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Encyclopedia > LORAN

## 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. A given constant time difference between the signals from the two stations can be represented by a hyperbolic line of position (LOP). 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. (In ideal conditions, this is proportionally equivalent to the difference of the distances from the receiver to each of the two stations.) Crude diagram of time-difference principle. ... Crude diagram of time-difference principle. ... In information theory, a signal is the sequence of states of a communications channel that encodes a message. ... 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. ... 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 radio terminology, a receiver is an electronic circuit that receives a radio signal from an antenna and decodes the signal for use as sound, pictures, navigational-position information, etc. ... Distance is a numerical description of how far apart objects are at any given moment in time. ...

By itself, with only two stations, the 2-dimensional position of the receiver cannot be fixed. 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. Dimension (from Latin measured out) is, in essence, the number of degrees of freedom available for movement in a space. ... 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. ... In mathematics, the concept of a curve tries to capture the intuitive idea of a geometrical one-dimensional and continuous object. ...

## LORAN method

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. These curves are often referred to as "TD lines." Physical map of the Earth (Medium) (Large 2 MB) Geography is the scientific study of the locational and spatial variation in both physical and human phenomena on Earth. ...

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. The master station transmits a series of pulses, then pauses for that amount of time before transmitting the next set of pulses. This article does not cite any references or sources. ... To help compare orders of magnitude of different times this page lists times between 10âˆ’6 seconds and 10âˆ’5 seconds (1. ...

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. 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). One millisecond is one-thousandth of a second. ... In its general sense, delay refers to a lapse of time. ...

### LORAN chains (GRIs)

Each LORAN chain in the world uses a unique GRI (Group Repetition Interval), which is designated by the number of microseconds divided by 10 (in practice the GRI delays 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. Motto: (Out Of Many, One) (traditional) In God We Trust (1956 to date) Anthem: The Star-Spangled Banner Capital Washington D.C. Largest city New York City None at federal level (English de facto) Government Federal constitutional republic  - President George Walker Bush (R)  - Vice President Dick Cheney (R) Independence from...

Due to the nature of hyperbolic curves, it is possible for a particular combination of a master and 2 slave stations to result in a "grid" where the axes intersect at acute angles. For ideal positional accuracy, it is desirable to operate on a navigational grid where the axes are as Cartesian as possible -- i.e., the axes are at right angles to each other. As the receiver travels through a chain, a certain selection of secondaries whose TD lines initially formed a near-Cartesian grid can become a grid that is sharply angular. 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. A coordinate axis is one of a set of vectors that defines a coordinate system. ... âˆ , the angle symbol. ... Fig. ... This article is about angles in geometry. ...

## LORAN charts

This nautical chart of New York Harbor includes LORAN-A TD lines. 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. Download high resolution version (906x595, 171 KB)Nautical chart including LORAN TD lines for ocean approaches to New York Harbor. ... Download high resolution version (906x595, 171 KB)Nautical chart including LORAN TD lines for ocean approaches to New York Harbor. ... â€œNYâ€ redirects here. ...

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-C transmitters operate at peak powers of 100 kilowatts to four megawatts, comparable to longwave broadcasting stations. 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). A well known-example of a station using such an antenna is LORAN-C transmitter Rantum. This article does not cite any references or sources. ... In electronics, a loading coil is a coil (inductor) that does not provide coupling to any other circuit, but is inserted in a circuit to increase its inductance. ... This article, image, template or category should belong in one or more categories. ... The LORAN-C transmitter Rantum is a transmission facility for LORAN-C on the German island Sylt near the village Rantum. ...

Free-standing tower radiators in this height range are also used. LORAN-C transmitter Carolina Beach uses a free-standing antenna tower. A typical mast radiator Base feed: mast is fed from Aerial Tuning Unit on right via conductor to top of brown ceramic insulator. ... LORAN-C transmitter Carolina Beach is the Zulu secondary station of the U.S. Southeast chain ( GRI 7270) with a transmission power of 800 kW. LORAN-C transmitter Carolina Beach, situated near Carolina Beach, North Carolina, USA at 34Â°346. ...

