Environmental sensitivities of precision frequency sources

Issues that relate to the environmental sensitivity of the frequency of precision frequency sources are presented. As a definition of precision sources, an aging rate of 10^-9 per day or less is used. Included in this definition are high-performance quartz crystal oscillators, rubidium gas cell devices, cesium beam standards, and hydrogen masers. The typical environmental sensitivities of these four classes of precision frequency sources are outlined. This is followed by a discussion of interrelationships between two or more environmental stimuli and of the limits of measurability of the frequency changes imposed by the basic noise performance of the frequency source under test. A review is presented of standardization efforts in the area of time and frequency. This includes the IEEE Standard 1139 approved at the end of 1988. Also reported are efforts toward a standard characterizing environmental sensitivities which has been authorized by the IEEE as Project 1193