Frequency Modulator

The frequency deviation obtainable in a reactance-tube frequency-modulator-oscillator combination is limited by two resistances which shunt the oscillator tank. The first is due to the plate resistance of the reactance tube and the second, to the fact that the voltage on the reactance-tube´s grid is less than 90 degrees out of phase with the plate voltage. A method is deduced from a simple mathematical analysis whereby the phase of the reactance-tube grid voltage may be adjusted for cancellation of these two effects. This eliminates the tendency of the reactance tube to amplitude-modulate the oscillator output, makes possible the use of somewhat higher reactance values in the oscillator tank, and permits the satisfactory use of more powerful reactance tubes. The principle is of importance only where wide frequency deviation may be required without resorting to frequency multiplication, but will possibly find many uses as the art of frequency-modulated-wave transmission and reception progresses.