Frequency control developments

CRYSTAL VIBRATORS and atomic frequency standards are continuing to attract the interest of engineers and physicists. In particular, the energy‐trapping concept has assisted in the application of theory to practical quartz resonators. Thus filter crystals have been extended to 125 MHz. Similarly, multiple‐mode resonators of piezoelectric ceramic and quartz can now be made on a single crystal wafer, making possible a filter in a monolithic integrated form. Crystal oscillators, too, have been made, in which the crystal serves both as a control element and as an active device.

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