1920] Thermionic Valve in Wireless Telegraphy & Telephony 185 



was first suggested by R. A. Fessenclen the only practical method of 

 producing the local high frequency, but controlled, oscillations was 



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Fig. 19.— Valve Receiver Set for -C.W. Waves, Heterodyne Receptor, 



by the expensive high frequency alternator. The method was there- 

 fore not much used. But the discovery of the oscillation-producing 

 power of the thermionic valve put a fresh face on matters. It now 



V 





^p 



X 



c 



Fig. 20. — Round's IIethod of Beat Reception with a 

 Single Three-Electbode Valve. 



became quite easy to produce high frequency oscillations, of any 

 required periodicity, by coupling a three-electrode valve to the 

 aerial and then coupling the grid and plate circuits of the valve. 



