UL TRA -HIGH-FREQ UENC Y OSCILLA TIONS 



287 



justable reflecting pistons. By thus completely enclosing the tube, 

 escape of energy into free space is avoided, and the losses external to the 

 tube are reduced to the ohmic losses (including dielectric losses) incident 

 to the existence of the wave within the guide. The presence of wave 

 power within the guide is indicated by a crystal detector-microammeter 

 combination connected to an antenna extending a short distance within 

 the guide, as shown in Fig. 4. Adjustment of the pistons closing the 



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Fig. 4 — Apparatus arrangement for "No Load" test of diode. 



ends of the wave guide system allowed the attainment, for each value of 

 anode current and voltage, of the most favorable impedance conditions 

 for abstraction of energy from the diode. 



The results of this experiment are shown on Fig. 5, which gives the 

 boundaries of the domain of oscillation of the two tubes whose dimen- 

 sions are given on Fig. 1. The large gain in extent of the oscillation 

 region of tube no. 24 is immediately apparent; the free space oscillation 

 limit of Ep = 300 volts, /p = 500 ma. has been lowered to £p = 210 

 volts, /p = 110 ma. For tube no. 37 oscillations occur at much lower 

 voltages, as is to be expected from the smaller anode-cathode distance, 

 and the minimum plate current required to maintain oscillations is 

 also somewhat smaller. 



In the arrangement of Fig. 4 no useful power is extracted from the 

 diode. To examine the oscillation domain of the diodes when deliver- 

 ing useful power, the arrangement of Fig. 6 was used. Here in a 

 section of wave guide closed at both ends by tightly fitting but longi- 

 tudinally adjustable pistons there are placed the diode mounting shown 

 on Fig. 3 and a power absorbing and measuring element. The 

 assemblage constitutes in effect a wave guide transformer, for by 



