LORAN (LOng RAnge Navigation) is a terrestrial radio navigation system using low frequency radio transmitters that uses multiple transmitters (multilateration) to determine location and/or speed of the receiver. Radio navigation or radionavigation is the application of Radio frequencies to determining a position on the Earth. Low Frequency or LF refers to Radio Frequencies (RF in the range of 30 kHz&ndash300 kHz For biologic transmitters see Transmitter substance. A transmitter is an electronic device which usually with the aid of an antenna Multilateration, also known as hyperbolic positioning, is the process of locating an object by accurately computing the time difference of arrival ( TDOA The current version of LORAN in common use is LORAN-C, which operates in the low frequency portion of the EM spectrum from 90 to 110 kHz. The hertz (symbol Hz) is a measure of Frequency, informally defined as the number of events occurring per Second. Many nations are users of the system, including the United States, Japan, and several European countries. The United States of America —commonly referred to as the For a topic outline on this subject see List of basic Japan topics. Russia uses a nearly identical system in the same frequency range, called CHAYKA. Chayka (Чайка lit seagull) is a Russian terrestrial Radio navigation system similar to LORAN-C. LORAN use is in steep decline, with GPS being the primary replacement. Basic concept of GPS operation A GPS receiver calculates its position by carefully timing the signals sent by the constellation of GPS Satellites high above the Earth However, there are current attempts to enhance and re-popularize LORAN, mainly because it has proven to be a very reliable and simple system.

History

LORAN was an American development of the British GEE radio navigation system (used during World War II). The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom, the UK or Britain,is a Sovereign state located GEE or AMES Type 7000 was a British Radio navigation system used by the Royal Air Force during World War II. Radio navigation or radionavigation is the application of Radio frequencies to determining a position on the Earth. World War II, or the Second World War, (often abbreviated WWII) was a global military conflict which involved a majority of the world's nations, including While GEE had a range of about 400 miles (644 km), early LORAN systems had a range of 1,200 miles (1,930 km). A mile is a unit of Length, usually used to measure Distance, in a number of different systems including Imperial units United States The kilometre ( American spelling: kilometer) symbol km is a unit of Length in the Metric system, equal to one thousand LORAN systems were built during World War II and were used extensively by the US Navy and Royal Navy. The Royal Navy of the United Kingdom is the oldest of the British armed services (and is therefore known as the Senior Service) It was originally known as "LRN" for Loomis radio navigation, after millionaire and physicist Alfred Lee Loomis, who invented LORAN and played a crucial role in military research and development during WWII. Alfred Lee Loomis ( November 4, 1887 &ndash August 11, 1975) was an American Attorney, Investment banker, Physicist

Principle

A crude diagram of the LORAN principle. The difference between the time of receipt of synchronized signals from radio stations A and B is constant along each hyperbolic curve.

The navigational method provided by LORAN is based on the principle of the time difference between the receipt of signals from a pair of radio transmitters. Multilateration, also known as hyperbolic positioning, is the process of locating an object by accurately computing the time difference of arrival ( TDOA In the fields of communications, Signal processing, and in Electrical engineering more generally a signal is any time-varying or spatial-varying quantity Radio is the transmission of signals by Modulation of electromagnetic waves with frequencies below those of visible Light. A given constant time difference between the signals from the two stations can be represented by a hyperbolic line of position (LOP). In Geometry, a hyperbola ( Greek, "over-thrown" has several equivalent definitions 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. If the positions of the two synchronized stations are known, then the position of the receiver can be determined as being somewhere on a particular hyperbolic curve where the time difference between the received signals is constant. This article is about a radio receiver for other uses see Radio (disambiguation. (In ideal conditions, this is proportionally equivalent to the difference of the distances from the receiver to each of the two stations. The great-circle distance is the shortest Distance between any two points on the surface of a Sphere measured along a path on the surface of the sphere (as )

