The Future Model of TA (TL)

Abstract : Telecommunication Laboratories (TL, Taiwan) published a local atomic time scale TA (TL) in November, 2004 and uses this time scale and the Circular T monthly report to calibrate a hydrogen maser/micro-phase-stepper system to be the local coordinated time scale UTC (TL). The TA (TL) is based on an ensemble of 7-9 high-performance Agilent-5071A cesium clocks. The weight of each clock was set to be proportional to the inverse exponential with the index of each clock's frequency deviation. We removed the long-term frequency drift of each clock and then weighted the residual fluctuations, in order that the frequency drift of our time scale not change too rapidly when we add or remove one clock from the ensemble. A mechanism was also developed to convert the virtual paper clock into physical output. Through this mechanism, the phase difference between the paper clock and the physical output can always be kept to within 250 picoseconds. The stability of TA (TL) is about 3 10-15 (tau = 30 days vs. UTC); here, the average stability of the cesium clocks in ensemble is about 1 10-14. We estimate this time scale to have an accuracy of 10 ns/month, and it s quite good enough to be TL's local coordinated time scale, UTC (TL).