PHASE DISTORTION IN TELEPHONE APPARATUS 



505 



circuit ^® for regular long distance telephone message service designed 

 to transmit with negligible distortion frequencies between 200 and 

 3000 cycles. 



Fig. 11 shows the insertion phase characteristic of a 50 mile length 

 of the cable for program transmission (exclusive of repeater). The 

 broken line is drawn to bring out more clearly the curvature in the 



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Fig. 12 — Schematic of the jjhase corrector for a 50 mile length of cable for program 



transmission. 



phase characteristic. Fig. 12 shows a schematic of the phase corrector 

 used to correct for a 50 mile length of this cable. The insertion phase 

 characteristic of this corrector as well as that of both the cable and 

 corrector combined are also shown in Fig. 11. It will be noticed that a 



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in 

 o 



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 UJ 



in 



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0.001 



1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000 



FREQUENCY IN CYCLES PER SECOND 



Fig. 13 — Insertion delay characteristics corresponding to phase characteristics of 



Fig. 11. 



single phase corrector consists of eleven sections, seven of one kind, 

 three of another, and one of a third. Each section contains one two- 

 terminal inductance coil and one three-terminal coil with mutual 

 between the two windings and also two condensers. Fig. 13 gives 



'^ This cable consists of No. 19 gauge copper wire with 44 millihenry loading coils 

 spaced every 6000 feet. 



