CONSTANT FREQUENCY OSCILLATORS 69 



that the oscillator be operative over a range of frequencies are also 

 indicated. 



Before proceeding with a detailed description of the various specific 

 embodiments necessary to secure independence of frequency and bat- 

 tery voltage, it will be well to lay down the physical conditions upon 

 which the frequency of any vacuum tube oscillator depends. 



In general, all such oscillators consist of or may be resolved into, a 

 tuned electrical circuit or network to which is attached a vacuum tube. 

 Irrespective of any particular circuit, the frequency of the oscillator is 

 completely determined by the following quantities, the designations 

 used here being uniformly employed throughout the subsequent analy- 

 sis: 



L, the self-inductance in the network 



M, the mutual inductance in the network 



C, the capacity in the network 



R, the resistance in the network 



Tp, the plate resistance of the vacuum tube 



Yg, the grid resistance of the vacuum tube 



H, the amplification factor of the vacuum tube 



Of these quantities, L, C, and M require little comment. They are 

 merely symbolic of the elements of the electrical network. The quan- 

 tity C includes the interelectrode capacities of the tube when they 

 become of consequence. These three quantities are assumed to be 

 constant, an assumption which has been found very reasonable in prac- 

 tice. The quantity R represents the resistance in the network. For 

 the purpose of this discussion the oscillator is assumed to deliver only 

 a small amount of power, being used most often in such a manner as 

 to supply voltage to the grid of an amplifier tube. Consequently, the 

 electrical network external to the vacuum tube may, and should, be 

 constructed in such a manner as to include a minimum amount of 

 resistance. Under these conditions the losses in the circuit have been 

 found to be practically all the result of the internal resistances, fp and 

 Tg of the vacuum tube. 



These two quantities, Tp and ry, are very important, being princi- 

 pally responsible for changes in condition of the circuit as a whole. It 

 should be realized that Tg has the same relation to the static values of 

 grid current and potential that rp has to the plate current and poten- 

 tial. The effect of varying the applied potential of the grid or plate, 

 or of changing the filament current is directly to cause rp and fg to 

 vary, usually in opposite directions. Further, when amplitude of os- 

 cillation varies, for which variation of battery voltages (grid, plate, 



