Decca navigation system

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Accuracy of the different navigation systems
Decca Navigator Mk 21
worldwide locations of the Decca broadcasting chains

The Decca navigation system ( Decca for short ; English also Decca Navigator System ) was a radio navigation- based, ground-based navigation system that was developed by the British company Decca during the Second World War . In the maritime and particularly in the coastal navigation of the coastal shipping as well as in the deep-sea and coastal fishing , it was very widespread. On March 31, 2000, it was finally shut down. It worked in the long-wave range according to the principle of hyperbola navigation and allowed continuous, automatic and relatively precise two-dimensional location determination by determining the superimposition of the radio waves emitted by several transmitters. The phase difference between the signals received was measured at the location where the position was determined.

During its wedding, the Decca navigation system was the most common and popular system for short and medium-range maritime navigation, especially in Europe. Within the transmitter range, the Decca navigation provided continuous and precise position information.

history

The Allies needed during World War II, a navigation system that their aircraft could find even in poor visibility their way back to the home airfield. The Decca navigation system was originally developed for this purpose. After the war, however, like the LORAN navigation system, it was mainly used for ship navigation in coastal waters , especially for fishing close to the coast.

The Decca system was mainly used by fishing boats after the war, but it was also used in airplanes which, from 1949 onwards, were using a very early version of a moving map display .

The Decca navigation system was greatly expanded , especially in the North Sea , and was also used there by helicopters that approached the drilling platforms in the North Sea for supply purposes.

After the service was discontinued in the spring of 2000, the Decca navigation system was replaced by the American GPS system , to which the planned European GALILEO navigation system will soon be added.

Origins

Meint Harms (1897 to 1974) was already thinking about the subject of future navigation at the Lübeck Seafaring School in 1931 . They were originally intended as a contribution to a beer newspaper at the end of a captaincy course, but then also seemed feasible. As a seafaring school teacher for mathematics, physics and navigation, he tried to prove in the physics hall and in the vicinity of the school building above the Kaisertor in the Hanseatic city of Lübeck that it was possible to determine position with relatively simple transmitters and receivers. He applied for patent protection for his invention, which he obtained under patent no. 546000 received from the Reich Patent Office on February 18, 1932. In Germany, the circles and companies in question showed no interest in the invention.

The American engineer William J. O'Brien contracted tuberculosis in 1936, which imposed a two-year compulsory break in his professional career. During this time he had the idea for a position determination system based on phase comparison of continuously ( continuous wave - unmodulated wave) emitted electromagnetic waves.

The aircraft industry originally envisaged him as the customer for such a position determination system, and he wanted to use his method to measure the absolute speed of aircraft in particular, since airspeed indicators only show the relative speed to the surrounding air mass.

In 1938 some experiments were carried out in California. However, the US Army and Navy found this approach too complicated.

O'Brien's friend Harvey F. Schwarz was a chief engineer at the Decca Record Company in England. O'Brien sent him the details of his system in September 1939 to be offered to the British military.

Robert Watson-Watt initially dealt with this system, but did not pursue it any further. However, in October 1941 the British Admiralty Signal Establishment (ASE) showed interest in the system and they were classified as secret.

O'Brien came to Great Britain and carried out on September 16, 1942 the first practical location attempts in the sea area between the islands of Anglesey and Isle of Man , using the frequencies 305 and 610 kHz. The tests were successful and further tests followed in April 1943 in the northern Irish Sea on the frequencies 70 and 130 kHz. In connection with a large-scale attack and landing exercise in February and March 1944 (in preparation for the D-Day a few months later on June 6, 1944) in the Scottish Moray Firth , a test was carried out with three transmitter stations.

The success of the trials and the relatively easy handling of the system resulted in Decca receiving an order for 27 recipients. The receivers were delivered under the name Admirality Outfit "QM1". Later models of Decca receivers bore the designation "Decca Navigator" (hence the English designation "Decca Navigator System" for the Decca navigation system) and, among other things, carried the type designations "QM2", "QM3", "Mark III", " Mark IV "," Mark IV A "(for aircraft)," Mk V "," Mk XII "or" Mk 12 "," Mk 19 "," Mk 21 "," Mk 22 "," Mk 23 "," Mk 24 "," Mk 30 "," Mk 51 "," Mk 52 "," Mk 53 "," Recall Decca MN2000 "," RX Recall RACAL-Decca MNS 2000 ". The receivers consisted of an electronic unit with two "dials" and which were called "gas meters" because of their round design. The work for the operator on the Decca receiver was therefore nicknamed the “Blue Gas Meter Job.” The newer Decca receivers were equipped with microprocessors and had an alphanumeric display. They displayed the "Decca Navigator Hyperbola Coordinates" as well as longitude and latitude, course, speed, course, direction, distance, remaining travel time (time to go) and the required heading for preselected waypoints.

The Decca chain that was established consisted of a main station in Chichester and secondary stations in Swanage and Beachy Head . A fourth transmitter was set up as a "bait" at the Thames Estuary as a distraction, as part of the diversion plan that was supposed to simulate an Allied landing on D-Day in Calais ( Operation Fortitude ). 21 anti-mine vehicles and other ships were equipped with the Admirality Outfit QM receiver. On June 5, 1944 (one day before D-Day on June 6, 1944) these ships crossed the English Channel using the Decca receiver for precise navigation to clear the mine barriers in the planned areas of sea ​​mines . The cleared areas were marked with buoys in preparation for the landing in Normandy the following day.

After the initial tests in ships, tests were carried out in cars. The Decca Company also had high hopes that their system would find use on airplanes to provide accurate navigation in the critical, overcrowded airspace around larger airfields.

financing

The navigation system under the brand name Decca was developed by the Decca Navigator Company Ltd. developed and operated and got its name from it. The company later merged with Racal to form Racal-Decca Navigator Ltd. The company emerged from the Decca Records record company , which is now part of the Universal Music Group . This company also operated the transmission stations at its own expense, for which the receiving systems had to be rented from the company.

Introduction and dissemination

Decca chain map E2

After the end of the Second World War, Decca Navigator Co. Ltd. was founded in 1945 . and the use of the Decca navigation system expanded worldwide - especially in regions where the British Empire had influence. The method was introduced to merchant shipping and deep-sea fishing from 1947 to 1950. In 1964 over 9000 ships were equipped with Decca receivers. After the war it was used in Great Britain , Ireland , Norway , Canada and Japan, among others .

