Evaluation of Modern Hydrogen Masers

Abstract : During the last two years the Jet Propulsion Laboratory (JPL) has been conducting an evaluation of modern hydrogen masers in a program sponsored by the National Aeronautics and Space Administration (NASA). The goal was to perform a series of tests and evaluations which would be as complete, accurate and unbiased as possible. Aboard of nationally recognized experts in hydrogen masers and in frequency and time was selected to design the testing program, supervise the tests and release the final report. The maser types tested were the SAO VLG-11B, the GSFC NR and, as a result of the testing process, the JPL DSN. The masers were tested for environmental sensitivities (magnetic field, temperature, barometric pressure) and long-term aging. Allan variance runs of 72 days were made in order to attain averaging times from several seconds to 106 seconds. Auto- and cross-correlation techniques were used to determine the effects of uncontrolled parameters such as humidity. Three-cornered-hat and other data reduction techniques were used to determine the characteristics of the individual masers.