A Prototype Cesium Clock Ensemble for The Loran-C Radionavigation System
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 plus-or-minus 15 nanosecond phase difference relative to UTC via GPS without user interaction. Additionally, it has been shown to maintain plus-or-minus 50 nanoseconds 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).
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 01, 2008
- Accession Number
- ADA503340
Entities
People
- Aaron P. Dahlen