Basic Wireless Telegraphy
In wireless telegraphy, the conducting medium is not wire but simply air. The transmitting antenna radiates the electromagnetic field created by the originating current from the spark coilsat the speed of light in every direction. This signal is then available to any receiving antenna within its range.
A receiving antenna reverses the process, converting the airborne electromagnetic radiation it detects to an electric current which is translated at the receiving station.
From Senato del Regno to George A. Hoadley,
Envelope originating in the Italian Senate, 5/21/1918;
received in Philadelphia on 6/10/1918.
Envelope reverse (252K)
Reverse of the above envelope.