582 BELL SYSTEM TECHNICAL JOURNAL 



difficulties of equalization and a minimum practical aperture width 

 is thereby determined. If the distortion is corrected by narrowing 

 the aperture, it is apparent that the apparatus will generate, at but 

 little lower than the correct relative efficiency, frequencies much 

 higher than those thought necessary from the more general con- 

 siderations in Mr. Ives' introductory paper. Decision as to the 

 desirable frequency transmission band for the connecting communi- 

 cation channel would be no different for either method of reducing 

 the distortion due to the aperture. 



Fig. 19 



In summary, then, we may say that experiment and theory show 

 that the lowest frequency essential to satisfactory results is the picture 

 frequency, and the highest frequency required is approximately one 

 half the number of picture elements scanned per second. 



{h) Requirements upon the Signal Wave Set by the Characteristics of 

 Available Transmission Channels. The limitations upon the signal 

 wave set by present available communication channels are: 



1. The magnitude of the signal necessary to override the interference 

 to which such channels are subject. 



2. The frequency range which such channels can transmit. 



The first of these is self-explanatory. It determines the required 

 amplification and load capacity of the transmitting apparatus. In 

 the companion paper on Wire Transmission Systems for Television are 



