FUNDAMENTAL PLANS FOR TOLL TELEPHONE PLANT 843 



Fig. 9 — Coaxial Cable. Cross section of cable containing four pairs of coaxials. 

 Each pair can accommodate one two-way coaxial carrier system. 



other conditions affecting service continuity and the transmission re- 

 quirements of the circuits to be provided. 



Voice frequency facihties equipped with repeaters as required are used 

 on both open wire lines and cables. At voice frequencies it is customary 

 to derive three trunks known as a phantom group, from two pairs of 

 open wires or from one "quad" (two pairs) of loaded cable conductors. 

 In general the use of voice frequency facilities is now limited to shorter 

 circuits. 



Considerations of economy and service improvement led to the intro- 

 duction of carrier operation into all types of toll plant as rapidly as the 

 state of the art permitted. This directly affects the toll switching plan 

 from the standpoint of routing and location of switching centers. 



At present, carrier systems use four broad categories of facilities : open 

 wire, conventional paired or quadded cables, coaxial cable and radio. 



Several types of open wire carrier systems permitting from one to 

 fifteen telephone channels above the frequency band of the voice channel 

 are now in use. In general these systems are used when> trunk cross-sec- 

 tions are relatively small and where the terrain and weather conditions 

 make open wire lines economical. 



Cable carrier systems at present permit the operation of up to twelve 

 telephone channels on two pairs of cable conductors. These conductors 

 may be in one cable or divided between two separate cables, depending 



