Institute for Telecommunication Sciences / December 1901

December 1901: First Radio Transmission Across the Atlantic

On December 11, 1901 Guillermo Marconi demonstrated that radio signals could be sent across the Atlantic. Marconi left a team at Poldhu in Cornwall, England, to transmit the signal, while he made his way to Signal Point in Newfoundland. Marconi set up his receiver and used a kite to raise his antenna. At the appointed time his staff in England sent three Morse code “dots” (S). The shortwave (1.6–30 MHz) radio signals reflected off the atmosphere to the receiver and Marconi heard the “S.” Because Marconi knew the signal to be transmitted ahead of time and when it was scheduled, some questioned his methods and even if he really heard the signal. However, repeated tests proved that the connection between Newfoundland and Cornwall was feasible. Within a year the Marconi Company was connecting ships up to 2,000 miles at sea to land based radio-telegraphs. Although Marconi had proved empirically that this method of reflecting radio waves beyond the earth’s horizon made radio viable for international messages, the principles of ionospheric reflection that allowed the feat were not well understood at the time. The use of shortwave communications by both commercial and amateur operators grew rapidly, while researchers rushed to explain it. The study of “skywave propagation” became a key focus of National Bureau of Standards radio research. Researchers began to map the ionosphere and perform extensive radio propagation measurements to understand how, when, and how far reflected radio signals could travel. In 1939 the first maps of the ionosphere were published in NBS reports, and in 1942 the Interservice Radio Propagation Laboratory (a predecessor to ITS) began providing the military with quarterly ionospheric propagation prediction reports. Changes in ionospheric conditions and solar flares strongly impact ionospheric propagation, but with improved understanding of the physics, better forecasting methods, and more sophisticated equipment, short wave radio is still used today, primarily for long range broadcasting, amateur radio, and over-the-horizon radar.