By itself, with only two stations, the 2-dimensional position of the receiver cannot be fixed. In mathematics the dimension of a Space is roughly defined as the minimum number of Coordinates needed to specify every point within it A position fix or simply a fix is a term used in Position fixing in Navigation to describe a position derived from measuring external reference points A second application of the same principle must be used, based on the time difference of a different pair of stations. By determining the intersection of the two hyperbolic curves identified by the application of this method, a geographic fix can be determined. In Mathematics, the concept of a curve tries to capture the intuitive idea of a geometrical one-dimensional and continuous object

LORAN method

LORAN pulse

In the case of LORAN, one station remains constant in each application of the principle, the master, being paired up separately with two other slave, or secondary, stations. Given two secondary stations, the time difference (TD) between the master and first secondary identifies one curve, and the time difference between the master and second secondary identifies another curve, the intersections of which will determine a geographic point in relation to the position of the three stations. Geography (from Greek γεωγραφία - geografia) is the study of the Earth and its lands features inhabitants and phenomena These curves are often referred to as "TD lines. "

In practice, LORAN is implemented in integrated regional arrays, or chains, consisting of one master station and at least two (but often more) secondary stations, with a uniform "group repetition interval" (GRI) defined in microseconds. In Computer science an array is a Data structure consisting of a group of elements that are accessed by indexing. To help compare Orders of magnitude of different Times this page lists times between 10&minus6 seconds and 10&minus5 seconds (1 micro The master station transmits a series of pulses, then pauses for that amount of time before transmitting the next set of pulses.

The secondary stations receive this pulse signal from the master, then wait a preset amount of milliseconds, known as the secondary coding delay, to transmit a response signal. A millisecond (from Milli- and Second; abbreviation ms is one thousandth of a Second. In a given chain, each secondary's coding delay is different, allowing for separate identification of each secondary's signal (though in practice, modern LORAN receivers do not rely on this for secondary identification).

LORAN chains (GRIs)

LORAN Station Malone, Malone, Florida Great Lakes chain (GRI 8970) / Southeast U. Malone is a town in Jackson County, Florida, United States. The population was 2007 at the 2000 census. S. chain (GRI 7980)

Every LORAN chain in the world uses a unique Group Repetition Interval, the number of which, when multiplied by ten, gives how many microseconds pass between pulses from a given station in the chain (in practice, the GRI delays in many, but not all, chains are multiples of 100 microseconds). LORAN chains are often referred to by this designation, e. g. GRI 9960, the designation for the LORAN chain serving the Northeast U.S.

Due to the nature of hyperbolic curves, it is possible for a particular combination of a master and two slave stations to result in a "grid" where the axes intersect at acute angles. The United States of America —commonly referred to as the In Mathematics and its applications a coordinate system is a system for assigning an n - Tuple of Numbers or scalars to each point In Geometry and Trigonometry, an angle (in full plane angle) is the figure formed by two rays sharing a common Endpoint, called For ideal positional accuracy, it is desirable to operate on a navigational grid where the axes are as orthogonal as possible -- i. In Mathematics, the Cartesian coordinate system (also called rectangular coordinate system) is used to determine each point uniquely in a plane e. , the axes are at right angles to each other. In Geometry and Trigonometry, a right angle is an angle of 90 degrees corresponding to a quarter turn (that is a quarter of a full circle As the receiver travels through a chain, a certain selection of secondaries whose TD lines initially formed a near-orthogonal grid can become a grid that is significantly skewed. As a result, the selection of one or both secondaries should be changed so that the TD lines of the new combination are closer to right angles. To allow this, nearly all chains provide at least three, and as many as five, secondaries.

LORAN charts

This nautical chart of New York Harbor includes LORAN-A TD lines. New York ( is a state in the Mid-Atlantic and Northeastern regions of the United States and is the nation's third most populous Note that the printed lines do not extend into inland waterway areas.

Where available, common marine navigational charts include visible representations of TD lines at regular intervals over water areas. The TD lines representing a given master-slave pairing are printed with distinct colors, and include an indication of the specific time difference indicated by each line.

Due to interference and propagation issues suffered by low-frequency signals from land features and man-made structures the accuracy of the LORAN signal is degraded considerably in inland areas. (See Limitations. ) As a result, nautical charts will not print any TD lines in those areas, to prevent reliance on LORAN for navigation in such areas.

