382 BELL SYSTEM TECHNICAL JOURNAL 



be spanned economically with open wire, cable is used. In the past, 

 the circuits in such cables were frequently loaded to reduce their 

 attenuation and to match the impedance of the open-wire circuits in 

 order to avoid reflection effects and degradation of voice-frequency 

 repeater balance. To load paper-insulated cable pairs for frequencies 

 up to 150 kilocycles would require exceedingly short loading spacing, 

 of the order of 200 feet, which would be expensive and in many cases 

 impractical with existing manhole locations. An alternative, the use 

 of a transformer to match the open wire and cable impedances, was 

 rejected as it was found impractical to design a transformer which 

 would be adequate over the entire frequency range. 



To overcome these difficulties, a new low-capacitance type of cable 

 was developed which could be loaded to match the open-wire impedance 

 with coil spacings about the same as those previously used. Loading 

 coils of different sizes were developed to provide for loading to the 

 different impedances of the open-wire circuits. 



The new cable employs 16-gauge conductors in a spiral-four arrange- 

 ment, supported by hard rubber disc spacers about 0.6 inch in diameter. 

 These are surrounded by copper and iron tapes for shielding and 

 strengthening purposes. The units so formed may be assembled 

 either in single units in a lead sheath as for lead-in purposes, or in 

 multiple units, up to a maximum of seven for full-sized cable, within 

 the same lead sheath. For duct runs or submarine cables, the multiple 

 assembly is usually employed, and, in the latter case, with outside 

 armoring and jute protection. If the submarine span is more than 

 about 600 feet, intermediate submarine loading is employed. 



As an alternative, it sometimes happens that where a long inter- 

 mediate cable is involved, an auxiliary type J repeater station can be 

 placed conveniently at one end of this cable. In this case, the filter 

 hut described in the discussion of toll entrance arrangements in the next 

 section may be used at the end of the cable opposite the repeater 

 station and the cable treated as a toll entrance cable for the auxiliary 

 office, A further alternative is to provide filter huts at the two ends 

 of a non-loaded intermediate cable. However, if the cable is short, the 

 new disc-insulated cable with loading is to be preferred. 



Previous practice at the ends of open-wire lines has been to use 

 paired bridle wire with weather-proof insulation and usually of smaller 

 gauge than the line wire to connect the open-wire pairs to cable 

 terminals mounted on the pole. Other pairs of bridle wire were 

 connected between the open wires and protectors. Because of the 

 much more severe reflection requirements at the higher frequencies of 

 the type J system, these arrangements were no longer satisfactory. The 



