In 1904, Valdemar Poulsen, the same Danish scientist who
invented the magnetic recording process did the first transmission
of voice by the radio, through the telegrafone, an invention
based originally in the telephone. (a) However, the communications
through the radio had only been possible with the invention
and the improvement of the thermionic valve.
Thus, its application in the military communication is related
with some technological developments as:
- The valves used as repeater in telephony
- The metallic valves
- The miniature valves
- Valves for high frequency.