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BELL SYSTEM TECHNICAL JOURNAL 



form the function of the rooter in circuit No. 1 when s = t = n. We 

 may write for this circuit 



Eq = kiE^Rs, 

 Eo = kiE^, 



1 1 



Rb = 



E, = 



kzE^-^ hE,^-^ ' 



kiE, 



kiE, 





(7) 



which is the same as equation (6) for circuit No. 1. 



In Fig. 5 is shown the Expandor Circuit. If the resistances r are 



LINEAR 

 RECTIFIER 



Fig. 5 — Expandor circuit, 

 kept small compared with those of the control tubes, we may write 



(8) 



This relation is just the inverse of that given in equations (6) and 

 (7). The increment ratio in db of output to input is n and the expan- 

 sion ratio may be said to be n. When a compressor and expandor 

 having the same value of n in their indices are put in tandem, the final 

 output and input intensity ranges are the same. However, between 

 the compressor and expandor the range of signal intensities, whose 



