232 BELL SYSTEM TECHNICAL JOURNAL 



Transmission Networks and Wave Filters.-' T. E. Shea. In this 

 book is summarized the research and experience of the Bell System in 

 the application of electric wave filters, equalizers, balancing networks 

 and similar electrical systems. The preface discusses the nature of the 

 signals transmitted over communication systems and a statement f)f 

 the principal ways in which selective networks are used to modify sig- 

 nal transmission. A detailed example of the application of selective 

 networks to an actual long distance telephone circuit gives specific en- 

 gineering requirements and limitations. 



The next portion of the book deals with some of the more general 

 principles governing network analysis. The engineering terms used to 

 evaluate network performance are described and a number of general 

 theorems and equivalences which simplify the analytic treatment of 

 networks are demonstrated. A considerable discussion is also given of 

 the characteristics of the elementary two-terminal networks most used 

 as constituents of larger structures. 



With this background the author is now ready to consider the proper- 

 ties of wave filters. Conditions for free transmission and attenuation 

 in ladder networks are set up and the particular networks of chief 

 practical importance are described in detail. The various structures 

 revealed by this listing differ widely among themselves as regards 

 propagative and impedance characteristics even when they transmit 

 the same frequency bands. Since the ideal network characteristics 

 seldom correspond exactly to any one of these structures, filter re- 

 quirements are usually met most efficiently by composite networks, 

 containing sections of several different types. The author describes 

 the conditions which must be satisfied before different sections are 

 joined together and gives several examples of methods of computing 

 the performance of such composite structures. 



This treatment of networks deals only with their response to steady 

 single-frequency electrical impulses. It cannot be applied directly to 

 communication systems, since signals are of more complicated wave 

 forms and are transient in character. In the last portion of the book 

 therefore, the author discusses the use of Fourier analysis in relating the 

 characteristic of the network computed on a steady-state basis to its 

 response to a transient impulse of arbitrary character. 



Some Principles of Broadcast Frequency Allocation}'^ L. E. Whitte- 

 MORE. This paper discusses some of the technical factors which must 

 be considered in the allocation of frequencies to broadcasting stations 



8 D. Van Nostrand Company, New York. 

 ^^Proceedings, Institute of Radio Engineers, August, 1929. 



