554 BELL SYSTEM TECHNICAL JOURNAL 



quired in the paired cable placed for carrier operation between Greens- 

 boro and Charlotte. 



Far-end crosstalk was still further reduced by means of balancing 

 coils installed at the end of each repeater section connected to the 

 repeater inputs.^' ^ After the splicing operations just discussed were 

 completed and the balancing coils were installed and connected to the 

 carrier pairs, the coupling between each pair and each other pair of 

 the carrier complement was reduced to the lowest value practicable by 

 adjustment of these coils. This was accomplished by sending a dis- 

 turbing testing tone on one pair, receiving on each other pair in turn, 

 and adjusting the coil which couples each combination of two pairs 

 until a minimum amount of the testing tone was measured on the 

 disturbed pair. Figure 3 shows these adjustments in progress while 

 Table 3 shows a summary of the final crosstalk measurements made 

 after the adjustments. About 19,000 balancing coils have been in- 

 stalled on the carrier routes equipped to date. 



At two points on the New York-Charlotte route, retardation coils 

 which are described later were used to increase the attenuation in 

 potential crosstalk paths. At Petersburg, Va., and Burlington, N. C, 

 60 and 4 voice quads, respectively, connected direct from one carrier 

 cable to the other. These quads, through secondary induction, were 

 likely to serve as crosstalk paths at carrier frequencies between the 

 two cables. Retardation coils were installed in each quad to limit 

 crosstalk currents. Two other situations, where quads connected be- 

 tween the carrier cables, were eliminated by cable rearrangements. 



Lateral Cables 

 At each carrier repeater station four lateral cables were installed 

 to bring the carrier pairs into the repeater building. One of these 

 was required for each direction of transmission for each cable; that is, 

 two input cables and two output cables were required. As a result 

 of the transposition of directions of transmission at each repeater point, 

 the two input cables connect to one toll cable and the two output 

 cables to the other. Figure 4 shows these cables installed at an aerial 

 cable repeater point. All lateral cables were installed for the prob- 

 able ultimate capacity for carrier systems of the cables being developed ; 

 that is, 100 systems on the Detroit-South Bend route, 100 systems 

 north and 60 systems south of Richmond, Va., on the New York- 

 Charlotte route. 



The Location of Carrier Repeater Station Sites 

 The next important step in the development of a route for type K 

 carrier operation is the selection of points at which intermediate 



