[R-390] Crystals

[Gordon Hayward]

> So, it's the thickness that matters more than overall size, correct?

Yes. For a first overtone crystal the thickness is a half wave at the acoustic frequency
corrected by the mass of the metal electrodes and, as seen on the picture, by the extra
metal used for the final frequency trim.

> Actually it's still two 17 MHz crystals. A jumper from the unconnected post to the unconnected
> electrode likely would get it to oscillate (sort of). By the way, I'm not in any way suggesting
> doing this.

I assume you mean half of the cracked crystal. It probably wouldn't run because the moving part
(these crystals are AT cut and move in a thikness shear mode) is whre the electrodes overlap.
There is no overlap where the usual connections are made.  If it did oscillate there would be
a lot of spurious modes.

The R-390 is stable enough that I listen to crystals to hear the neat modes the crystal goes
through when water or other liquid on the surface evaporates.  I'm the crazy person who puts
homogenized sheep brain on a coated crystal to detect scapie (a cousin of mad cow disease).

Cheers, Gord VE3EOS