5th EUROPEAN FREQUENCY AND TIME FORUM BESANGON- 12-13-14 MARCH 1991 Promise into Practice: Implementing TA2 on Real Clocks at NIST

TA2 is a time scale algorithm designed to run as a post-processor by smoothing, i.e. combining estimates from runs in both forward and backward temporal directions. It has been tasted using the time-scale data at NIST from 1989 through the first half of 1990. We review the characterization parameters for clocks with white Fn, om, and random-walk FU, a,, and the dependence of these estimates on integration tine, r. We also discuss the transformation of these parameters from their use as time deviations to frequency variances. Ue compare the scale generated by TA2 over 541 d starting at the beginning of 1989, with the two other scales at NIST, AT1 and TA. We find that TA2 and AT1 agree well in frequency, though TA, the pure Kalnan-filter algorithm, walks off more than 2 parts in 10 " over the interval. Using GPS data to link with other time scales around the world, ve compute the stabilities of the three NIST scales, ATl, TA, and TA2 using N-cornered hat estimates. We find that they have similar short-term stabilities for integration times out to 16 d, within the confidence of our estimates. TA appears to be worse in stability than the other two scales by a factor of about 2. There is some indication that TA2 improves slightly over AT1 in the long term, matching previous results from simulation, though the confidence on these estimates is poor