Short-Term Frequency Stability Measurement of BVA Oscillators

This paper discusses the time-domain measurement of short-term frequency stability of ultra-stable BVA oscillators with flicker frequency modulation noise on the order of 10^-14 in terms of Allan deviation at averaging intervals from hundreds of milliseconds to tens of seconds. The stability has been measured with a highly sensitive phase-time comparator based on the dual-mixer time-difference multiplication with a background instability of ~7times10^-15/tau. A discrepancy has been observed in the comparator background noise found with two signals from a single oscillator (comparator test) and with two signals from two oscillators (stability measurement).