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Vision by radio, radio photographs, radio photograms cover

Vision by radio, radio photographs, radio photograms

Chapter 48: Prismatic Disc Machines
By C. Francis Jenkins
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About This Book

This work discusses the early innovations in transmitting images via radio, highlighting the patent by Nipkow in 1884, which proposed a system using a selenium cell and a rotating perforated disc to capture scenes. It also examines the contributions of Shelford Bidwell, who earlier described a method for telegraphic transmission of images. The text details the technological advancements in the field, including the use of polarizing light valves for image reception, and provides insight into the author's background as an inventor and pioneer in motion picture technology and radio photography.

Prismatic Disc Machines

These machines are principally used in radio transmission of photographs; employ four overlapping prismatic discs or “rings” in both the sending and the receiving machines. Either a transparent or an opaque picture is used in the sending instrument; and in the receiving camera a filament lamp, modulated by the incoming radio signals, recorded on a photographic negative plate.

In the sending machine (first illustration) the picture is projected with a magic lantern (1) through four overlapping prismatic rings, (2) two of which in rotation sweep the picture vertically across the light sensitive cell, at the same time the image is moved laterally by the other pair of prisms. The different light values of the picture are changed into electric values in light cell 4, and broadcast. A rotating perforated disc, (3) interposed between the lens and light cell, produces a pulsating direct current which can immediately be amplified through the usual radio transformers, on its way to the broadcasting set.

In the radio camera (second illustration) a photographic negative (1) is used and a pencil of light from lamp 2. The rotating plates (3) draw the lines and the radio signals vary the light intensities of the lamp to give gradations of exposure on the negative plate. (See next page.)