At its peak, the Decca navigation system was used on major shipping routes around the world. Over 15,000 Decca receivers were used on board ships in 1970. There were four Decca chains around England, one chain in Ireland, two chains in Scotland, 12 chains in Scandinavia (five each in Norway and Sweden, and one each in Denmark and Finland), and four other chains in other regions in Northern Europe and two chains in Spain.

In the late 1950s, an experimental Decca chain was set up in the United States, in the New York area. You should navigating the helicopter of New York Airways type Boeing Vertol 107 serve.

These helicopters operated from New York Airports John F. Kennedy , Newark , LaGuardia and from what was then the PanAm Building (now the MetLife Building ) on Park Avenue.

The use of the Decca navigation system was necessary for the helicopters, as the Decca signal could still be received even at low altitude (down to sea level). The signal was not subject to line of sight restrictions as required for the VOR / DME signal. In addition, the Decca signal in the vicinity of the transmitter was not falsified by the slant-range error , like the VOR / DME signal.

The Decca receivers in the New York Airways helicopters also included a unique " roller map " display ( later also: DANAC moving map ), which showed the pilot his location at a glance, which was also available at the time could not be implemented with VOR / DME navigation. The roll card was a strip of card that was wound back and forth between two reels.

The establishment of this Decca chain in New York was highly controversial at the time for protectionist reasons. It got to the point that the US Coast Guard , which was also subject to the instructions of the US Treasury Department , banned all ships entering the New York harbor from using the Decca receivers, as it was feared that the Decca system would become de facto -Standard ( industry standard ), as it had already happened in Europe and other regions of the world. This ban was also intended to protect the market interests of the American company Hoffman Electronics , a subsidiary of ITT Corporation and the leading manufacturer and supplier of the VOR / DME navigation system.

The situation was exacerbated by the heavy workload of the air traffic controllers , which resulted from the fact that they were forced, under the executive director of the Air Traffic Control Association (ATCA) Francis McDermott, to transmit the radar data of the aircraft position to the aircraft by radio.

As a result of this work overload, for example, a Boeing 70f and a Lockheed Constellation collided over Staten Island. According to experts, this collision would have been avoidable if these aircraft had been equipped with Decca receivers. So they could have determined their location more precisely.

Further Decca chains were made in Japan (6 chains), Namibia and South Africa (5 chains), India and Bangladesh (4 chains), Canada (4 chains around Newfoundland, Labrador and Nova Scotia), Northwest Australia (2 chains), Persian Golf (1 chain with stations in Qatar and the United Arab Emirates) and a second chain north of the Persian Gulf (with stations in Iran) and in the Bahamas (1 chain).

Four chains were planned for Nigeria, but ultimately only two chains were set up, but they did not go into service. Two chains were set up for helicopter navigation in Vietnam during the Vietnam War.

During the Cold War, the Royal Air Force set up a secret Decca chain in Germany. The main station was in Bad Iburg near Osnabrück, there were two secondary stations. This should enable precise navigation for the flight corridor between West Germany and Berlin, in the event that a mass evacuation of Allied personnel from Berlin would become necessary. For the purpose of secrecy, the transmission frequency was changed at irregular intervals.

Decca, Racal and the closure

The headquarters of Decca Navigator Company Ltd. was located in New Malden in the Royal Borough of Kingston upon Thames in southwest Greater London . There was a Decca school in Brixham where staff were sent from time to time for courses.

The British arms and communications company Racal Electronics acquired Decca Radar (Decca Marine Group) in 1980 and turned it into Racal-Decca , headquartered in the USA. Racal-Decca was bought by Litton Industries in 1997 and is now part of Sperry Marine , a subsidiary of Northrop Grumman .

In 1988, the Commission of the European Union found that Decca-Racal's anti-competitive behavior towards competitors had breached Articles 85 and 86 of the Treaty of Rome .

As Racal's acquisition of Decca was primarily a pursuit of the acquisition of Decca's radar company (Decca Radar) rather than the acquisition of Decca's avionics division, Racal sold Decca's other interests, including Decca Navigator , the operator of Decca navigation systems.

The monopoly on the leased , rather than bought, Decca receivers brought the company big profits. This monopoly was later broken and in the early 1980s the Decca receivers could be bought by users. With the expiry of the patent on the system technology, the follow-up costs for the customer were reduced.

“AP Navigator” from Philips , a Decca receiver from the 1980s, which the customer could buy instead of just leasing as before. The device gave the coordinates directly without the need for Decca cards.

A Danish company started making Decca receivers for fishing boats. These were used together with Decca cards and the customer no longer incurred rental costs for the system.

After a court decision, the Decca company lost its monopoly on navigation receivers of its Decca transmitters, which heralded the end of the company. Income dwindled and finally the British Department of Transport arranged for the British Lighthouse Authority (General Lighthouse Authority in Trinity House ) to be given responsibility for the operation of the Decca transmitter system in the early 1990s.

A decision by the European Union forced the British government to stop subsidizing the use of the system, particularly for fishermen. Ultimately, the operation of the Decca transmitter system then had to be stopped and the equipment scrapped.

The Decca system, operated by the Beacon Authority, ceased operations at midnight on March 31, 2000. The Irish Decca chain, operated by the Irish Sea Fisheries Authority ( Bord Iascaigh Mhara ), continued to broadcast until May 19, 2000.

Japan was the last country to operate a Decca navigation chain with the Hokkaidō -Decca chain 9C, which finally ceased operations in March 2001. This Decca chain was also the first Japanese Decca chain when it opened in 1967.

functionality

The system worked with continuously broadcast radio waves in the frequency range from 68 to 150 kHz. This was used to determine the position on a baseline - a hyperbola. The position was determined from the intersection of two hyperbola lines. The onboard Decca receiver carried out a phase comparison, the comparison of the relative phases of cooperating transmitters, the received radio waves and displayed the result directly for reading with pointers on a scale. For a transmission pair (main transmitter and respective secondary transmitter) the locations of the same phase difference are on a hyperbola. Later Decca receivers were partly equipped with track plotters.

At the time of its development, the system was the most user-friendly navigation aid for maritime shipping because the position did not have to be constructed with course triangles and / or compasses on the map, but could be read from the display device (see below: Decometer ) and entered directly. For this purpose, there were so-called Decca maps , these were nautical maps in which the interference hyperbolas (lines of equal phase shift ) were printed between two transmitters. The Decca chain responsible for the North Sea and the western Baltic Sea consisted of three transmitters in Bushmills , Hoek van Holland and Stavanger .

The disadvantage was that you could only determine your position from a known point with a continuous measurement. To mitigate this negative point, Decca brought out special counting devices and even card writers, the latter recording the vehicle movement on paper.

