Radio and broadcasting Plan: Radio and broadcasting Use of a sound broadcasting station

Radio and broadcasting
Plan:
1. Radio and broadcasting
2. Use of a sound broadcasting station
3. AM broadcasting stations in 2006



Radio and broadcasting
Broadcasting tower in Trondheim, NorwayRadio broadcasting is transmission of audio (sound), sometimes with related metadata, by radio waves intended to reach a wide audience. 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. To receive the content the listener must have a broadcast radio receiver (radio). Stations are often affiliated with a radio network which provides content in a common radio format, either in broadcast syndication or simulcast or both. 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).Television broadcasting is a separate service which also uses radio frequencies to broadcast television (video) signals
The earliest radio stations were radiotelegraphy systems and did not carry audio. For audio broadcasts to be possible, electronic detection and amplification devices had to be incorporated.
The thermionic valve (a kind of vacuum tube) was invented in 1904 by the English physicist John Ambrose Fleming. He developed a device he called an "oscillation valve" (because it passes current in only one direction). The heated filament, or cathode, was capable of thermionic emission of electrons that would flow to the plate (or anode) when it was at a higher voltage. Electrons, however, could not pass in the reverse direction because the plate was not heated and thus not capable of thermionic emission of electrons. Later known as the Fleming valve, it could be used as a rectifier of alternating current and as a radio wave detector.^[2] This greatly improved the crystal set which rectified the radio signal using an early solid-state diode based on a crystal and a so-called cat's whisker. However, what was still required was an amplifier.