
a turnover above or below this, depending on minor angle changes.
Some crystal fabs make a so called "fake SC" cut where they attempt
to change the inflection point.  However, when this is done the stress
compensation is degraded or lost.

Rick Karlquist N6RK