TELEPHONE SYSTEM OF THE UNITED STATES 49 



the long haul system in common use are shown in Fig. 39 and typical 

 transmission characteristics for a carrier channel are shown in Fig. 40. 



The long haul carrier systems give very satisfactory service and 

 form a part of some of the longest circuits in the country. For ex- 

 ample, the direct circuits between New York and Los Angeles, Cali- 

 fornia, 5,100 kilometers in length, are made up of cable circuits from 

 New York to Pittsburgh connected permanently to a Pittsburgh- 

 St. Louis carrier system, and a St. Louis-Los Angeles carrier system. 

 These two carrier systems connected together total 4,550 kilometers 

 in length with 13 intermediate repeaters. Similarly the New York- 

 San Francisco circuits are in cable from New York to Chicago and 

 there permanently connected to the Chicago-Sacramento carrier sys- 

 tem 3,800 kilometers long with 10 intermediate repeaters. 



The short haul carrier system is similar in its general character- 

 istics but is simplified and provides a single carrier circuit for each 

 pair of wires. In the case of both systems, single side-band carrier 

 suppression circuits are used. 



In Fig. 37 showing the standard arrangement of open wires on pole 

 lines are indicated the carrier telephone channels and also the carrier 

 telegraph channels which can be superposed on these circuits without 

 mutual interference, after the installation of suitable transpositions 

 which have been designed to neutralize the mutual induction between 

 the circuits. It is noted that with this arrangement it is possible to 

 obtain from 40 wires 54 telephone circuits. Also 80 telegraph circuits 

 are obtained, used for special contract service as described later in 

 this paper. 



On a number of the open wire toll routes carrying very long circuits, 

 it has become important to provide arrangements for using a larger 

 number of long haul carrier telephone systems, thus obtaining a 

 larger number of circuits. Whereas a number of arrangements using 

 the standard spacing of wires have been tried out, it is found ex- 

 tremely difficult to continue the use of phantoms and to so transpose 

 the wires as to provide adequate freedom of interference between 

 the higher frequency carrier channels if these are used on all pairs. 

 The difficulty of doing this is evident in considering that in order to 

 avoid overhearing it is necessary that the power transfer between 

 different circuits should not exceed one part in a million even though 

 they are parallel to each other for long distances. 



In order to make possible the maximum use of long haul carrier 

 systems where desired, trials have been made with the arrangement 

 of wires shown in Fig. 41 and these trials have shown very satisfactory 

 results. With this arrangement the spacing of the two wires of each 



