246 



BELL SYSTEM TECHNICAL JOURNAL 



nor is any attempt made to discuss questions of practical design be- 

 yond pointing out something of the nature of the problems involved. 

 Equations for this anti-sidetone circuit are given and discussed in an 

 appendix, and a vector diagram is shown which illustrates graphically 

 relations among the currents and voltages under the ideal condition of 

 exact balances. 



Rearrangement of Circuit Patterns 

 Simplified explanations of anti-sidetone sets are most frequently 

 based upon analogues with balanced arrangements resembling the 



SIDETONE CIRCUIT (S) 



ANTI-SIDETONE CIRCUIT (a) 



Imr. 1 



Fig. 2 



I OJ^yjP 



^WT^ 



I — ^rnr^ 



A 



B 



C 



rXla 2s rM] |l 1a -k^ ^A rM] 3a |n 



Fig. 3 

 Group I — Convenient schematic rearrangements 



familiar circuit pattern of the Wheatstone bridge, and several such 

 explanations have been devised for the set now to be considered. 

 A wholly different approach will, however, be employed here. The 

 schematics supplementing the present discussion have been arranged 

 in groups to assist in visualizing and coordinating the steps in the 

 explanation. The diagrams of Group I rearrange the familiar con- 

 ventional schematics of the common battery sidetone and anti-sidetone 

 circuits in Fig. 1 into the patterns most convenient for present purposes 



