From his earliest experiments Guglielmo Marconi sent messages between shore stations and lightships. In 1900 the Marconi International Marine Communication Company was formed to put wireless on board ships and to establish shore stations to serve them. The frequency used was on or around 500kHz
The Berlin Telegraph Convention 1906 nominated 600m (500 kHz) as an operating frequency. It also made SOS the international distress call.
For over 100 years a continuous watch has been kept on 500 kHz. SOS has saved over 10,000 lives (including over 700 on the Titanic), and 500 kHz has made a priceless contribution to Safety of Life at Sea (SOLAS).
The operating system in the medium wave maritime band has been, mainly Morse code, an international signalling system which enables mutual understanding and collaboration between wireless operators of all nations. On 500kHz two silence periods were observed every hour to listen for distant distress signals on 500kHz.
500kHz was the distress and calling frequency and spot frequencies above it were used as “working” frequencies. Other frequencies in the band were used for direction finding, very important before modern radar. It was the foundation of the maritime communications industry resulting in the refinement of transmitters, receivers and radar equipment.
500kHz is the only spot frequency in the whole spectrum that can be identified as having life saving historical significance. It can be retained and continue to be used to demonstrate is past role for the benefit of future generations. It is an identifiable location on the wireless spectrum that should be maintained as a heritage site, with its international morse code and own signalling techniques it will continue to be a conduit of peace, cooperation and universal respect.