REFLEX OSCILLATORS 485 



real admittances (conductar.ces). In this section the steady state operation 

 in the case of complex circuit and electronic admittances will be discussed. 

 The general condition for cscillaticn states that, breaking the circuit at any 

 point the sum of the admittances looking in the two directions is zero. Par- 

 ticularly, the electronic admittance Ye looking from the circuit to the 

 electron stream, must be minus the circuit admittance Yc , looking from the 

 electron stream to the circuit. Here electronic admittance is used in the 

 sense of an admittance averaged over a cycle of oscillation and fulfilling the 

 above condition. 



It is particularly useful to consider the junction of the electron stream 

 and the circuit because the electronic admittance Ye and the circuit admit- 

 tance Yc have very different properties, and if conditions are considered 

 elsewhere these properties are somewhat mixed and full advantage cannot 

 be taken of their difference. 



The average electronic admittance with which we are concerned is a 

 function chiefly of the amplitude of oscillation. Usually its magnitude 

 decreases with increasing ampUtude of oscillation, and its phase may vary 

 as well, although this is a large signal effect not shown by the simple theory. 

 In reflex oscillators the phase may be controlled by changing the repeller 

 voltage. The phase and magnitude of the electronic admittance also vary 

 with frequency. Usually, however, the rate of change with frequency is 

 slow compared with that of the circuit admittance in the vicinity of any one 

 resonant mode. By neglecting this change of electronic admittance with 

 frequency in the following work, and concentrating our attention on the 

 variation with amplitude and repeller voltage, we will emphasize the im- 

 portant aspects without serious error. However, the variation of electronic 

 admittance with frequency should be kept in mind in considering behavior 

 over frequency ranges of several per cent.^ 



The circuit admittance is, of course, independent of amplitude and is a 

 rapidly varying function of frequency. It is partly dependent on what is 

 commonly thought of as the resonator or resonant circuit of the oscillator, 

 but is also profoundly affected by the load, which of course forms a part of 

 the circuit seen from the electron stream. The behavior of the oscillator is 

 determined, then, by the electronic admittance, the resonant circuit and 

 the load. The behavior due to circuit and load effects applies generally 

 to all oscillators, and the simplicity of behavior of the electronic admittance 

 is such that similarities of behavior are far more striking than differences. 



We have seen from Appendix I that at a frequency Aw away from the 

 resonant frequency wo where Aw<<Ca;o , the admittance at the gap may be 

 expressed as: 



Yc = Gc + i2MAa;/a;o. (7.1) 



* Appendix IV discusses the variation of phase with frequency and repeller voltage. 

 The variation of phase of electronic admittance with frequency is included in Section IX A. 



