INDUCTIVE LOADING FOR TELEPHONE FACILITIES 733 



84 phantom loading units of the P-type, and up to 108 loading units of the 

 PB-type. These very large loading complements had an interesting economic 

 significance. At the time they became available the demand for additional 

 toll cable facilities was increasing by leaps and bounds, and it was not un- 

 common for standard-size and over-size cables to be fully loaded at the time 

 of the installation of the cables. In this connection, full loading for a 50% 

 over-size, quadded, composite 19 and 16 ga. cable could be provided with 

 two of the maximum-size potting complements of phantom loading units. 

 This contrasts with fairly common experience in early installations of full- 

 size cables, where four, five or six cases were used to provide complete 

 loading. 



The further size-reductions in toll cable loading coils that were achieved 

 with the standardization of the M-type phantom loading units and later 

 with the MF-type units occurred during a period of greatly reduced demand 

 for toll cable loading, influenced by the exploitation of carrier systems on 

 conductors from which loading was removed and on new non-loaded cables. 

 The maximum potting complements were accordingly held to 80-unit and 

 48-unit sizes for the M-type and MF-type loading units, respectively. 



Assembly Methods and Stub Cables 



General: From the beginning of commercial manufacture, multi-coil com- 

 plements of cable loading were coaxially assembled on spindles which were 

 held infixed positions in the cases. Preceding this operation, the accumulated 

 moisture was expelled from the coil windings and the coils were dipped in a 

 moisture-resisting compound. In the multi-spindle cases, the different 

 spindle-assemblies were mounted in separate compartments of the cases, 

 with the compartment partitions providing shielding to control crosstalk 

 among the spindle-assemblies. On the individual spindle-assemblies, cross- 

 talk was controlled by using steel washers between adjacent coils and mount- 

 ing the coils so that their small, external, magnetic fields would be substan- 

 tially non-interfering. The winding ends of the coils were connected to textile- 

 insulated twisted-pair leads in spindle unit-cables, treated with wax for 

 moisture protection. 



After the spindle-assemblies had been fixed in position in the case compart- 

 ments, the spindle unit-cables were formed by hand into a stub cable core 

 over which a somewhat loose-fitting lead sheath was drawn. A color code 

 on the conductor insulation provided identification for "wire" and "mate" 

 conductors, and for IN and OUT coil terminals. The final assembly 

 operations included filling the case compartments with a viscous rosin-oil 

 compound, and a top layer of asphalt compound; and the stub cable sheath 

 was soldered to a nipple in the case cover. At various stages in the assembly 



