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BELL SYSTEM TECHNICAL JOURNAL 



At the other extreme, frequencies as high as 5.X10 7 cycles per 

 second can be obtained by means of tuned vacuum tube circuits 

 of the Hartley or Colpitt type. At this point the coupling reactance 

 of the tube becomes appreciable with that of the circuit. 



Circuits capable of considerably higher frequencies have been 

 described by Van der Pol, 37 Southworth, 38 Gutton and Touly, 39 and 

 Holborn. 40 In all of these cases the oscillatory circuit is made up of 

 distributed inductance and capacity connected to the tube in such a 

 way as to utilize the capacity between the elements of the tube as a 

 means of coupling. 



The circuit shown in Fig. 68, when properly arranged, is as efficient 

 as those used for lower frequencies and will give frequencies as high 

 as 3X10 8 cycles per second. The oscillatory circuit is indicated by 

 the heavy lines. It consists of a rectangle whose dimensions are 

 appreciable with the wave length. Therefore, waves produced by 

 variations in the electron emission through the grid are guided along 

 the rectangle and are reflected at the ends. The reflected waves 

 produce the proper voltage changes on the grid to sustain oscilla- 



tions. The ground imposed by the power leads places at least one 

 point of the circuit at earth potential. If the condenser C is properly 

 adjusted relative to the capacity between the grid and the plate the 

 wave front can be made essentially perpendicular to the sides of the 

 rectangle. It has been found that a large part of the power loss in 

 the circuit is due to radiation. This circuit has been used as a basis 



" B. van der Pol, Phil. Mag., 38, July, 1919. 



38 G. C. Southworth, Radio Rev., 1, Sept., 1920. 



39 Gutton and Touly, Comptes Rendus. 168, Feb. 3, 1919. 



40 F. Holborn, Zs. fur Physik, 6, p. 328. 



