COMMON BATTERY ANTI-SIDETONE SUBSCRIBER SET 247 



From the intermediate step in Fig. 2 the circuits in Fig. 3 will be seen 

 to be the same electrically as those in Fig. 1. Inasmuch as its effects 

 upon the features to be discussed are negligible, the ringer branch has 

 been omitted. The circuit meshes in Fig. 3 are numbered for identifi- 

 cation, subscripts 5 and A suggestively differentiating meshes of the 

 sidetone and anti-sidetone circuits. Mesh currents and e.m.f.'s in all 

 subsequent schematics are correspondingly identified as later described. 



Complementary Sidetone Circuit 



From Fig. 3 the three-mesh anti-sidetone circuit is seen to differ 

 schematically from the two-mesh sidetone circuit only by having a 

 balancing branch consisting of a third induction coil winding C and a 

 network N bridged across the receiver to form the third mesh. In this 

 theoretical discussion, N may be assumed to be a network of whatever 

 form is capable of providing the impedance characteristics needed to 

 meet the requirements later discussed; in practice, it becomes merely 

 a resistance integrally comprised within the resistance component of 

 the self-impedance of winding C. The sidetone circuit which would 

 remain if this added branch were disconnected will be called the 

 complementary sidetone circuit or the sidetone complement of the 

 anti-sidetone circuit. In every reference to a sidetone circuit here- 

 after, the sidetone complement of the associated anti-sidetone circuit 

 is meant. 



Receiving and Transmitting Features 



The theoretical features of the anti-sidetone circuit to be explained 

 are: 



1. The receiving efficiency is the same as that of the complementary 



sidetone circuit. 



2. The transmitting efficiency is the same as that of the complementary 



sidetone circuit. 



3. The current through the receiver when transmitting, i.e., the side- 



tone, is zero. 



The above efficiencies, it should be noted, are purely circuit efficiencies; 

 they do not include electro-acoustic conversions by the instruments, 

 and they should not be confused with questions pertaining to effective 

 transmission performance. 



Circuit Conditions When Receiving and When Transmitting 



The following discussion of the diagrams in Groups II and III applies 

 to both the sidetone and the anti-sidetone circuits. 



