WIDE-BAND TRANSMISSION OVER COAXIAL LINES 655 



each circuit, and with sufificient shielding balance may be entirely 

 dispensed with. 



A form of circuit which differs from existing types in that it is un- 

 balanced (one of the conductors being grounded), is the coaxial or 

 concentric circuit. This consists essentially of an outer conducting 

 tube which envelops a centrally-disposed conductor. The high- 

 frequency transmission circuit is formed between the inner surface of 

 the outer conductor and the outer surface of the inner conductor. 

 Unduly large losses at the higher frequencies are prevented by the 

 nature of the construction, the inner conductor being so supported 

 within the tube that the intervening dielectric is largely gaseous, the 

 separation between the conductors being substantial, and the outer 

 conductor presenting a relatively large surface. By virtue of skin 

 effect, the outer tube serves both as a conductor and a shield, the 

 desired currents concentrating on its inner surface and the undesired 

 interfering currents on the outer surface. Thus, the same skin effect 

 which increases the losses within the conductors provides the shield- 

 ing which protects the transmission path from outside influences, this 

 protection being more effective the higher the frequency. 



The system which this paper outlines has been based primarily upon 

 the use of the coaxial line. The repeater and terminal apparatus 

 described, however, are generally applicable to any type of line, either 

 balanced or unbalanced, which is capable of transmitting the frequency 

 range desired. 



The Coaxial System 



A general picture of the type of wide band transmission system which 

 is to be discussed is briefly as follows: A coaxial line about 1/2 inch in 

 outside diameter is used to transmit a frequency band of about 

 1,000,000 cycles, with repeaters capable of handling the entire band 

 placed at intervals of about 10 miles. Terminal apparatus may be 

 provided which will enable this band either to be subdivided into more 

 than 200 telephone circuits or to be used en bloc for television. 



Such a wide-band system is illustrated in Fig. 1. It is shown to 

 comprise several portions, namely, the line sections, the repeaters, and 

 the terminal apparatus, the latter being indicated in this case as for 

 multiplex telephony. Two-way operation is secured by using two 

 lines, one for either direction. It would be possible, however, to 

 divide the frequency band and use dift'erent parts for transmission in 

 opposite directions. 



A form of flexible line which has been found convenient in the ex- 

 perimental work is illustrated in Fig. 2 and will be described more fully 



