170 



BELL SYSTEM TECIIMCAL JOIRXAL 



\'\'g. 5. The carrier systems are much less iiiHuenced by noise iiuluc- 

 lion from power circuits because they occupy a range of frequencies 

 (5000 to 30,000 cycles) in which the harmonic power voltages or cur- 

 rents ordinarily are extremely small. Furthermore, in order to obtain 

 economies inherent in the use of large numbers of carrier systems on the 

 same telephone pole line it has been necessary to design systems of 



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LEGEND 



FACILITY 



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VOICE FREQUENCY-PHYSICAL 



VOICE FREQUENCY-PHANTOM 



CARRIER TELEPHONE 



D-C TELEGRAPH 



CARRIER TELEGRAPH (10 CHANNELS) 

 TOTAL TELEPHONE 

 TOTAL TELEGRAPH 



TOTAL CIRCUITS 



20 

 2 

 48 

 40 

 40 



70 

 80 



Fig. 7 — Pole line configuration. 

 Xon-piiantonied construction — 8-inch spacing between wires of non-pole pairs. 



transpositions of much increased effectiveness and even to change the 

 configuration of the wires in order to greatly reduce the inductive effects 

 between the telephone circuits. These changes also result in reduced 

 susceptiveness to outside inductive influences. The type of construc- 

 tion now recommended for new aerial wire lines in cases where the 

 extensive use of carrier is anticipated is shown in Fig. 7. The two 

 wires of each pair, except pole pairs, are spaced 8 in. apart compared 



