AM broadcasting is the process of
radio broadcasting using
amplitude modulation (AM). AM was the first method of impressing sound on a radio signal and is still widely used today. Commercial and public AM broadcasting is authorized in the
medium wave band worldwide, and also in parts of the
longwave and
shortwave bands. Radio broadcasting was made possible by the invention of the amplifying
vacuum tube, the
Audion (
triode), by
Lee de Forest in 1906, which led to the development of inexpensive vacuum tube AM
radio receivers and
transmitters during World War I. Commercial AM broadcasting developed from amateur broadcasts around 1920, and was the only commercially important form of radio broadcasting until
FM broadcasting began after World War II. This period is known as the "
Golden Age of Radio". Today, AM competes with FM, as well as with various
digital radio broadcasting services distributed from terrestrial and satellite transmitters. In many countries the higher levels of
interference experienced with AM transmission have caused AM broadcasters to specialize in
news,
sports and
talk radio, leaving transmission of music mainly to FM and digital broadcasters.