THEORY or NEGATIVE IMPEDANCE CONVERTER 109 



can be seen a reversed current type. This device can be made to approach 

 the ideal only over a finite frequency range. At some frequencies k will not 

 be a numeric. Likewise, at some frequencies the two internal networks will 

 produce appreciable effect. Stability can be ascertained readily from a 

 working knowledge of the components of the equivalent circuit. Designs 

 are practical wherein variations in battery voltages and vacuum tube 

 constants are second-order effects. 



Acknowledgements 



The writer acknowledges the help of Messrs. K. G. Van Wynen, K. S. 

 Johnson and F. B. Llewellyn with the concept of negative impedance and 

 the contributions of Messrs. J. A. Weller, H. Kahl and W. J. Kopp relating 

 to the practical design of negative impedance converters. He is also in- 

 debted to Miss A. B. Strimaitis for the many computations which were 

 required in this development and to Messrs. R. Black, J. A. Lee and J. M. 

 Manley for their comments on this paper. 



In recent years there has been a growing need for an inexpensive two- 

 wire repeater having a cost lower than that of the 22 type for use in the 

 exchange plant. Mr. G. C. Reier encouraged the study of negative impedance 

 devices as a possible way of meeting this need. Had it not been for his 

 encouragement the El repeater development might not have been under- 

 taken. 



