The Decca Navigator System was a
hyperbolic
Hyperbolic is an adjective describing something that resembles or pertains to a hyperbola (a curve), to hyperbole (an overstatement or exaggeration), or to hyperbolic geometry.
The following phenomena are described as ''hyperbolic'' because they ...
radio navigation
Radio navigation or radionavigation is the application of radio frequencies to determine a position of an object on the Earth, either the vessel or an obstruction. Like radiolocation, it is a type of radiodetermination.
The basic principles a ...
system which allowed ships and aircraft to determine their position by using radio signals from a dedicated system of static radio transmitters. The system used phase comparison of two
low frequency
Low frequency (LF) is the ITU designation for radio frequencies (RF) in the range of 30–300 kHz. Since its wavelengths range from 10–1 km, respectively, it is also known as the kilometre band or kilometre wave.
LF radio waves exh ...
signals between 70 and 129
kHz
The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose expression in terms of SI base units is s−1, meaning that on ...
, as opposed to pulse timing systems like
Gee and
LORAN
LORAN, short for long range navigation, was a hyperbolic radio navigation system developed in the United States during World War II. It was similar to the UK's Gee system but operated at lower frequencies in order to provide an improved range u ...
. This made it much easier to design receivers using 1940s electronics, and operation was simplified by giving a direct readout of Decca coordinates without the complexity of a
cathode ray tube
A cathode-ray tube (CRT) is a vacuum tube containing one or more electron guns, which emit electron beams that are manipulated to display images on a phosphorescent screen. The images may represent electrical waveforms ( oscilloscope), pictu ...
and highly skilled operator.
The system was invented in the U.S., but development was carried out by
Decca Decca may refer to:
Music
* Decca Records or Decca Music Group, a record label
* Decca Gold, a classical music record label owned by Universal Music Group
* Decca Broadway, a musical theater record label
* Decca Studios, a recording facility in W ...
in the UK. It was first deployed by the
Royal Navy
The Royal Navy (RN) is the United Kingdom's naval warfare force. Although warships were used by English and Scottish kings from the early medieval period, the first major maritime engagements were fought in the Hundred Years' War against F ...
during
World War II
World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...
for the vital task of clearing the minefields to enable the
D-Day
The Normandy landings were the landing operations and associated airborne operations on Tuesday, 6 June 1944 of the Allied invasion of Normandy in Operation Overlord during World War II. Codenamed Operation Neptune and often referred to as D ...
landings. The Allied forces needed an accurate system not known to the Germans and thus free of jamming. After the war, it came off the secret list and was commercially developed by the Decca Company and deployed around UK and later used in many areas around the world. At its peak there were about 180 transmitting stations using "chains" of three or four transmitters each to allow position fixing by plotting intersecting electronic lines. Decca's primary use was for ship navigation in coastal waters, offering much better accuracy than the competing LORAN system. Fishing vessels were major post-war users, but it was also used on some aircraft, including a very early (1949) application of
moving map display
A moving map display is a type of navigation system output that, instead of numerically displaying the current geographical coordinates determined by the navigation unit or an heading and distance indication of a certain waypoint, displays the u ...
s. The system was deployed extensively in the
North Sea
The North Sea lies between Great Britain, Norway, Denmark, Germany, the Netherlands and Belgium. An epeiric sea on the European continental shelf, it connects to the Atlantic Ocean through the English Channel in the south and the Norwegian S ...
and was used by helicopters operating to
oil platform
An oil platform (or oil rig, offshore platform, oil production platform, and similar terms) is a large structure with facilities to extract and process petroleum and natural gas that lie in rock formations beneath the seabed. Many oil platfor ...
s.
The opening of the more accurate
Loran-C
Loran-C is a hyperbolic radio navigation system that allows a receiver to determine its position by listening to low frequency radio signals that are transmitted by fixed land-based radio beacons. Loran-C combined two different techniques to p ...
system to civilian use in 1974 offered stiff competition, but Decca was well established by this time and continued operations to 2000. Decca Navigator was eventually replaced, along with Loran and similar systems, by the
GPS
The Global Positioning System (GPS), originally Navstar GPS, is a Radionavigation-satellite service, satellite-based radionavigation system owned by the United States government and operated by the United States Space Force. It is one of t ...
in 2000, when that became available for public use.
Principles of operation
Overview
The Decca Navigator System consisted of individual groups of land-based radio transmitters organised into ''chains'' of three or four stations. Each chain consisted of a
master station In telecommunication, a master station is a station that controls or coordinates the activities of other stations in the system.
