EVOLUTION OF INDUCTIVE LOADING 1227 



The requirements for and the possibihties of using electroplated loading 

 in the exchange area services were given priority in the theoretical cost 

 studies — largely because of their extensive use of small conductor cables. 

 These studies indicated some attractive possibilities of using light-weight 

 electroplated loading on fine wires (26 and 24-gauge) as substitutes for 

 larger size wires without loading, provided satisfactory solutions could be 

 worked out for the circuit balance and magnetic instability problems. The 

 balance problem arises from the difficulty of securing sufficient uniformity 

 among the loaded conductors used as wire and mate in the individual 

 pairs. This is complicated by the sensitivity of the permalloy continuous 

 loading to magnetization by steady and intermittent superposed signaling 

 currents. On the larger-size exchange cable wires that are not now used 

 extensively without coil loading, the comparative cost estimates were not 

 attractive for the electroplated loading. 



The inflexibility of continuous loading is an adverse general factor, since 

 it is not feasible to decrease or increase the weight of the loading after 

 manufacture, in order to accommodate changes in transmission require- 

 ments made desirable by changes in performance standards or alterations 

 in circuit layouts. Also, there would be inflexibility in conforming to changing 

 requirements in complement sizes of loaded circuits in areas where it is 

 necessary to have loaded and non-loaded circuits within the same cable 

 sheath. 



Theoretically, one of the flexibility limitations of the coiitmuous loading 

 could be reduced by using coil loading in combination with it, in order to 

 extend its transmission range. However, this would reduce the width of the 

 transmission band below that obtainable with the coil loading on a circuit 

 not having continuous loading — the decrease in effective cutoff being a 

 complex function of the ratio of distributed inductance to coil inductance. 

 Combinations of high cutoff, low impedance, coil loading with low in- 

 ductance continuous loading could be designed to have satisfactory band 

 width properties. For a given grade of transmission performance, however, 

 such combinations appear to be inherently more expensive than coil loading 

 or continuous loading by themselves. 



The experimental work on electroplated continuous loading for exchange 

 area cables was carried on somewhat intermittently during the 1930's. At 

 no time did the prospects of securing satisfactory over-all transmission 

 performance, at costs which would encourage competition with coil loading, 

 appear to be sufficient to warrant an all-out sustained attack on the many 

 difficult technical problems involved. Although the development project 

 has not been permanently abandoned, it had to be discontinued in the late 

 1930's on account of the great pressure of more urgent work. 



