ARMSTRONG, OPERATING FEATURES OF THE AUDI ON 231 



state is reached an increase in the amplitude of the grid oscillations by 

 any means whatever will increase the negative charge in the grid con- 

 denser, producing a decrease in the average value of the wing current, 

 and hence a, decrease in the telephone current. On the other hand, a 

 decrease in the amplitude of the oscillations will allow some of the nega- 

 tive charge in the grid condenser to leak ofE and thereb}^ permit an in- 

 crease in the telephone current. Hence, when incoming and local oscil- 

 lations add up, the negative charge in the grid condenser is increased 

 and a decrease in the telephone current results. When the two frequen- 

 cies are opposed, some of the charge in the grid condenser leaks oS and 

 an increase in the telephone current occurs. The result is the production 

 in the telephones of an alternating current having a frequency equal to 

 the difference in the frequencies of the local and incoming oscillations 

 and having the very important property of being almost simple harmonic. 

 Fig. 24 illustrates the characteristics of this method of reception. The 

 complete phenomena may be summed up as follows. Incoming oscilla- 

 tions are simultaneously amplified and combined in the system to pro- 

 duce beats with a local oscillation continuously maintained by the audion. 

 The radio frequency beats are then rectified by the audion to charge the 

 grid and the grid condenser, and this charge varies the electron current 

 to produce an amplifying action on the current in the telephones. 



When the grid condenser is omitted, the beat phenomenon is slightly 

 modified, and the audio frequency variation of the telephone current is 

 produced according to the asymmetric action outlined in a previous pub- 

 lication dealing with the operating features of the audion. The system 

 is more sensitive with the grid condenser, but the same general result is 

 obtained by either method of reception. 



Peculiak Features of Oscillation 



Some very interesting features of operation accompany the production 

 of oscillations in the system. Suppose the audion is not oscillating, and 

 the grid and wing coupling is fairly weak. As this coupling is increased, 

 the point at which oscillations begin is indicated by a faint click in the 

 telephones accompanied by a slight change in the character of the static. 

 The oscillations produced are usually so high in frequency and constant 

 in amplitude that they are entirely inaudible. As the coupling is still 

 further increased, a rough note is heard in the telephones, the pitch de- 

 creasing with increase of coupling. This note is produced by the break- 

 ing up of the oscillations into groups, and it occurs whenever electricity 

 is supplied to the grid condenser at a greater rate than that at which it 



