Broadcasting

General information

Broadcasting with the characteristic (like other media) to allow an asymmetrical communication. I.e. the means necessary to the emission and the reception are not the same ones. Indeed, the emission since the studio revêt a degree of technicality higher than that of the listener who receives a program on an english bond, whose adjustments are summary (Fréquence, Volume, Tonalité).

a radio station is an installation which emits electromagnetic waves using a broadcasting transmitter and of a antenna. A commercial station transmits sound programs of entertainment and information.
a radio station (Receiving radio operator) is an apparatus making it possible to receive the emissions of the radio stations.
a tuner is a receiver alone, without amplifier nor loudspeakers.

Modulation

Various techniques of modulation of the waves are used in broadcasting:

amplitude modulation (AM) - to see Radio operator AM
frequency modulation (FM) - to see Radio operator FM

Amplitude modulation

The amplitude modulation was most usually used dice the beginnings of the radio transmissions. Indeed it is écoutable with average tiny rooms (stations with Galène). It is obtained while modulating, as its name indicates it, the amplitude, therefore the power, of the carrying signal with the audio signal (word or music)… One varies the amplitude of the carrier wave according to the tension modulation collected by the microphone, then it is amplified.

Frequency modulation

The frequency modulation is a technique used in a commercial way more recently. It consists in varying the frequency of a carrier wave on both sides a basic center frequency. A receiver using this type of modulation is not very sensitive to the parasites which them, are modulated in amplitude and more easily allows the reception of sounds with high fidelity and consequently the emissions stereophonic.

The amplitude of the carrier wave is constant but this time Ci it is its frequency which varies.

The transmitters FM modify the signal by amplifying the acute ones in order to improve the signal-to-noise report/ratio. This preemphasis (called “pre-emphasis” in English) is of 6 dB by Octave with the top 3,18 Khz for Europe and 3 dB by Octave starting from 2,12 Khz for North America and the Japan. That is equivalent to one duration of “de-emphasis” of 50 µs with 75 µs. The receivers ( tuners in English or French syntonisor) of good quality have the possibility of adapting to it, either easily by the means of a switch, or by the replacement of some components in the apparatus.

Wavelength or Frequency

Medium waves

Short waves

The least known broadcasting is that using the short waves . The characteristic of the short waves is their faculty with being considered by the ionized layers of the upper atmosphere, which enables them to cross very long distances, of a Continent with the other. However, the low bandwidth usable, distributed internationally does not allow a communication of quality, and its application is limited to the transmission of the word without musical quality. Moreover this signal often received very slightly at long distances is easily scrambled by the environmental disturbances, or the natural radioelectric activity in the atmosphere.

But which satisfaction to be able to hear the Zealand news or Australia on a simple receiver equipped with the short waves. More enthralling, the reception of the African or South American domestic radio stations is possible of night to certain periods of the year.

Bandage FM

In Europe, this waveband goes from 87,5 M Hz to 107,9 M Hz.

Evolution

Since the years 1990, various techniques of numerical broadcasting made their appearance - to see numerical Radio. Examples:

DRM DIGITAL Radio World, system for numerical broadcasting in short waves, average and long.
DAB Audio DIGITAL Broadcasting, numerical system of broadcasting for the ultra-short waves.

Technology DRM improves the range radically and the quality of listening of the international stations, while guaranteeing an occupation of the radio frequencies similar to that of the stations AMNDT On the other hand, for the listener not team of a radio DRM, the modulation is unpleasant to listening.

Technology DAB requires the occupation of new wavebands (band III and bandages L), it uses a technique of multiplexing making it possible to diffuse several programs as well as data starting from one only transmitter.

One can think that the other technologies, inherited the world of the data processing and not of that of the radio (for example, diffusion of audio stream of the type MP3 in real-time on IP, receipts in residence or on wandering mobile Wi-Fi) will answer better than DAB the evolution of the local emissions towards digital technologies. The common point with the whole of these technologies remains, obviously, the connection without wire, only able to bring the mobility which we require of the radio.

Companies of broadcasting

See also: Amorce=Voir or to create the article, List of companies of broadcasting

See too

Simple: Broadcasting

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