AM radio

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 narrow audio bandwidth (lower audio fidelity) and higher levels of interference experienced with AM transmission have led AM broadcasters to specialise in spoken-word programming such as news, sports and talk radio, leaving transmission of music mainly to FM and digital broadcasters.

The technology of amplitude modulation (AM) radio transmission (then called radiotelephony) was developed between 1900 and 1920. Before AM came into wide use around 1920, the first radios transmitted information by wireless telegraphy (radiotelegraphy), in which the radio signal did not carry audio (sound) but was switched on and off to create pulses that carried text messages in Morse code. This was used for private person-to-person communication and message traffic, such as telegrams.

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