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The Maidenhead Locator System (a.k.a. QTH Locator and IARU Locator) is a
geocode system A geocode is a code that represents a geographic entity (location or Geographical feature, object). It is a unique identifier of the entity, to distinguish it from others in a finite set of geographic entities. In general the ''geocode'' is a ...
used by
amateur radio Amateur radio, also known as ham radio, is the use of the radio frequency spectrum for purposes of non-commercial exchange of messages, wireless experimentation, self-training, private recreation, radiosport, contesting, and emergency communic ...
operators to succinctly describe their
geographic coordinates The geographic coordinate system (GCS) is a spherical or ellipsoidal coordinate system for measuring and communicating positions directly on the Earth as latitude and longitude. It is the simplest, oldest and most widely used of the various ...
, which replaced the deprecated
QRA locator The QRA locator, also called QTH locator in some publications, is an obsolete geographic coordinate system used by amateur radio operators in Europe before the introduction of the Maidenhead Locator System. As a radio transmitter or receiver locati ...
, which was limited to European
contact Contact may refer to: Interaction Physical interaction * Contact (geology), a common geological feature * Contact lens or contact, a lens placed on the eye * Contact sport, a sport in which players make contact with other players or objects * ...
s. Its purpose is to be concise, accurate, and robust in the face of
interference Interference is the act of interfering, invading, or poaching. Interference may also refer to: Communications * Interference (communication), anything which alters, modifies, or disrupts a message * Adjacent-channel interference, caused by extr ...
and other adverse transmission conditions. The ''Maidenhead Locator System'' can describe locations anywhere in the world. Maidenhead locators are also commonly referred to as ''QTH locators'', ''grid locators'' or ''grid squares'', although the "squares" are distorted on any non- equirectangular cartographic projection. Use of the terms ''QTH locator'' and ''QRA locator'' was initially discouraged, as it caused confusion with the older QRA locator system. The only abbreviation recommended to indicate a Maidenhead reference in Morse code and radio teleprinter transmission was LOC, as in LOC KN28LH. John Morris G4ANB originally devised the system and it was adopted at a meeting of the IARU VHF Working Group in Maidenhead, England in 1980.


History

Amateur radio Amateur radio, also known as ham radio, is the use of the radio frequency spectrum for purposes of non-commercial exchange of messages, wireless experimentation, self-training, private recreation, radiosport, contesting, and emergency communic ...
contests on VHF and UHF are often scored based on the distance of
contact Contact may refer to: Interaction Physical interaction * Contact (geology), a common geological feature * Contact lens or contact, a lens placed on the eye * Contact sport, a sport in which players make contact with other players or objects * ...
s, typically 1 point per kilometre, so there is a need for amateurs to exchange their locations over the air. To facilitate this, following the growth of the sport in the 1950s, the German
QRA locator The QRA locator, also called QTH locator in some publications, is an obsolete geographic coordinate system used by amateur radio operators in Europe before the introduction of the Maidenhead Locator System. As a radio transmitter or receiver locati ...
system was adopted in 1959. The QRA locator system was limited to describing European coordinates, by the mid-1970s there was growing need for a global locator system. By the time of their April 1980 meeting, in Maidenhead, England, the VHF Working Group had received twenty different proposals to replace the QRA locator grid. That devised by Dr. John Morris (G4ANB) was deemed to be the best. At the 1999 IARU Conference in Lillehammer it was decided that the latitude and longitude to be used as a reference for the determining of locators should be based on the World Geodetic System 1984 (WGS-84).


