Analysis of medium-term frequency instability of high stability quartz oscillators

Various types of high stability quartz oscillators have been elaborated and produced on a small scale. Systematic investigations of long-term frequency stability of the oscillators have been carried out. Typical parameters of currently manufactured ITR OCXOs are shown as well as measurement results of short-term frequency stability, for average time from 1 ms to 100 s. According to definitions given in actual standardization documents, long-term instability is the frequency change observed in conditions assuring elimination of other influences on oscillator frequency, especially temperature and supply voltage. During investigations we observed and determined the slow frequency fluctuations of the true long-term characteristics of the measured oscillators. The results of investigation and calculation procedures used for data processing in order to increase the confidence level of frequency/time characteristics determination, are presented.