Examples:
*In a data network, the control station may designate a master station to ensure data transfer to one or more ...
and three (occasionally two) secondary stations, termed Red, Green and Purple. Ideally, the secondaries would be positioned at the vertices of an equilateral triangle with the master at the centre. The baseline length, that is, the master-secondary distance, was typically .
Each station transmitted a continuous wave signal that, by comparing the
phase
Phase or phases may refer to:
Science
*State of matter, or phase, one of the distinct forms in which matter can exist
*Phase (matter), a region of space throughout which all physical properties are essentially uniform
* Phase space, a mathematic ...
difference of the signals from the master and one of the secondaries, produced a relative phase measure that was presented on a clock-like display. The phase difference was caused by the relative distance between the stations as seen by the receiver. As the receiver moves these distances change and those changes are represented by the movement of the hands on the displays.
If one selects a particular phase difference, say 30 degrees, and plots all the locations where that phase difference occurs, the result is a set of
hyperbolic
Hyperbolic is an adjective describing something that resembles or pertains to a hyperbola (a curve), to hyperbole (an overstatement or exaggeration), or to hyperbolic geometry.
The following phenomena are described as ''hyperbolic'' because they ...
''
lines of position
A position line or line of position (LOP) is a line (or, on the surface of the earth, a curve) that can be both identified on a chart (nautical chart or aeronautical chart) and translated to the surface of the earth. The intersection of a minimum o ...
'' called a ''pattern''. As there were three secondaries there were three patterns, also termed Red, Green and Purple. The patterns were drawn on
nautical chart
A nautical chart is a graphic representation of a sea area and adjacent coastal regions. Depending on the scale of the chart, it may show depths of water and heights of land (topographic map), natural features of the seabed, details of the coa ...
s as a set of hyperbolic lines in the appropriate colour.
Receivers determined their location by measuring the phase difference from two or more of the patterns from the displays. They could then look at the chart to find where the two closest charted hyperbolas crossed. The accuracy of this measurement was improved by choosing the set of two patterns that resulted in the lines crossing at as close to a right angle as possible.
Detailed principles of operation
When two stations transmit at the
phase-locked frequency, the difference in phase between the two signals is constant along a hyperbolic path. If two stations transmit on the same frequency, it is impossible for the receiver to separate them. Instead, each chain was allocated a nominal frequency, known as 1f, and each station in the chain transmitted at a harmonic of this base frequency, as follows:
The frequencies given are those for Chain 5B, known as the English Chain, but all chains used similar frequencies between 70 kHz and 129 kHz.
Decca receivers multiplied the signals received from the Master and each Slave by different values to arrive at a common frequency (
least common multiple
In arithmetic and number theory, the least common multiple, lowest common multiple, or smallest common multiple of two integers ''a'' and ''b'', usually denoted by lcm(''a'', ''b''), is the smallest positive integer that is divisible by bot ...
, LCM) for each Master/Slave pair, as follows:
It was phase comparison at this common frequency that resulted in the hyperbolic lines of position. The interval between two adjacent hyperbolas on which the signals are in phase was called a ''lane''. Since the wavelength of the common frequency was small compared with the distance between the Master and Slave stations there were many possible lines of position for a given phase difference, and so a unique position could not be arrived at by this method.
Other receivers, typically for aeronautical applications, divided the transmitted frequencies down to the basic frequency (1f) for phase comparison, rather than multiplying them up to the LCM frequency.
Lanes and zones
Early Decca receivers were fitted with three rotating ''Decometers'' that indicated the phase difference for each pattern. Each Decometer drove a second indicator that counted the number of lanes traversed – each 360 degrees of phase difference was one lane traversed. In this way, assuming the point of departure was known, a more or less distinct location could be identified.
The lanes were grouped into ''zones'', with 18 green, 24 red, or 30 purple lanes in each zone. This meant that on the baseline (the straight line between the Master and its Slave) the zone width was the same for all three patterns of a given chain. Typical lane and zone widths on the baseline are shown in the table below (for chain 5B):
The lanes were numbered 0 to 23 for red, 30 to 47 for green and 50 to 79 for purple. The zones were labelled A to J, repeating after J. A Decca position coordinate could thus be written: Red I 16.30; Green D 35.80. Later receivers incorporated a microprocessor and displayed a position in latitude and longitude.
Multipulse
''Multipulse'' provided an automatic method of lane and zone identification by using the same phase comparison techniques described above on lower frequency signals.
The nominally continuous wave transmissions were in fact divided into a 20-second cycle, with each station in turn simultaneously transmitting all four Decca frequencies (5f, 6f, 8f and 9f) in a phase-coherent relationship for a brief period of 0.45 seconds each cycle. This transmission, known as Multipulse, allowed the receiver to extract the 1f frequency and so to identify which lane the receiver was in (to a resolution of a zone).
