BELL SYSTEM TECHNICAL JOURNAL 



65 



Fig. 1, of the recently installed Baltimore-Washington coaxial cable. A similar 

 construction was used in a cable completed last summer between Stevens Point, 

 Wisconsin and MinneapoHs, Minnesota. 



These cables each contain 4 coaxial units. Two of these are used to provide a 

 normal broad-band system having one pipe for each direction of transmission. 

 The other two provide spare facilities for each direction. The construction of the 

 coaxial unit itself can be seen from the photograph to use a single longitudinal 

 copper tape for the outer conductor. This is formed into a tube which is held 

 to a fixed diameter by the width of the tape and is prevented from collapsing by 

 the interlocking of its saw-toothed edges. Two layers of steel tape provide the 

 needed support against buckling and also give additional shielding. This construc- 



Fig. 4 — 3-Megacycle amplifier in hand 



tion results in somewhat improved transmission characteristics and lower manu- 

 facturing costs as compared with other types of construction with which we have 

 experimented. Improvements in transmission include lower attenuation, due to a 

 reduction in the effective resistance of the outer conductor, and a smoother imped- 

 ance frequency characteristic due to greater mechanical uniformity. In spite of 

 the thinner outer conductor satisfactory crosstalk characteristics are obtained.* 

 Typical attenuation, crosstalk and impedance characteristics of this cable as a 

 function of frequency are shown in Figs. 2 and 3 for a 5-mile length of installed 

 cable. 



Repeaters 



The band width of a coaxial system, at least over regions which we have studied, 

 is limited only by the amplifiers with which it is provided. The ampHfiers which 



