Hydrogen maser ensemble performance and characterization of frequency standards

The performance of a post-processed clock ensemble dominated by active, cavity-tuned, hydrogen masers has been evaluated. The ensemble has an average frequency drift of less than /spl plusmn/3/spl times/10/sup -15/ per year, and an Allan deviation less than 1/spl times/10/sup -15/ for /spl tau/ between 4 hours and 100 days. This ensemble has been used to help characterize the frequency stability of a number of commercially available, high performance frequency standards.