Maidenhead Locator System

Lore & Background

The Maidenhead Locator System was devised by John Morris G4ANB and adopted at a meeting of the IARU VHF Working Group in Maidenhead, England in 1980. It replaced the QRA locator system, which had been adopted in 1959 following the growth of the sport in the 1950s but was limited to describing European coordinates. By the mid-1970s there was growing need for a global locator system, and by the time of the April 1980 meeting, the VHF Working Group had received twenty different proposals to replace the QRA locator grid; that devised by John Morris was deemed the best.

The system compresses latitude and longitude into a short string of characters, using alternating pairs of letters and digits. The first pair (field) uses base 18 and letters A through R; the second pair (square) uses base 10 and digits 0 through 9; the third pair (subsquare) uses base 24 and letters A through X; and the fourth pair (extended square) uses base 10 and digits 0 through 9. Latitude is measured from the South Pole to the North Pole, and longitude eastward from the antimeridian of Greenwich. The terms QTH locator and QRA locator were initially discouraged to avoid confusion with the older QRA system; the recommended abbreviation in Morse code and radio teleprinter transmission was LOC.

Reader's Guide

The Maidenhead Locator System is significant in amateur radio for enabling distance-based scoring in VHF and UHF contests, typically 1 point per kilometre. It was enthusiastically adopted beyond contesting and is now in widespread use. It serves as the basis for awards like the American Radio Relay League's VHF/UHF Century Club and URE TTLOC operating contests. Under IARU Region 1 rules, VHF distance calculations are carried out between Maidenhead subsquare centres assuming a spherical Earth, which introduces a small error but simplifies calculations. The system's adoption of WGS 84 as the official geodetic datum in 1999 caused some stations near square edges to change their locators. The FT8 narrowband digital mode transmits the 4-character locator square within 15 bits of the transmitted string. In 2019 the IARU clarified the latest position on use of the locator at various levels of precision, including a fifth pair of characters and that all letters should be uppercase. Hardware and software support includes BASIC routines published by the Radio Society of Great Britain in 1985, a Universal Gridlocator program from ARRL in 1986, Perl module Ham::Locator, Python maidenhead module, and many GPS receivers with the option to display Maidenhead locator format.