A Twelve-Channel Carrier Telephone System for 

 Open- Wire Lines 



By E. W. KENDALL and H. A. AFFEL 



A new carrier telephone system is described, together with its 

 application in the long distance telephone plant. By its use, an 

 open-wire pair which already furnishes one voice circuit and three 

 carrier circuits may have twelve more telephone circuits added. 

 Thus in all sixteen telephone circuits are obtained on a single pair. 

 Several such systems may be operated on a pole line. 



Various problems incident to the extension of the frequency 

 range, from about 30 kilocycles, the highest frequency previously 

 used, to above 140 kilocycles, are discussed. Among the more im- 

 portant of these are the control of crosstalk between several systems 

 on a pole line, arrangements for taking care of intermediate and 

 terminal cables, and automatic means for compensating for the 

 effects of weather variations on the transmission over this wide 

 frequency range. 



Introduction 



BARE wires supported on insulators, stretched between poles, 

 make up the pioneer electrical communication circuit, the open- 

 wire line. Although great advances have been made in the applica- 

 tion of cable structures, the open-wire lines still hold their own in some 

 sections of the country. This is because, to offset their physical 

 vulnerability, they have several unique virtues. They are flexible 

 and permit adding one pair of wires at a time. They are also com- 

 paratively economical where conditions favor their use. Furthermore, 

 they are low-attenuation circuits and for this reason were the first 

 to be used for high-frequency carrier systems. 



The first carrier systems, beginning in 1918, added three or four 

 channels to the existing voice circuit on a pair. To keep pace with 

 this development, improvements in transposition systems were de- 

 vised so that many such carrier systems might be operated on the 

 same pole line. Such carrier systems, typified by the three-channel 

 type C ^ system, have seen continuous growth in use in the long dis- 

 tance plant. Now a twelve-channel system, the type J, is being made 



^ "Carrier Systems on Long Distance Telephone Lines," H, A. Affel, C. S. Dema- 

 rest and C. W. Green, Bell System Technical Journal, July 1928, and A. I. E. E. 

 Transactions, Oct. 1928, pp. 1360-1387. "A New Three-Channel Carrier Telephone 

 System," J. T. O'Leary, E. C. Blessing and J. W. Beyer, Bell System Technical 

 Journal, this issue. 



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