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Home Electronic Applications in Communication Oscillators Inductance-Capacitance (L-C) Oscillators
 
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Inductance-Capacitance (L-C) Oscillators

The frequency of oscillation of Fig. 35 is approximately the frequency of parallel resonance of the L2-C combination in the plate circuit. The feedback, necessary to sustain oscillations, is from coil L2 to L1. The grid is driven positive by an amount determined by the self-biasing Rg-Cg combination and by the coupling between L1 and L2. Often the tube is operated in class C. This is a tuned-plate oscillator. If capacitor C is placed in parallel with inductor L1, it becomes a tuned-grid oscillator.

self-biased class C radio-frequency oscillator
Figure 35. Basic circuit of a self-biased class C radio-frequency oscillator. Power can be drawn by coupling a coil with L2.

A convenient oscillator for many purposes is the so-called resistance-stabilized oscillator of Fig. 36. Alternating voltage is developed across choke coil L, and alternating current is fed back to the parallel L2-C circuit through the series R-C' combination. The reactance of C' should be low at the frequency of oscillation, and R should be reasonably high, often about 50,000 ohms. The second tube of Fig. 36 is an isolating tube known as a buffer. This operates as an amplifier but, in addition, prevents changes in the impedance of the connected load from affecting the frequency of oscillation.

audio-frequency oscillator
Figure 36. Simplified circuit of an audio-frequency oscillator.


Home Electronic Applications in Communication Oscillators Inductance-Capacitance (L-C) Oscillators

Last Update: 2011-05-30