Fundamental Characteristics of Electronic Oscillations

Abstract

THE precise nature of the electronic oscillations produced by thermionic valves is still, fifteen years after their discovery in the three-electrode valve by Barkhausen and Kurz, imperfectly understood. The characteristic feature of these oscillations is that their period bears some more or less definite relation to a time of electron transit in the valve. It has often been suggested that such oscillations can be maintained without the co-operation of a resonant circuit external to the cloud of moving electrons, but a recent survey of the literature¹ led me to conclude that this view was not supported by unambiguous experimental evidence. While many workers have tacitly assumed that only a single frequency, or a harmonically related series of frequencies, is present when electronic oscillations are generated, the conclusion² that the Maxwellian distribution of initial electron velocities, apart from other causes of variation in transit time, leads necessarily to the production of a band of frequencies, has recently found wide acceptance. Experimental evidence has now been obtained which shows quite definitely that electronic oscillations can be produced without any external resonant circuit and that they can have a single frequency.