The Bridge Stabilized Oscillator

T HE problem of improving the stability of constant frequency oscillators may be divided conveniently into two parts, one relating to the frequency controlling resonant element or circuit, and the other to the means for supplying energy to sustain oscillations. The ideal control element would be a high-Q electrical resonant circuit, or a mechanical resonator such as a tuning fork or crystal, whose properties were exactly constant, unaffected by atmospheric conditions, jar, amplitude of oscillation, age, or any other possible parameter. The ideal driving circuit would take full advantage of the resonator's constancy by causing it to oscillate at a stable amplitude and at a frequency determined completely by the resonator itself, regardless of power supply variations, aging of vacuum tubes or other circuit elements, or the changing of any other operating condition. This paper, concerning itself principally with the second part of the problem, describes an oscillator circuit which attains a very close approximation to the latter objective. The "Bridge Stabilized Oscillator" provides both frequency and amplitude stabilization, and as it operates with no tube overloading, it has the added merit of delivering a very pure sinusoidal output. OSCILLATOR CIRCUIT