ARMSTRONG, OPERATING FEATURES OF THE AUDI ON 



241 



the telephone current. These; two currents are therefore in phase with 

 each other. On replacing each telephone by the primary of a trans- 

 former, and. connecting their secondaries through a telephone in the 

 proper phase, it is possible to balance out the static and at the same time 

 secure an additive response of the signals from each receiver. 



An arrangement of circuits by means of which this method can be 

 carried out is shown in Fig. 31. Here two oscillating receiving systems 



^^1 E^ 



C^ I.sJ^/\f' 



Cj 



Cs 



Lt Is 



l^'I^^ I^\ 



Ck 



^ 







Fig. 31 



are kept in step by means of the circuits L^C^C^L^. L^C^ and L-^G^ 

 are identical, and each is tuned separately to the frequency to be received. 

 When both audions are oscillating in step, the flow of current in these 

 circuits, as indicated by the vectors of Fig. 31, will be alternately up on 

 one side and down on the other. The point between the condenser C^ 

 and G^ will be a node; and the antenna may be connected to this point 

 without disturbing the conditions appreciably if a resistance U, placed 

 as indicated, is included in the antenna. This resistance need not be 

 large enough to interfere seriously with the signal strength ; it need only 

 be large with respect to the resistance of the circuit L^GJJ^'L^', which 

 circuit has a very low resistance. 



Incoming oscillations pass through the divided circuit as indicated in 

 the diagram, and therefore are in phase with the local oscillations of one 