Traditional LORAN receivers generally display the time difference between each pairing of the master and one of the two selected secondary stations. These numbers can then be found in relation to those of the TD lines printed on the chart.

Modern LORAN receivers display latitude and longitude instead of time differences, and with improved accuracy.

Transmitters and antennas

LORAN transmitter bank

LORAN-C transmitters operate at peak powers of 100 kilowatts to four megawatts, comparable to longwave broadcasting stations. The longwave Radio band is a range of frequencies used for AM broadcasting, which extends from 148 Most LORAN-C transmitters use mast radiators insulated from ground with heights between 190 and 220 metres. The masts are inductively lengthened and fed by a loading coil (see: electrical lengthening). In Electronics, a loading coil or load coil is a Coil ( Inductor) that does not provide coupling to any other circuit, but Electrical lengthening is the modification of an aerial which is shorter than a whole-number multiple of a quarter of the radiated Wavelength, by A well known-example of a station using such an antenna is LORAN-C transmitter Rantum. The LORAN-C transmitter Rantum is a transmission facility for LORAN-C on the German island Sylt near the village Rantum at 54°48'30″N 8°17'37″W(

Free-standing tower radiators in this height range are also used. A mast radiator (aka 'radiating tower' is a radio mast or tower in which the whole structure works LORAN-C transmitter Carolina Beach uses a free-standing antenna tower. LORAN-C transmitter Carolina Beach is the Zulu secondary station of the U

Caesium atomic clocks used for LORAN signal synchronization

LORAN-C transmitters with output powers of 1000 kW and higher sometimes use supertall mast radiators (see below). While determining the world's tallest structure has generally been straightforward the definition of the world's tallest building or the

Other high power LORAN-C stations, like LORAN-C transmitter George, use four T-antennas mounted on four guyed masts arranged in a square. LORAN-C transmitter George serves the GRI 5990 (Canadian West Coast and GRI 9940 (US WestCoast chains

All LORAN-C antennas radiate an omnidirectional pattern. Unlike longwave broadcasting stations, LORAN-C stations cannot use backup antennas. The slightly different physical location of a backup antenna would produce Lines of Position different from those of the primary antenna.

Limitations

LORAN suffers from electronic effects of weather and the ionospheric effects of sunrise and sunset. The most accurate signal is the groundwave that follows the Earth's surface, ideally over seawater. In Physics, surface wave can refer to a Mechanical wave that propagates along the interface between differing media usually two fluids with different densities At night the indirect skywave, bent back to the surface by the ionosphere, is a problem as multiple signals may arrive via different paths. Skywave is the propagation of electromagnetic waves bent (refracted back to the Earth's surface by the Ionosphere. The ionosphere is the uppermost part of the atmosphere, distinguished because it is Ionized by solar radiation Multipath Interference is a phenomenon in the physics of Waves whereby a wave from a source travels to a detector via two or more paths and under the right condition The ionosphere's reaction to sunrise and sunset accounts for the particular disturbance during those periods. Magnetic storms have serious effects as with any radio based system. A geomagnetic storm or solar storm is a temporary disturbance of the Earth 's Magnetosphere caused by a disturbance in Space weather.

Loran uses ground based transmitters that only cover certain regions. Coverage is quite good in North America, Europe, and the Pacific Rim.

The absolute accuracy of Loran-C varies from 0. 1 to 0. 25 nautical miles. A nautical mile or sea mile is a unit of Length. It corresponds approximately to one minute of Latitude along any meridian. Repeatable accuracy is much greater, typically from 60 to 300 feet. ^[1]

LORAN-A and other systems

LORAN-A was a less accurate system operating in the upper mediumwave frequency band prior to deployment of the more accurate LORAN-C system. For LORAN-A the transmission frequencies 1750 kHz, 1850 kHz, 1900 kHz and 1950 kHz were used. LORAN-A continued in operation partly due to the economy of the receivers and widespread use in civilian recreational and commercial navigation. LORAN-B was a phase comparison variation of LORAN-A while LORAN-D was a short-range tactical system designed for USAF bombers. The unofficial "LORAN-F" was a drone control system. None of these went much beyond the experimental stage. An external link to them is listed below.

