The Transmission of Motion Pictures over a Coaxial Cable

The transmission of television signals over wire lines a number of years ago used signals corresponding to images of coarse detail, and required frequency bands accommodated by existing types of circuits. The television images now considered necessary correspond to frequency bands of greatly increased width, and require special wire networks and transmission means. — The coaxial conductor recently in operation for experimental purposes between New York and Philadelphia can transmit a band of frequencies of approximately 1000 kc. While designed primarily for multiple telephone channels, it offered the possibility of transmitting a single wide band as required for television. — The experiment consisted in providing television-type terminal apparatus for producing signals falling within the available band, and of developing and utilizing methods of transmission that would make most complete use of the frequency band available. For convenience in experimental work, the signals were generated from motion picture film. The film was scanned mechanically by means of a lens disk containing 240 lenses. The film was moved continuously 24 frames per second, and its motion, together with the motion of the lenses in the disk, swept each frame of the film in 240 juxtaposed lines. Light passing through the film was received on a photosensitive surface; the resulting photoelectric current was amplified and by means of modulating and demodulating apparatus transmitted as a single side-band between approximately 150 and 950 kc. At the receiving end the single side-band signal was restored as a signal from zero to 800 kc. — For reception, special cathode-ray tubes were used in which particular attention was paid to the definition of the spot and the linearity of response. Synchronism between the two ends was obtained by sending a single frequency over a separate channel and using it to operate sweep circuits at the receiving end. The use of mechanical scanning and the high-definition receiving tubes resulted in pictures of very satisfactory quality within the limitations set by the frequency band.

Print ISSN

0097-5834

Published

1938-09

Content type

Original Research

DOI

10.5594/J08482