MODES OF VIBRATION
There are three general modes of vibration for which quartz crystal
units are commercially designed: extensional, shear and flexure.
Fundamental vibrations of each of these modes of thickness shear
are available at the 3rd, 5th, 7th, 9th and 11th to180 MHz.
MODES OF OSCILLATION
A crystal is designed to operate on its fundamental or overtone
mode. The overtone modes are odd multiples of the fundamental
frequency. For example, a 15 MHz fundamental mode crystal will
also display overtone modes at approximately 45 MHz on its 3rd,
75 MHz on its 5th, 105 MHz on its 7th, 135 MHz on its 9th overtone
and 165 MHz on its 11th. This information is important when ordering
a crystal of 22-29 MHz because it could be either a fundamental
or a 3rd overtone. Although we offer fundamental mode crystals
up to 29.0 MHz, generally 3rd's are 18-75 MHz, 5th's are 50-120
MHz and 7th's are 80-180 MHz.
By far the most common cut used is the AT since this cut delivers
the best temperature coefficient and provides the widest range
of frequencies. The AT cut is available from Cal Crystal for
frequencies from approximately 1.0 MHz to as high as 29 MHz in
the fundamental mode and up to 180 MHz with overtone operation.
The other cuts (AC, CT, GT, ET, BT, DT, FT and BC) are for frequencies
below 1.0 MHz, and are used rarely and usually in much smaller