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Inscribedon label: MODEL #2 RESNATRON / TUBE SERIAL #15 / RRL-28953 IT-1 / BS-3L373-R
FunctionThe Resnatron was an extremely large vacuum tube designed at the Radio Research Laboratory, Harvard's secret radar countermeasures facility in World War II. It is a transmitter of microwaves used to disable enemy radars. In particular, it was the microwave source for the gigantic "Tuba" anti-radar system, used to jam the radars from German fighter planes from the ground in England as they pursued allied bombers at night over the Continent.
The production model was manufactured by Westinghouse.
The resnatron has the basic form of a tetrode, brought to an enormous scale. Inside it, it has a cathode, anode, control grid and screen, each of which has to be cooled by a large stream of flowing water. The interior needs to be in a vacuum, but due to its size, during its use it had to be continuously evacuated with a vacuum pump. Technically, these features were based on peacetime cyclotrons, which also required very large electrical currents and voltages, cooling and continuous evacuation.
It had an output power between 30 and 100kW (about 100 microwave ovens), and its frequency could be tuned between 340 and 625 MHz by altering its inner geometry, which is the purpose of the visible chain drive mechanism. The emitted waveform was random noise.
It was designed to be easily maintainable by a field crew with no college education, and had interchangeable parts. (See RS0080 and RS0081 for a cathode).
Resnatrons were the microwave source used for the "Tuba" systems, one of the largest technological weapons of the time. A team was composed of ten trucks and a trailer carrying the following:
- Two transmitter trucks, each carrying two resnatrons with associated output systems, vacuum pumps, water-circulating system, heat exchanger and blower, modulator, panels for determination and control of vacuum, and panels for control of resnatrons and modulator.
- Three primary power generation trucks, each carrying a 75kW diesel engine generator unit with generator switching and synchronizing equipment
- Two rectifier trucks, containing transformers and tube racks for the main power rectifier, which supplied 100kW of DC power; also remote-control switching, protective, and relaying apparatus
- One workshop truck
- One water trailer
- Two antenna trucks. The antennas were about 50ft high, in what was called the parabolic half-cheese type. The transmitter antennas were placed about 200ft from the other trucks, connected to the resnatron's output by copper waveguides (pipes). An alternative arrangement used a fixed antenna in the shape of a horn of chicken wire, about 150ft long.
Historical AttributesThe resnatron was one of the major developments of the Radio Research Laboratory at Harvard University during World War II.
Primary SourcesThe Resnatron is described in detail in: Herbert J. Reich (Ed.) Very High-Frequency Techniques; Compiled by the Staff of the Radio Research Laboratory, Harvard University (McGraw Hill, 1947). Chapter 19.
A good source about countermeasures in general from the period is "Radar Countermeasures", Electronics (January 1946), pg. 92-97. Available online at CECOM Historical Office here.
The Harvard Archives contain the papers of the Radio Research Laboratory. For a Finding Aid, click here.