As well as transmitting the Decca frequencies of 5f, 6f, 8f and 9f, an 8.2f signal, known as Orange, was also transmitted. The beat frequency between the 8.0f (Red) and 8.2f (Orange) signals allowed a 0.2f signal to be derived and so resulted in a hyperbolic pattern in which one cycle (360°) of phase difference equates to 5 zones.
Assuming that one's position was known to this accuracy, this gave an effectively unique position.
Range and accuracy
During daylight, ranges of around could be obtained, reducing at night to 200 to , depending on propagation conditions.
The accuracy depended on:
* Width of the lanes
* Angle of cut of the hyperbolic lines of position
* Instrumental errors
* Propagation errors (for example,
Skywave
In radio communication, skywave or skip refers to the propagation of radio waves reflected or refracted back toward Earth from the ionosphere, an electrically charged layer of the upper atmosphere. Since it is not limited by the curvature of ...
)
By day these errors could range from a few meters on the baseline up to a nautical mile at the edge of coverage. At night, skywave errors were greater and, on receivers without multipulse capabilities, it was not unusual for the position to jump a lane, sometimes without the navigator knowing.
Although in the days of differential
GPS
The Global Positioning System (GPS), originally Navstar GPS, is a Radionavigation-satellite service, satellite-based radionavigation system owned by the United States government and operated by the United States Space Force. It is one of t ...
this range and accuracy may appear poor, in its day the Decca system was one of the few, if not the only, position fixing system available to many mariners. Since the need for an accurate position is less when the vessel is further from land, the reduced accuracy at long ranges was not a great problem.
History
Origins
In 1936 William J. O'Brien, an engineer, contracted
tuberculosis
Tuberculosis (TB) is an infectious disease usually caused by '' Mycobacterium tuberculosis'' (MTB) bacteria. Tuberculosis generally affects the lungs, but it can also affect other parts of the body. Most infections show no symptoms, in ...
which put his career on hold for a period of two years. During this period he had the idea of position fixing by means of phase comparison of continuous wave transmissions. This was not the first such system, but O'Brien apparently developed his version without knowledge of the others, and made several advancements in the art that would prove useful. He initially imagined the system being used for aircraft testing, specifically the accurate calculation of ground speed. Some experiments were carried out in California in 1938, selecting frequencies with harmonic "beats" that would allow for station identification in a network of transmitters. Both the
U.S. Army
The United States Army (USA) is the land service branch of the United States Armed Forces. It is one of the eight U.S. uniformed services, and is designated as the Army of the United States in the U.S. Constitution.Article II, section 2, cl ...
and
Navy
A navy, naval force, or maritime force is the branch of a nation's armed forces principally designated for naval warfare, naval and amphibious warfare; namely, lake-borne, riverine, littoral zone, littoral, or ocean-borne combat operations and ...
considered the idea too complicated and work ended in 1939.
O’Brien's friend, Harvey F. Schwarz, was chief engineer of the
Decca Record company in England. In 1939 O’Brien sent him details of the system so it could be put forward to the British military. Initially
Robert Watson-Watt
Sir Robert Alexander Watson Watt (13 April 1892 – 5 December 1973) was a Scottish pioneer of radio direction finding and radar technology.
Watt began his career in radio physics with a job at the Met Office, where he began looking for accura ...
reviewed the system but he did not follow it up, deeming it too easily jammed (and likely due to the existing work on the
Gee system, being carried out by Watt's group). However, in October 1941 the British Admiralty Signal Establishment (ASE) became interested in the system, which was then classified as ''Admiralty Outfit QM''. O’Brien brought the Californian equipment to the UK and conducted the first marine trials between
Anglesey
Anglesey (; cy, (Ynys) Môn ) is an island off the north-west coast of Wales. It forms a principal area known as the Isle of Anglesey, that includes Holy Island across the narrow Cymyran Strait and some islets and skerries. Anglesey island ...
and the
Isle of Man
)
, anthem = "O Land of Our Birth"
, image = Isle of Man by Sentinel-2.jpg
, image_map = Europe-Isle_of_Man.svg
, mapsize =
, map_alt = Location of the Isle of Man in Europe
, map_caption = Location of the Isle of Man (green)
in Europe ...
, at frequencies of 305/610 kHz, on 16 September 1942.
