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.)
[Illustration: [Photographs]]
[Illustration: [Photographs]]