Two backward-wave oscillators covering the 30-75 KMC frequency range

This paper describes two developmental backward-wave oscillators which tune over the frequency ranges from 35 to 50 kmc and from 48 to 74 kmc and deliver power of the order of milliwatts. The tubes incorporate a parallel-flow electron gun using an impregnated cathode, and a tape helix supported by three quartz rods. RF output is taken out through a standard rectangular waveguide, to which the helix is matched by a tapered section having choke collars. Ceramic guns, stems, and output windows developed for use with these tubes are described. The tubes operate at collector currents of 3 to 5 ma, and require a magnetic focusing field of 1200 gauss. The helix voltage is varied from 800 to 3500 volts to cover the complete frequency range of oscillation. Design features are discussed, and calculated and observed performance curves for these tubes are shown.