Further trials were conducted in the northern
Irish Sea
The Irish Sea or , gv, Y Keayn Yernagh, sco, Erse Sie, gd, Muir Èireann , Ulster-Scots: ''Airish Sea'', cy, Môr Iwerddon . is an extensive body of water that separates the islands of Ireland and Great Britain. It is linked to the Ce ...
in April 1943 at 70/130 kHz. It was decided that the original frequencies were not ideal, and a new system using a 14 kHz inter-signal spacing was selected. This led to the common 5, 6, 8 and 9''f'' frequencies, used throughout the life of the Decca system. 7''f'' was reserved for a
Loran-C
Loran-C is a hyperbolic radio navigation system that allows a receiver to determine its position by listening to low frequency radio signals that are transmitted by fixed land-based radio beacons. Loran-C combined two different techniques to p ...
-like extension, but never developed. A follow-up test was carried out in the
Irish Sea
The Irish Sea or , gv, Y Keayn Yernagh, sco, Erse Sie, gd, Muir Èireann , Ulster-Scots: ''Airish Sea'', cy, Môr Iwerddon . is an extensive body of water that separates the islands of Ireland and Great Britain. It is linked to the Ce ...
in January 1944 to test a wide variety of upgrades and production equipment. By this time the competing Gee system was known to the Admiralty and the two systems were tested head-to-head under the code names QM and QH. QM was found to have better sea-level range and accuracy, which led to its adoption.
D-Day landings
A three-station trial was held in conjunction with a large-scale assault and landing exercise in the
Moray Firth
The Moray Firth (; Scottish Gaelic: ''An Cuan Moireach'', ''Linne Mhoireibh'' or ''Caolas Mhoireibh'') is a roughly triangular inlet (or firth) of the North Sea, north and east of Inverness, which is in the Highland council area of north of Scotl ...
in February/March 1944. The success of the trials and the relative ease of use and accuracy of the system resulted in Decca receiving an order for 27 ''Admiralty Outfit QM'' receivers. The receiver consisted of an electronics unit with two dials and was known to its operators as the "Blue Gasmeter Job". A Decca chain was set up, consisting of a master station at
Chichester
Chichester () is a cathedral city and civil parish in West Sussex, England.OS Explorer map 120: Chichester, South Harting and Selsey Scale: 1:25 000. Publisher:Ordnance Survey – Southampton B2 edition. Publishing Date:2009. It is the only ci ...
and slaves at
Swanage
Swanage () is a coastal town and civil parish in the south east of Dorset, England. It is at the eastern end of the Isle of Purbeck and one of its two towns, approximately south of Poole and east of Dorchester. In the 2011 census the civil ...
and
Beachy Head
Beachy Head is a chalk headland in East Sussex, England. It is situated close to Eastbourne, immediately east of the Seven Sisters.
Beachy Head is located within the administrative area of Eastbourne Borough Council which owns the land, formin ...
. A fourth decoy transmitter was located in the
Thames Estuary
The Thames Estuary is where the River Thames meets the waters of the North Sea, in the south-east of Great Britain.
Limits
An estuary can be defined according to different criteria (e.g. tidal, geographical, navigational or in terms of salini ...
as part of the deception that the invasion would be focussed on the
Calais
Calais ( , , traditionally , ) is a port city in the Pas-de-Calais department, of which it is a subprefecture. Although Calais is by far the largest city in Pas-de-Calais, the department's prefecture is its third-largest city of Arras. Th ...
area.
21 minesweepers and other vessels were fitted with ''Admiralty Outfit QM'' and, on 5 June 1944, 17 of these ships used it to accurately navigate across the
English Channel
The English Channel, "The Sleeve"; nrf, la Maunche, "The Sleeve" (Cotentinais) or ( Jèrriais), (Guernésiais), "The Channel"; br, Mor Breizh, "Sea of Brittany"; cy, Môr Udd, "Lord's Sea"; kw, Mor Bretannek, "British Sea"; nl, Het Kana ...
and to sweep the minefields in the planned areas. The swept areas were marked with buoys in preparation for the
Normandy Landings
The Normandy landings were the landing operations and associated airborne operations on Tuesday, 6 June 1944 of the Allied invasion of Normandy in Operation Overlord during World War II. Codenamed Operation Neptune and often referred to as ...
.
After the initial ship tests, Decca conducted tests in cars, driving in the
Kingston By-Pass area to verify receiver accuracy. In the car installation, it was found possible to navigate within an individual traffic lane. The company entertained high hopes that the system could be used in aircraft, to permit much more precise navigation in the critical airspace around airports and urban centres where traffic density was highest.
