During 2003 the IEN-PTB Two-Way Satellite Time and Frequency Transfer (TWSTFT) link was calibrated using a portable reference station. The calibration activity was conducted in the framework of the Galileo System Test Bed Version 1 (GSTB V1), under a contract with Joanneum Research G.m.b.H. (Austria). The calibration constant was determined with an uncertainty lower than 1 ns. Only few months after the calibration, the satellite provider moved the TWSTFT service to a different satellite; this caused changes non-reciprocal delays of the link (Sagnac and earth stations delays) and the calibration constant had to be re-evaluated. A recalculation of the Sagnac delays is presented together with a re-evaluation of earth stations delays with different measurements techniques.
Laboratory sources for standard frequency and time that receive external time signals to control their built-in oscillators are widely used wherever accurate and stable frequency and time, optionally with universal synchronization, are required. We propose a method to obtain traceability of such signals to Coordinated Universal Time (UTC) and particularly to UTC(PTB), its realization by the Physikalisch-Technische Bundesanstalt (PTB). The role of PTB's weekly published Time Service Bulletin is discussed in detail, and the metrological steps for establishing and maintaining traceability are described and uncertainty contributions are stated. Furthermore, we discuss how to possibly meet financial sector regulations according to European MiFID II. A procedure as a component for the assessment to provide accurate time through telecommunication networks using, eg, the Network Time Protocol (NTP) is presented. It checks outputs of an NTP server to validate that its time reference and provided timeof-day information is in accordance with specific requirements.
The realization of Coordinated Universal Time, one of the tasks of the International Bureau of Weights and Measures, relies on a network of international time links which currently is organized in a star-like scheme that links all contributing laboratories. GPS signal reception is the technique most widely employed by the laboratories. The PTB currently plays a unique role in the process due to its function as the central pivot in the time transfer between the participating laboratories. We discuss how the PTB meets its obligations to the international timekeeping community as well as to its users in Germany. In its role as an National Metrology Institute (NMI), PTB is entrusted with the realization and dissemination of legal time in Germany. The services were offered to the public support measurements and timing applications traceable to the national and international standards to be made in calibration laboratories and in many industrial sectors. We thus discuss the meaning and definition of traceability, how different GNSS systems can be used to establish traceability and their performance in doing so.
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