162 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1951 



non-phantom type coils on non-quadded exchange type cables for short 

 haul toll facilities, in place of phantom group loading on quadded toll 

 cables. 



(2) Loaded Coarse-Gauge Quadded Toll Cables 



The need for extending the telephone transmission range in storm-proof 

 toll cable, and the unavailability of telephone repeaters suitable for use on 

 loaded circuits, led to a great activity in the development of composite 

 coarse-gauge quadded cables and of entirely new loading coils for these 

 cables, beginning during 1910. The first application (1911) was the new 

 Philadelphia- Washington Section of the Boston- Washington underground 

 cable system. ^«^ 



The new coils for the 10 AWG sides and phantoms were generally similar 

 in design to the open-wire loading coils, even in their use of stranded copper 

 conductors, and were only about 20% smaller. The coils for the 13-gauge 

 conductors were intermediate in size (approx. geometrical mean) between 

 the coils for the 10-gauge conductors, and the coils previously developed 

 for 19 and 16 ga. cables. The size and efficiency relations among these three 

 series of coils were approximately in cost-equilibrium for the grades of 

 cable involved. 



In new underground sections of these coarse-gauge cables a new standard 

 * 'medium-heavy" weight of loading was used, the coil spacing and inductance 

 being midway between those for standard heavy and medium loading and 

 having the same cut-off frequency. The new weight of loading was nearly 

 as good in transmission performance as the heavy loading that was used in 

 old parts of the Boston- Washing ton route and other routes where the 

 loading vaults had been laid out for heavy loading, and was considerably 

 less expensive. In the medium-heavy loaded 10-gauge circuits, the attenua- 

 tion was 0.050 and 0.040 db/mi, respectively for the sides and phantoms; 

 the corresponding values in the 13 ga. circuits were 0.069 and 0.085 db/mi, 

 respectively. The 10 ga. loaded circuits were designed for service between 

 Boston and New York, and between New York and Washington. On an 

 emergency basis, the phantoms could be used for Boston- Washington 

 service. 



It is appropriate at this point to mention the substantial reduction in 

 toll cable dielectric losses that was worked out in the period under discus- 

 sion. The extensive use of loading for the first time on long 10 gauge and 13 

 gauge circuits greatly increased the importance of reducing the amount of 

 moisture that unavoidably accumulated in the conductor insulation during 



(«> A more comprehensive account of this development and associated quadded cable 

 developments is given in References (8) and (9). 



