Autonomous characterization of clock drift for timescale improvement at the AHU/APL time and frequency laboratory

We have reported on continuous improvements in the capability of our time and frequency laboratory. A substantial portion of our progress in capability was achieved through the incorporation of new clock hardware, improvement in GPS time recovery and coordination of our clocks into the computation of TAI. We have discussed our ensemble of hydrogen maser and cesium beam atomic clocks into a timescale that enables UTC (APL) to be steered within plusmn 30 nanoseconds per month of UTC. The propagation of the APL timescale is based on a modified version of the Percival method, requiring regular characterization of each clock's frequency rate and drift. Here, we discuss our results in an autonomous characterization of the individual clocks contributing to the APL timescale. This improvement in our operation has minimized the need for routine operator timescale maintenance and realizes the advantages in clock estimation using frequency, described by J.A. Barnes and D.W. Allan (1985). We discuss how our approach at characterizing the nonlinear drift observed in our hydrogen masers has aided our attempt to discipline the long term frequency drift behavior of quartz ultra-stable oscillators in the space environment. As in previous reports, we present updated laboratory performance in the form of UTC-UTC(APL)