INTERMITTEXT BEHAVIOR L\ OSCILLATORS 



11 



may be reduced to zero, but actual looping of the point (1,0) is not indi- 

 cated. Parasitic elements, not here considered, can readily affect the 

 performance enough to produce instability. 



Fig. 12 — Nyquist diagram applying to Fig. 6. 



Fig. 13 — Hartley circuit. 



VII. Analysis of the Hartley Oscillator 



The familiar Hartley Oscillator circuit is shown in Fig. 13. In this 

 arrangement the tube serves as amplifier and limiter by the action of over- 

 loading. Harmonic voltages and currents are produced but if the selectivity 

 of the tuned circuit is high the voltage returned to the grid of the tube is 

 nearly sinusoidal. 



The stability of this circuit is tested in exactly the same way as was that 

 of the previous circuit. The loop is opened at the plate of the tube to 

 determine the transmission of a modulated signal. If, as is usually the case, 

 the coupling of the coil is close, the filter reduces to a single tuned circuit. 

 The limiting action results from bias produced by rectification at the grid. 

 Accordingly the block diagram of Fig. 7 is directly applicable, and the 

 behavior of the filter is correctly given by Fig. 9. 



Generally the circuit operates in class "C" with high bias and large grid 



