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ANNALS NEW YORK ACADEMY OF SCIENCES 



can leak off. The result is that the grid is periodically charged to a 

 negative potential sufficient to cut off entirely the wing current, causing 

 a stoppage of the local oscillations until the grid charge leaks off and, the 

 wing current reestablishes itself. The frequency of this interruption 

 depends largely on the capacity of the grid condenser, the resistance of 

 its leakage path, and the amplitude of the local oscillations ; it may be 

 varied from several hundred down to one or less per second. This effect 

 is sometimes troublesome in the reception of signals, especially with high 

 vacuum tubes. It may be eliminated, however, by increasing the leak of 

 the grid condenser by means of a high resistance shunt. The best coup- 

 ling for receiving continuous waves lies somewhere between the point at 

 which oscillations start and the point at which interruption begins, and 



Pig. 25 



can only be determined by trial. In this region, trouble is sometimes 

 experienced by the appearance of a smooth musical note in the telephone. 

 This occurs under certain critical conditions of coupling with the' an- 

 tenna when the grid circuit oscillates with two degrees of freedom." Two 

 slightly different frequencies are therefore set up, producing beats which 

 are rectified by the audion in the usual way. This effect is quite critical, 

 and when it causes interference with signals, a slight readjustment of the 

 circuit will usually make it disappear. It may, however, be made per- 

 fectly steady and reproduced at will by the system shown in Pig. 25, 

 where two grid circuits of different periods are provided. Two frequen- 

 cies are therefore generated, one having the frequency of the circuit 

 LCL^, and the other the frequency of the circuit UO^LnC This arrange- 

 ment may replace to advantage the ordinary buzzer for producing groups 

 of oscillations. The foregoing explanations refer to the audion only 



