1o) Metric, decimetre or centimetric waves being propagated only in hot line (there is no reflexion on the ionized layer of the atmosphere), the receiver must be "in sight" of the transmitter, 2 networks were set up:

I. Terrestrial radio relay system. The transmitters are placed in places the highest possible to extend to the maximum their range (examples: peak of the South of Bigorre 2 888 m, puy of Dome 1 465 m, switches South 3 842 m). The center of Romainville (close to Paris) ensures coordination.

Transmitter. Sound sources: discs, tape recorders, microphones (the sound or acoustic wave is transformed into pulse of very weak energy in a microphone). Processes of emission: amplitude modulation (the impulse modifies the amplitude of the carrying electromagnetic wave). Frequency modulation: it modifies its number of oscillations a second. An oscillating circuit (formed of a condenser and a reel), in resonance with the wave which traverses it, diffuses the wave by the antenna. A transistor or a vacuum tube compensates for the losses of energy and allows a permanent operation.

Receiver. Its antenna collects the emitted waves. By modifying the characteristics of an oscillating circuit, one varies the frequency (and the wavelength) of the electrical current of resonance and one thus selects the waves of a transmitting station. Then the circuit of demodulation separates the audio oscillations of frequencies, of the high frequency carrier waves. The amplifier (transistor or tube) supplied with the tension of the sector increases the amplitude of the audible waves. The loudspeaker transforms the electromagnetic oscillations into sounds.

A number of transmitters and relay transmitters (to the 1-1-2002) in Metropolitan France. Radio France: emissions with frequency modulation: 2 106 principal transmitters and relay transmitters of which France Inter 511, - Culture 507, - Music 505, - Blue 360, - Information 206, Mouv' 11, Fip 6. In amplitude modulation: network A, the transmitter with kilometric waves (long waves) in Allouis (Expensive) ray 400 to 500 km, following geographical or geological conditions, 10 transmitters with hectometric waves (medium waves) with the periphery of the territory diffusing France Inter. Network B, 20 transmitters with hectometric waves diffusing Radio operator Blue.

Peripheral radios: equipped each one, for a part of the French territory, frequencies bandages II of them (frequency modulation), in kilometric waves (Luxembourg, Europe 1, Radio Assemble-Carlo) and a station in hectometric waves (Southern Radio, in Andorra).

Television (as of 1-3-2002): 13 488 transmitters out of 3 940 sites for the 6 chains (TF1, France 2, France 3, Canal+, Arte/France 5, M6) and 471 out of 228 sites for RFO.

II. By satellites. Satellites of transmission. 1st generation: used as reflectors of waves, they can ensure the connections only part-time the moment when they are of simultaneous visibility of the stations to be connected. They require on the ground of the expensive installations and a qualified personnel (the power of the signals of a satellite collected on the ground is approximately 1 millionth of 1 millionth of Watt). 1958-18-1 Score (the USA), altitude 185 to 1 492 km. 1960-12-8 Echo I (the USA), 598 to 1 691 km. -4-10 Mail IB (the USA). 1962-10-7 TELSTAR (the USA), 952 to 5 634 km, specialized in the relay of telecommunications à.large.bande [ from the images sent of Andover (the USA) relayed by TELSTAR are received in France with Pleumeur-Bodou ]. -17-9: 1st retransmission of programs in Mondovision (homage to Dag Hammarskjöld, former secretary-general of UNO, diffused simultaneously in New York, Paris and Uppsala, in Sweden). 1964-16-4: 1st transmission on line Japan-France (and about thirty other countries) by Relay (alt. 1 323 to 7 433 km) at the time when it flies over Mandchourie. Stations on the ground: more than 100 of which Germany 3 (Raisting). GB 2 (Goonhilly Downs). Brazil 1 (Rio de Janeiro). Canada 4. France 5 (including 1 with TDF, for the satellite Symphony, Pleumeur-Bodou). Italy 4 (Fucino). Japan 4. Puerto Rico 1. Sweden 2. Trinidad 1. The USA 32 plus 1 on board Kingport, etc.

2e generation: allowing permanent relations. Molnyia/soviétiques placed since 1965 on the same orbit (460 to 40 000 km); there is of them always one in the good position to relay the communications. Synchronous and geostationary American placed since 1963 on an orbit such (alt. 35 786 km, ray 42 164 km) which they puts to turn around the Earth same time that puts this one to turn on itself: 23. 56 min 4 S. For an observer on Earth, they appear motionless. 3 Syncom (I: 14-2-1963, II: 27-7-1963, III: 9-4-1964) ensured, in Oct.. 1964, the retransmission on line in the USA of the OJ of T·ky·, then by record printer in Europe. Early Bird placed 6-4-1965, above the Atlantic, allowed regular commercial connections the France-USA. Radouga, placed 1975, satellite synchronous Soviet.

Satellites of diffusion. 3e generation: ATS 6 (THE USA, 30-5-1974), STOPPED 1979. CTS (Hermes) [ Canada, 17-1-1976 ], Stopped 1978. Symphony 1 and 2, launched 18-12 and 26-8-1974: built by 3 co.s all. (MBB, Siemens, AEG Telefunken) and 3 co.s france (Thomson CSF, SAT, Snias) stopped.

See also p. 1136.

2o)By cable. Definition: vector of audio or video signals starting from a network head to the connected television sets. 2 techniques: coaxial (copper wire which transmits electric signals) and the optical fibre (tiny transporting silicon wire of the light signals) which makes it possible to convey a greater number of signals and to dialogue with the subscriber, but is more expensive. Origin: created after 1945 in the USA to solve the problems of bad reception of hertzian television downtown, the cable television developed because of its capacity to propose a great number of chains sets of themes being addressed to the public specific ones. the 1948 USA: John Walson installs a community aerial with Manoha City (Pennsylvania). 1950 Canada: rural zones. GB: zones of shade. 1960 P.-Low: dispersed networks, often exploited by the municipalities. the 1966 USA: fight of the broadcasters to protect their hertzian stations. the 1972 USA: authorized nonlocal programs. 1973 Belgium: 300 000 hearths equipped. 1982 GB: development. 1983: France (see p. 1135 b).