Overview

Decca chain with primary and secondary transmitters
The principle of Decca radio navigation: The phase difference between a main transmitter (here A) and a secondary transmitter (here B) is constant along a hyperbolic curve. The focal points of the hyperbolas are the two transmitters A and B.

Decca navigation is based on determining the distance to different transmitters ( range range navigation ). The different distance to the various transmitters is determined by interpreting the phase differences. Lines with the same phase differences result in groups of hyperbolas whose focal point is at the location of the transmitter. As with all hyperbola navigation, the hyperbolas of the Decca system are places of constant time differences between the incoming signals of two transmitters (main transmitter and secondary transmitter). The transit time differences are determined by comparing the phases of the two received signals.

The Decca navigation system consists of a number of land-based stations, each organized in chains. Each Decca chain consists of a main transmitter (sometimes with "L" - for leading transmitter - designated; English master station ; marked with the color black ) and three (sometimes only two) secondary transmitters (English slave station ), which are connected to the color codes red (R; engl. red ), green (G; engl. green ), and purple (P;. engl purple ) are referred to; occasionally also with A, B and C. In places a secondary transmitter was also used jointly by several Decca chains - for example in Northwest Australia.

The Decca chains 8E (Dampier; in the west) and 4A (Port Hedland; in the east) both used the secondary transmitter Mundabullangana

The three secondary transmitters are ideally arranged in a star shape around the main transmitter with an angular difference of approximately 120 °; In other words: the secondary transmitters are arranged at the corners of an imaginary equilateral triangle, with the main transmitter in the middle of this triangle.

The distance between the main and secondary transmitters, i.e. the length of the base, is typically 60 to 120 nautical miles (110 to 220 km). Navigation was typically possible up to a distance of 240 nautical miles from the main transmitter. Each of the four transmitters in a Decca chain emits an omnidirectional continuous signal on a different frequency (transmission frequency ), these signals are synchronized with one another. The Decca receiver compares the phase difference of the signals received from the transmitter pairs - a secondary transmitter signal in each case with the main transmitter signal - and thus determines its position relative to this transmitter pair.

Location determination: the intersection of two hyperbola lines that intersect almost at right angles

As a result of measuring the phase angle between the received signals from two transmitters to obtain a set of hyperbolic position lines (engl. Line of position ), the (engl. Patterned pattern hereinafter) are. Corresponding to the colors of the three secondary stations are on a nautical map (Hyperbelkarte - with hyperbole flock - Decca hyperboles) printed red, green and purple Hyperbelstandlinien.

A Decca chain has three sets of hyperbolas. - red, green and purple

The Decca receiver identifies the corresponding hyperbola line for each of the three colors (secondary transmitters). The position is then obtained from the intersection of the three identified hyperbola stand lines. The point of intersection of those two hyperbolic base lines is preferred, which ideally intersect at right angles - this results in the highest accuracy - or as far as possible at right angles.

This Decca system was called MainChain.

Details

Block diagram of a Decca receiver

If two stations on the same frequency with constant phase shift (phase locked), engl. send phase-locked , then the phase shift between the two signals along a hyperbola is constant. However, if both transmitters were transmitting on the same frequency, then it would be practically impossible for the receiver to separate the signal. The phase difference between two electromagnetic waves of the same frequency that overlap cannot be measured directly. This is why the four stations in a Decca chain do not transmit on the same frequency. Instead, each Decca chain was assigned a fundamental frequency (1f) (engl. Fundamental frequency ). The transmitters of a Decca chain work together on the various multiples of this fundamental frequency, which are in a harmonious relationship to one another. Each station in a Decca chain transmits on an integer multiplied frequency based on this basic frequency. The frequencies used have a fixed relationship to one another and are synchronized with one another. Each transmitter in the Decca chain continuously broadcasts a different multiple of the same basic frequency.

As an example, the frequencies of the Decca chain 5B, known as the “English chain”, are given in the following table, all other chains similarly use frequencies between 70 and 129 kHz. The basic frequency is about 15 kHz. In the present example, the base frequency is 14.16667 kHz.

station harmonic frequency
(multiplication factor
for the fundamental frequency)
transmitted
frequency
(transmission frequency)
Main station 6f 85,000 kHz
Violet sub-transmitter 5f 70.833 kHz
Red secondary transmitter 8f 113.333 kHz
Green secondary transmitter 9f 127.500 kHz

This example results in a comparison frequency (main transmitter - red secondary transmitter) of 340 kHz (main transmitter: 85 kHz × 4 = 340 kHz [see table below - fields highlighted in yellow]; 113.333 kHz × 3 = 340 kHz). This comparison frequency corresponds to the basic frequency 14.16667 kHz × 24 = 340 kHz.

The Decca receivers multiply the signal received from the main transmitter and also the signals from the secondary transmitters and a certain integer amount that is different for each transmitter. This results in a common frequency for main and secondary transmitters according to the rule of the least common multiple (LCM):

  Purple red green
harmonic frequency of the secondary transmitter 5f 8f 9f
Secondary transmitter multiplier × 6 × 3 × 2
harmonic frequency of the main transmitter 6f 6f 6f
Main channel multiplier × 5 × 4 × 3
common frequency 30f 24f 18f

The phase comparison can now be carried out on the common frequency ( comparison frequency ). This technical trick enables the phase of two signals of the same frequency (comparison frequency) to be compared, which were previously received on different frequencies (transmission frequency ). Otherwise it is technically not possible to separate two signals sent on the same frequency.

The hyperbola stand line results from the phase comparison of this common frequency. The interval between two adjacent hyperbola lines in which the signals are in phase is referred to as the lane ; in other words: a channel is the distance between two consecutive hyperbolas.

Since the wavelength of the common frequency is relatively small compared to the distance between the main and sub-transmitters, there are many possible position lines for a given phase difference and thus no clear position can be determined with this method.

The Decca receiver receives the four signals from the Decca chain on four different channels and amplifies them in four amplifiers. The four signals are received with a common antenna that is tuned to the four transmitters.

By frequency division and multiplication of the main transmitter signal and a secondary transmitter signal, it generates three comparison frequencies ( common frequency ). The phase differences of the three comparison frequencies are measured in phase measuring bridges and displayed on three instruments (the decometers).

Other Decca receivers, which are used in aircraft in particular, divide the transmitted frequency (frequency division by frequency divider ) up to the base frequency (f1) for the phase comparison, instead of multiplying the frequency according to the LCA principle.