Description of the system

A Maidenhead locator compresses
latitude In geography, latitude is a coordinate that specifies the north– south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north pol ...
and
longitude Longitude (, ) is a geographic coordinate that specifies the east– west position of a point on the surface of the Earth, or another celestial body. It is an angular measurement, usually expressed in degrees and denoted by the Greek lette ...
into a short string of characters, which is similar in concept to the
World Geographic Reference System The World Geographic Reference System (GEOREF) is a geocode, a grid-based method of specifying locations on the surface of the Earth. GEOREF is essentially based on the geographic system of latitude and longitude, but using a simpler and more fle ...
or GEOREF. This position information is presented in a limited level of precision to limit the number of characters needed for its transmission using voice,
Morse code Morse code is a method used in telecommunication to encode text characters as standardized sequences of two different signal durations, called ''dots'' and ''dashes'', or ''dits'' and ''dahs''. Morse code is named after Samuel Morse, one of ...
, or any other operating mode. The chosen coding uses alternating pairs of letters and digits, like so: * BL11bh16 In each pair, the first character encodes longitude and the second character encodes latitude. These character pairs also have traditional names, and in the case of letters, the range of characters (or "encoding base number") used in each pair does vary. To avoid negative numbers in the input data, the system specifies that latitude is measured from the
South Pole The South Pole, also known as the Geographic South Pole, Terrestrial South Pole or 90th Parallel South, is one of the two points where Earth's axis of rotation intersects its surface. It is the southernmost point on Earth and lies antipod ...
to the
North Pole The North Pole, also known as the Geographic North Pole or Terrestrial North Pole, is the point in the Northern Hemisphere where the Earth's axis of rotation meets its surface. It is called the True North Pole to distinguish from the Mag ...
, and longitude measured eastward from the
antimeridian The 180th meridian or antimeridian is the meridian 180° both east and west of the prime meridian in a geographical coordinate system. The longitude at this line can be given as either east or west. On Earth, these two meridians form a ...
of
Greenwich Greenwich ( , ,) is a town in south-east London, England, within the ceremonial county of Greater London. It is situated east-southeast of Charing Cross. Greenwich is notable for its maritime history and for giving its name to the Greenwich ...
, giving the
Prime Meridian A prime meridian is an arbitrary meridian (a line of longitude) in a geographic coordinate system at which longitude is defined to be 0°. Together, a prime meridian and its anti-meridian (the 180th meridian in a 360°-system) form a great ...
a
false easting A projected coordinate system, also known as a projected coordinate reference system, a planar coordinate system, or grid reference system, is a type of spatial reference system that represents locations on the Earth using cartesian coordin ...
of 180° and the
equator The equator is a circle of latitude, about in circumference, that divides Earth into the Northern and Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the North and South poles. The term can als ...
a
false northing A projected coordinate system, also known as a projected coordinate reference system, a planar coordinate system, or grid reference system, is a type of spatial reference system that represents locations on the Earth using cartesian coordin ...
of 90°. To simplify manual encoding, the base for the first pair of letters—traditionally called a ''field''—was chosen to be 18, thus dividing the globe into 18 zones of longitude of 20° each, and 18 zones of latitude 10° each. These zones are encoded with the letters "A" through "R". The second pair of numbers, called a ''square'' and placed after the first pair of letters, uses a base number of 10, and is encoded using the digits "0" to "9". This is where the alternative name "grid squares" comes from. Each of these squares represents 1° of latitude by 2° of longitude. For additional precision, each square can optionally be sub-divided further, into ''subsquares''. These are encoded into a second pair of letters, often (but not always) presented in lowercase. Again, to make manual calculations from degrees and minutes easier, 24 was chosen as the base number, giving these subsquares dimensions of 2.5' of latitude by 5' of longitude. The letters used are "a" through "x". The resulting Maidenhead subsquare locator string is hence composed of two letters, two digits, and two more letters. To give an example, W1AW, the
American Radio Relay League The American Radio Relay League (ARRL) is the largest membership association of amateur radio enthusiasts in the United States. ARRL is a non-profit organization, and was co-founded on April 6, 1914, by Hiram Percy Maxim and Clarence D. Tuska o ...
's
Hiram Percy Maxim Hiram Percy Maxim (September 2, 1869 – February 17, 1936) was an American radio pioneer and inventor, and co-founder (with Clarence D. Tuska) of the American Radio Relay League (ARRL). Hiram Percy Maxim is credited with inventing and sellin ...
Memorial Station in
Newington, Connecticut Newington is a town in Hartford County, Connecticut, United States. Located south of downtown Hartford, Newington is an older, mainly residential suburb located in Greater Hartford. As of the 2020 census, the population was 30,536. The Connectic ...
, is found in grid locator . Two points within the same Maidenhead subsquare are always less than apart, which means a Maidenhead locator can give adequate precision from only six easily transmissible characters. For even more precise location mapping, two additional digits were proposed and ratified as an ''extended locator'', making it altogether eight characters long, and dividing ''subsquares'' into even smaller ones with dimensions 15” of latitude by 30” of longitude. Such precision has uses in very short communication spans. Beyond this, no common definition exists to extend the system further into even smaller squares. Most often the extending is done by repeating alternating subsquare and square rules (base numbers 24 and 10 respectively). However, other bases for letter encodings have also been observed, and therefore such ''extended extended'' locators might not be compatible. To summarise: * Character pairs encode
longitude Longitude (, ) is a geographic coordinate that specifies the east– west position of a point on the surface of the Earth, or another celestial body. It is an angular measurement, usually expressed in degrees and denoted by the Greek lette ...
first, and then
latitude In geography, latitude is a coordinate that specifies the north– south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north pol ...
. * The first pair (a ''field'') encodes with base 18 and the letters "A" to "R". * The second pair (''square'') encodes with base 10 and the digits "0" to "9". * The third pair (''subsquare'') encodes with base 24 and the letters "a" to "x". * The fourth pair (''extended square'') encodes with base 10 and the digits "0" to "9". (The fifth and subsequent pairs are not formally defined, but recursing to the third and fourth pair algorithms is a possibility, e.g.: BL11bh16oo66) On shortwave frequencies, positions are reported at ''square'' precision, and on VHF and UHF, ''subsquare'' precision is used. At high microwave frequencies ''extended square'' and ''extended subsquare'' precision is often used.


