We present NPL’s recent contributions to timekeeping applications of optical clocks. The first of these in-volves optical clocks at NPL and SYRTE being simultaneously used to steer experimental time scales, in a similar manner to Cs fountains steering the national time scales. The resulting optically-steered time scales at NPL and SYRTE (denoted UTCx(NPL) and UTCx(OP) respectively) will be presented along with compari-sons against both Coordinated Universal Time (UTC) and each other via satellite techniques.
We will then present how optical clocks can be used in the evaluation and steering of International Atomic Time (TAI) and, subsequently, UTC – a feat which has recently been achieved by NPL’s Sr lattice optical clock. We will discuss the process by which this was achieved, and we will show the recent frequency data and analysis that has been used to perform recent calibrations of TAI.
The details of the MeerKAT radio telescope’s time and frequency reference subsystem that enables sampling via low-jitter, low-drift microwave clock signals, and absolute timing (≤5 ns accurate) are discussed. The subsystem’s microwave and pulse per second transmission parts are now fully qualified and commissioned for the ultra high frequency (UHF) and L-bands and also provide for a 100-MHz interface and timing interfaces for S-band receivers that were installed. The subsystem includes a cable measurement system called the Karoo array timing system (KATS). Performance and differences on different bands and seasonal drift of the cable delay measurement of KATS are reported. A time scale called the Karoo Telescope Time (KTT) (which is estimated from tracking a few atomic clocks via new software) and the issuing of timing bulletins to users have been largely implemented and verified. Absolute timing calibration and linkage of KTT to the global positioning system time scale and to different UTC(k) realizations of the Coordinated Universal Time (UTC) instances are described. The subsystem uniquely enables high-fidelity sampling and stable tied array configuration. The latter configuration enables timing and transient science over time spans of 5 to 10 years. Simultaneous subarraying is supported. The backend is unique for radio telescopes in terms of being very deterministic as far as timing is concerned.
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