Decometer

Decometer (for the green secondary transmitter) - detailed view of the Decca Navigator Mk 12
With increasing distance from the baseline (blue), which directly connects the transmitters (here A and B) with each other, the zone between two identical states becomes wider and wider (here: bottom left and top right), which is why the accuracy of a location determination there is less and less becomes.

Early Decca receivers were equipped with three rotating decometers that displayed the determined phase difference for each of the three reference frequencies.

The three decometers are differentiated by colors: LA red, LB green, LC purple. The letters and numbers of the hyperbolas associated with the measured phase differences can be read directly on the dials of the decometers. The evaluation is then carried out on nautical charts with an overprint of the same-colored Decca hyperbolas.

Each decometer had a second display that counted the number of canals that had been traversed. Each phase difference of 360 ° passed through was counted as one channel passed through. Assuming that the starting point was known, a more or less precise location was determined in this way.

Channels and Zones

The phase comparison in the receiver only gives the position within a channel. The exact location must therefore be known at the start of the journey and the signal must be received continuously from then on, so that the number of channel boundaries passed can be counted exactly.

The hyperbola stand line at the starting point is the zero hyperbola. Precondition and a certain disadvantage for the position determination is the exact logging of the actual zero hyperbola. Problems arise with prolonged signal failure, which can lead to an unreliable zero hyperbola counting. Problems also arise with a "blind start" from an unknown location. Then the location cannot be determined despite the reception of valid Decca signals. A problem similar to that of the "blind start" arises when the ship is outside the Decca reception area and cannot determine its exact position when entering the reception area (e.g. from the sea side).

The channels were grouped into zones with 18 green, 24 red, and 30 purple channels in each zone. This meant that the width of the zones for all three colors of a Decca chain was the same on the baseline (the direct line connecting the main and secondary transmitters). Because of the multiplication, different numbers of channels have space in a zone, depending on the color.

Typical channel and zone widths at the baseline are shown in the following table using the Decca chain 5B as an example:

Channels or zone Width at the baseline
purple channel 352.1 m
red channel 440.1 m
green channel 586.8 m
Zones (all colors) 10,563 m

The channels were numbered 0 to 23 for the red channels, 30 to 47 for the green and 50 to 79 for the purple channels. The zones were designated A to J and repeated after J again. A Decca position coordinate could look like this, for example: Red I 16.30; Green D 35.80.

The wavelength for the comparison frequency 340 kHz (see the table above ) is 880.2 m. At the antenna base ( base line ), the width of a channel corresponds to half the wavelength of the reference frequency, in this example 440.1 m.

Later receivers had a built-in microprocessor that enabled instant position indication in latitude and longitude.

Multipulse

Decca Navigator Mk 12 (Decca Hyperbola Navigator); the display for rough localization is the colored round scale in the top center. The Mark 12 is designed for 63 Decca chains on the transmitter and receiver side, which do not interfere with each other. The Decca Navigator Mk 12 and the Decca Navigator Mk 21 could receive all 63 possible frequencies. Older models were only designed for frequency groups A, B and C, but not for D, E and F. The Mark 5 receiver was only designed for receiving 9 Decca chains.

Multipulse enabled an automatic method to identify channels and zones without having to rely on counting the phase passes from a known starting position ( MP lane identification ). For this purpose, the same phase comparison technique described above was used for low-frequency signals. The zero hyperbola is identified with a second method. The Decca company calls the signal for rough location “V-Type Transmission”.

The transmission on the basic frequency is no longer continuous, but was divided into 20-second cycles: each station alternately broadcasts simultaneously on the four frequencies of the Decca chain (5f, 6f, 8f and 9f) in a phase-coherent relationship (phases coherence = constant phase difference) for a brief moment of 0.45 s in every 20-second cycle. This transmission, known as multipulse , allowed the receivers to extract the fundamental frequency f1 and thus identify the channel on which the receiver was currently located (to resolve a zone). The "normal" signal transmission is therefore briefly and periodically interrupted in order to transmit a multi-pulse signal from the main and secondary transmitters at the assigned times. In addition to the signals on the Decca frequencies 5f, 6f, 8f and 9f, a signal marked orange was sent on the frequency 8.2. The beating between the signals with the frequency 8.0f (red) and 8.2f (orange) allows a 0.2f signal to be derived. The result was a hyperbola pattern in which one phase cycle (360 °) corresponded to five zones.

Provided that one's own position was known at least with this rough accuracy, one had the possibility of determining one's position with the Decca multipulse method.

Range and accuracy

During the daylight period, a Decca transmitter can have a range of approximately 740 km (400 nautical miles ). At night, this range is reduced to 370 to 460 km (200 to 250 nautical miles), depending on the propagation conditions of the unmodulated long-wave signal.

The accuracy of the location determination depends on:

  • the width of the channels
  • the angle at which the hyperbolic base lines intersect
  • the instrument failure
  • daylight-dependent propagation error - because of the phase shift at the day-night boundary ( diurnal effect , diurnal phase shift ) or because of the space wave
  • Weather and changes in the ionosphere
  • local errors compared to the geometrically expected position; these fixed errors (for example in the vicinity of reflections) were specified in data sheets by the Decca company .

During the day, under favorable reception conditions, these errors are on the order of a few meters (20 to 50 meters; close to the transmitters located on land; on the baseline) and increase with increasing distance from the transmitter chains up to one nautical mile at the edges of the coverage area .

At night, the system error can be significantly greater, especially because of the sky wave error and changes in the ionosphere (day / night influence). The error is caused by the interference between the sky wave and the ground wave . At night, the sky wave is stronger, its amplitude is then just as large or even greater than the amplitude of the ground wave - the actual measurement signal for the Decca method. Interferences between ground and sky waves lead to undesired phase fluctuations. Since the receiver cannot differentiate between ground and sky waves, it cannot separate these two either, but only process the resulting phase. Only statistical predictions can be made about the resulting error.

It is not uncommon, especially for receivers without multipulse capability, for the position displayed to deviate from the real position by a whole channel at night.

Although the range and accuracy of positioning using Decca navigation today could be viewed as poor in times of GPS , it was at that time one of the few positioning systems that was used by seafarers in radio navigation alongside Consol , radio direction finder , Loran and radar was available.

In particular, if the ship is further away from land, the requirement for the accuracy of the position determination is lower, so the lower accuracy of the Decca system at greater distances from the transmitter was not a major problem.

