Marconi Rotating Beam Transmitter at the South Foreland Lighthouse. c1930

Tinted colour postcard of the South Foreland Lighthouse showing Marconi’s Rotating Beam transmitter and hut installed in 1923 and dismantled in 1932.
The transmitter projected a horizontal ray of very short wireless waves which swept around the horizon in about two minutes sending out at every quarter point of the compass a distinctive signal indicating the direction which the beam was pointing at that moment. A ship in fog needing to know its location in relation to the Lighthouse only required to note on a simple short wave wireless receiver the particular signal being received at each revolution of the beam.
This indicated absolutely the bearing of the lighthouse.