ARMSTRONG, OPERATING FEATURES OF THE AUDION 



creased. The amplified grid oscillations then react on the wing circuit 

 by means of the grid to produce larger variations in the wing current, 

 thus still further reenforcing the oscillations of the system. Simul- 

 taneously with this procedure the regailar detecting action goes on; the 

 condenser C^ is charged in the usual way, but accumulates a charge which 

 is proportional, not to the original signal strength, but to the final am- 

 plitude of the oscillations in the grid circuit. The result is an increased 

 response in the telephone proportional to the energy amplification of the 

 original oscillations in the grid circuit. It will be observed from the 

 operating characteristic (the relation between the grid potential and 

 wing current) that the amplitude of the variation in the wing current 

 is directly dependent on the variation of the grid potential. This indi- 



FiG. 17 



Fig. 18 



cates that the grid circuit should be made up of large inductance and 

 small capacity to obtain the maximum voltage which it is possible to im- 

 press on the grid. For moderate wave lengths the tuning condenser C 

 of the grid circuit may be omitted altogether and the capacity of the 

 audion alone used to tune the circuit. For long wave lengths the dis- 

 tributed capacity of the grid circuit inductance becomes so high with 

 respect to the capacity of the audion that better results are obtained by 

 the use of a tuning condenser to fix definitely the points of maximum 

 potential difference across the grid and filament of the audion. 



In the second method of reenforcing the oscillations of the grid circuit 

 the wing circuit of the audion is tuned by means of an inductance in- 

 troduced as shown by Fig. 17. This differs from the ordinary detector 

 circuit of Fig. 13 by the addition of the coil L^ and the condenser C,. 

 The manner in which the grid oscillations are amplified may best be 

 ■understood by the following analysis. With no oscillations in the system, 

 the potential difference between filament and wing will be approxi- 

 mately the voltage of the battery B2, but when oscillations are set up in 