Commercial deployment
![DECCA unit, NMS](https://upload.wikimedia.org/wikipedia/commons/7/7a/DECCA_unit%2C_NMS.jpg)
After the end of
World War II
World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...
the Decca Navigator Co. Ltd. was formed (1945) and the system expanded rapidly, particularly in areas of
British influence
British Influence, formally the Centre for British Influence Through Europe, was an independent, cross-party, pro-single market foreign affairs think tank based in the United Kingdom, founded in 2012 to make the case for the European Union ami ...
; at its peak it was deployed in many of the world's major shipping areas. More than 15,000 receiving sets were in use aboard ships in 1970. There were 4 chains around England, 1 in Ireland and 2 in Scotland, 12 in Scandinavia (5 each in Norway and Sweden and 1 each in Denmark and Finland), a further 4 elsewhere in northern Europe and 2 in Spain.
Canada was another early user, with branch offices set up in
Toronto
Toronto ( ; or ) is the capital city of the Canadian province of Ontario. With a recorded population of 2,794,356 in 2021, it is the most populous city in Canada and the fourth most populous city in North America. The city is the ancho ...
in 1953. The first chain was installed in southwest
Newfoundland
Newfoundland and Labrador (; french: Terre-Neuve-et-Labrador; frequently abbreviated as NL) is the easternmost province of Canada, in the country's Atlantic region. The province comprises the island of Newfoundland and the continental region ...
in 1956 as part of a joint Canada-US Navy surveying program. This led to commercial deployments the next year in
Nova Scotia
Nova Scotia ( ; ; ) is one of the thirteen provinces and territories of Canada. It is one of the three Maritime provinces and one of the four Atlantic provinces. Nova Scotia is Latin for "New Scotland".
Most of the population are native Eng ...
and an inland system for air traffic in the busy
Quebec City
Quebec City ( or ; french: Ville de Québec), officially Québec (), is the capital city of the Provinces and territories of Canada, Canadian province of Quebec. As of July 2021, the city had a population of 549,459, and the Communauté métrop ...
-
Montreal
Montreal ( ; officially Montréal, ) is the List of the largest municipalities in Canada by population, second-most populous city in Canada and List of towns in Quebec, most populous city in the Provinces and territories of Canada, Canadian ...
area. A fourth chain covering eastern Newfoundland was added in 1958. When meetings in Montreal in 1958 led to VOR and DME being selected as the standard aviation navigation systems, the Montreal system was moved eastward to cover the
Anticosti Island
; moe, Notiskuan; mic, Natigostec
, sobriquet =
, image_name = RiviereHuileAnticosti.jpg
, image_caption = Salmon fisherman on Rivière à l'Huile
, image_map ...
area of the
Gulf of St. Lawrence, and the western Newfoundland chain was later repositioned to better cover the
Cabot Strait
Cabot Strait
(; french: détroit de Cabot, ) is a strait in eastern Canada approximately 110 kilometres wide between Cape Ray, Newfoundland and Cape North, Cape Breton Island.
It is the widest of the three outlets for the Gulf of Saint L ...
. A series of chains was also proposed to cover the
Northwest Passage
The Northwest Passage (NWP) is the sea route between the Atlantic and Pacific oceans through the Arctic Ocean, along the northern coast of North America via waterways through the Canadian Arctic Archipelago. The eastern route along the Arct ...
had oil tanker traffic used the area, but this never came to be. Another was briefly set up covering
Lake Ontario
Lake Ontario is one of the five Great Lakes of North America. It is bounded on the north, west, and southwest by the Canadian province of Ontario, and on the south and east by the U.S. state of New York. The Canada–United States border sp ...
in 1971 for the
International Field Year for the Great Lakes. The last Canadian chain shut down in 1986, after Loran-C became widespread.
In the late 1950s an experimental Decca chain was set up in the United States, in the New York area, to be used for navigating the
Vertol 107 helicopters of
New York Airways
New York Airways was a helicopter airline in the New York City area, founded in 1949 as a mail and cargo carrier. On 9 July 1953 it may have been the first scheduled helicopter airline to carry passengers in the United States, with headquarters ...
