Frequency Stable LC Oscillators

A simple theory of the conditions for oscillation, and of the frequency stability of inductance-capacitance oscillators is evolved from a survey of a number of papers on this subject. As some of these papers appeared in publications which are not readily accessible, some of the material may be new to workers in the United States. The condition for oscillation is shown to depend only upon the mutual conductance of the tube and the impedances, tapped on the tuned circuit, presented to the grid and plate circuits of the tube. For linear operation, the stability depends only on the Q of the controlling circuit, and the ratio of the change of interelectrode capacitance to mutual conductance of the tube, and is independent of the LC ratio. For nonlinear operation, however, the stability depends upon the factors given above and on the LC ratio, being improved when a high LC ratio is used. The best tube for high stability is shown to be the tube having the lowest ratio of interelectrode capacitance change to mutual conductance. For highest possible stability, very low level operation with some form of automatic level control is required. A brief historical chronology is included.