Samuel of Bell Telephone Laboratories in 1934, leading to designs by Postumus in 1934 and Hans Hollmann in 1935. The development of magnetrons with multiple cathodes was proposed by A. ![]() Further research was limited until Okabe's 1929 Japanese paper noting the production of centimeter-wavelength signals, which led to worldwide interest. Other experimenters picked up on Hull's work and a key advance, the use of two cathodes, was introduced by Habann in Germany in 1924. ![]() Albert Hull of General Electric Research Laboratory, USA, began development of magnetrons to avoid de Forest's patents, but these were never completely successful. The use of magnetic fields as a means to control the flow of an electric current was spurred by the invention of the Audion by Lee de Forest in 1906. Unlike other vacuum tubes, such as a klystron or a traveling-wave tube (TWT), the magnetron cannot function as an amplifier for increasing the intensity of an applied microwave signal the magnetron serves solely as an electronic oscillator generating a microwave signal from direct current electricity supplied to the vacuum tube. ![]() The resonant frequency of the arrangement is determined by the cavities' physical dimensions. Electrons pass by the cavities and cause microwaves to oscillate within, similar to the functioning of a whistle producing a tone when excited by an air stream blown past its opening. A cavity magnetron generates microwaves using the interaction of a stream of electrons with a magnetic field, while moving past a series of cavity resonators, which are small, open cavities in a metal block. The cavity magnetron is a high-power vacuum tube used in early radar systems and subsequently in microwave ovens and in linear particle accelerators. Modern tubes use rare-earth magnets, electromagnets or ferrite magnets which are much less bulky. The microwaves are emitted from the waveguide aperture (top) which in use is attached to a waveguide conducting the microwaves to the radar antenna. The tube is embraced between the poles of two horseshoe-shaped alnico magnets (top, bottom), which create a magnetic field along the axis of the tube. Obsolete 9 GHz magnetron tube and magnets from a Soviet aircraft radar. Central cathode is visible antenna conducting microwaves at the top magnets are not shown. A similar magnetron with a different section removed. The magnets producing a field parallel to the long axis of the device are not shown. The antenna emitting microwaves is at the left. The cathode in the center is not visible. ![]() I did have a lot of fun though.Device for generating microwaves Magnetron with section removed to exhibit the cavities. I had a problem with noise causing some of the relays to switch back and forth rapidly at the beginning and end of the signal which would result in constantly having to replace relays - being completely oblivious to what a capacitor was, this turned out to be pretty expensive! I have since learnt proper electronics. It was configurable by about 4 switches on the outside and had latching relays, AND and NOT gates. It used a stack of relays and a timer with various sensor inputs running to some of the relays (just reading from the LED line on a buch of sensor kits) and motors or LEDs being triggered by sensor input. Looking back it was terrible but I was pretty proud of it at the time (not knowing anything about electronics) - my lecturer wasn't so impressed. By no means complete computer functionality but for my first ever electronics related project I made a re-configurable relay system to perform various logic operations for a first year engineering robotics course.
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