He developed a device he called an "oscillation valve" (because it passes current in only one direction).
The thermionic valve (a kind of vacuum tube) was invented in 1904 by the English physicist John Ambrose Fleming. For audio broadcasts to be possible, electronic detection and amplification devices had to be incorporated. The earliest radio stations were radiotelegraphy systems and did not carry audio. Television broadcasting is a separate service which also uses radio frequencies to broadcast television ( video) signals. Radio stations broadcast with several different types of modulation: AM radio stations transmit in AM ( amplitude modulation), FM radio stations transmit in FM ( frequency modulation), which are older analog audio standards, while newer digital radio stations transmit in several digital audio standards: DAB ( digital audio broadcasting), HD radio, DRM ( Digital Radio Mondiale). Stations are often affiliated with a radio network which provides content in a common radio format, either in broadcast syndication or simulcast or both. To receive the content the listener must have a broadcast radio receiver ( radio). In terrestrial radio broadcasting the radio waves are broadcast by a land-based radio station, while in satellite radio the radio waves are broadcast by a satellite in Earth orbit. Radio broadcasting is transmission of audio (sound), sometimes with related metadata, by radio waves intended to reach a wide audience.
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