[time-nuts] Re: Custom Quartz crystals

[Richard (Rick) Karlquist]

On 8/14/2022 1:08 PM, Bob kb8tq via time-nuts wrote:
> Hi
> 
> Crystals (of any sort) have whatever turnover the manufacturer decided
> they wanted them to have. There is no “standard” target for any crystal
> cut. It needs to be specified when the crystal is ordered.  That is true
>

And indeed only about half of the 10811 crystals even exhibit a turnover
of any kind.  Instead, these crystals merely have a temperature range 
with very low tempco.  For all of those crystals, they would set the 
oven to 82 degrees.  Because of the double rotation, there isn't
actually any very strict definition of an "SC cut".  They can't
even agree on whether "SC" stands for "stress compensated" or
"Santa Clara"  :-)

The E1938 crystals were just repackaged 10811 crystals, but the cut
had to be adjusted to always have a turnover.  We actually used the
upper turnover because the E1938 had to operate at ambient up 85 
degrees.  BTW, the E1938 crystals had to be calibrated for 10.000000 MHz
at series resonance, unlike the 10811 crystals which were calibrated
for 20 pF (IIRC).

Rick N6RK