Omega Navigation System 1969 US Navy Training Film MN-10782A

more at http://quickfound.net/

'Describes the technology and science behind the Omega Navigation System, used for long range navigation by military ships and aircraft.'

Originally a public domain film, slightly cropped to remove uneven edges, with the aspect ratio corrected, and one-pass brightness-contrast-color correction & mild video noise reduction applied.

The soundtrack was also processed with volume normalization, noise reduction, clipping reduction, and/or equalization (the resulting sound, though not perfect, is far less noisy than the original).

https://en.wikipedia.org/wiki/Omega_(navigation_system)

Wikipedia license: http://creativecommons.org/licenses/by-sa/3.0/

OMEGA was the first global-range radio navigation system, operated by the United States in cooperation with six partner nations. It enabled ships and aircraft to determine their position by receiving very low frequency (VLF) radio signals in the range 10 to 14 kHz, transmitted by a network of fixed terrestrial radio beacons, using a receiver unit. It became operational around 1971 and was shut down in 1997 in favour of the Global Positioning System...

Taking a "fix" in any navigation system requires the determination of two measurements...

The introduction of radio systems during the 20th century dramatically increased the distances over which measurements could be taken... 

The first of these hyperbolic navigation systems was the UK'S Gee and Decca, followed by the US LORAN and LORAN-C systems. LORAN-C offered accurate navigation at distances over 1,000 kilometres (620 mi), and by locating "chains" of stations around the world, they offered moderately widespread coverage....

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...

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...