voLLMH XXVIII OCTOBER, 1949 no. 4 



Pubfic LtDrary 



nsas City, Mo. 



THE BELL SYSTEM 



TECHNICAL JOURNAL 



DEVOTED TO THE SCIENTIFIC AND ENGINEERING ASPECTS 

 OF ELECTRICAL COMMUNICATION 



Reactance Tube Modulation of Phase Shift Oscillators 



F. R. Dennis and E. P. Fetch 601 



A Broad -Band Microwave Noise Source 



W. W. Mumford 608 



Electronic Admittances of Parallel-Plane Electron Tubes 



at 4000 Megacycles Sloan D. Robertson 619 



Passive Four-Pole Admittances of Microwave Triodes 



Sloan D. Robertson 647 



Communication Theory of Secrecy Systems 



C. E. Shannon 656 



The Design of Reactive Equalizers A. P. Brogle, Jr. 716 



Abstracts of Technical Articles by Bell System Authors. .751 



Contributors to this Issue 753 



AMERICAN TELEPHONE AND TELEGRAPH COMPANY 



NEW YORK 



50 i per copy $1.50 per Year 



