Impact of new high stability frequency standards on the performance of the NIST AT1 time scale

The recent addition of new commercial high stability frequency standards to the National Institute of Standards and Technology (NIST) real time AT1 time scale has resulted in significant improvements in the performance of the scale. The frequency stability of the scale at one day has increased by a factor of 2 to 4/spl times/10/sup -15/ and the stability at 100 days has improved to approximately 1/spl times/10/sup -15/. As a result UTC (NIST) has been kept within 50 ns of UTC (Coordinated Universal Time) for the last year. Further improvements are anticipated as more high performance clocks are added to the AT1 ensemble.