LORAN-A was used in the Vietnam War for navigation by large United States aircraft (C-124, C-130, C-97, C-123, HU-16, etc). The Vietnam War, also known as the Second Indochina War, or the Vietnam Conflict, occurred in Vietnam, Laos and Cambodia A common airborne receiver of that era was the R-65/APN-9 which combined the receiver and cathode ray tube (CRT) indicator into a single relatively lightweight unit replacing the two larger, separate receiver and indicator units which comprised the predecessor APN-4 system. The cathode ray tube (CRT is a Vacuum tube containing an Electron gun (a source of electrons and a Fluorescent screen with internal or The APN-9 and APN-4 systems found wide post-World War II use on fishing vessels in the U. World War II, or the Second World War, (often abbreviated WWII) was a global military conflict which involved a majority of the world's nations, including S. They were cheap, accurate and plentiful. The main drawback for use on boats was their need for aircraft power, 115 VAC at 400 Hz. The volt (symbol V) is the SI derived unit of electric Potential difference or Electromotive force. The hertz (symbol Hz) is a measure of Frequency, informally defined as the number of events occurring per Second. This was solved initially by the use of rotary inverters, typically 28 VDC input and 115 VAC output at 400 Hz. The volt (symbol V) is the SI derived unit of electric Potential difference or Electromotive force. The inverters were big and loud and were power hogs. In the 1960s, several firms such as Topaz and Linear Systems marketed solid state inverters specifically designed for these surplus LORAN-A sets. The availability of solid state inverters that used 12 VDC input opened up the surplus LORAN-A sets for use on much smaller vessels which typically did not have the 24-28 VDC systems found on larger vessels. The solid state inverters were very power efficient and widely replaced the more trouble prone rotary inverters.

LORAN-A saved many lives by allowing offshore boats in distress to give accurate position reports. It also guided many boats whose owners could not afford radar safely into fog bound harbors or around treacherous offshore reefs. The low price of surplus LORAN-A receivers (often under $150) meant that owners of many small fishing vessels could afford this equipment, thus greatly enhancing safety. Surplus LORAN-A equipment, which was common on commercial fishing boats, was rarely seen on yachts. The unrefined cosmetic appearance of the surplus equipment was probably a deciding factor.

Pan American World Airways used APN 9s in early Boeing 707 operations. The World War II surplus APN-9 looked out of place in the modern 707 cockpit, but was needed. There is an R65A APN-9 set displayed in the museum at SFO Airport, painted gold. It was a retirement present to an ex Pan Am captain.

An elusive final variant of the APN 9 set was the APN 9A. A USAF technical manual (with photographs and schematics) shows that it had the same case as the APN-9 but a radically different front panel and internal circuitry on the non-RF portions. The APN-9A had vacuum tube flipflop digital divider circuits so that TDs (time delays) between the master and slave signal could be selected on front panel rotary decade switches. In Digital circuits a flip-flop is a term referring to an Electronic circuit (a Bistable Multivibrator) that has two stable states and thereby The older APN-9 set required the user to perform a visual count of crystal oscillator timing marker pips on the CRT and add them up to get a TD. The APN 9A did not make it into widespread military use, if it was used at all, but it did exist and represented a big advance in military LORAN-A receiver technology.

In the 1970s one U. S. company, SRD Labs in Campbell, California, made modern LORAN-A sets including one that was completely automatic with a digital TD readout on the CRT, and autotracking so that TDs were continuously updated. Campbell (ˈkæmbəl is a city in Santa Clara County, California, part of Silicon Valley, in the San Francisco Bay Area. Other SRD models required the user to manually align the master and slave signals on the CRT and then a phase locked loop would keep them lined up and provide updated TD readouts thereafter. These SRD LORAN-A sets would track only one pair of stations, giving you just one LOP (line of position). If one wanted a continuously updated position (two TDs giving intersecting LOPs) rather than just a single LOP, one needed two sets.