. These helicopters were operating from the principal local airports—
Idlewild Airport
John F. Kennedy International Airport (colloquially referred to as JFK Airport, Kennedy Airport, New York-JFK, or simply JFK) is the main international airport serving New York City. The airport is the busiest of the seven airports in the New ...
on Long Island,
Newark Airport
Newark Liberty International Airport , originally Newark Metropolitan Airport and later Newark International Airport, is an international airport straddling the boundary between the cities of Newark in Essex County and Elizabeth in Union Count ...
in New Jersey,
LaGuardia Airport
LaGuardia Airport is a civil airport in East Elmhurst, Queens, New York City. Covering , the facility was established in 1929 and began operating as a public airport in 1939. It is named after former New York City mayor Fiorello La Guardia. ...
in the Borough of Queens, nearer to Manhattan, and a site on the top of the (then)
PanAm Building
The MetLife Building (also 200 Park Avenue and formerly the Pan Am Building) is a skyscraper at Park Avenue and 45th Street, north of Grand Central Terminal, in the Midtown Manhattan neighborhood of New York City. Designed in the Internation ...
on Park Avenue. Use of Decca was essential because its signals could be received down to sea level, were not subject to the line-of-sight limitations of
VOR
VOR or vor may refer to:
Organizations
* Vale of Rheidol Railway in Wales
* Voice of Russia, a radio broadcaster
* Volvo Ocean Race, a yacht race
Science, technology and medicine
* VHF omnidirectional range, a radio navigation aid used in a ...
/
DME and did not suffer the slant-range errors that create problems with VOR/DME close to the transmitters. The Decca installations in the New York Airways helicopters included the unique Decca 'roller map' displays that enabled the pilot to see his or her position at a glance, a concept infeasible with VOR/DME.
This chain installation was considered highly controversial at the time, for political reasons. This led to the U.S. Coast Guard, under instructions from the Treasury Department to which it reported, banning the use of Decca receivers in ships entering New York harbour for fear that the system might create a de facto standard (as it had become in other areas of the world). It also served to protect the marketing interests of the Hoffman Electronics division of ITT, a principal supplier of VOR/DME systems, that Decca might have been poised to usurp.
This situation was exacerbated by the workload problems of the Air Traffic Controllers Association (ATCA), under its executive director Francis McDermott, whose members were forced to use radar data on aircraft positions, relaying those positions by radio to the aircraft from their control locations. An example of the problem, cited by experts, was the
collision of a Douglas DC8 and a Lockheed Constellation over Staten Island, New York, that—according to some experts—could have been avoided if the aircraft had been Decca-equipped and could not only have determined their positions more precisely but would not have suffered from the rho-theta position errors inherent in VOR/DME.
Other chains were established in Japan (6 chains); Namibia and South Africa (5 chains); India and Bangladesh (4 chains); North-West Australia (2 chains); the
Persian Gulf
The Persian Gulf ( fa, خلیج فارس, translit=xalij-e fârs, lit=Gulf of Persis, Fars, ), sometimes called the ( ar, اَلْخَلِيْجُ ٱلْعَرَبِيُّ, Al-Khalīj al-ˁArabī), is a Mediterranean sea (oceanography), me ...
(1 chain with stations in Qatar and the United Arab Emirates and a second chain in the north of the Gulf with stations in Iran) and the Bahamas (1 chain). Four chains were planned for Nigeria but only two were built and these did not enter into public service. Two chains in Vietnam were used during the
Vietnam War
The Vietnam War (also known by #Names, other names) was a conflict in Vietnam, Laos, and Cambodia from 1 November 1955 to the fall of Saigon on 30 April 1975. It was the second of the Indochina Wars and was officially fought between North Vie ...
for helicopter navigation, with limited success.
During the Cold War period, following WWII, the R.A.F. established a confidential chain in Germany. The Master station was in
Bad Iburg
Bad Iburg (; Westphalian: ''Bad Ibig'') is a spa town in the district of Osnabrück, in Lower Saxony, Germany. It is situated in the Teutoburg Forest, 16 km south of Osnabrück.
Bad Iburg is also the name of a municipality which includes ...
near Osnabrück and there were two Slaves. The purpose of this chain was to provide accurate air navigation for the corridor between Western Germany and Berlin in the event that a mass evacuation of allied personnel may be required. In order to maintain secrecy, frequencies were changed at irregular intervals.
Decca, Racal, and the closedown
![Decca Receiver Philips](https://upload.wikimedia.org/wikipedia/commons/b/b5/Decca_Receiver_Philips.jpg)
The headquarters of Decca Navigator were at New Malden, Surrey, just off the Kingston by-pass. There was a Decca School, at
Brixham
Brixham is a coastal town and civil parish, the smallest and southernmost of the three main population centres (the others being Paignton and Torquay) on the coast of Torbay in the county of Devon, in the south-west of England. Commercial fish ...
,
Devon
Devon ( , historically known as Devonshire , ) is a ceremonial and non-metropolitan county in South West England. The most populous settlement in Devon is the city of Plymouth, followed by Devon's county town, the city of Exeter. Devon is ...
, where employees were sent on courses from time to time.
Racal
Racal Electronics plc was a British electronics company that was founded in 1950.