Adoption and use

Like the QRA system before it, Maidenhead locators were enthusiastically adopted by radio amateurs beyond contesting, and it is now in widespread use. Maidenhead locators are still used as part of the formulas for scoring in many VHF amateur radio contests and as the basis of earning awards like the American Radio Relay League's VHF/UHF Century Club, URE TTLOC, etc. operating contests. Under IARU Region 1 rules, VHF distance calculations are carried out between Maidenhead subsquare centres, assuming a ''spherical'' Earth. This results in a small error in distance, but makes calculations simpler and, given the inherent imprecision in the input data used, it is not the biggest error source. Until the adoption of
WGS 84 The World Geodetic System (WGS) is a standard used in cartography, geodesy, and satellite navigation including GPS. The current version, WGS 84, defines an Earth-centered, Earth-fixed coordinate system and a geodetic datum, and also descri ...
as the official
geodetic datum A geodetic datum or geodetic system (also: geodetic reference datum, geodetic reference system, or geodetic reference frame) is a global datum reference or reference frame for precisely representing the position of locations on Earth or other pla ...
of the Maidenhead locator system in 1999, operators had usually specified their location based on their local national datum. Consequently, stations very near the edges of squares (at denoted precision) may have changed their locators when changing over to the use of WGS 84. The relatively new
FT8 FT8 or Franke & Taylor 8 is a frequency shift keying digital mode which was released on June 29, 2017, by the creators Joe Taylor, K1JT and Steve Franke, K9AN along with the software package WSJT.Burmester, Dale March 12, 2019. Amateur Radio Dig ...
narrowband digital mode transmits Maidenhead locator square as part of standard messages, with the 4 character locator square being efficiently represented within 15 bits of the transmitted string. In 2019 the IARU clarified the latest position on use of the IARU locator at various levels of precision.


Hardware and software support

In 1985, the Radio Society of Great Britain published a small set of BASIC language routines to convert from locator references to geographical coordinates (latitude and longitude) for further processing. A complete program in BASIC called ''Universal Gridlocator'' was made available the following year by ARRL for a nominal cost of US$3. Many other utilities exist to convert latitude and longitude to locators, as this is a favourite
hack Hack may refer to: Arts, entertainment, and media Games * ''Hack'' (Unix video game), a 1984 roguelike video game * ''.hack'' (video game series), a series of video games by the multimedia franchise ''.hack'' Music * ''Hack'' (album), a 199 ...
for programmers who are also radio amateurs.
Perl Perl is a family of two high-level, general-purpose, interpreted, dynamic programming languages. "Perl" refers to Perl 5, but from 2000 to 2019 it also referred to its redesigned "sister language", Perl 6, before the latter's name was offic ...
supports conversion between geographical coordinates and Maidenhead locators in module Ham::Locator by Andy Smith, available on
CPAN The Comprehensive Perl Archive Network (CPAN) is a repository of over 250,000 software modules and accompanying documentation for 39,000 distributions, written in the Perl programming language by over 12,000 contributors. ''CPAN'' can denote eit ...
. Many commercially available general purpose (civil)
Global Positioning System The Global Positioning System (GPS), originally Navstar GPS, is a satellite-based radionavigation system owned by the United States government and operated by the United States Space Force. It is one of the global navigation satellite sy ...
(GPS) receivers (e.g. Garmin GPS-12) have the option to display positions in Maidenhead Locator format.


See also

*
Military Grid Reference System The Military Grid Reference System (MGRS)
Datums, Ellipsoids, Grids, and Grid Reference Sys ...
*
Ordnance Survey National Grid The Ordnance Survey National Grid reference system (OSGB) (also known as British National Grid (BNG)) is a system of geographic grid references used in Great Britain, distinct from latitude and longitude. The Ordnance Survey (OS) devised the ...
*
QRA locator The QRA locator, also called QTH locator in some publications, is an obsolete geographic coordinate system used by amateur radio operators in Europe before the introduction of the Maidenhead Locator System. As a radio transmitter or receiver locati ...
*
United States National Grid The United States National Grid (USNG) is a multi-purpose location system of grid references used in the United States. It provides a nationally consistent "language of location", optimized for local applications, in a compact, user friendly for ...
*
World Geographic Reference System The World Geographic Reference System (GEOREF) is a geocode, a grid-based method of specifying locations on the surface of the Earth. GEOREF is essentially based on the geographic system of latitude and longitude, but using a simpler and more fle ...
(GEOREF)


References


Maps with Maidenhead Locator grid

* * * *


External links

* * * "Click on the TH Locatorcheckbox in upper right corner menu to activate." * * * * * * * * {{geocoding-systems Amateur radio Geographic coordinate systems Maidenhead Science and technology in Berkshire 1980 in radio Geocodes