Omega

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Abstract
Omega is a very-long-range, very-low-frequency (VLF) radio navigation system which now provides continuous global coverage for ships and aircraft. The final eighth station was completed in Australia in 1982. Coverage is not only global but is also redundant with more than the minimum required number of signals usually available in most locations. The system is in general use in both the marine and aeronautical environments both commercially and militarily. Although use by maritime shipping has recently decreased, acceptance by commercial airlines has been cially rapid. Receivers range from simple phase comparison units which must be supported by special propagation tables and plotting charts to fully automatic receivers which read out in latitude and longitude after being initialized with no more than approximate location and time. Realizable fix accuracy is usually on the order of 1 to 2 nmi circular error probable (c.e.p.). The paper provides a general overview of Omega with attention to Administration, Synchronization, Traditional Applications, Lane Ambiguity Resolution, Special Applications, and Differential Omega. Combined systems using both Omega and other navigational techniques such as Transit or VLF communications signals are mentioned. This paper also gives attention to VLF propagation, the properties of which determine the fundamental advantages and limitations of Omega. Special attention is directed to the subject of signal coverage. For communications, it is only needed to receive a signal with adequate signal-to-noise ratio. For navigation, it is also necessary that the signals have a well-defined or characterized phase variation in space. Omega coverage considerations have proved to be more formidable than was originally envisaged.

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