Low-power resonant-segment magnetrons for centimetre waves

This paper describes the development and use of a range of small glass magnetrons for use as low-power sources in the centimetre band. Although originally designed for measurement purposes and as local oscillators in receivers, they have proved most useful as oscillators for centimetre-wave transmitters. These magnetrons have an anode system consisting of a number of interleaved segments and are provided with an indirectly-heated oxide-cathode; they are generally similar in form to a small glass receiving valve. They oscillate at a wavelength which is largely decided by the length of the anode segments, but can be tuned over a narrow range by variation of the applied magnetic field, or by adjustment of the external circuit. A series of experimental valves has been made covering a wavelength range of 4.5 to 11 cm with outputs of the order of 0.1 watt at 4.5 cm increasing to 0.5 watt at 11 cm. Three types taken from this experimental range were modified for production in larger quantities, namely the E1210 for 9.1 cm and the CV79 and CV89 for two wavelengths in the region of 6.5 cm. Some characteristics of these established designs are presented together with descriptions of their associated circuits. Methods of modulation are referred to, particularly the application of pulse-width modulation. With a transmitter using this system of modulation applied to an E1210, radio telephony at centimetre waves is possible with quality comparable with that obtainable at longer wavelengths.