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BELL SYSTEM TECHNICAL JOURNAL 



ever, would very greatly increase the space occupied by each program 

 circuit and, therefore, considerably increase the cost. By careful 

 design of the cable and control of methods of splicing, it was found 

 possible to avoid the use of shields. It was not found practicable, 

 however, to make use of the phantom possibilities on the program 

 pairs. 





< 



UJ 



o 



z 



10 



30 50 100 200 500 



CYCLES PER SECOND 



1000 2000 



5000 8000 



Pig. 6 — Attenuation variation of 100 miles of 16-ga. B-22 loaded cable circuit for a 

 temperature change from 55° F. to 109° F. 



The method adopted was as follows: Restrict transmission over a 

 particular 16-gauge program transmission pair, as a general propo- 

 sition, to one direction only. Place the program pairs assigned to 

 transmission in one direction among the 19-gauge quads used for 

 four-wire transmission paths going in the same direction, and the 

 program pairs transmitting in the other direction in the oppositely- 

 bound four-wire group. Fig. 7 shows a cross-section of a typical cable 

 containing six program transmission pairs, three for transmission in 

 each direction. 



Loading Coils 



The 22-milhenry loading coils used on the program transmission 

 circuit have cores of compressed powered permalloy, which is the 

 magnetic material now generally used in the Bell System loading 

 coils.'* Their overall dimensions are the same as those of the loading 

 coils for the ordinary telephone circuits in toll cables. 



■* W. J. Shackelton and I. C. Barber, "Compressed Powdered Permalloy — 

 Manufacture and Magnetic Projjerties," Transactions, A. I. E. E., Vol. 47, No. 2, 

 Al)ril, 1928. 



