344 BELL SYSTEM TECHNICAL JOURNAL 



given to the possible coupling between type J systems by interaction 

 paths involving other conductors adjacent to the toll line. 



Before definite selection of repeater station locations may be made, 

 it is necessary that each repeater section be checked in detail and in 

 this check the entrance cable arrangement may be controlling. The 

 newly developed spacer insulated spiral-four cable, either loaded or 

 non-loaded, or non-loaded pairs of the conventional paper insulated 

 cable may be used between the open wire and equipment. Generally 

 the existing voice and C carrier circuits use loaded entrance cable pairs 

 and in most cases a change to non-loaded facilities would require 

 extensive rearrangements in these circuits. In order to use non-loaded 

 pairs for the J carrier and leave the C carrier and voice on loaded 

 facilities, filters are placed at the terminal pole to separate the J 

 carrier frequencies from the C and voice frequencies at that point. A 

 limitation on the use of existing cable is that suitable pairs must be 

 selected by crosstalk measurements and balanced at 140 kilocycles to 

 meet the requirements of the system. The paper insulated conductors 

 have the largest attenuation of any of these facilities, and the loaded 

 spiral-four the least. The various entrance arrangements from the 

 open wire to the office equipment are described in more detail else- 

 where.^ The choice of the facility used in any particular case will 

 depend upon the resultant overall economy. 



The large number of non-loaded pairs in the existing 1 .6 mile entrance 

 cable at San Antonio indicated that sufficient pairs could be selected 

 which would be satisfactory from the crosstalk standpoint for J carrier 

 operation. Six pairs were subsequently selected and balanced. 



At Austin a single toll entrance cable, one mile in length, with two 

 complements, terminates the line from the two directions. Although 

 the two complements are separated by a layer shield, this cable is not 

 suitable from a crosstalk standpoint for operation of the J carrier in 

 and out of the office; therefore, at least one additional cable is required 

 from the central office to the toll line. For this purpose a new non- 

 loaded spiral-four entrance cable was indicated for the type J system 

 with the type C and voice circuits continuing to use the existing cable. 

 The separation of the type J circuits from the non-J circuits on the 

 same pairs is accomplished by filters which are located in a small 

 building at the junction of the toll line and the entrance cables. The 

 use of a single entrance cable for the non-J wire in both directions on 

 the telephone line indicated that it might be necessary in the future to 

 use crosstalk suppression filters at this point. Accordingly, the filter 

 hut was made large enough to include future crosstalk suppression 



^ Loc. cit. 



