Loran-C

LORAN-C is a long-range terrestrial hyperbolic radionavigation system that fixed position from the time difference between pulsed signals received from a master and two or more secondary transmitters in a chain. The transmitters worked on 100 kHz; each constant time difference defined a hyperbolic line of position, and two crossing lines gave a fix accurate to roughly 0.25 nautical mile with repeatable accuracy better than that. Operators read the time differences against a Loran-overprinted chart or a receiver’s lat-long conversion. The US and most other chains were shut down from 2010 as GNSS took over, though the enhanced successor eLoran is studied as a GPS backup. Bowditch documents the system and its additional secondary factor corrections.