Radio direction-finding

Commonly known as RDF, and even more commonly as DF, this useful navigational aid is now rarely used. Lighthouse authorities would maintain transmitting beacons at well-chosen locations, anyone of which can be identifIed by its own call sign in Morse code. The receiver’s aerial is rotated until the reception reaches a minimum – the null¬† point. When the signal is at a null, the aerial is pointing towards the station.