New realization strategy for UTC(PTB)

The Physikalisch-Technische Bundesanstalt (PTB) realizes its atomic time scale UTC(PTB) as approximation to the international time reference UTC. It serves as the basis for PTB´s time services, for the local clock comparisons and for international time comparisons. Since February 2010 UTC(PTB) has been realized using an active hydrogen maser steered in frequency via a phase micro stepper according to an algorithm described in this paper. Thereby the long-term stability and accuracy of PTB´s primary clocks is combined with the typical short-term frequency stability of a hydrogen maser. During the last 12 months, the caesium fountain clock CSF1 was used as the steering reference on more than 98% of the days, which resulted in an excellent stability of UTC(PTB). During the last six months, including March 2011, its deviation from UTC was less than 4 ns.