page_title: Omega (navigation system)
section_title: OMEGA
hierarchical_section_title: Omega (navigation system) / History / OMEGA
caption_attribution_description: English: Omega Navigation Tower, Liberia (decommissioned Sep 30, 1997, currently unused) Tower is 1,400 feet (426&#160;m), built in 1976 Wires connected to the top of the tower are the "umbrella" antenna, not supporting structures. View is from approx 5 miles
context_page_description: OMEGA was the first global-range radio navigation system, operated by the United States in cooperation with six partner nations. It was a hyperbolic navigation system, enabling ships and aircraft to determine their position by receiving very low frequency radio signals in the range 10 to 14 kHz, transmitted by a global network of eight fixed terrestrial radio beacons, using a navigation receiver unit. It became operational around 1971 and was shut down in 1997 in favour of the Global Positioning System.
context_section_description: Omega was approved for development in 1968 with eight transmitters and the ability to achieve a 4-mile (6.4 km) accuracy when fixing a position. Each Omega station transmitted a sequence of three very low frequency (VLF) signals (10.2 kHz, 13.6 kHz, 11.333... kHz in that order) plus a fourth frequency which was unique to each of the eight stations.  The duration of each pulse (ranging from 0.9 to 1.2 seconds, with 0.2 second blank intervals between each pulse) differed in a fixed pattern, and repeated every ten seconds; the 10-second pattern was common to all 8 stations and synchronized with the carrier phase angle, which itself was synchronized with the local master atomic clock.  The pulses within each 10-second group were identified by the first 8 letters of the alphabet within Omega publications of the time.
  The envelope of the individual pulses could be used to establish a receiver's internal timing within the 10-second pattern.  However, it was the phase of the received signals within each pulse that was used to determine the transit time from transmitter to receiver.  Using hyperbolic geometry and radionavigation principles, a position fix with an accuracy on the order of 5–10 kilometres (3.1–6.2 mi) was realizable over the entire globe at any time of the day. Omega employed hyperbolic radionavigation techniques and the chain operated in the VLF portion of the spectrum between 10 and 14 kHz. Near the end of its service life of 26 years, Omega evolved into a system used primarily by the civil community. By receiving signals from three stations, an Omega receiver could locate a position to within 4 nautical miles (7.4 km) using the principle of phase comparison of signals.
  Omega stations used very extensive antennas to transmit at their very low frequencies (VLF).  This is because wavelength is inversely proportional to frequency (wavelength in metres = 299,792,458 / frequency in Hz), and transmitter efficiency is severely degraded if the length of the antenna is shorter than 1/4 wavelength. They used grounded or insulated guyed masts with umbrella antennas, or wire-spans across both valleys and fjords. Some Omega antennas were the tallest constructions on the continent where they stood or still stand.
  When six of the eight station chain became operational in 1971, day-to-day operations were managed by the United States Coast Guard in partnership with Argentina, Norway, Liberia, and France. The Japanese and Australian stations became operational several years later. Coast Guard personnel operated two US stations: one in LaMoure, North Dakota and the other in Kaneohe, Hawaii on the island of Oahu.
  Due to the success of the Global Positioning System, the use of Omega declined during the 1990s, to a point where the cost of operating Omega could no longer be justified.  Omega was shut down permanently on 30 September 1997.  Several of the towers were then soon demolished.
  Some of the stations, such as the LaMoure station, are now used for submarine communications.
caption: Omega Tower Paynesville, Liberia
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