Long after LORAN-A broadcasts were terminated, commercial fishermen still referred to old LORAN-A TDs, e. g. , "I am on the 4100 [microsecond] line in 35 fathoms", referring to a position outside of Bodega Bay. Bodega Bay is a shallow rocky Inlet of the Pacific Ocean on the coast of northern California in the United States. Many LORAN-C sets incorporated LORAN A TD converters so that a LORAN-C set could be used to navigate to a LORAN-A TD defined line or position.

LORAN Data Channel (LDC)

LORAN Data Channel (LDC) is a project underway between the FAA and USCG to send low bit rate data using the LORAN system. The Federal Aviation Administration ( FAA) is an agency of the United States Department of Transportation with authority to regulate and oversee all aspects of Messages to be sent include station identification, absolute time, and position correction messages. In 2001, data similar to Wide Area Augmentation System (WAAS) GPS correction messages were sent as part of a test of the Alaskan LORAN chain. WAAS Objectives Accuracy The WAAS specification requires it to provide a position accuracy of 7 Basic concept of GPS operation A GPS receiver calculates its position by carefully timing the signals sent by the constellation of GPS Satellites high above the Earth As of November 2005, test messages using LDC were being broadcast from several U. S. LORAN stations.

In recent years, LORAN-C has been used in Europe to send differential GPS and other messages, employing a similar method of transmission known as EUROFIX.

The future of LORAN

Worldwide Loran coverage

As LORAN systems are government maintained and operated, their continued existence is subject to public policy. With the evolution of other electronic navigation systems, such as Global Navigation Satellite Systems (GNSS), funding for existing systems is not always assured. Global Navigation Satellite System (GNSS is the standard generic term for satellite navigation systems that provide autonomous geo-spatial positioning with global coverage

Critics, who have called for the elimination of the system, state that the Loran system has too few users, lacks cost-effectiveness, and that GNSS signals are superior to Loran. Supporters of continued and improved Loran operation note that Loran uses a strong signal, which is difficult to jam, and that Loran is an independent, dissimilar, and complementary system to other forms of electronic navigation, which helps ensure availability of navigation signals. ^[2]

Recently both the US and European governments have announced political decisions to maintain and upgrade their Loran systems.

eLORAN

With the perceived vulnerability of GNSS systems, and their own propagation and reception limitations, renewed interest in LORAN applications and development has appeared. Enhanced LORAN, also known as eLORAN or E-LORAN, comprises an advancement in receiver design and transmission characteristics which increase the accuracy and usefulness of traditional LORAN. With reported accuracy as high as 8m, the system becomes competitive with unenhanced GPS. eLoran also includes additional pulses which can transmit auxiliary data such as DGPS corrections. Differential Global Positioning System (DGPS is an enhancement to Global Positioning System that uses a network of fixed ground-based reference stations to broadcast the difference eLoran receivers now use "all in view" reception, incorporating signals from all stations in range, not solely those from a single GRI, incorporating time signals and other data from up to 40 stations. These enhancements in LORAN make it adequate as a substitute for scenarios where GPS is unavailable or degraded.

United Kingdom eLORAN implementation

On 31 May 2007, the UK Department for Transport (DfT), via the General Lighthouse Authorities (GLA), awarded a 15 year contract to provide a state-of-the-art enhanced LORAN (eLORAN) service to improve the safety of mariners in the UK and Western Europe. Events 1279 BC - Rameses II (The Great (19th dynasty becomes pharaoh of Ancient Egypt. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. A General Lighthouse Authority (GLA is defined as being a dedicated Government Agency of a Country or Nation tasked with and responsible for the provision and maintenance of Lighthouses The service contract will operate in two phases, with development work and further focus for European agreement on eLORAN service provision from 2007 through 2010, and full operation of the eLORAN service from 2010 through 2022. The eLORAN transmitter is situated at Anthorn transmitting station Cumbria, UK, and operated by VT Communications, which is part of the VT Group PLC. The Anthorn Transmitting Station is located near Anthorn, Cumbria, England and is operated by VT Communications. VT Communications is a part of VT Group plc VT Communications was essentially the company formed from the privatisation of the BBC World Service transmitter sites ^[3]

