COMMON BATTERY ANTI-SIDETONE SUBSCRIBER SET 257 



These cover both transmitting and receiving conditions: when trans- 

 mitting, El = E2\ and when receiving, Ei — 0. 



The relation which the induction coil must meet in order to provide 

 neutralizing balance can be determined by solving eqs. (5) under the 

 receiving condition £2 = 0, and imposing the requirement that /3'J = 0. 

 This gives as the relation to be met. 



ZaC ZaB — Zt />.n 



(6) 



Zbc + Zr Zt + Zb + Zr + Zs 



In like manner, the value of Zn needed to provide sidetone balance 

 can be determined by solving eqs. (5) under the transmitting condition 

 El = £2, and imposing the requirement that I2A + -^3^^ = 0. This 

 value of Z\, regardless of whether or not eq. (2) is imposed as a further 

 condition in its derivation, is found to be 



r^ ry V \ Z ,\ c{Z A C 4" ZbC " ZaB " Zb " Z ^) ,_, 



ZjV — ^BC — Z.C -\ ^ j y 1 7^ • \l ) 



^ L -r ^A -\- ^AB 



Note that Zn is here independent of Zt and Zr, except as these may 

 enter implicitly as factors affecting the impedances at right in de- 

 signing the coil for optimum performance with specified instruments. 

 In other words, the transmitter and receiver may be changed without 

 disturbing the sidetone balance. Such a change would, however, 

 upset the neutralizing balance, thereby altering the efficiencies from 

 those of the sidetone circuit. 



Vector Diagram 



Relations among the component mesh currents in an anti-sidetone 

 circuit of this type under ideal conditions of exact neutralizing and 

 sidetone balances, are illustrated by the vector diagram in Fig. 11. 

 As all of the current vectors indicate current per volt impressed, those 

 for the mesh currents under the receiving condition in Fig. AA are 

 identical with those under the component of the transmitting condi- 

 tion in Fig. 9A. Vector sums of the mesh currents show the current 

 through the receiver and that fed into the line when transmitting, and 

 illustrate the sidetone balance. Vectors of the three voltages acting 

 around the third mesh in Figs. 4^ and 9 A are also shown, together 

 with their summation. The latter illustrates the neutralizing balance 

 of eq. (2). 



