Environmental sensitivities of cavity-tuned hydrogen masers

With the increasing number of cavity-tuned hydrogen masers in use around the world in time scales and as reference oscillators for primary frequency standards, it is necessary to have a complete understanding of the environmental sensitivities of the masers. Common-mode frequency fluctuations are of great concern and the degradation of maser frequency stability due to environmental fluctuations should be minimized. Measurements of environmental sensitivities (temperature, relative humidity, atmospheric pressure, line voltage and magnetic field) have demonstrated that the frequency stability of cavity-tuned hydrogen masers is not significantly degraded if the masers are contained in a reasonably controlled environment.