Frequency Modulation of Resistance-Capacitance 0scillators

A method is described for direct-frequency modulation of a resistance-capacitance oscillator which is simpler and more stable than the beat oscillators formerly used. Spurious amplitude modulation is reduced to a negligible value without the use of limiters and without introducing appreciable harmonics in the output wave. Balanced control tubes prevent transients or signal frequencies from appearing in the output. Curves are given which provide an easy method of choosing the network and constants for any desired condition. The device is especially suited to facsimile transmission by sub-carrier frequency modulation.