Noise in cut-off magnetrons

Experiments have been made on the characteristics of magnetron oscillators at anode voltages from zero to the value at which the oscillations start. In particular, the noise in the anode current was investigated. Discrete peaks of noise were found in the spectrum, and the frequency at which they occurred varied in a regular manner with anode voltage and magnetic field strength. A qualitative explanation of these peaks is given, and the implication of these results on the mechanism of build-up of oscillations and the selection of modes of oscillation is discussed.