List of LORAN-C transmitters

A list of LORAN-C transmitters. Stations with an antenna tower taller than 300 metres (984 feet) are shown in bold. The metre or meter is a unit of Length. It is the basic unit of Length in the Metric system and in the International A foot (plural feet or foot; symbol or abbreviation ft or sometimes &prime – the prime symbol) is a non-SI unit

See also

• CHAYKA, the Russian counterpart of LORAN
• Alpha, the Russian counterpart of the Omega Navigation System, still in use as of 2006. Chayka (Чайка lit seagull) is a Russian terrestrial Radio navigation system similar to LORAN-C. Alpha (also called RSDN-20) is a Russian system for long range Radio navigation. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar.
• OMEGA, the Western counterpart of the Alpha Navigation System, no longer in use. OMEGA was the first truly global Radio navigation system for aircraft operated by the United States in cooperation with six partner nations
• Decca Navigator System, a British system that used phase difference instead of time difference. The Decca Navigator System was a hyperbolic Low frequency Radio navigation system (also known as Multilateration) that was first deployed during The phase of an oscillation or wave is the fraction of a complete cycle corresponding to an offset in the displacement from a specified reference point at time t = 0
• SHORAN
• Oboe (navigation)
• G-H (navigation)
• GEE (navigation)
• GPS

References

• Jennet Conant, Tuxedo Park: A Wall Street Tycoon and the Secret Palace of Science That Changed the Course of World War II (New York: Simon & Schuster, 2002, ISBN 0-684-87287-0) pp. 231-232.
• Department of Transportation and Department of Defense (2006-02). 2005 Federal Radionavigation Plan (PDF). Retrieved on 2006-02-26. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 747 BC - Epoch (origin of Ptolemy 's Nabonassar Era 364 - Valentinian I is proclaimed

External links

• The Case for LORAN- It is a good backup, and very accurate.
• United States Coast Guard's official site- how to use LORAN C
• 9th Pulse Modulation / LORAN Data Channel (LDC) - will provide information using pulse position modulation of the broadcast signal.
• United States National Institute of Standards and Technology Site- Using LORAN C for time-keeping.
• LORAN-C Transmitter (Rantum) in the Structurae database
• Hellissandur Transmission Tower in the Structurae database — former LORAN-C transmitter mast, now used for longwave broadcasting
• LORAN-C facility antenna (Gillette, Wyoming) in the Structurae database
• LORAN-C facility antenna (Port Clarence, Alaska) in the Structurae database
• http://www.jproc.ca/hyperbolic/loran_a.html More in-depth discussion of the Loran-A system. Structurae is an online Database containing works of structural and Civil engineering of all kinds such as Bridges High-rise buildings Structurae is an online Database containing works of structural and Civil engineering of all kinds such as Bridges High-rise buildings Structurae is an online Database containing works of structural and Civil engineering of all kinds such as Bridges High-rise buildings Structurae is an online Database containing works of structural and Civil engineering of all kinds such as Bridges High-rise buildings
• http://www.jproc.ca/hyperbolic/loran_b_d.html Histories of Lorans-B, -D, and "-F".
• Integrated GPS/Loran Prototypes for Aviation Applications
• Loran-C Introduction: eLoran
• The Migration to Enhanced or eLoran
• The Case for eLoran at GPS World
• GNSS/eLoran for Timing and Frequency by Locus, Inc.
• Loran's Capability to Mitigate the Impact of a GPS Outage on GPS Position, Navigation, and Time Applications by Locus, Inc.
• New Potential of Low-Frequency Radionavigation in the 21st Century Ph. D. dissertation
• LORAN-C chains in service
• Excel-File with information about LORAN-C transmitters
• SDR in action: The last LORAN-C receiver is a technical description of using a software-defined radio to decode LORAN-C signals. A Software-Defined Radio (SDR system is a Radio communication system where components that have typically been implemented in hardware (i
• New UK eLORAN service provision news article News article re: UK leading the way in eLORAN service provision.