A Prototype Cesium Clock Ensemble for the Loran-C Radionavigation System

Aaron P. Dahlen

Abstract:	This paper presents a prototype real time clock ensemble designed for semi-autonomous operation at unmanned Loran-C radionavigation transmitting stations. This clock is designed to mitigate a doomsday scenario where all space-based timing assets are lost. It is implemented using three free-running commercial cesium oscillators, a traditional measurement system, and an Auxiliary Output Generator (AOG) phase-locked to the weighted mean of the cesium ensemble. A relatively inexpensive rubidium oscillator is used as the AOG with Proportional Integral (PI) compensator steering. A robust design ensures continuous clock operation when several components have failed or are otherwise unavailable. Measurements are made to multiple external timing sources, any one of which may be used to discipline the clock. The clock maintains a ±15 ns phase difference relative to UTC via GPS without user interaction. Additionally, it has been shown to maintain ±50ns for 70 days upon loss of all external timing reference. The clock is currently disciplined using one-way GPS broadcasts. Future implementation may include the ability to discipline using all-in-view GNSS and Two-Way Satellite Time and Frequency Transfer (TWSTFT).
Published in:	Proceedings of the 40th Annual Precise Time and Time Interval Systems and Applications Meeting December 1 - 4, 2008 Hyatt Regency Reston Town Center Reston, Virginia
Pages:	227 - 240
Cite this article:	Dahlen, Aaron P., "A Prototype Cesium Clock Ensemble for the Loran-C Radionavigation System," Proceedings of the 40th Annual Precise Time and Time Interval Systems and Applications Meeting, Reston, Virginia, December 2008, pp. 227-240.
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