Frequency steering of hydrogen masers

The two Master Clock (MC) systems at USNO are steered in frequency so as to equalize their times with that of a mean timescale produced by an ensemble of hydrogen masers and cesium standards weighted dynamically and revised by post-processing. Occasional steers are also made to keep UTC (USNO) close to TAI. Experiments have been made with different steering algorithms in a search for an optimal one, i.e. that equalizes the times of an MC and the mean timescale satisfactorily closely and quickly without destabilizing the MC´s maser to an extent noticeable by our users. Such a choice appears to be one wherein 10 or 90 days of data are averaged to determine the MC´s frequency, a damping factor (time constant) of 100 days is employed in the time equalization, and an upper limit of 3.5 parts in 10¹⁵ is set on the maximum daily frequency change. An algorithm utilizing linear quadratic Gaussian control of Kalman-filtered data is being tested on one MC. The absolute frequency stability of UTC (USNO) appears to be comparable to that of TAI. A back-up USNO MC has been established at Falcon AFB, CO