decca navigator system

DECCA NAVIGATOR SYSTEM

DECCA NAVIGATOR SYSTEMAlmendral, Jane Nicole L.Baylon, Mary Angelou L.Beconia, Lizzy-Ann S.

E4Q

INTRODUCTIONTheDecca Navigator Systemwas ahyperbolicradio navigationsystem which allowed ships and aircraft to determine their position by receiving radio signals from fixed navigational beacons. The system usedlow frequenciesfrom 70 to 129kHz. It was first deployed by theRoyal NavyduringWorld War IIwhen the Allied forces needed a system which could be used to achieve accurate landings. After the war it was extensively developed around theUKand later used in many areas around the world.

TheDecca Navigation Systemwas originally developed in the US, but eventually deployed by the Decca Radio company in the UK and commonly referred to as a British system. Initially developed for theRoyal Navyas an accurate adjunct to naval versions of Gee, Decca was first used on 5 June 1944 to guideminesweepersin preparation for the D-Dayinvasions. The system was developed post-war and competed with GEE and other systems for civilian use. A variety of reasons, notably its ease-of-use, kept it in widespread use into the 1990s, with a total 42 chains around the world. A number of stations were updated in the 1990s, but the widespread use of GPS led to Decca being turned off at midnight on 31 March 2000.

TheRoyal Navy(RN) is theUnited Kingdom's principalnaval warfare force.Aminesweeperis a smallnavalwarshipdesigned to engage inminesweeping, the use of various mechanisms intended to counter the threat posed bynaval mines. Minesweepers keep waterways clear for shipping.

ORIGIN1936 - William J. O'Brien had the idea of position fixing by means of phase comparison of continuous wave transmissions. He 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 theUS ArmyandNavyconsidered the idea too complicated and work ended in 1939.6

1939 - OBrien sent Harvey F. Schwarz (chief engineer of theDecca Record companyin England) his friend, details of the system so it could be put forward to the British military.October 1941 - the British Admiralty Signal Establishment (ASE) became interested in the system, which was then classified as Admiralty Outfit QM.16 September 1942 - OBrien brought the Californian equipment to the UK and conducted the first marine trials betweenAngleseyand theIsle of Man, at frequencies of 305/610kHz.

InitiallyRobert Watson-Wattreviewed 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).[2]However, in October 1941 the British Admiralty Signal Establishment (ASE) became interested in the system, which was then classified asAdmiralty Outfit QM. OBrien brought the Californian equipment to the UK and conducted the first marine trials betweenAngleseyand theIsle of Man, at frequencies of 305/610kHz, on 16 September 1942.7

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.

Decca Navigator MK12

Early Decca receivers were fitted with three rotatingDecometersthat 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 intozones, 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):

Range and Accuracy

During daylight ranges of around 400 nautical miles (740km) could be obtained, reducing at night to 200 to 250 nautical miles (460km), depending on propagation conditions.The accuracy depended on:Width of the lanesAngle of cut of the hyperbolic lines of positionInstrumental errorsPropagation errors (for example,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.Although in the days of differentialGPSthis 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.

Decca's primary use was for ship navigation in coastal waters, offering much better accuracy than the competingLORAN system. Fishing vessels were major post-war users, but it was also used on aircraft, including a very early (1949) application ofmoving map displays. The system was deployed extensively in theNorth Seaand was used by helicopters operating tooil platforms. The opening of the more accurateLoran-Csystem to civilian use in 1974 offered stiff competition, but Decca was well established by this time and continued operations into the 1990s. Decca was eventually replaced, along with Loran and other similar systems, by theGPSduring the 1990s. The Decca system in Europe was shut down in the spring of 2000, and the last worldwide chain, in Japan, in 2001.

Other applications

DelracIn the immediate post-war era, Decca began studying a long-range system like Decca, but using much lower frequencies to enable reception ofskywavesat long distances. This was known asDelrac, short for "Decca Long Range Area Cover". A further development, including features of theGeneral Post Office'sPOPIsystem, was introduced in 1954, proposing 28 stations that provided worldwide coverage.The system was predicted to offer 10 miles (16,000m) accuracy at 2,000 miles (3,200km) range 95% of the time. Further development was ended in favour of the Dectra system.

Other applications

DectraIn the early 1960s theRadio Technical Commission for Aeronautics(RTCA), as part of a widerInternational Civil Aviation Organization (ICAO)effort, began the process of introducing a standard long-range radio navigation system for aviation use. Decca proposed a system that could offer both high-accuracy at short ranges and trans-Atlantic navigation with less accuracy, using a single receiver. The system was known asDectra, short for "Decca Track".

Other applications

Hi-FixA 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 and by the Royal Navy for detailed mapping and surveying of coasts and harbours.

Thank You and good day