Decca chains

The first Decca chain went into operation in 1946. Their number grew to over 50 Decca chains over the years. The coding of the Decca chains can be repeated for different chains that are located in different, far apart regions, as soon as both chains cannot be received at the same time. Decca chains that shared the same frequency had to be at least 2000 km apart (examples: the North West Spanish Chain and the Japanese Shikoku Chain both worked with the identifier 4C; the South Spanish Chain and the South African Cape Chain both worked with the identifier 6A; the North Scottish Chain and the Bangladesh Chain worked with the identifier 6C). This was possible because only the ground wave was used for the Decca navigation and not the much more far reaching sky wave. The receiver is switched from one chain to the next adjacent chain only at a line printed on the nautical chart.

Some Decca chains only had two secondary transmitters, then the red and the green secondary transmitter were always used, as these allowed the most precise positioning.

List of 57 former Decca chains Positions
serial no. Real name Identifier master red green Purple
00 South Baltic Chain 0A 56 ° 27 ′ 20 "  N , 15 ° 41 ′ 34"  E 55 ° 24 '48 "  N , 14 ° 12' 53"  E 57 ° 1 ′ 3 ″  N , 18 ° 15 ′ 12 ″  E N / A
01 Vestlandet 0E 60 ° 24 ′ 24 "  N , 5 ° 0 ′ 34"  E 62 ° 11 ′ 35 "  N , 5 ° 7 ′ 31"  E 60 ° 2 ′ 54 "  N , 1 ° 14 ′ 33"  W. 58 ° 47 '15 "  N , 5 ° 32' 42"  E
02 South West British Chain 1B 50 ° 13 ′ 59 "  N , 3 ° 49 ′ 59"  E 49 ° 14 ′ 51 ″  N , 2 ° 5 ′ 8 ″  E 49 ° 55 ′ 57 ″  N , 6 ° 18 ′ 19 ″  E 49 ° 55 ′ 57 ″  N , 6 ° 18 ′ 19 ″  E
03 Northumbrian Chain 2A 55 ° 42 ′ 0 ″  N , 2 ° 1 ′ 59 ″  E 56 ° 4 ′ 21 ″  N , 4 ° 3 ′ 28 ″  E 57 ° 31 ′ 1 ″  N , 1 ° 51 ′ 0 ″  E 54 ° 7 ′ 59 ″  N , 0 ° 19 ′ 2 ″  E
04 Holland 2E 51 ° 37 ′ 3 ″  N , 4 ° 55 ′ 3 ″  E 52 ° 35 ′ 27 ″  N , 4 ° 43 ′ 42 ″  E (Alkmaar) 51 ° 13 ′ 58 "  N , 4 ° 50 ′ 0"  E 52 ° 10 ′ 0 ″  N , 1 ° 37 ′ 0 ″  E
05 British (or North British Chain) 3B 54 ° 42 ′ 0 ″  N , 4 ° 25 ′ 1 ″  E 54 ° 30 ′ 0 ″  N , 6 ° 19 ′ 59 ″  E 53 ° 16 ′ 1 ″  N , 3 ° 3 ′ 0 ″  E 56 ° 4 ′ 21 ″  N , 4 ° 3 ′ 28 ″  E
06 Lofoten 3E 69 ° 8 ′ 45 "  N , 16 ° 1 ′ 53"  E 70 ° 14 ′ 51 ″  N , 19 ° 30 ′ 5 ″  E 67 ° 31 '44 "  N , 12 ° 9' 30"  E 68 ° 27 ′ 57 ″  N , 17 ° 6 ′ 2 ″  E
07 German chain 3F 51 ° 26 ′ 26 ″  N , 8 ° 42 ′ 42 ″  E (Brilon) 50 ° 19 ′ 20 ″  N , 10 ° 59 ′ 15 ″  E (Coburg) 53 ° 17 ′ 4 ″  N , 9 ° 15 ′ 45 ″  E (Zeven) 50 ° 21 ′ 51 ″  N , 6 ° 32 ′ 2 ″  E (Stadtkyll)
08 North Baltic Chain 4B 58 ° 56 ′ 43 "  N , 17 ° 57 ′ 31"  E 60 ° 7 ′ 13 ″  N , 19 ° 49 ′ 29 ″  E 57 ° 54 ′ 52 "  N , 18 ° 57 ′ 18"  E 58 ° 50 ′ 30 "  N , 16 ° 34 ′ 32"  E
09 North West Spanish Chain 4C 42 ° 22 ′ 54 "  N , 7 ° 17 ′ 38"  W. 42 ° 44 '27 "  N , 8 ° 56" 51 "  W. 43 ° 26 ′ 40 "  N , 6 ° 49 ′ 52"  W. 41 ° 1 ′ 5 ″  N , 6 ° 25 ′ 59 ″  W.
10 Trondelag 4E 63 ° 19 ′ 57 ″  N , 8 ° 27 ′ 14 ″  E 64 ° 54 '32 "  N , 11 ° 11' 49"  E 62 ° 11 ′ 2 "  N , 5 ° 9 ′ 57"  E 62 ° 5 ′ 22 ″  N , 19 ° 24 ′ 7 ″  E (???)
11 English chain 5B 51 ° 49 ′ 2 "  N , 0 ° 4 ′ 57"  E 52 ° 33 ′ 3 ″  N , 1 ° 20 ′ 9 ″  E 50 ° 55 ′ 1 ″  N , 0 ° 9 ′ 0 ″  E 51 ° 11 ′ 50 "  N , 1 ° 21 ′ 59"  E
