AN EXPERIMENTAL-STUDY OF FREQUENCY JUMPS DURING THE AGING OF QUARTZ OSCILLATORS

The cause of abrupt frequency jumps observed during the aging of high- stability quartz oscillators is investigated. For this purpose a preci se method of measuring the resonant frequency versus drive current is used, and this method is applied to AT-cut crystal resonators used in oven controlled crystal oscillators (OCXO's). Experimental results sho w that there are some cases where the resonance frequency jumps when c rystal current is changed, this phenomenon originates with spurious re sonances near the fundamental mode, and the current that causes coupli ng between the spurious and fundamental modes shifts according to crys tal driving time. Furthermore, we show that the abrupt jumping in long -term frequency observation is caused by a ''shift'' of the current th at causes the couplings.