Constant Frequency Oscillators

N recent years the commercial requirements of vacuum tube oscillators have grown more rigid. The tremendous increase in the number of radio broadcast stations with the consequent narrowing of frequency band available to each, the analogous demands by the carrier telephone, and the tendency toward higher frequencies where a small percentage frequency change defeats the universal effort to secure better quality, all have united in creating a need for very constant frequencies. This need has led to a study of methods for holding the frequency constant. The most notable of these is the piezo-electric crystal. However, it has been known for some time that certain oscillator circuits have the inherent property of maintaining their frequency quite constant even though not crystal controlled. Some of these circuits have the additional advantage of combining constant frequency at a given wave-length with the ability to maintain this constancy at other wave-lengths, thus giving a range of available frequencies, any one of which may be depended upon to stay constant. The elements which cause the frequency of oscillators which are not crystal controlled to vary are such things as vibration, changing temperature, fluctuating voltage, and changing load. Vibration and temperature affect primarily the inductance and capacity in the circuit which naturally causes the frequency to change. Fluctuating voltages change the tube resistance, which in turn affects the frequency. * Presented at Sixth Annual Convention of I.