salut voici le message que j'ai reçu d'un ami sur le forum italie 35 45
"Le "photophone" en français a été inventé par Alexandre Graham Bell dans les année 1880 : Cet appareil permettait de transmettre la lumière sur une distance de 200 mètres. La voix, amplifiée par un microphone, faisait vibrer un miroir qui réfléchissait la lumière du soleil. Quelque 200 mètres plus loin, un second miroir captait cette lumière pour activer un cristal de sélénium et reproduire le son voulu. Le récepteur de cet appareil était presque identique à celui du premier téléphone. Bien qu'opérationnelle en terrain découvert, cette méthode s'avéra peu utilisée. La pluie, la neige et les obstacles qui empêchaient la transmission du signal condamnèrent cette invention, bien qu'il considérait lui-même que le photophone était sa plus grande invention, puisqu'elle permettait une communication sans fil
Sinon d'autre pays l'on utilisé : comme ici http://modulatedlight.org/Modulated_Light_DX/GrothArticle1.html un bout de l'article:
"Interest in photophones appears to have been dormant until the turn of the century, when German and Austrian experiments with current modulated carbon arc lamps, led to the production of a military photophone by the Siemens-Halske company in 1917. This unit used a current modulated carbon arc transmitter, and a selenium cell receiver, to give a night range of about 8 km. The German Navy was reported to have used voice modulated searchlights for ship to ship communication up to a distance of 7 miles (11 km).
The British were also active in photophone research during the First World War, and the vibrating mirror modulator was developed by Rankine as part of a research project for The Admiralty in 19162. Other methods of producing modulated light, including current modulation of carbon arcs and fine filament lamps were found to have very poor modulation characteristics.
The selenium cell was the only photoelectric detector available until the development of the thalofide (oxidized thallous sulphide) and molybdenite detectors in 1917. These had a lower noise level than selenium and a faster response to infra-red radiation.
An experimental photophone was developed in the U.S.A. by the Case Research Laboratories in 1918, which used a pressure modulated acetylene lamp (Figure 4) in the transmitter, and a thalofide cell with a valve amplifier in the receiver. A clear night range of 8 km was claimed with 24" (600 mm) reflectors at each end.
1919 - 1935
Improvements were made to optical modulators and detectors in the 1920s, by motion picture engineers developing the optical sound tracks on movie films. Photophones became a technical novelty for display at industrial exhibitions and science fairs, with the occasional construction project in the popular radio magazines.
Military Photophones 1939- 1950
There was a renewed military interest in optical telephony in the 1930s, and the German Army introduced the Zeiss Lichtsprecher infra-red photophones in 1935. The light source was a tungsten filament lamp with an infra-red transmitting filter, which was modulated by a vibrating mirror (or prism in the Li80). The receiver used a lead sulphide detector with an infra-red filter, and a valve amplifier. They were virtually unaffected by daylight, with a clear weather range of 3 km for the Li 50/60, to nearly 14 km for the Li 250/130.
The Japanese Army visible light photophone incorporated a vibrating mirror modulator and a caesium photocell detector, with an operating range of about 1 km in daylight and 2.5 km at night. An Italian Army photophone used a current modulated filament lamp as the light source, but few details appear to have been published outside of the military reports.
Both the German and American Navies used high pressure vapour lamps as modulated infra-red sources for navigation, identification and short range communication. The Germans employed mercury arc lamps of 500 to 2000 W, while the Americans developed the caesium arc lamp. Some military laboratories continued the development of high pressure arc lamps for optical communication until the 1950s.
Didier"
https://air-radiorama.blogspot.com/2016/11/cassettina-aggiuntiva-geloso-per.html
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