Frequency Modulation Noise in Oscillators

Noise in oscillator tubes due to the discrete nature of the electron can result in frequency fluctuations equivalent to frequency modulation by a wide band of Gaussian noise at small mean-square frequency deviations. Amplitude fluctuations are ignored. Also, low-frequency noise due to flicker and similar phenomena is ignored. The effect of the band-pass filter normally present in an oscillator on the parameters of the noise modulation is determined. Also, the power spectrum of the oscillator output is evaluated which, as a practical measure, implies little more than the phase correlation time of the carrier. Finally, the theory is applied to reactance-modulated oscillators, some fixed-tuned conventional oscillators, and magnetrons. Noise equations which evaluate the mean-square frequency deviation and the spectral width at the output of oscillators are given.