2 April 2015
The timescale UTC(OP) is the real time realization of UTC in France generated at Observatoire de Paris (OP). This timescale is at the basis of legal time disseminated in France. It is also the pivot for French contributions to international timescales (commercial clocks, primary frequency standards) calculated by the BIPM. UTC(OP) has been significantly improved recently. Its operation is based on the output signal of a hydrogen maser frequency steered thanks to the calibrations provided by the SYRTE atomic fountains (FO1, FO2 and FOM) using a micro phase stepper. The frequency corrections, updated daily, are the sum of two terms. First, the current frequency of the maser is estimated daily by extrapolating data of the frequency comparison between the maser and the fountain. Second, a small steering to maintain UTC(OP) close to UTC is added. This term is updated monthly using data published in the last available Circular T, to compensate for the slope and for the phase offset of UTC – UTC(OP). This fine steering is typically of the order of 10-15 or 10-16.
The new method, implemented in October 2012, allowed a significant improvement of UTC(OP): the departure between UTC and UTC(OP) remained of the order of a few ns. The graphs presented below show comparisons of different UTC(k) to UTC, including UTC(OP) in black. The corresponding TDev are also plotted. UTC(OP) is one of the best real time realization of UTC together with UTC(PTB), that is the pivot of the time transfers for international contributions to TAI, and with UTC(USNO), that provides the main number of commercial clocks contributing to EAL computation.
Currently, UTC(OP) is generated using a commercial 5 MHz micro phase stepper. In order to improve the robustness of the system and the short term stability, we have developed a new generation of micro phase stepper operating at 100 MHz, in collaboration with SKK Electronics. The noise of these new instruments corresponds to an Allan deviation of 1 or 2 x 10-14, even for a detuning as large as 10-12. This is negligible compared to the stability of a hydrogen maser. We are also developing a switch allowing a swapping between nominal and redundant timescales generated using two different masers and two micro phase stepper with a negligible impact on the output signal phase and amplitude.
All these improvements benefit to many activities in the laboratory:
Operational activities (legal time dissemination, reference provided to French laboratories …)
Contribution to international timescales (TAI, UTC, UTCr) calculated by the BIPM
Contribution to European satellite navigation systems GALILEO and EGNOS
Test of new time and frequency transfer techniques
ACES/PHARAO space mission