Increased resistance of crystal units at oscillator noise levels

Problems have been experienced with inoperative military equipment which have been traced to a defect in some quartz crystal units. This defect has been determined to be an increase in resistance (loss of Q) of crystal resonators when excited at very low power levels. The typical crystal oscillator, when first turned on, excites the resonator with thermal noise and consequently the power dissipated is very small. Simple instrumentation has been assembled to show clearly the low power increased crystal resistance effect. Tests have shown that surface defects, due to the final lapping process, contribute to the problem. The necessity of surface etch to remove the damaged surface layer is shown to be required to avoid defective crystal units.