A Variable Phase-Shift Frequency-Modulated Oscillator

The theory of operation of a phase-shift type of oscillator is discussed briefly. This oscillator consists of a broad-band amplifier, the output of which is fed back to the input through an electronic phase-shifting circuit. The instantaneous frequency is controlled by the phase shift through this latter circuit. True FM is obtained in that frequency deviation is directly proportional to the instantaneous amplitude of the modulating signal and substantially independent of modulation frequency. A practical oscillator using this circuit at 65 Mc is described.