Development of Transmitters for Frequencies above 300 Megacycles

The fundamental functions of the electrons and their work cycle, in the interelectrode space of high vacuum tubes, are discussed. It is shown how the triode feed-back circuit becomes inoperable at very high frequencies due to space-time and reactance characteristics. It is further shown how the space-time conditions can be organized to benefit the maintenance of oscillation instead of becoming a detriment. Some of the more familiar arrangements, such as the Barkhausen and the magnetron circuits, which are based on this principle, are discussed in some detail. With these illustrations as a background the author describes a new method of frequency multiplication at very high frequencies. This method yields much greater power outpuds than hitherto possible and promises to become very useful. Various means for frequency stabilization are referred to and the merits of frequency controlling devices, such as crystals and low power factor circuits, are compared. Special problems encountered in the application of modulation at very high frequences are described and reference is made to methods developed to meet these problems. Practical considerations of circuit arrangements are described in some detail. Several examples of transmitter design are given. These sections are illustrated with photographs. Important points in connection with antennas and transmission lines are discussed and the results of some measurements are given. The paper ends with a brief reference to some propagation results obtained by RCA Communications engineers and others.