Decca Navigator Mk 12

The Decca Navigator System was a hyperbolic low frequency radio navigation system (also known as multilateration) that was first deployed during World War II when the Allied forces needed a system which could be used to achieve accurate landings. As was the case with Loran C, its primary use was for ship navigation in coastal waters. Fishing vessels were major post-war users, but it was also used on aircraft, including a very early (1949) application of moving-map displays. The system was deployed extensively in the North Sea and was used by helicopters operating to oil platforms. After being shut down in the spring of 2000, it has been superseded by systems such as the American GPS and the planned European Galileo positioning system. Image File history File links Size of this preview: 666 × 599 pixelsFull resolution (999 × 899 pixel, file size: 186 KB, MIME type: image/jpeg) Decca Navigator Mk 12 eigenes Bild File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Image File history File links Size of this preview: 666 × 599 pixelsFull resolution (999 × 899 pixel, file size: 186 KB, MIME type: image/jpeg) Decca Navigator Mk 12 eigenes Bild File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... In mathematics, a hyperbola (Greek literally overshooting or excess) is a type of conic section defined as the intersection between a right circular conical surface and a plane which cuts through both halves of the cone. ... Low Frequency or LF refers to Radio Frequencies (RF) in the range of 30–300 kHz. ... Radio navigation is the application of radio frequencies to determining a position on the earth. ... Multilateration, also known as hyperbolic positioning, is the process of locating an object by accurately computing the time difference of arrival (TDOA) of a signal emitted from the object to three or more receivers. ... Combatants Allied powers: China France Great Britain Soviet Union United States and others Axis powers: Germany Italy Japan and others Commanders Chiang Kai-shek Charles de Gaulle Winston Churchill Joseph Stalin Franklin Roosevelt Adolf Hitler Benito Mussolini Hideki Tōjō Casualties Military dead: 17,000,000 Civilian dead: 33,000... LORAN (LOng RAnge Navigation) is a terrestrial navigation system using low frequency radio transmitters. ... The Hibernia platform is the worlds largest oil platform. ... The Global Positioning System (GPS) is currently the only fully functional Global Navigation Satellite System (GNSS). ... The Galileo positioning system, referred to simply as Galileo, is a proposed Global Navigation Satellite System, to be built by the European Satellite Navigation Industries for the European Union and European Space Agency (ESA) as an alternative to the United States operated Global Positioning System (GPS) and the Russian GLONASS...

It was deployed in the United Kingdom after World War II and later used in many areas around the world. Decca employees used to joke that DECCA was an acronym for Dedicated Englishmen Causing Chaos Abroad.

Principles of Operation

Overview

The Decca Navigator principle.
The phase difference between the signals received from stations A (Master) and B (Slave) is constant along each hyperbolic curve. The foci of the hyperbola are at the transmitting stations, A and B.

The Decca Navigator System consisted of a number of land-based stations organised into chains. Each chain consisted of a Master station and three (occasionally two) Slave stations, termed Red, Green and Purple. Ideally, the Slaves would be positioned at the vertices of an equilateral triangle with the Master at the centre. The baseline length, i.e. the Master-Slave distance, was typically 60~120 nautical miles. Each station transmitted a continuous wave signal that, by comparing the phase difference of the signals from the Master and one of the Slaves, resulted in a set of hyperbolic lines of position called a pattern. As there were three Slaves there were three patterns, termed Red, Green and Purple. The patterns were drawn on nautical charts as a set of hyperbolic lines in the appropriate colour. Receivers identified which hyperbola they were on and a position could be plotted at the intersection of the hyperbola from different patterns, usually by using the pair with the best angle of cut. Crude diagram of time-difference principle. ... Crude diagram of time-difference principle. ... In telecommunication, the term master station has the following meanings: 1. ... This article is about a portion of a periodic process. ... A position line is a line that can be identified both on a nautical chart or aeronautical chart and by observation out on the surface of the earth. ... In mathematics, a hyperbola (Greek literally overshooting or excess) is a type of conic section defined as the intersection between a right circular conical surface and a plane which cuts through both halves of the cone. ... In mathematics, a hyperbola (Greek literally overshooting or excess) is a type of conic section defined as the intersection between a right circular conical surface and a plane which cuts through both halves of the cone. ...

Detailed Principles of Operation

When two stations transmit at the same phase-locked frequency, the difference in phase between the two signals is constant along a hyperbolic path. Of course, if two stations transmit on the same frequency, it as practically impossible for the receiver to separate them; so instead of all stations transmitting at the same frequency, each chain was allocated a nominal frequency, 1f, and each station in the chain transmitted at a harmonic of this base frequency, as follows: Circle map showing mode-locked regions or Arnold tongues in black. ... FreQuency is a music video game developed by Harmonix and published by SCEI. It was released in November 2001. ...

The frequencies given are those for Chain 5B, known as the English Chain, but all chains used similar frequencies between 70kHz and 129kHz.

Decca receivers multiplied the signals received from the Master and each Slave by different values to arrive at a common frequency (least common multiple, LCM) for each Master/Slave pair, as follows: In arithmetic and number theory the least common multiple or lowest common multiple (lcm) or smallest common multiple of two integers a and b is the smallest positive integer that is a multiple of both a and b. ...

