TYFIO-O CAHIIIKH SYSTEM 089 



loaded carrier pairs, or by the use of autotrausformers. In addition, 

 transposition schemes are needed to reduce the crosstalk coupling be- 

 tween open-wire pairs to tolerable amounts, and longitudinal and metallic 

 filtering is necessary at repeater points to control interaction crosstalk, 

 'i'he C and J carriers have been designed essentially for long-haul use, 

 and when the line transposition costs are added, these systems are likely 

 to be more expensi\-e than adding wire for providing relief for the shorter 

 circuits, which are recjuired in increasing number as the length decreases. 



In contrast to the heavy back-bone toll lead carrying both long and 

 short haul circuits is the one or two arm line which may be a secondary 

 route, or a line which terminates in a small town. The demands along 

 this line are for short-haul toll service, trunks between tributary offices 

 and their toll centers, and for exchange service. Because growth has 

 been relatively slow, carrier has been employed only to a limited extent. 

 Single-channel D or H systems ma}^ be found on these lines, or an adapta- 

 tion of the M system for toll service, and possibly other miscellaneous 

 systems. Only minor rearrangements of the line and entrance cables 

 has been necessary because of the small percentage of circuits equipped 

 with carrier facilities. 



A typical need for expansion on this type of line occurs when a manual 

 tiibutary office is cut over to dial operation, and the operators are moved 

 to the toll center. Additional circuits are immediately needed from the 

 toll center to the tributary office because of certain factors introduced 

 when the operators are moved some miles away. Experience has shown 

 the desirability of being able to reach an operator a fairly large percent- 

 age of the time because of special services, such as directory information, 

 reports on the a^'ailability of toll circuits, service complaints, etc. This 

 requires a substantial increase in the number of circuits to the tributary 

 office in such instances. Development of this line, then, proceeds by 

 adding single-channel carrier systems, until a point is reached where it 

 is necessary to string more copper wire, which is costly and maj^ be in 

 short supply, or to add multi-channel carrier systems. 



The situation in Iowa is typical of many areas in the Southern and 

 Western parts of the country. Fig. 1 shows the principal open-wire and 

 cable routes in Iowa used by the Bell System for toll business. The 

 type-K transcontinental cable crosses the state, passing through Daven- 

 port and Des Moines on its way to Omaha. Small branch cables serve 

 Muscatine, Cedar Rapids and Atlantic, where the circuits are extended 

 by open-wire facilities. In general, the transcontinental TD-2 radio relay 

 system follows the K carrier route. A coaxial cable route extends north 

 from Des Moines to Minneapohs, connecting at Iowa Falls with short 