Listed on the London Stock Exchange and once a constituent of the FTSE 100 Index, Racal was a diversified company, offering products including voice loggers and ...
, the UK weapons and communications company, acquired Decca in 1980. Merging Decca's radar assets with their own, Racal began selling off the other portions of the company, including avionics and Decca Navigator.
A significant amount of income from the Decca system was due to the receivers being leased to users, not sold outright. This guaranteed predictable annual income. When the patents on the original technology lapsed in the early 1980s, new receivers were quickly built by a number of companies. In particular, Aktieselskabet Dansk Philips ('Danish Philips', ''ap'') introduced receivers that could be purchased outright, and were much smaller and easier to use than the current Decca counterparts. The "ap" versions directly output the longitude and latitude to two decimals (originally in datum
ED50
ED50 ("European Datum 1950", EPSG:4230) is a geodetic datum which was defined after World War II for the international connection of geodetic networks.
Background
Some of the important battles of World War II were fought on the borders of Germ ...
only) instead of using the "deco meter" displays, offering accuracy better than ±9.3 m, much better than the Decca units. This also eliminated the need for the special charts printed with Decca lanes and zones.
Decca sued ap for infringement and, in the ensuing court battle, Decca lost the monopoly. That signalled the beginning of the end for the company. Income dwindled and eventually, the UK
Ministry of Transport
A ministry of transport or transportation is a ministry responsible for transportation within a country. It usually is administered by the ''minister for transport''. The term is also sometimes applied to the departments or other government age ...
stepped in, having the
lighthouse authorities take responsibility for operating the system in the early 1990s.
A ruling from the European Union forced the UK government to withdraw funding. The
general lighthouse authority
A general lighthouse authority (GLA) is one of three agencies primarily responsible for aids to navigation in the United Kingdom and the Republic of Ireland. They are divided into regions as follows:
*Trinity House: England & Wales, Channel Island ...
ceased Decca transmissions at midnight on 31 March 2000. The Irish chain provided by
Bórd Iascaigh Mhara continued transmitting until 19 May 2000. Japan continued operating their
Hokkaidō
is Japan's second largest island and comprises the largest and northernmost prefecture, making up its own region. The Tsugaru Strait separates Hokkaidō from Honshu; the two islands are connected by the undersea railway Seikan Tunnel.
The la ...
chain until March 2001, the last Decca chain in operation.
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
In radio communication, skywave or skip refers to the propagation of radio waves reflected or refracted back toward Earth from the ionosphere, an electrically charged layer of the upper atmosphere. Since it is not limited by the curvature of ...
s at long distances. In February 1946 the company proposed a system with two main stations located at
Shannon Airport
Shannon Airport ( ga, Aerfort na Sionainne) is an international airport located in County Clare in the Republic of Ireland. It is adjacent to the Shannon Estuary and lies halfway between Ennis and Limerick. The airport is the third busiest ai ...
in Ireland and
Gander International Airport
Gander International Airport is located in Gander, Newfoundland and Labrador, Canada, and is operated by the Gander International Airport Authority. Canadian Forces Base Gander shares the airfield but is a separate entity from the airport. The ...
in
Newfoundland
Newfoundland and Labrador (; french: Terre-Neuve-et-Labrador; frequently abbreviated as NL) is the easternmost province of Canada, in the country's Atlantic region. The province comprises the island of Newfoundland and the continental region ...
(today part of Canada). Together, these stations would provide navigation over the main
great circle route
Great-circle navigation or orthodromic navigation (related to orthodromic course; from the Greek ''ορθóς'', right angle, and ''δρóμος'', path) is the practice of navigating a vessel (a ship or aircraft) along a great circle. Such rout ...
between London and New York. A third station in
Bermuda
)
, anthem = "God Save the King"
, song_type = National song
, song = " Hail to Bermuda"
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would provide general ranging information to measure progress along the main track.
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
The General Post Office (GPO) was the state postal system and telecommunications carrier of the United Kingdom until 1969. Before the Acts of Union 1707, it was the postal system of the Kingdom of England, established by Charles II in 1660. ...
's
POPI
''Popi'' is a 1969 American comedy-drama film directed by Arthur Hiller, and starring Alan Arkin (in the title role) and Rita Moreno. The screenplay was written by Tina Pine and Lester Pine. The film focuses on a Puerto Rican widower strugglin ...
system, was introduced in 1954, proposing 28 stations that provided worldwide coverage. The system was predicted to offer accuracy at range 95% of the time. Further development was ended in favour of the Dectra system.
