104 BELL SYSTEM TECHNICAL JOURNAL 



A heterodyne oscillator having a frequency range from 60 cycles to 

 150 kilocycles has been developed for use in testing this and other 

 carrier systems. Its frequency is calibrated at 60 cycles against the 

 power mains and at 100 kilocycles against a quartz crystal. This 

 oscillator is shown in Fig. 19. A portable test set, developed for 

 measuring transmission gains and losses with high precision, is shown 

 with the cover removed in Fig. 20. 



Conclusion 



The type K system makes possible the application of carrier to toll 

 cables of existing type, whether installed underground or aerially. 

 The blocks of 12 circuits each, which it furnishes, seem to be a con- 

 venient size for routes where large numbers of circuits are concen- 

 trated. It is to be expected, of course, that substantial modifications 

 and improvements will be made in this system through further develop- 

 ment effort. In its present form, however, it constitutes an important 

 stage in the history of carrier development. Plans already under way 

 call for the application of large numbers of such systems to meet rapid 

 growth in long distance traffic. 



This new system forms merely one phase of a concerted development 

 effort on broad-band carrier transmission systems.^- ^° There is 

 every indication that, taken collectively, these broad-band systems 

 will have far reaching effects upon the toll telephone plant of the Bell 

 System. A transition is already under way from the time when carrier 

 was used only on open wire, and comprised only a small part of the 

 toll plant, to a time when carrier systems will furnish a major part of 

 the toll circuit mileage of the Bell System. The type K system is 

 clearly destined to play an outstanding part in this evolution of the 

 tolPplant along carrier lines. 



References 



1. "Carrier in Cable" by A. B. Clark and B. W. Kendall, Electrical Engineering, 



Vol. 52, page 477, July 1933; also Bell Sys. Tech. Jour., Vol. XII, p. 251, 

 July 1933. 



2. "Carrier Systems on Long Distance Telephone Lines" by H. A. AflFel, C. S. 



Demarest and C. W. Green, Bell Sys. Tech. Jour., Vol. VII, pages 564-629, 

 July 1928; also Electrical Engineering, Vol. 47, pp. 1360-1367, October 1928. 



3. "Transmitted Frequency Range for Circuits in Broad Band Systems" by H. A. 



Affel, Bell Sys. Tech. Jour.,\o\. XVI, p. 487, October 1937. 



4. A. G. Chapman, U. S. Pat. No. 1863651; M. A. Weaver and O. H. Coolidge, 



U. S. Pat. No. 2008061; M. A. Weaver, U. S. Pat. No. 2080217. 



5. "The Time Factor in Telephone Transmission" by O. B. Blackwell, A.I.E.E. 



Transactions, Vol. 51, pages 141-147, March, 1932; also Bell Sys. Tech. Jour., 

 Vol. XI, pp. 53-66, January 1932. 



6. "Stabilized Feed-Back Amplifiers" by H. S. Black, Electrical Engineering, 



Vol.53, p. 114, January 1934. 



