Radio direction finding
Once the mainstay of maritime position fixing the medium frequency RDF receivers and the large loop antenna that once dominated a ship’s superstructure, have now been assigned to the scrap heap. But RDF is still alive and modern vessels do carry VHF RDF equipment. It is still an efficient system for localized position fixing and remains the only method for finding the bearing of a transmitter in an unknown location. If the relative bearings taken by two suitably equipped ships are laid-out on a chart, the two bearing lines will intersect at the position of the unknown transmitting station. Such a station need not be a radio beacon. It could be a vessel in distress and thus the two receiving ships are able, by triangulation, to pinpoint the distress position at the intersection of vectors drawn on a chart from their two known locations. Naturally, the same holds true for two land-based RDF stations.