Dectra
In the early 1960s the
Radio Technical Commission for Aeronautics
RTCA, Inc. (formerly known as Radio Technical Commission for Aeronautics) is a United States non-profit organization that develops technical guidance for use by government regulatory authorities and by industry. It was founded in 1935 and was re-in ...
(RTCA), as part of a wider
ICAO
The International Civil Aviation Organization (ICAO, ) is a specialized agency of the United Nations that coordinates the principles and techniques of international air navigation, and fosters the planning and development of international a ...
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 trans-Atlantic navigation with less accuracy, using a single receiver. The system was known as Dectra, short for "Decca Track".
Unlike the Delrac system, Dectra was essentially the normal Decca Navigator system with the modification of several existing transmitter sites. 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.
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
In radio navigation, a VOR/DME is a radio beacon that combines a VHF omnidirectional range (VOR) with a distance-measuring equipment (DME). The VOR allows the receiver to measure its bearing to or from the beacon, while the DME provides the slan ...
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. Additionally, as the Decca system provided an X and Y location, as opposed to the 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 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.
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
)
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. 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
British Overseas Airways Corporation (BOAC) was the British state-owned airline created in 1939 by the merger of Imperial Airways and British Airways Ltd. It continued operating overseas services throughout World War II. After the passi ...
Vickers VC10
The Vickers VC10 is a mid-sized, narrow-body long-range British jet airliner designed and built by Vickers-Armstrongs (Aircraft) Ltd and first flown at Brooklands, Surrey, in 1962. The airliner was designed to operate on long-distance route ...
. 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 lat/long output along with bearing, distance-to-go, bearing and an autopilot coupling.
["Dectra in Iceland", Decca Navigator News, October 1967] Their efforts to standardize this were eventually abandoned as
inertial navigation system
An inertial navigation system (INS) is a navigation device that uses motion sensors (accelerometers), rotation sensors ( gyroscopes) and a computer to continuously calculate by dead reckoning the position, the orientation, and the velocity (dire ...
s began to be installed for these needs.
Hi-Fix
A more accurate system named Hi-Fix was developed using signalling in the 1.6 MHz range. It was used for specialised applications such as precision measurements involved with oil-drilling and by the
Royal Navy
The Royal Navy (RN) is the United Kingdom's naval warfare force. Although warships were used by English and Scottish kings from the early medieval period, the first major maritime engagements were fought in the Hundred Years' War against F ...
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. 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.
Special DECCA towers
*
Puckeridge DECCA tower
*
Zeven DECCA-transmitter
The Zeven DECCA-transmitter was a transmitting facility for DECCA transmission at Zeven, Germany. It used a 93 metre tall guyed mast antenna, which is insulated against ground. As backup antenna, a 46-meter mast radiator also insulated against gr ...
See also
*
GEE (navigation)
Gee, sometimes written GEE, was a radio navigation system used by the Royal Air Force during World War II. It measured the time delay between two radio signals to produce a fix, with accuracy on the order of a few hundred metres at ranges up ...
*
Loran-C
Loran-C is a hyperbolic radio navigation system that allows a receiver to determine its position by listening to low frequency radio signals that are transmitted by fixed land-based radio beacons. Loran-C combined two different techniques to p ...
*
Omega (navigation system)
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 ...
*
Local positioning system
A positioning system is a system for determining the position of an object in space. One of the most well-known and commonly used positioning systems is the Global Positioning System (GPS).
Positioning system technologies exist ranging from worl ...
*
Datatrak Datatrak was a hyperbolic radio navigation system similar to Decca Decca may refer to:
Music
* Decca Records or Decca Music Group, a record label
* Decca Gold, a classical music record label owned by Universal Music Group
* Decca Broadway, a musi ...
References
Citations
Bibliography
*
**A modified version is = Jerry Proc
"The GEE System" 14 January 2001
* The Decca Navigator - Principles and Performance of the System, The Decca Navigator Company Limited, July 1976
* Night Passage to Normandy, Lieutenant-Commander Oliver Dawkins, R.N.V.R, Decca, 1969
* The Decca Navigator System on D-Day, 6 June 1944, An Acid Test, Commander Hugh St. A. Malleson, R.N. (Ret.)
* Hyperbolic Radionavigation Systems, Compiled by Jerry Proc VE3FAB, 200
* Navigation Systems: A Survey of Modern Electronic Aids, ed. G.E. Beck, van Nostrand Reinhold, 1971
External links
Decca Navigator System by Jerry ProcDecca Navigator Spain by Santiago Insua (in Spanish)* {{Internet Archive short film, id=gov.dod.dimoc.26968, name=STAFF FILM REPORT 66-19A (1966)
Radio navigation
Navigational equipment
Navigator System