LORAN-C transmitters with output powers of 1000 kW and higher sometimes use supertall mast radiators (see below). This article does not cite any references or sources. ...

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 is a LORAN-C transmitter serving the LORAN-C grids GRI 5990 and GRI 9940 with a transmission power of 1600 kW. LORAN-C transmitter George is situated at George at 47Â°348. ...

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. At night the indirect skywave, bent back to the surface by the ionosphere, is a problem as multiple signals may arrive via different paths. 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. Groundwave is the propagation of radio waves close to the surface of the Earth. ... It has been suggested that this article or section be merged with Ionosphere. ... Relationship of the atmosphere and 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 two (or more) components of the wave interfere. ... A Magnetic storm is also known as a geomagnetic storm. ...

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

## 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 Air Force 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 Viet Nam war for navigation by large US aircraft (C 124, C 130, C 97, C 123, HU 16 etc). A common airborne receiver of that era was the R 65 APN 9 which combined the receiver and 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 APN 9 and APN 4 systems found wide post-WW 2 use on fishing vessels in the US. They were cheap, accurate and plentiful. The main drawback for use on boats was their need for aircraft power, 115 VAC at 400 Hz. This was solved initially by the use of rotary inverters, typically 28 VDC input and 115 VAC output at 400 Hz. The inverters were big and loud and were power hogs. In the 1960s several firms (e.g. 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 many small fishing vessels' owners could afford this gear, thus greatly enhancing safety. Surplus Loran A gear, which was common on commercial fishing boats, was rarely seen on yachts. The unrefined cosmetic appearance of the surplus gear was probably a deciding factor.

Pan Am used APN 9s in early Boeing 707 operations. The WW 2 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 flip-flop digital divider circuits so that TDs (time delays) between the master and slave signal could be dialed up on front panel rotary decade switches. The older APN 9 set required the user to do an eyeball 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 US 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. 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 you wanted a continuously updated position (two TDs giving intersecting LOPs) rather than just a single LOP, you needed two sets.

Long after Loran A shut down, 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 California. Many Loran C sets incorporated Loran A TD converters so that a Loran C set could 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. 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. As of November 2005, test messages using LDC were being broadcast from several U.S. LORAN stations. â€œFAAâ€ redirects here. ... USCG HH-65 Dolphin USCG HH-60J JayHawk The United States Coast Guard (USCG) is a branch of the United States armed forces and is involved in maritime law enforcement, mariner assistance, search and rescue, and national defense. ... WAAS System Overview The Wide Area Augmentation System (WAAS) is an extremely accurate navigation system developed for civil aviation by the Federal Aviation Administration (FAA), a division of the United States Department of Transportation (DOT). ... The Global Positioning System (GPS) is the only fully functional Global Navigation Satellite System (GNSS). ...

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. Image File history File links Download high resolution version (872x510, 327 KB)A map of worldwide loran coverage. ... Image File history File links Download high resolution version (872x510, 327 KB)A map of worldwide loran coverage. ... 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.[citation needed] 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.[1]

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. 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. Over fifty GPS satellites such as this NAVSTAR have been launched since 1978. ...

### United Kingdom eLORAN implementation

On 31st 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. 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 will be situated in Cumbria, UK, and operated by VT Communications, which is part of the VT Group PLC. Cumbria (IPA: ), is a shire county in the extreme North West of England. ...

