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living M. Gottlieb W6HDM 931 OJive

Menlo Park CA 94025

HIGH STABILITY "LUMPED LINE OSCILLATOR

living M. Gottlieb W6HDM 931 OJive

Menlo Park CA 94025

Many self-excited oscillator circuits have stimulated the interest of the designer and constructor. Each of these can be readily optimized for a particular performance feature, or exploited for some practical advantage. When frequency stability commands high priority, the Clapp oscillator is likely to be the chosen circuit. Although it has been shown that the attributes of the Clapp circuit can be attained by directing special design approaches to other configurations, the fact remains that frequency stability is a readily forthcoming operating feature of the practical Clapp oscillator. It is for this reason that this circuit is so frequently used as vfo in both amateur transmitters and commercial equipment. When one considers the extent and tenure of the popularity enjoyed by the Clapp oscillator circuit, the question naturally arises, "Does the possibility exist for further upgrading of self-excited oscillator performance?" In the exploration of such a possibility, we would not be concerned with such techniques as temperature compensating components, regulated power supplies, feedback limitation, etc, These performance-enhancements can be applied to any oscillator circuit. Rather, we would like to see a new or modified approach which would possess inherent virtues prior to ap plication of such compensation and optimization methods..

In seeking to displace or improve the basic Clapp circuit, it is only apropos that we first citc some of its real or alleged shortcomings. The most obvious one is likely to receive the least attention because of general acceptance as the "nature of the beast." In the Clapp, as well as tn all other sclf-excited oscillators employing L-C frequency determining "tank" circuits, oscillation frequency is profoundly susceptible to conditions associated with the inductor. This sensitivity includes turn-spacing, dieletric between turns, moisture, dust, temperature.

Fig. 1. Basic "lumped-line" oscillator. Tank circuit has apperance of conventional coil but functions as futi-v/ave transmission line with no exposed high-impedance or "hot" points.

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