Noise in reflex klystrons and backward-wave oscillators

The paper describes a.m. and f.m. direct-detection and superheterodyne noise spectrum measurements on various types of backward-wave oscillator and reflex klystron. A procedure has been developed by which the individual a.m., f.m. and background noise components can be separated. The results show that the predominant component at low sideband frequencies is f.m. noise and at high sideband frequencies is background noise. The a.m. noise is not a significant component. The presence of positive ions in the beam of a backward-wave oscillator causes noise peaks at frequencies near 1 Mc/s and an increase of modulation noise over a wide frequency range. Positive ions can be relatively easily removed by transverse ion drainage. Large noise peaks may also be generated at frequencies near those of spurious oscillations. The results of measurements of carrier frequency deviation, and of correlation between a.m. and f.m. noise, and between modulation and beam noise are also given.