628 BELL SYSTEM TECHNICAL JOURNAL 



Bell System. It is naturally finding its most extensive use in the 

 sections of the telephone plant where the shorter circuits predominate. 

 Because of the fact that the type "D" system development is only 

 now being completed it was thought desirable in the present paper to 

 confine attention to the long haul system (type "C") and to defer 

 the presentation of the detailed information on the short haul develop- 

 ment until a somewhat later date. 



While considerable progress has been made in the development and 

 application of these carrier systems since the beginning of their use 

 about ten years ago, there is still much to be done in the matter of 

 simplifications and further use of the high-frequency spectrum. 

 Automatic pilot channel arrangements are being tested whereby 

 manual maintenance costs can be reduced. Further developments 

 are anticipated in the matter of transposition arrangements to permit 

 an open-wire line to carry multi-channel long haul carrier systems on 

 most of its pairs. While the systems now in use in the field employ 

 frequencies no higher than approximately 30,000 cycles, frequencies 

 considerably higher than this can undoubtedly be economically em- 

 ployed. 



Bibliography 



The following more important papers and articles relating to 

 multiplex carrier telephony and telegraphy are offered, with no 

 pretensions as to completeness, as an addition to the bibliography 

 which forms part of the Colpitts-Blackwell paper. Reference should, 

 therefore, be made to the latter for articles published prior to 1921. 



H. S. Osborne. The Design of Transpositions for Parallel Power and Telephone Circuits. A. I.E. E. 

 Transactions, V. 37. June 1918. pp. 897-936. 



E. H. CoLPiTTS AND O. B. Blackwell. Carrier Current Telephony and Telegraphy. A. I. E. E. 



Transactions, V. 40, 1921, pp. 205-300. 

 G. A. Culver. Guided Wave Telephony. Jl. of Franklin Institute, V. 191, March 1921, pp. 301-328. 

 R. A. Heising. Modulation in Radio Telephony. /. R. E. Proceedings. V. 9, August 1921, pp. 305- 



352. 

 G. A. Campbell. Physical Theory of the Electric Wave-Filter. Bell System Tech. JL, V. 1, No. 2, 



November 1922, pp. 1-32. 

 O. J. ZoBEL. Theory and Design of Uniform and Composite Electric Wave Filters. Bell System 



Tech. JL, V. 2, No. 1, January 1923, pp. 1-46. 

 R. V. L. Hartley. Relation of Carrier and Side Bands in Radio Transmission. Btll System Tech. 



JL, V. 2, April 1923, pp. 90-112, and Proceedings of I. R. £.. V. 11. No. 1, February 1923, pp. 



34-56. 

 A. F. Rose. Practical Application of Carrier Telephone and Telegraph in the Bell System. Bell 



System Tech. JL. V. 2, No. 2, April 1923, pp. 41-52. 

 Paolo Borgatti. Telefonia e Telegrafia ad Alta-Frequenza au Fill. L' Elettrotecnica, V. 10, August 



16. 1923, pp. 531-541. 

 H. S. Osborne. Telephone Transmission over Long Distances. A. I. E. E. JL. V. 42, No. 10, 



October 1923, pp. 1051-1062. 

 Rudolph Fiedler. Die Ruhmerschen Hochfrequenz Apparate fur Mehrfachferusprechen auf 



Leitungen im Rciclispostmuseum in Berlin. Archiv f. Post u. Telcg.. V. 52, 1924, pp. 123. 

 Rudolph Fiedler. Die Aussichten der Leitungsgerichteten Hochfrequenztelephonie u. -Telegraphic 



in Deutschland. Teleg. u. Fernsprech, V. 1, January 1924, pp. 5-8. 

 Hans Muth. Mehrfach Telephonie und Telegraphic Langs Leitungen. Telef. Zeit., V. 6, No. 34, 



January 1924, pp. 27-44. 

 N. H. Slaughter and W. V. Wolfe. Carrier Telephony on Power Lines. A. I. E. E. JL, V. 43, 



No. 4, April 1924, pp. 377-381. 

 H. .ScHULZ AND K. W. Wagner. Der Drahtfunk. E. T. Z., V. 45. May 15, 1924, pp. 485-489. 

 R. V. L. Hartley. The Transmission Unit. Electrical Communication, V. 3, No. 1, July 1924, 



pp. 34-42. 



F. B. JEWETT. Making tlie Most of the Line. Electrical Communication, V. 3, July 1924, pp. 8-21. 