12 North Bothnian Chain 5F 64 ° 20 ′ 56 "  N , 21 ° 20 ′ 55"  E 63 ° 51 ′ 52 "  N , 23 ° 10 ′ 58"  E 65 ° 31 '46 "  N , 22 ° 4' 8"  E 63 ° 28 ′ 46 ″  N , 19 ° 39 ′ 13 ″  E
13 South Spanish Chain 6A 36 ° 51 ′ 52 "  N , 5 ° 8 ′ 16"  W. 37 ° 1 ′ 43 ″  N , 3 ° 41 ′ 3 ″  W. 36 ° 10 ′ 59 "  N , 5 ° 28 ′ 59"  W. 37 ° 17 ′ 51 ″  N , 6 ° 36 ′ 2 ″  W.
14th North Scottish Chain 6C 50 ° 4 ′ 0 ″  N , 3 ° 15 ′ 0 ″  W. 58 ° 30 ′ 0 ″  N , 6 ° 15 ′ 0 ″  W. 60 ° 10 ′ 0 ″  N , 1 ° 11 ′ 0 ″  W. 57 ° 31 ′ 0 ″  N , 1 ° 51 ′ 0 ″  W.
15th Finland (or Gulf of Finland ) 6E 60 ° 30 '59 "  N , 25 ° 10' 42"  E 60 ° 0 ′ 28 "  N , 22 ° 49 ′ 30"  E 60 ° 30 ′ 38 ″  N , 27 ° 26 ′ 18 ″  E N / A
16 Danish Chain 7B 55 ° 56 ′ 58 "  N , 10 ° 34 ′ 44"  E 54 ° 57 ′ 6 ″  N , 12 ° 28 ′ 0 ″  E 55 ° 1 ′ 1 ″  N , 8 ° 43 ′ 1 ″  E 57 ° 27 ′ 0 ″  N , 10 ° 3 ′ 0 ″  E
17th Irish Chain 7D 53 ° 15 ′ 19 ″  N , 8 ° 55 ′ 37 ″  W. 52 ° 12 ′ 1 ″  N , 10 ° 21 ′ 19 ″  W. 54 ° 51 ′ 31 "  N , 8 ° 20 ′ 25"  W. 51 ° 57 ′ 28 "  N , 7 ° 46 ′ 45"  W.
18th Finnmark 7E 70 ° 23 ′ 28 "  N , 25 ° 30 ′ 14"  E 69 ° 41 ′ 19 ″  N , 30 ° 3 ′ 14 ″  E 70 ° 6 ′ 20 ″  N , 20 ° 7 ′ 7 ″  E 71 ° 9 ′ 36 "  N , 25 ° 45 ′ 21"  E
19th French chain 8B 46 ° 19 ′ 0 ″  N , 2 ° 36 ′ 0 ″  E 47 ° 25 ′ 0 ″  N , 0 ° 58 ′ 0 ″  E 46 ° 42 ′ 0 ″  N , 4 ° 58 ′ 0 ″  E 44 ° 55 ′ 0 ″  N , 2 ° 27 ′ 0 ″  E
21st Hebridean Chain 8E 56 ° 59 ′ 0 ″  N , 7 ° 25 ′ 0 ″  W. 56 ° 45 ′ 0 ″  N , 5 ° 49 ′ 0 ″  W. 58 ° 30 ′ 0 ″  N , 6 ° 16 ′ 0 ″  W. 54 ° 53 ′ 0 ″  N , 8 ° 23 ′ 0 ″  W.
22nd Frisian Islands Chain 9B 53 ° 11 ′ 58 ″  N , 7 ° 6 ′ 1 ″  E 55 ° 0 ′ 59 ″  N , 8 ° 43 ′ 2 ″  E 53 ° 36 ′ 0 "  N , 4 ° 43 ′ 43"  E 53 ° 17 ′ 2 ″  N , 9 ° 16 ′ 6 ″  E
23 Helgeland 9E 66 ° 11 ′ 29 ″  N , 12 ° 29 ′ 2 ″  E 64 ° 31 ′ 40 "  N , 12 ° 8 ′ 17"  E 64 ° 54 ′ 32 "  N , 11 ° 10 ′ 48"  E 66 ° 18 ′ 21 ″  N , 14 ° 9 ′ 42 ″  E
24 Skagerrak 10B 58 ° 30 ′ 56 "  N , 11 ° 17 ′ 54"  E 58 ° 52 ′ 1 ″  N , 9 ° 36 ′ 0 ″  E 57 ° 28 ′ 22 "  N , 11 ° 57 ′ 11"  E 59 ° 21 ′ 20 "  N , 12 ° 11 ′ 32"  E
25th North Persian Gulf 5C 30 ° 1 ′ 7 ″  N , 50 ° 9 ′ 29 ″  E 30 ° 24 ′ 0 ″  N , 48 ° 12 ′ 0 ″  E 28 ° 58 ′ 38 "  N , 50 ° 51 ′ 9"  E N / A
26th South Persian Gulf 1C 24 ° 56 '7 "  N , 52 ° 50' 59"  E 25 ° 15 ′ 40 "  N , 51 ° 33 ′ 54"  E 26 ° 47 '25 "  N , 53 ° 13' 0"  E 24 ° 20 ′ 0 ″  N , 54 ° 10 ′ 0 ″  E
27 Bombay 7B Location unknown 20 ° 45 ′ 40 "  N , 73 ° 2 ′ 17"  E 20 ° 57 ′ 7 ″  N , 70 ° 20 ′ 13 ″  E 23 ° 0 ′ 14 "  N , 71 ° 31 ′ 39"  E
28 Calcutta 8B 21 ° 29 ′ 8 ″  N , 86 ° 55 ′ 18 ″  E 20 ° 45 ′ 40 "  N , 73 ° 2 ′ 17"  E Location unknown 22 ° 10 ′ 18 "  N , 88 ° 12 ′ 25"  E
29 Bangladesh 6C 23 ° 27 ′ 0 ″  N , 91 ° 12 ′ 0 ″  E 22 ° 9 '46 "  N , 92 ° 3' 31"  E 22 ° 9 '46 "  N , 92 ° 3' 31"  E 24 ° 42 ′ 0 ″  N , 90 ° 24 ′ 0 ″  E
30th Hokkaido 9C 43 ° 35 ′ 55 "  N , 142 ° 26 ′ 59"  E 43 ° 3 ′ 51 ″  N , 144 ° 47 ′ 41 ″  E 45 ° 23 ′ 10 "  N , 141 ° 39 ′ 18"  E 42 ° 30 '8 "  N , 140 ° 21' 47"  E
31 Tohoku 6C 38 ° 52 ′ 0 ″  N , 141 ° 4 ′ 57 ″  E 37 ° 22 '10 "  N , 140 ° 51' 9"  E 40 ° 17 ′ 35 "  N , 141 ° 45 ′ 13"  E 38 ° 27 '38 "  N , 139 ° 14' 43"  E
32 Kyusyu (or Kita Kyushu) 7C 33 ° 27 '44 "  N , 130 ° 10' 41"  E 34 ° 38 '24 "  N , 129 ° 21' 21"  E 32 ° 7 ′ 57 ″  N , 130 ° 8 ′ 39 ″  E 33 ° 25 ′ 55 "  N , 132 ° 13 ′ 32"  E
33 Namaqua 4A 28 ° S, 17 ° E 27 ° S, 17 ° E 29 ° S, 19 ° E 29 ° S, 16 ° E
