In article ,
John Fields wrote:
[..]
You can use a fundamental mode crystal as an overtone oscillator, but
even if you can get it to oscillate, it won't be generating an
overtone at 100MHz, since overtone modes of oscillation aren't
harmonically related to the fundamental. It's more like the slab of
crystal is vibrating like the drumhead of a steel drum with small
areas of the slab vibrating at higher frequencies, instead of the
entire slab virbarting at just one frequency.

No, its more like a jello when you jiggle the dish side to side. The main
action of an AT cut is shear mode. In the harmonics, the motion looks
kind of like this:









If you think about the top two lines of text in my little drawing. I
think it is obvious that if the maker thinned it down by one line of text
just as you come to the edge, that portion of the crystal would not work
well at this harmonic. This is what they do in crystals intended for
fundamental operation. It knocks that activity down by several dB at the
overtone. This makes it very unlikely that a simple oscillator will take
off at an overtone.
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