Patent GB-677881-A (GB)
Title: Improvements in or relating to electron discharge tube arrangements of the magnetrontype
IPC: H01J25/52
Filed: 1947-01-08
Abstract: 677,881. Magnetrons. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Jan. 8, 1947 [Jan. 8, 1946], No. 695/47. Class 39 (i). An electron discharge tube includes two split-anode magnetrons coaxially disposed within a common envelope, said magnetrons being adjusted to operate at the same frequency and being of different power ratings and/or sizes, means being provided for causing the magnetron of smaller power rating and/or size to control the other magnetron by electron spacecharge coupling. The amplifier shown in Fig. 1 comprises within a single evacuated glass envelope 16 of elliptical cross-section a relatively small split-anode magnetron 10 and a larger split-anode magnetron 12 coaxially disposed about a common cathode filament 18 heated by a battery B through a metallic tension spring 9 which takes up the expansion of the filament. Surrounding the envelope is a metal shield 26 which serves as a high-pass filter having a cut-off lower in frequency than the amplifier operating frequency and surrounding the shield is a magnetic coil 20 fed with direct current from the battery B. The filament and coil circuits are provided with rheostats 22 and 24, respectively. Each magnetron comprises a pair of spaced semi-cylindrical anode electrodes, the anodes of the smaller magnetron 10 being coupled to opposite ends of an input coupling loop 11 positioned within an inputwave-guide 13 and the anodes of the larger magnetron 12 being coupled to opposite ends of an output coupling loop 15 positioned within an output wave-guide 17 coupled to a utilization circuit. The anodes of the magnetrons are supplied with direct current from batteries C and A for the anodes of the larger magnetron and by batteries B and A for the smaller magnetron through the connections 21 and 19. The magnetrons may be of the same size but of different energy rating. The glass envelope 16 has a thin coating 100 of resistance material to which a potential is applied which increases from the region of the smaller magnetron 10 to the region of the larger magnetron 12 and this results in a whirling electron stream 14 between the two magnetrons. The only substantial coupling between the magnetrons is through the electron space charge. Any very small coupling between the magnetrons could be balanced out by displacing the anodes of the magnetrons by 90 degrees relatively to each other around the axis. Multiple anode construction may be employed for each magnetron with corresponding multiple longitudinal furrowing of the envelope, Fig. 3, at least in the space between the magnetrons, to produce multiple distortions or eccentricities of the growing electron space charge. This requires proportioning of cathode and envelope effective diameters to give electron " hops " a correct circumferential angle to match the number of anode segments. Amplifier operation at very high frequencies will be at a frequency synchronized with the electron transit time or frequency but at lower frequencies there need be no direct relation between operating frequency and the electron transit time. The apparatus can be used as a radio transmitter if the anode-tocathode potential of the smaller magnetron be adjusted to make it self-oscillating and such transmitter may be amplitude or frequency modulated by known means. The apparatus may also be used as a receiver and demodulator of modulated waves.