wires. The application of repeaters to such a group of four wires in 

 cable (spoken of as a phantomed group or a quad) is shown schemati- 

 cally in Fig. 13. In this figure, the boxes denoted "Telephone Re- 

 peater" I'epresent the complete repeater circuit shown in Fig. 10. 

 It is necessary to separate the telephone currents of the phantom cir- 

 cuit from those of the two side circuits by applying to the phantom 

 group highly balanced repeating coils, just as is done at the terminals 

 of the circuit, and providing separate repeaters for each of the two side 

 circuits and the phantom as is illustrated in the figure. The figure also 

 shows a typical telegraph circuit arrangement — a metallic telegraph 

 circuit on each pair, separated from the telephone channel by composite 

 sets as previously described, and passing through telegraph repeaters 

 at the telephone repeater point. 



COMPOSITE 

 WEST SETS 



COMPOSITE 



SETS EAST 



Fig. 13 — Showing schematically the association of the four wires of a phantom group 

 and composite sets, repeating coils, telephone repeaters and telegraph repeaters. 



Phantom operation through cables, without crosstalk between the 

 phantom and its side circuits and between the circuits in different 

 quads of the cable, has involved a long train of developments in 

 decreasing the tolerances of manufacture and increasing the uniformity 

 in the characteristics of the cable. The cables must meet a double 

 requirement, namely, freedom from crosstalk, which is made more 

 difiicult with the application of repeaters, and uniformity of charac- 

 teristics to provide for suitable repeater operation. This double 

 requirement has been met by niceties in design, construction, and 



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