Abstracts of Technical Articles by Bell System Authors 



Pulse Code Modulation} H. S. Black and J. O. Edson. A radically 

 new modulation technique for multichannel telephony has been developed 

 which involves the conversion of speech waves into coded pulses. An 

 8-channel system embodying these principles was produced. The method 

 appears to have exceptional possibilities from the standpoint of freedom 

 from interference, but its full significance in connection with future radio 

 and wire transmission may take some time to reveal. 



Modulation in Communication r F. A. Cowan. Any signaling system 

 requires some means for introducing a change in conditions at the sending 

 end which may be recognized at the receiving end. The process by which 

 the conditions are changed has come to be called modulation. There are 

 many varieties of forms of change as well as a large number of conditions 

 which are subject to change in response to the signals to be transmitted. 



In early systems for communication at a distance the signal information 

 might have been impressed upon a rising column of smoke, a light, a stone 

 tablet, or a sheet of parchment. For modern communication wide use is 

 made of systems in which the signals change the magnitude or condition 

 of electric energy. 



Starting with the electric telegraph a little more than a hundred years ago 

 this medium of communication has grown steadily more important and more 

 complex. To meet a variety of needs many systems of modulation have 

 been developed and papers describing them in detail are available in the 

 technical literature. Various aspects of the modulation processes have 

 been analyzed carefully and presented and some of the earlier conceptions 

 have acquired a classical textbook status. Recent trends have placed 

 emphasis on modulation systems which more readily may be understood 

 when viewed in a somewhat different manner. It is the purpose of this 

 paper to present certain conceptions which may facilitate the understanding 

 of the various systems of modulation and permit an improved perspective. 



Frequency Division Techniques for a Coaxial Cable Network.^ R. E. 

 Crane, J. T. Dixon and G. H. Huber. A description is given of develop- 

 ments employing frequency division techniques by which the telephone- 

 message-carrying potentialities of the coaxial cable system are realized. 

 By these methods 480 high quality telephone messages are prepared for 



1 Trans. A. I.E. £,vol. 66, 1947 (pp. 895-899). 



2 Trans. A. I. E. £., vol. 66, 1947 (pp. 792-796). 



3 Trans. A. I. E. E., vol. 66, 1947 (pp. 1451-1459). 



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