Loran-C is a system of
hyperbolic radio navigation which developed from the earlier
LORAN system. It uses low frequency signals from beacons to allow the receiver to determine their position. Conventional navigation involves measuring the distance from two known locations, radio navigation works in a similar way but using
radio direction finding. Radio navigation systems use a chain of three or four transmitters which are synchronised. Each chain has a primary station and the others are called secondaries. Each chain has a group repetition interval (GRI) which, multiplied by ten, is the time difference between pulses. The GRI identifies which chain a vessel is receiving. Loran-C was replaced by civilian
satellite navigation systems starting in the 1990s. The first services to close were in the United States and Canada in 2010. In 2014 France and Norway announced they were closing their transmitters, leaving the remaining stations in England and Germany unable to operate. The stations in Norway closed on 31 December 2015. ==Estartit transmitter==