## List of LORAN-C transmitters

 LORAN Station Malone, Malone, Florida LORAN transmitter bank Timing devices used for LORAN transmission control Cesium atomic clocks used for LORAN signal synchronization

A list of LORAN-C transmitters. Stations with an antenna tower taller than 300 metres (984 feet) are shown in bold. LORAN Station Malone, Florida: Outside of station File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... LORAN Station Malone, Florida: Outside of station File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Malone is a town located in Jackson County, Florida. ... LORAN Station Malone, Florida: View of middle section of transmitter banks. ... LORAN Station Malone, Florida: View of middle section of transmitter banks. ... LORAN Station Malone, Florida: Timing devices File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... LORAN Station Malone, Florida: Timing devices File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Download high resolution version (480x640, 90 KB)LORAN Station Malone, Florida: Cesium clocks File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Download high resolution version (480x640, 90 KB)LORAN Station Malone, Florida: Cesium clocks File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... The metre (or meter, see spelling differences) is a measure of length. ... A foot (plural: feet or foot;[1] symbol or abbreviation: ft or, sometimes, â€² â€“ a prime) is a unit of length, in a number of different systems, including English units, Imperial units, and United States customary units. ...

Station Country Chain Remarks
Afif Saudi-Arabia Saudi Arabia South (GRI 7030)/Saudi Arabia North (GRI 8830)
Al Khamasin Saudi-Arabia Saudi Arabia South (GRI 7030)/Saudi Arabia North (GRI 8830)
Al Muwassam Saudi-Arabia Saudi Arabia South (GRI 7030)/Saudi Arabia North (GRI 8830)
Angissq Greenland shutdown on December 31, 1994 used until July 27, 1964 a 411.48 metre tower
Ash Shayk Saudi-Arabia Saudi Arabia South (GRI 7030)/Saudi Arabia North (GRI 8830)
Attu, Alaska U.S. North Pacific (GRI 9990)/Russian-American (GRI 5980)
Balasore India Calcutta (GRI 5543)
Baudette, Minnesota U.S. North Central U.S. (GRI 8290)/Great Lakes (GRI 8970)
Berlevåg Norway Bø (GRI 7001)
Billamora India Bombay (GRI 6042)
Boise City, Oklahoma U.S. Great Lakes (GRI 8970)/ South Central U.S. (GRI 9610)
Cambridge Bay Canada shut-down free-standing lattice tower, used as NDB
Cape Race Canada Canadian East Coast (GRI 5930)/Newfoundland East Coast (GRI 7270) used until February 2, 1993 a 411.48 metre tall tower, uses now a 260.3 metre tall tower
Caribou, Maine U.S. Canadian East Coast (GRI 5930) / Northeast U.S. (GRI 9960)
Carolina Beach, North Carolina U.S. Northeast US (GRI 9960)/ Southeast U.S. (GRI 7980)
Chongzuo China China South Sea (GRI 6780)/ Southeast U.S. (GRI 7980)
Comfort Cove Canada Newfoundland East Coast (GRI 7270)
Dana, Indiana U.S. Great Lakes (GRI 8970)/ Northeast US (GRI 9960)
Diamond Harbor India Calcutta (GRI 5543)
Eiði Faroe Islands Ejde (GRI 9007)
Estartit Spain Mediterranean Sea (GRI 7990); shut down
Fallon, Nevada U.S. U.S. West Coast (GRI 9940)
Fox Harbour Canada Newfoundland East Coast (GRI 7270)/ Canadian East Coast (GRI 5930)
George United States Canadian West Coast (GRI 5990)/ U.S. West Coast (GRI 9940)
Gesashi Japan East Asia (GRI 9930)/ North West Pacific (GRI 8930)
Gillette, Wyoming U.S. South Central U.S. (GRI 9610)/ North Central U.S. (GRI 8290)
Grangeville, Idaho U.S. South Central U.S. (GRI 9610)/ Southeast U.S. (GRI 7980)
Havre U.S. North Central U.S. (GRI 8290)
