DESIGN OF REACTIVE EQUALIZERS 



717 



has indicated the advantage of adapting reactive input and output coupHng 

 networks, ordinarily employed solely as impedance matching devices, to the 

 additional role of partial distortion equalization.^ 



As a reactive equalizer, a lossless input or output coupling network 

 partially equalizes the loss characteristic of a transmission line or cai^le by 

 j)rovi(ling an insertion gain characteristic to compensate for the line loss 

 characteristic. However, before the rigorous formulation of the problem is 

 undertaken in the following section, it is necessary to discuss briefly the role 

 of input and output coupling networks as equalizers in communications 



LATTICE SHUNT 



Fig. 1 — Constant resistance networks. 



SERIES 



Fig. 2 — Simplified section of a broad-band transmission system. 



systems, and to outline the external requirements and limitations imposed 

 by the system itself on these networks. 



The characteristics of input and output coupling networks which are of 

 engineering interest are: 



(1) The contribution of the coupling circuits to the transmission per- 

 formance of the system as a whole. 



(2) The impedance matching requirements between the coupling net- 

 works and the transmission line. 



(3) The limitation on the maximum performance of a coupling network 

 imposed by the parasitic capacitance usually present in the termination. 



These characteristics are perhaps best illustrated by a somewhat idealized 

 section of a broad-band transmission system. Figure 2 represents the output 



2Ref. 1, pp. 383-392. 



