660 BELL SYSTEM TECHNICAL JOURNAL 



Fig. 4 — Phoenixville installation showing conductors entering test house. 



a practical coaxial circuit, with its inevitable mechanical departures 

 from the ideal, showed transmission properties substantially in agree- 

 ment with the theoretical predictions. 



Small Flexible Structures 



Development work on wide-band amplifiers, as discussed later, 

 indicated the practicability of employing repeaters at fairly close in- 

 tervals. This pointed toward the desirability of using sizes of coaxial 

 circuit somewhat smaller than the smaller of those used in the pre- 

 liminary experiments, and having correspondingly greater attenua- 

 tion. Furthermore, it was desired to secure flexible structures which 

 could be handled on reels after the fashion of ordinary cable. Ac- 

 cordingly, several types of flexible construction, ranging in outer 

 diameter from about .3 inch to .6 inch, have been experimented with. 

 Structures were desired which would be mechanically and electrically 

 satisfactory, and which could be manufactured economically, prefer- 

 ably with a continuous process of fabrication. 



One type of small flexible structure which has been developed is 

 shown in Fig. 2. The outer conductor is formed of overlapping copper 

 strips held in place with a binding of iron or brass tape. The insula- 

 tion consists of a cotton string wound spirally around the inner con- 

 ductor, which is a solid copper wire. This structure has been made in 

 several sizes of the order of 1 /2 inch diameter or less. When it is to be 

 used as an individual cable, the outer conductor is surrounded by a 



