The Type-0 Carrier System 



BY PAUL G. EDWARDS AND L. R. MONTFORT 



(Manuscript received June 11, 1952) 



INTRODUCTION 



While the sight of an open-wire toll line is a rarity in many parts of 

 the East, considerable use is made of open- wire facilities in other sections 

 of the country to provide toll and exchange service. At the present 

 time there are about 170,000-route-miles of open-wire in the Bell System 

 which carry some 1,400,000 pair-miles of wire used for toll service. It is 

 estimated that about 60 per cent of this pair-mileage is used for carrier, 

 although only about 10 per cent carries the full fifteen carrier channels, 

 which is possible by employing type-C and type- J carrier systems. It 

 is obvious that some of the remaining line pairs are available for addi- 

 tional carrier growth, provided, of course, the demand for additional 

 circuits exists, and there are carrier systems which can meet these de- 

 mands economically. Type O is a multi-channel, open-wire carrier sys- 

 tem which has been designed to pro\'ide, economically, additional circuits 

 in the range from a minimum of about 15 up to a maximum of 150 miles, 

 or more. The type-0 system is the open-wire counterpart of the type N 

 short-haul cable system. 



Present open-wire toll lines vary from a single-arm line, with one or 

 two pairs of wires, up to lines with five or six arms carrying thirty pairs. 

 These lines may carry long-haul toll circuits up to about 1000 miles in 

 length, short-haul toll circuits up to 150 miles, as well as tributary trunks 

 and exchange circuits. Growth in the past of toll and tributary circuits 

 on these lines has been provided by the addition of single-channel D or 

 H systems, three-channel C systems, twelve-channel J systems or by 

 other similar carrier systems. 



The full development of a line for open-wire carrier has, in the past, 

 required expensive line rearrangements. For instance, most lines reach 

 terminal and repeater offices over entrance cables which may be several 

 miles in length. Impedance matching at the junction of the open-wire 

 and cable is reciuired, and is provided by loading the cable at both voice 

 and carrier frequencies, by employing junction line filters using non- 