Hellissandur Iceland shut down on December 31, 1994 411.48 metre tall tower, now used for longwave broadcasting of RÚV on 189 kHz
Helong China China North Sea (GRI 7430)
Hexian China China South Sea (GRI 6780)
Jan Mayen Norway Bø (GRI 7001)/ Ejde (GRI 9007)
Johnston Island U.S. shut-down
Iwo Jima Japan shut down in September 1993, dismantled used a 411.48 metre tall tower
Jupiter, Florida U.S. Southeast U.S. (GRI 7980)
Kargaburan Turkey Mediterranean Sea (GRI 7990); shut down
Kwang Ju South Korea East Asia (GRI 9930)
Lampedusa Italy Mediterranean Sea (GRI 7990); shut down
Las Cruces, New Mexico U.S. South Central U.S. (GRI 9610)
Lessay France Lessay (GRI 6731) / Sylt (GRI 7499)
Loop Head Ireland was planned (GRI 6731 and 9007), but never operational
Malone, Florida U.S. Great Lakes (GRI 8970) / Southeast U.S. (GRI 7980)
Minamitorishima Japan North West Pacific (GRI 8930) used until 1985 a 411.48 metre tall tower
Nantucket, Massachusetts U.S. Canadian East Coast (GRI 5930) / Northeast U.S. (GRI 9960)
Narrow Cape Alaska North Pacific (GRI 9990) / Gulf of Alaska (GRI 7960)
Niijima Japan North West Pacific (GRI 8930) / East Asia (GRI 9930)
Patpur India Calcutta (GRI 5543)
Pohang South Korea North West Pacific (GRI 8930) / East Asia (GRI 9930)
Port Clarence Alaska Gulf of Alaska (GRI 7960)/North Pacific (GRI 9990) uses a 411.48 metre tall tower
Rantum Germany Sylt (GRI 7499)/ Lessay (GRI 6731)
Raymondville, Texas U.S. South Central U.S. (GRI 9610)/ Southeast U.S. (GRI 7980)
Raoping China China South Sea (GRI 6780)/ China East Sea (GRI 8930)
Rongcheng China China North Sea (GRI 7430)/ China East Sea (GRI 8930)
Rugby UK experimental (GRI 6731); shut down at the end of July 2007
Saint Paul Alaska North Pacific (GRI 9990)
Salwa Saudi-Arabia Saudi Arabia North (GRI 8830)/Saudi Arabia South (GRI 7030)
Searchlight, Nevada U.S. U.S. West Coast (GRI 9940)/South Central U.S. (GRI 9610)
Sellia Marina Italy Mediterranean Sea (GRI 7990); shut down
Seneca, New York U.S. Great Lakes (GRI 8970)/Northeast U.S. (GRI 9960)
Soustons France Lessay (GRI 6731)
Tokachibuto Japan Eastern Russia Chayka (GRI 7950)/ North West Pacific (GRI 8930)
Upolo Point, Hawaii U.S. shut-down
Værlandet Norway Sylt (GRI 7499)/ Ejde (GRI 9007)
Veraval India Bombay (GRI 6042)
Xuancheng China China North Sea (GRI 7430)/ China East Sea (GRI 8930)
Yap Micronesia shut down in 1987, dismantled used a 304.8 metre tall tower

## References

• Jennet Conan, 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. ... is the 57th day of the year in the Gregorian calendar. ...

Results from FactBites:

 LORAN (1014 words) LORAN (LOng RAnge Navigation) is a terrestrial radio-navigation system using ground-based transmitters. Hyperbolic LORAN lines of position (LOP) are formed by measuring the difference in reception times of synchronized signals. LORAN suffers from electronic effects of weather and in particular atmospheric effects related to sunrise and sunset.
 loran: Definition and Much More from Answers.com (2610 words) LORAN (LOng RAnge Navigation) is a terrestrial navigation system using low frequency radio transmitters that use the time interval between radio signals received from three or more stations to determine the position of a ship or aircraft. LORAN use is in deep decline, with GPS being the primary replacement, however there are current attempts to enhance and re-popularize LORAN. 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 2 slave stations to result in a "grid" where the axis intersect at acute angles.
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