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 unique 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 400 nautical miles could be obtained, reducing at night to 200 to 250 nautical miles, depending on propagation conditions. A nautical mile or sea mile is a unit of length. ...

The accuracy depended on:

• Width of the lanes
• Angle of cut of the hyperbolic lines of position
• Instrumental errors
• Propagation errors (e.g. Skywave)

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. It has been suggested that this article or section be merged with Ionosphere. ...

Although in the days of differential GPS 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. The Global Positioning System (GPS) is currently the only fully functional Global Navigation Satellite System (GNSS). ...

History

Origins

In 1936 William J. O'Brien, an American engineer, contracted tuberculosis 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. The initial market envisaged was for aircraft and some experiments were carried out in California in 1938. However both the American Army and Navy considered the idea too complicated.

O’Brien had a friend, Harvey F. Schwarz, who was chief engineer of the Decca Record company in England, and in 1939 sent him details of the system so it could be put forward to the British military. Initially Robert Watson-Watt reviewed the system but he did not follow it up. 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 came over to the UK and conducted the first marine trials between Anglesey and the Isle of Man, at frequencies of 305/610 kHz, on 16 September 1942. These were successful and further trials were conducted in the northern Irish Sea in April 1943 at 70/130 kHz. A three-station trial was held in conjunction with a large-scale assault and landing exercise in the Moray Firth in February/March 1944. Sir Robert Alexander Watson-Watt, ca. ... Anglesey (historically Anglesea; Welsh: , pronounced (IPA)) is a predominantly Welsh-speaking island off the northwest coast of Wales. ... // 1400 - Owain Glyndŵr declared Prince of Wales by his followers. ... 1942 (MCMXLII) was a common year starting on Thursday (the link is to a full 1942 calendar). ... Relief map of the Irish Sea. ... The Moray Firth is a roughly triangular area of the North Sea, north and east of Inverness. ...

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 and slaves at Swanage and Beachy Head. A fourth, decoy, transmitter was located in the Thames Estuary as part of the deception that the invasion would be focussed on the Calais area. For the larger local government district, see Chichester (district). ... , Swanage station, the terminus of the Swanage heritage railway. ... The Beachy Head Lighthouse How the Beachy Head Lighthouse was built. ... The Thames Estuary is a large estuary where the River Thames flows into the North Sea. ... Calais (Kales in Dutch) is a town in northern France, located at 50°57N 1°52E. It is in the département of Pas-de-Calais, of which it is a sous-préfecture. ...

Twenty-one minesweepers and other vessels were fitted with Admiralty Outfit QM and on 5 June 1944 they used it to accurately navigate across the English Channel and to sweep the minefields in the planned areas. The swept areas were marked with buoys in preparation for the Normandy Landings. June 5 is the 156th day of the year (157th in leap years) in the Gregorian calendar. ... 1944 (MCMXLIV) was a leap year starting on Saturday. ... Satellite view of the English Channel The English Channel (French: (IPA: ), the sleeve) is the part of the Atlantic Ocean that separates the island of Great Britain from northern France and joins the North Sea to the Atlantic. ... The Battle of Normandy was fought in 1944 between the German forces occupying Western Europe and the invading Allies. ...

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 centers where traffic density was highest.

Deployment

After the end of World War II the Decca Navigator Co. Ltd. was formed (1945) and the system expanded rapidly, particularly in areas of British influence; 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. 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. These helicopters were operating from the principal local airports--John F. Kennedy Airport on Long Island, Newark Airport in New Jersey, LaGuardia Airport nearer to Manhattan and a site on the top of the (then) PanAm Building 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/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 unfeasible 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 harbor for fear that the system might create a de facto standard (as it had become in other areas of the world). Other chains were established in Japan (6 chains); Namibia and South Africa (5 chains); India and Bangladesh (4 chains); Canada (4 chains around Newfoundland and Nova Scotia); North-West Australia (2 chains); the Persian Gulf (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 2 chains were built and these did not enter into public service. There were also two chains in Vietnam which were used during the Vietnam War for helicopter navigation, with limited success. Combatants Allied powers: China France Great Britain Soviet Union United States and others Axis powers: Germany Italy Japan and others Commanders Chiang Kai-shek Charles de Gaulle Winston Churchill Joseph Stalin Franklin Roosevelt Adolf Hitler Benito Mussolini Hideki Tōjō Casualties Military dead: 17,000,000 Civilian dead: 33,000... Motto (French) God and my right Anthem No official anthem - the United Kingdom anthem God Save the Queen is commonly used England() – on the European continent() – in the United Kingdom() Capital (and largest city) London (de facto) Official languages English (de facto)1 Unified  -  by Athelstan 927 AD  Area  -  Total... Motto (Latin) No one provokes me with impunity Cha togar mfhearg gun dioladh (Scottish Gaelic) Wha daur meddle wi me?(Scots)1 Anthem (Multiple unofficial anthems) Scotlands location in Europe Capital Edinburgh Largest city Glasgow Official languages English, Gaelic and Scots1 Government Constitutional monarchy  -  Monarch Queen Elizabeth II... Scandinavia is a historical and geographical region centered on the Scandinavian Peninsula in Northern Europe and includes the three kingdoms of Denmark, Norway and Sweden. ... World map showing the location of Europe. ... For other uses, see Newfoundland (disambiguation). ... Motto: Munit Haec et Altera Vincit(Latin) One defends and the other conquers Capital Halifax Largest city Halifax Regional Municipality Official languages English Government - Lieutenant-Governor Mayann E. Francis - Premier Rodney MacDonald (PC) Federal representation in Canadian Parliament - House seats 11 - Senate seats 10 Confederation July 1, 1867 (1st) Area... Map of the Persian Gulf. ... Combatants Republic of Vietnam United States Republic of Korea Thailand Australia New Zealand The Philippines National Front for the Liberation of South Vietnam Democratic Republic of Vietnam People’s Republic of China Democratic Peoples Republic of Korea Strength US 1,000,000 South Korea 300,000 Australia 48,000...