34 Cape Chain 6A 33 ° S, 19 ° E 32 ° S, 18 ° E 28 ° S, 29 ° E 34 ° S, 19 ° E
35 Eastern Province (South Africa) 8A 33 ° S, 25 ° E 33 ° S, 26 ° E 34 ° S, 24 ° E Location unknown
36 Dampier 8E 20 ° 53 ′ 0 ″  S , 117 ° 8 ′ 0 ″  E 20 ° 59 ′ 0 ″  S , 116 ° 21 ′ 0 ″  E 20 ° 25 ′ 0 ″  S , 118 ° 4 ′ 0 ″  E N / A
37 Port Hedland 4A 20 ° 33 ′ 0 ″  S , 118 ° 29 ′ 0 ″  E 20 ° 25'S 118 ° 04'E 20 ° 21 ′ 0 ″  S , 118 ° 59 ′ 0 ″  E N / A
38 Hokuriku 2C 36 ° 14 ′ 43 "  N , 136 ° 8 ′ 31"  E 37 ° 26 ′ 42 "  N , 137 ° 13 ′ 13"  E 35 ° 31 ′ 7 "  N , 134 ° 15 ′ 58"  E N / A
39 Newfoundland (or East Newfoundland) 2C 48 ° 20 ′ 58 "  N , 54 ° 10 ′ 13"  W. 47 ° 46 ′ 1 ″  N , 52 ° 46 ′ 2 ″  W. 56 ° 55 ′ 0 ″  N , 55 ° 23 ′ 2 ″  W (???) 54 ° 52 ′ 2 ″  N , 49 ° 20 ′ 57 ″  W (???)
40 Cabot Strait (or West Newfoundland ) 6B 47 ° 21 '22 "  N , 61 ° 55' 44"  W. 45 ° 37 ′ 59 ″  N , 59 ° 13 ′ 59 ″  W (???) 45 ° 43 ′ 57 ″  N , 61 ° 54 ′ 4 ″  W. N / A
41 Nova Scotia 7C 45 ° 44 ′ 32 "  N , 64 ° 14 ′ 0"  W. 45 ° 34 ′ 13 ″  N , 64 ° 58 ′ 40 ″  W. 43 ° 41 ′ 57 ″  N , 65 ° 14 ′ 10 ″  W. 44 ° 58 ′ 1 ″  N , 62 ° 8 ′ 59 ″  W.
42 Salaya (in the Indian state of Gujarat ) 2F Coordinates: 22 ° 52 ′ 27 ″  N , 69 ° 24 ′ 0 ″  E 22 ° 3 ′ 30 "  N , 69 ° 10 ′ 30"  E 22 ° 28 ′ 49 "  N , 70 ° 7 ′ 43"  E 23 ° 15 ′ 4 ″  N , 68 ° 49 ′ 0 ″  E
43 Kanto 8C 34 ° 57 '36 "  N , 139 ° 53' 59"  E 33 ° 5 ′ 21 "  N , 139 ° 48 ′ 58"  E 36 ° 9 '35 "  N , 140 ° 33' 23"  E 34 ° 37 ′ 52 "  N , 138 ° 6 ′ 45"  E
44 South West Africa (South Africa) 9C 22 ° S, 15 ° E 20 ° S, 14 ° E 23 ° S, 16 ° E 22 ° S, 14 ° E
45 natal 10C 30 ° S, 28 ° E 31 ° S, 27 ° E 26 ° S, 20 ° E 30 ° S, 30 ° E
46 Shikoku 4C 33 ° 26 '10 "  N , 134 ° 5' 52"  E 32 ° 46 ′ 53 "  N , 132 ° 44 ′ 43"  E 33 ° 34 ′ 37 "  N , 135 ° 57 ′ 23"  E N / A
47 New York City 5C approximately 41 ° 16 ′ 0 ″  N , 73 ° 47 ′ 0 ″  W. approximately 40 ° 50 ′ 0 ″  N , 72 ° 55 ′ 0 ″  W. approximately 41 ° 3 ′ 0 ″  N , 74 ° 45 ′ 0 ″  W. approximately 41 ° 59 ′ 0 ″  N , 73 ° 53 ′ 0 ″  W.
48 Lagos 8F 6 ° 39 ′ 0 ″  N , 3 ° 35 ′ 0 ″  E 6 ° 30 ′ 0 ″  N , 4 ° 23 ′ 0 ″  E 6 ° 25 ′ 0 ″  N , 2 ° 56 ′ 0 ″  E 7 ° 17 ′ 0 ″  N , 3 ° 29 ′ 0 ″  E
49 Mid Western (Nigeria) 3A not built not built not built not built
50 Rivers (Nigeria) 7F Location unknown Location unknown Location unknown Location unknown
51 South Eastern (Nigeria) 2 B not built not built not built not built
52 AUTEC -Chain ( Bahamas ) 8E 24 ° 14 ′ 46 ″  N , 76 ° 31 ′ 20 ″  W. 23 ° 32 ′ 0 ″  N , 75 ° 46 ′ 20 ″  W. 23 ° 13 ′ 12 ″  N , 77 ° 36 ′ 10 ″  W. approximately 25 ° 15 ′ 0 ″  N , 76 ° 17 ′ 0 ″  W.
53 Anticosti Chain (Canada) 9C 49 ° 50 ′ 26 "  N , 64 ° 24 ′ 36"  W. 47 ° 50 ′ 57 "  N , 64 ° 40 ′ 46"  W. 50 ° 11 ′ 2 ″  N , 61 ° 49 ′ 1 ″  W. 50 ° 8 ′ 58 ″  N , 66 ° 37 ′ 3 ″  W.
54 South Bothnian Chain 8C 62 ° 16 ′ 48 "  N , 17 ° 25 ′ 31"  E 60 ° 37 ′ 18 ″  N , 17 ° 26 ′ 32 ″  E 63 ° 28 ′ 46 ″  N , 19 ° 39 ′ 13 ″  E N / A
55 Vietnam Central Chain ?? 14 ° 1 ′ 0 ″  N , 109 ° 2 ′ 0 ″  E 14 ° 0 ′ 11 "  N , 108 ° 1 ′ 17"  E 15 ° 23 ′ 0 ″  N , 109 ° 7 ′ 0 ″  E 13 ° 4 ′ 0 ″  N , 109 ° 17 ′ 0 ″  E
56 Vietnam South Chain ?? 10 ° 30 ′ 0 ″  N , 107 ° 10 ′ 0 ″  E 11 ° 18 ′ 0 ″  N , 106 ° 5 ′ 0 ″  E 10 ° 55 ′ 0 ″  N , 108 ° 5 ′ 0 ″  E 8 ° 40 ′ 0 ″  N , 106 ° 37 ′ 0 ″  E

