442 



BELL SYSTEM TECHNICAL JOURNAL 



equipment have been developed which enable a wide band to be split 

 up so as to obtain hundreds of telephone channels. 



For television transmission a quite different problem existed — 

 namely, can very wide band systems be used for the long distance 

 transmission of these complicated signals? In planning tests to be 

 significant of the operation of the cable system for such signals, it 

 was important to obtain as nearly as possible an ideal television 

 signal and as nearly as possible an ideal television receiver. In this 



200 300 400 500 600 700 800 

 FREQUENCY IN KILOCYCLES PER SECOND 



900 lOOOj 1100 

 1024 



Fig. 4 — Attenuation of the New York-Philadelphia type of cable under widely 

 different temperature conditions. 



way it was hoped that any defects in the cable transmission itself 

 could be discovered. 



Signal Generator 



Although television implies the transmission of an actual scene it 

 is much more satisfactory for engineering studies to transmit a motion 

 picture, since exactly the same picture can then be transmitted over 

 and over again as the circuit elements are changed or adjusted. 

 Moreover, it was decided to use mechanical scanning to obtain the 

 most nearly perfect signal possible, and with this form of scanning a 

 film can be much more brightly illuminated than an actual scene and 

 hence is much easier to use. Because of these factors a motion picture 

 film was chosen as the material for the recent experiments. 



The scanning disk used in these tests was developed under the 

 direction of Dr. H. E. Ives at the Bell Telephone Laboratories. It 

 consists of a six-foot disk with a circle of 240 lenses near its outer edge. 



