Environmental factors and hydrogen maser frequency stability

It is necessary to have a complete understanding of the environmental sensi tivities of cavity-tuned hydrogen masers to obtain optimum frequency stabil ity and to avoid common-mode frequency fluctuations. Measurements of enviro nmental sensitivities (temperature, relative humidity, atmospheric pressure , line voltage and magnetic field) made at the National Institute of Standa rds and Technology have demonstrated that the frequency stability of a cavi ty-tuned, active hydrogen maser is not significantly degraded if the maser is operated in a moderately controlled environment. Under these conditions, common-mode frequency fluctuations caused by the observed environmental fa ctors also are negligible.