Bin Jian, Scott Beattie, André Charbonneau, and Marina Gertsvolf, National Research Council Canada, Canada

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Abstract:

Recently, several changes were applied to UTC(NRC) generation and dissemination to improve its accuracy and reliability. First, the source clock that is used for UTC(NRC) generation was switched from a caesium thermal beam commercial clock to a commercial hydrogen maser, steered by an external frequency offset generator. The introduction of an automatic steering of UTC(NRC) to match the frequency of NRC caesium fountain primary frequency standard, NRC-FCs2 [1] was implemented next. The redundancy of the UTC(NRC) dissemination for NRC time services including telephone talking clocks, NTP servers, and NRC TimeLink™ system has been improved by a complete rerouting of RF, 1 PPS and DC power to provide stacks of fully independent systems. NRC-FCs2 has an overall systematic uncertainty of 2.3 × 10^-16 in fractional frequency and its typical stability, 1.95 × 10^-13 at 1 sec averaging time, is limited by the short term stability of the local oscillator. NRC-FCs2 has been reporting to the BIPM for the steering of International Atomic Time (TAI) / UTC since October 2019 with a typical uptime of more than 95% every month. This nearly continuous operation of FCs2 makes it ideal as a frequency reference for the automated steering of UTC(NRC). The new UTC(NRC) uses an active hydrogen maser (Vremya-CH, VCH-1003ML), VM1, as its source oscillator and an Auxiliary Output Generator (AOG) to generate UTC(NRC) 5 MHz signals. The frequency of the AOG output signal is steered to NRC-FCs2 daily and is used to generate the 1 PPS UTC(NRC) signal using a frequency divider. In order to select the steering algorithm time constants and thresholds, and to optimize the UTC(NRC) stability and accuracy, we performed a numerical study based on noise modeling of VM1 and FCs2. The modeling shows that UTC(NRC) remains within 2 ns of the reference with daily frequency adjustments. In the laboratory implementation, the AOG is steered daily with the predictive frequency correction calculated from a linear fit to several days of the measurement results between NRC-FCs2 and the VM1 maser. In the absence of FCs2 data, e.g. due to maintenance, the algorithm uses rapid UTC (UTCr) reports to steer UTC(NRC). We started the UTC(NRC) steering based on NRC-FCs2 on August 26, 2021 (MJD 59452). The upgraded UTC(NRC) has been aligned with the UTCr on the same day. From UTCr – UTC(NRC) reports we find that UTC(NRC) has not deviated from UTCr by more than 2 ns in one month. In addition to the upgrades to UTC(NRC) generation, we have been enhancing the NRC TimeLink™ (TL) dissemination system [2]. We implemented predictive frequency corrections to its rubidium frequency standard local oscillator that significantly improved its performance over 48 hours of holdover. We are also preparing the installation of the TL system in Inuvik Canada and will present the system performance over twice the baseline of more than 4,000 km from Ottawa to Inuvik and back. References: [1] S. Beattie, B. Jian, J. Alcock, M. Gertsvolf, R. Hendricks, K. Szymaniec, and K. Gibble, Metrologia 57 035010, 2020 [2] R. Douglas, A. Charbonneau and M. Gertsvolf, Metrologia, 58 055003, 2021.