Universal Film Transmitter

By using the Scophony optical principles it was possible to construct a successful film transmitter with all the advantages of optical scanning which result in a high light efficiency with full definition whilst using small and rigid receiving masses.

The mechanical construction of the apparatus is such that Its useful life is long approximately equal to the standard film projector, readjustments, and replacements are not necessary.

The apparatus is simple to handle and maintain in proper order, no greater skill being required than for the correct handling of a standard film projector. The source of Illumination can be an arc lamp or a special high-pressure mercury lamp.

Owing to the method of scanning used, the wear and tear on the film is very little, under no circumstances can the film ignite, even if is stationary at the gate.

The accuracy that can be obtained using the Scophony optical-mechanical principles makes the transmitter suitable for use both for Scophony optical as well as cathode ray receivers.

OPTICAL SYSTEM

An image of an illuminated aperture is formed on the film by a sphero-cylindrical optical system via two revolving polygons mounted at right angles to each other, one revolving slowly forming the vertical scan in conjunction with the film moving continuously in the opposite direction. This moving spot is picked up by sphero-cylindrical lens system and reproduced as a stationary image on the cathode of an electron multiplier photocell the variations of intensity of the spot as it traverses the film giving rise to variations in the output of the cell, so transforming every small section of the picture into an electrical impulse.

Sequential scanning is obtained by choosing a line frequency which is an integral multiple of the scanning frequency. If the line frequency Is an odd multiple or half the frame scanning frequency the resultant picture is an interlaced one The line frequency Is governed by the synchronising generator. The frame frequency can be 50 when a slow-speed scanner is running at 25 when stationary. Assuming a 50-cycle supply frequency, the transmitter can be used for interlaced or sequential scanning with 50 0r 25 frames per second.

HIGH-SPEED SCANNER

The high-speed scanner motor Is driven by a specially designed valve amplifier from the line frequency supplied in sinusoidal form from the Synchronising Generator. The motor consists essentially of a phonic wheel tuned to resonate at the line frequency. This Is connected directly in the anode circuit of a pair of 60 W valves in parallel operation in the Class C configuration. Direct current is also passed through the windings to the phonic wheel to prevent reversal of the magnetic flux. A subsidiary motor is mounted on the spindle to run the motor Into synchronism.

PERFORMANCE

The Spot definition is such that an 800-line picture could easily be obtained by reducing the aperture and increasing the scanner speed.

The focus of the spot is maintained up to the four edges of the gate and the illumination is uniform. In the model designed for the B.B.C. London Television standard, a film containing vertical lines with a spacing corresponding to 600 elements can be resolved perfectly. The quantity of light incident on the photocell is approximately 0.0005 lumens. The photocell Is of a multiplier type yielding approximately 0.01 volts of picture current for the amplifier. The amplifier Is or conventional design with a flat frequency response from 0 to 2.5 Mc/s  but can be made to suit special requirements.

Here you find 4 models, 4 with images and 0 with schematics for wireless sets etc. In French: TSF for Télégraphie sans fil.
All listed radios etc. from Scophony Ltd.; London