TRANSMISSION OF AUDIO SIGNALS BY INFRARED LIGHT CARRIER

A recently developed technique for the wireless transmission of audio signals makes use of invisible modulated infrared radiation. Infrared emitting gallium-arsenide diodes are used as radiators of the modulated signal. As a receiver, a photosensitive diode is used. Its plastic convex lens concentrates the incident infrared radiation on the rather small photosensitive diode surface. To eliminate the action of visible light, a so-called black filter - transparent only to infrared - is interposed. Amplitude modulation of the infrared emitter is possible, but cannot be used because other ambient light sources could create interference. To overcome this obstacle, frequency modulation of an amplitude-modulated standardized carrier frequency is used. The distribution of infrared radiators in a room is touched upon, and interference levels from ambient light sources are indicated. The components of a monophonic infrared audio transmission system are discussed.