Levels of flicker-of-frequency instability have been measured for several types of low noise, VHF, quartz crystal resonators. The results have been compared to those predicted using a formula proposed in a paper presented by Fred Walls at last year's Frequency Control Symposium [l]. In that paper, a S, (electroded crystal) data-fitting value of 4 was found to accurately describe best-measured crystal flicker-of-frequency instability. The formula suggests crystal Sy(f) flicker-of-frequency instability that varies as the (electroded) volume, and as the inverse of Q4.The data reported in this paper are the result of both passive, in-bridge as well as in-oscillator measurements for AT, SC, and BT-cut. overtone-mode resonators operating at 40, 80, 100, and 160MHz. Measurements were made using four-crystal oscillators as low noise reference signal generators [2]. The data indicates poor agreement between measured and modelpredicted resonator stability, especially for 5th overtone AT and SC-cut resonators operating at 40 and 160MHz.Measured data was also compared to that predicted using an alternative model (formula) recently proposed by T. Parker [3]. Using the Parker model, relatively poor agreement was found for the case of the BT-cut resonators. The data suggests that further refinement of resonator short-term stability models is necessary.
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