Decca, Racal, and the closedown

Decca Navigator was headquartered in a large residential property at Little Wymondley, Hertfordshire. There was a Decca School, at Brixham, Devon, where employees were sent on courses from time to time. Brixham (IPA: ) is a small town in the county of Devon, in the south-west of England. ... “Devonshire” redirects here. ...

Racal, the UK weapons and communications company, acquired Decca in 1980. Claiming the acquisition was to acquire Decca's radar company, rather than the avionics side of the business, it sold off parts including Decca Navigator. Racal Electronics plc was a British defence electronics firm purchased by Thomson-CSF (now Thales Group) in 2000. ...

The monopoly on leased, not purchased, receivers by Decca generated great wealth for the company. This monopoly was later broken the early 1980s when receivers could be purchased by users, thereby reducing the cost following the lapse of the patent on the basic system technology. A monopoly (from the Greek language monos, one + polein, to sell) is defined as a persistent market situation where there is only one provider of a product or service, in other words a firm that has no competitors in its industry. ...

A Danish company started manufacturing receivers for fishing boats which employed Decca's navigation charts, but users didn't pay rental for using the system.

In the ensuing court battle Decca lost the monopoly, and that signalled the beginning of the end. Income dwindled and eventually, the UK Ministry of Transport stepped in, having the lighthouse authorities take responsibility for operating the system in the early 1990s. This page meets Wikipedias criteria for speedy deletion. ... Trinity House, London (January 2007) A meeting at Trinity House circa 1808 // The Corporation of Trinity House is the official General Lighthouse Authority for England, Wales and other British Territtorial Waters (with the exception of Scotland, Northern Ireland and the Republic of Ireland). ...

A ruling from the European Union forced the UK government to withdraw funding - for fishermen users - and started the process which eventually resulted in the system being closed down and the installations scrapped.

The Decca Navigator System provided by the General Lighthouse Authorities ceased to operate at midnight on 31 March 2000. The Irish chain provided by Bórd Iascaigh Mhara continued transmitting until 19 May 2000. March 31 is the 90th day of the year in the Gregorian calendar (91st in leap years), with 275 days remaining. ... 2000 (MM) was a leap year starting on Saturday of the Gregorian calendar. ... is the 139th day of the year (140th in leap years) in the Gregorian calendar. ... 2000 (MM) was a leap year starting on Saturday of the Gregorian calendar. ...

Japan holds the distinction of being the last bastion of Decca having closed down the Hokkaidō chain (9C) in March 2001. This was one year later than the UK closure. Hokkaidō was also the first Decca chain to open in Japan in the year 1967.   literally North Sea Circuit, Ainu: Mosir), formerly known as Ezo, Yezo, Yeso, or Yesso, is Japans second largest island and the largest of its 47 prefectural-level subdivisions. ...

Other Applications

A more accurate system named Hi-Fix was developed using signalling in the 1.6MHz range. It was used for specialised applications such as precision measurements involved with oil-drilling, etc. Other systems were used in the Middle East.

An interesting characteristic 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 was never optioned by the UK government. Messages were clandestinely sent, however, between Decca stations thereby bypassing ancient international telephone calls, especially in non-UK chains.

Special DECCA towers

• Puckeridge DECCA tower
• Zeven DECCA-transmitter

( ) Zeven DECCA-transmitter was a transmitting facility for DECCA transmission at Zeven, in Germany. ...

References

• The Decca Navigator - Principles and Performance of the System, The Decca Navigator Company Limited, July 1976 [1]
• 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) [2]
• Navigation Systems: A Survey of Modern Electronic Aids, ed. G.E. Beck, van Nostrand Reinhold, 1971

is the 157th day of the year (158th in leap years) in the Gregorian calendar. ... 1944 (MCMXLIV) was a leap year starting on Saturday. ...

External links

• Decca Navigator System by Jerry Proc

• A virtual tour of a Decca Main Chain

• Decca Navigator Spain by Santiago Insua (in spanish)

• Decca Navigator Station Zeven (Germany)