Maidenhead Locator System

The Maidenhead Locator System also QTH or QRA grid system (deprecated) is a geographic co-ordinate system used by amateur radio operators to succinctly describe their locations. Its purpose is to be concise, accurate and robust in the face of interference and adverse transmission conditions. The Maidenhead Locator System can describe locations anywhere in the world, and replaced the previous QRA locator system which was limited to European contacts.

Maidenhead locators are also commonly referred to as QTH Locator, 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".

Dr. John Morris G4ANB originally devised the system and it was adopted at a meeting of the VHF Working Group in Maidenhead, England in 1980.

DX contesting is scored based on the distance of contacts, 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 GermanQRA locator system was adopted in 1959. The QRA locator system was limited to describing European coordinates, however, and by the mid-1970s there was growing recognition for a need for a global locator system.

By the time of their April 1980 meeting, in Maidenhead, England, the VHF Working Group had received 20 different proposals to replace the QRA locator grid. That devised by Dr. John Morris G4ANB was deemed to be the best.

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