20 BRLL SYSTEM TECHNICAL JOURNAL 



additional circuits so as to make it possible to obtain a greater number 

 of circuits by more intensive application of carrier current methods. 



It is the object of this paper to outline the fundamental principles 

 concerning crosstalk between open-wire circuits and recent develop- 

 ments in transposition design theory and technique which have led 

 to the latest pole line configurations and transposition designs. 



To those generally interested in electrical matters it is hoped that 

 this paper will give an insight into the problem of keeping crosstalk in 

 open-wire lines within proper bounds. To those interested in crosstalk 

 it is hoped that the paper will give a useful review of the whole matter 

 and perhaps an insight into the importance of some phenomena which 

 do not seem to be generally appreciated. 



The principles set forth in this paper will also be found of con- 

 siderable interest in connection with problems of control of cable 

 crosstalk, particularly for the high frequencies involved in carrier 

 transmission. It will also be recognized that use is made here of the 

 same general principles as are used in the calculation of effects of 

 impedance irregularities and echoes on repeater operation. These 

 general principles have also been found useful in the development of 

 combinations or arrays of radio antennas of the long horizontal wire 

 type. 



The art of crosstalk control in open-wire lines has grown up as a 

 result of the efforts of many workers. The individual contributions 

 are so numerous that it has not been considered practicable in this 

 paper to make individual mention of them except in a few special cases. 



General 



In the evolution of a satisfactory transposition design technique, 

 complicated electrical actions must be considered and it has been 

 convenient to divide the total crosstalk coupling into various types, 

 all of which may contribute in producing crosstalk between any two 

 circuits in proximity. The first portion of this paper is therefore 

 devoted largely to an examination of the underlying principles and the 

 definition of some of the special terms employed, such as transverse 

 crosstalk, interaction crosstalk, reflection crosstalk, etc. The paper then 

 considers the general effect of transpositions in reducing crosstalk and 

 how this effect depends on the attenuation and phase change accom- 

 panying the transmission of communication currents. Consideration 

 is next given to the practical significance of and methods for deter- 

 mining the crosstalk coefficients which are used in calculating the 

 crosstalk in a short part of a parallel between two currents. The 

 matter of type imbalances inherent in different arrangements of trans- 



