The Production and Utilization of Television Signals^ 



By FRANK GRAY, J. W. HORTON and R. C. MATHES 



Synopsis: The design of a television system, once the fundamental 

 principles are understood, involves a detailed consideration of the methods 

 by which the several important functions are to be performed. 



(1) In the present system the initial signal wave is obtained by sweeping 

 a spot of light over the subject in parallel lines completely scanning it 

 once every 18th of a second. The light reflected is collected by large 

 photoelectric cells which control the transmitted current. At the receiving 

 station the picture current controls the brightness of a neon lamp from 

 which the received image is built up by means of a small aperture moving in 

 synchronism with the spot of light at the transmitting station. For 

 presentation to a large audience television images may be produced by a neon 

 lamp in the form of a grid having a large number of separate electrodes. 

 A high frequency excitation controlled by the picture current is distributed 

 to the successive electrodes in synchronism with the spot of light at the 

 transmitting station. 



(2) Space and time variations in the reflecting power of the subject are 

 translated into time variations in signal strength. For design purposes 

 these time variations are represented by component frequencies, a minimum 

 band of which must be properly transmitted to insure an adequate repro- 

 duction of the image. Within this band there must be maintained a 

 certain degree of uniformity in the efficiency of transmission of the separate 

 components. Also, their phases must not be permitted to shift unduly in 

 relation to each other. 



(3) The design of the terminal amplifiers is based on the quantitatively 

 determined characteristics of the photoelectric cells and of the neon lamps 

 as well as on the limits imposed by the transmission study and by the 

 characteristics of available transmission media, whether telephone line or 

 radio system. The circuits employed at the transmitting station furnish 

 an amplification such that the power delivered to the transmission medium 

 is IQi^ times the power received from the photoelectric cells. 



Section I. Apparatus for the Analysis and Synthesis 

 OF THE Image 



THE introductory paper to this series of articles on television 

 explained principles along which any television system must 

 operate to transmit an image over a single pair of wires or other 

 channel of communication. As the first step in such a transmission, 

 the space variations in brightness from point to point in the view 

 must be translated into time variations in an electrical current that 

 can be sent over the channel of communication. This translation 

 may be accomplished by a scanning process that operates on the view 

 to produce the same effect as if the view were cut up into a single 

 long strip and passed rapidly in front of a light-sensitive cell to generate 

 an electrical current varying with the brightness along the strip. To 

 eliminate flicker in the reconstructed image and also to follow moving 



1 Presented at the Summer Convention of the A. I. E. E., Detroit, Mich., June 

 20-24, 1927. 



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