The individual frequencies of the main and secondary transmitters of the 63 Decca chains, as well as the associated basic frequencies, are listed in the list of Decca frequencies .

Further developments and other applications

Use of multiple Decca chains

A further development of the Decca navigator system allowed the use of two different Decca chains for location determination. This almost doubled the range and increased the accuracy of the location determination.

HiFix

Under the name HiFix (or Decca Hi-Fix) an even more precise navigation system was developed that used signals in the range of 1.6 MHz. It was used for special applications, such as precision measurements in oil drilling or for more precise mapping of coasts and ports.

The HiFix equipment was leased for a certain period of time, and temporary transmission chains were installed to cover the required area. HiFix was commercially distributed by Racal Survey in the 1980s.

Vehicle tracking on land

An experimental network was installed to cover central London. The appropriate receivers were placed in buses and other vehicles. This was an early vehicle location and tracking system. Each vehicle then automatically transmitted its location over a standard VHF radio by transmitting the data over a voice radio channel. In principle, it was therefore a forerunner of various geolocation applications, such as the GPS system for vehicle location, which was used by London taxis in the 1990s, for example .

Modulated signals

An interesting property of this Decca VLF signal ( long wave ) was found on a BOAC test flight to Moscow:

The normally constant Decca signal was briefly interrupted, although the Decca signal was received with sufficient strength during the flight to enable navigation. This showed that the Decca signal could be used as a carrier wave for message transmission. The long wave signal of the Decca system could also be received by submarines. An "improvement" of the Decca system was to enable the transmission of tactile signals using Morse code to signal the start of a nuclear war to the submarines .

In the early days of the British Decca chains, morse keys and radio receivers were installed in all transmitters in the British Decca chains. During the Cold War, for example, if war broke out, a message that was keyed on the Decca signal could be sent to the British nuclear submarines . However, no military officer was stationed at the Decca station. Ultimately, however, this application was not considered by the British government.

However, messages were secretly transmitted between Decca stations and international telephone calls were made, especially in non-British Decca chains.

DECTRA

From the mid-1950s, a long-range navigation system for the North Atlantic under the name DECTRA was in operation, which was used for flight navigation. It consisted of two channels in Newfoundland and two channels in Scotland. Normal Decca transmitters were used, but with a much higher transmission power.

DECTRA: Location of the main and secondary transmitters on the flight route
Dectra route across the North Atlantic (transmitter position only roughly shown)

The DECTRA navigation system was designed to support navigation along a specific route. For this purpose, a pair of transmitters (a main transmitter and a secondary transmitter) were placed at both ends of the route. The actual route perpendicularly intersects the line halfway along the main and secondary transmitters at the end of a route.

With DECTRA, the main and secondary transmitters do not transmit simultaneously as with Decca, but alternately.

After the main transmitter has broadcast for a certain period of time, it briefly changes the transmission frequency and thus signals the secondary transmitter to begin transmitting its signals. The secondary transmitter then transmits phase-locked to the previous signal from the main transmitter. After a certain time, the cycle starts again and the main station starts broadcasting again. In order to keep the alternating signal from the main and sub transmitter phase-locked, the sub transmitter uses a stable oscillator to control its transmitter.

The DECTRA receiver on the aircraft works similarly, with the help of an oscillator. The signal received from the main transmitter is used to phase-lock an oscillator in the receiver that is very stable for a short time. Then the signal from the secondary transmitter is received and the phase of this signal is compared with the phase of the oscillator.

At each end of the route, the primary and secondary transmitter pair use different frequencies.

As transmitters for the Dectra route across the North Atlantic, regular Decca transmitters in Scotland (Earl's Hill near Stirling - the Purple Station of the North British Chain 3B, as well as Prestwick , both part of the Scottish Decca chain) and Newfoundland (East Newfoundland Chain; 2C; used by Gander ). However, these transmitters were equipped with a higher antenna (600 ft instead of 300 ft; 183 m instead of 91 m) and the transmission power was increased (10 kW instead of 1 kW).

With the advent of jet airliners such as the De Havilland Comet and Boeing 707 in the late 1950s and the associated increase in transatlantic air traffic, the need for a better navigation system increased. The dead reckoning used by propeller aircraft up to that point was no longer sufficient for the much faster jet aircraft. That is why the Dectra navigation system was developed, but in the end it was never used by the aircraft industry, which opted for the inertial navigation system . In the late 1960s, the Dectra transmitters ceased to operate.

There are three different explanations for the name Dectra:

  • Dec ca Tra cks
  • Dec ca T racking and Ra nging
  • Dec ca Tra nsatlantic

DECCA broadcasters in Germany

The German Decca chain was manufactured by Telefunken under license from Decca Navigator Company Ltd., London. The following DECCA broadcasters were in Germany:

Compare Decca and LORAN

The transmission frequencies of Decca did not differ much from the frequencies of the LORAN C navigation system, but the transmission power of Decca was lower and the range was shorter. Both the Decca and the LORAN navigation functioned on the principle of hyperbola navigation. While the Decca system was based exclusively on the principle of phase difference measurement , the LORAN system - like the OMEGA navigation system - also used a pulse measurement.

See also

literature

  • The Journal of the Decca Navigator Co. Ltd (1950 to 1980); No. April 1-May 1950; No 2 July-August 1950; ... No. 77 April 1980; No. 78 September 1980
  • Gerrit Jacobus Sonnenberg: Radar and Electronic Navigation. 5th ed .; Newnes-Butterworth Publishing House; ISBN 9780408000031
  • Stephen F. Appleyard, RS Linford and Peter Yarwood: Marine Electronic Navigation. Routledge & Kagan Paul Ltd .; London 1988; ISBN 0710212712 - at google-books
  • Leo Brandt (Ed.): Radio location systems for aviation and seafaring. A comparative comparison. Publisher: Committee for radio location, special library of radio location; 1959
  • Leo Brandt (Ed.): Radio location systems for aviation and seafaring. A comparative comparison. (From the series: German Society for Positioning and Navigation eV, Main Library, Volume 9 .; 1961) Verkehrs- und Wirtschafts-Verlag Borgmann; Dortmund 1962

Web links

Commons : Decca navigation system  - collection of images, videos and audio files

Individual evidence

  1. Festschrift 175 Years of the Lübeck Seafaring School
  2. Meldau-Steppes, Textbook of Navigation, Volume 2, page 7.142, Bremen 1958
  3. The Commission of the European Communities has decided that Racal Decca ... (English)
  4. Jerry Proc: Hyperbolic radionavigation systems, DECCA - North British