Editing Decca Navigator System (section)

== Other applications ==

=== Delrac ===
In the immediate post-war era, Decca began studying a long-range system like Decca, but using much lower frequencies to enable reception of [[skywave]]s at long distances. In February 1946 the company proposed a system with two main stations located at [[Shannon Airport]] in Ireland and [[Gander International Airport]] in [[Newfoundland]] (today part of Canada). Together, these stations would provide navigation over the main [[great circle route]] between London and New York. A third station in [[Bermuda]] would provide general ranging information to measure progress along the main track.{{sfn|Blanchard|1991|p=303}}

Work on this concept continued, and in 1951 a modified version was presented that offered navigation over very wide areas. This was known as '''Delrac''', short for "Decca Long Range Area Cover". A further development, including features of the [[General Post Office]]'s [[POPI]] system, was introduced in 1954, proposing 28 stations that provided worldwide coverage.{{sfn|Blanchard|1991|p=303}} The system was predicted to offer {{convert|10|mile|m}} accuracy at {{convert|2000|mile|km}} range 95% of the time. Further development was ended in favour of the Dectra system.{{sfn|Blanchard|1991|p=304}}

=== Dectra ===
In the early 1960s the [[Radio Technical Commission for Aeronautics]] (RTCA), as part of a wider [[ICAO]] effort, began the process of introducing a standard long-range radio navigation system for aviation use. Decca proposed a system that could offer both high accuracy at short ranges and transatlantic navigation with less accuracy, using a single receiver. The system was known as '''Dectra''', short for "Decca Track".{{sfn|Blanchard|1991|p=304}}

Unlike the Delrac system, Dectra was essentially the normal Decca Navigator system with the modification of several existing transmitter sites.{{sfn|Blanchard|1991|p=304}} These were located at the East Newfoundland and Scottish chains, which were equipped with larger antennas and high-power transmitters, broadcasting 20 times as much energy as normal chain stations. Given that the length of the chain baselines did not change, and were relatively short, at long distance the signal offered almost no accuracy. Instead, Dectra operated as a track system; aircraft would navigate by keeping themselves within the signal defined by a particular Decca lane.{{sfn|Blanchard|1991|p=305}}

The main advantage of Dectra compared to other systems being proposed for the RTCA solution was that it could be used for both medium-range navigation over land, as well as long-range navigation over the Atlantic. In comparison, the [[VOR/DME]] system that ultimately won the competition offered navigation over perhaps a 200-mile radius, and could not offer a solution to the long-distance problem.{{sfn|Blanchard|1991|p=305}} Additionally, as the Decca system provided an X and Y location, as opposed to the [[Rho Theta Navigation|angle-and-range]] VOR/DME, Decca proposed offering it with their Decca Flight Log moving map display to further improve ease of navigation. In spite of these advantages, the RTCA ultimately chose VOR/DME for two primary reasons; VOR offered coverage over about the same range as Decca, about 200&nbsp;miles, but did so with a single transmitter instead of Decca's four, and Decca's frequencies proved susceptible to interference from static due to lightning, while VOR's higher frequencies were not quite as sensitive.{{sfn|Blanchard|1991|p=303}}

Decca continued to propose that Dectra be used for the long-range role. In 1967 they installed another transmitter in Iceland to provide ranging along the Scotland-Newfoundland track, with a second proposed to be installed on the [[Azores]]. They also installed Dectra receivers with Omnitrac computers and a lightweight version of the Flight Log on a number of commercial airliners, notably a [[BOAC]] [[Vickers VC10]]. The Omnitrac could take inputs from Decca (and Dectra), Loran-C, VOR/DME, an air data computer and doppler radars and combine them all to produce a latitude/longitude output along with bearing, distance-to-go, bearing and an autopilot coupling.<ref>"Dectra in Iceland", Decca Navigator News, October 1967</ref> Their efforts to standardize this were eventually abandoned as [[inertial navigation system]]s began to be installed for these needs.{{sfn|Blanchard|1991|p=305}}

===Hi-Fix===
A more accurate system named Hi-Fix was developed using signalling in the 1.6&nbsp;MHz range. It was used for specialised applications such as precision measurements involved with oil-drilling and by the [[Royal Navy]] for detailed mapping and surveying of coasts and harbours. The Hi-Fix equipment was leased for a period with temporary chains established to provide coverage of the area required, Hi-Fix was commercialised by Racal Survey in the early 1980s. An experimental chain was installed with coverage of central London and receivers placed in London buses and other vehicles to demonstrate an early vehicle location and tracking system. Each vehicle would report its location automatically via a conventional VHF two-way radio link, the data added to a voice channel.

Another application was developed by the Bendix Pacific division of Bendix Corporation, with offices in North Hollywood, California, but not deployed: PFNS—Personal Field Navigation System—that would enable individual soldiers to ascertain their geographic position, long before this capability was made possible by the satellite-based GPS (Global Positioning System).

A further application of the Decca system was implemented by the U.S. Navy in the late 1950s and early 1960s for use in the Tongue of the Ocean/Eleuthera Sound area near The Bahamas, separating the islands of Andros and New Providence. The application was for sonar studies made possible by the unique characteristics of the ocean floor.

An interesting characteristic of the Decca VLF signal discovered on BOAC, later British Airways, test flights to Moscow, was that the carrier switching could not be detected even though the carrier could be received with sufficient strength to provide navigation.{{clarify|date=March 2014}} Such testing, involving civilian aircraft, is quite common and may well not be in the knowledge of a pilot.

The 'low frequency' signalling of the Decca system also permitted its use on submarines. One 'enhancement' of the Decca system was to offer the potential of keying the signal, using Morse code, to signal the onset of nuclear war. This option was never taken up by the UK government. Messages were clandestinely sent, however, between Decca stations thereby bypassing international telephone calls, especially in non-UK chains.