40:. The first micropup, the VT90, was introduced in 1939 and capable of operating at wavelengths as low as 25 cm, although at low power. The VT90 was much more widely used in a broad variety of radars operating in the 1.5 m band, around 200 MHz, which remained in widespread use for the rest of the war. Improved versions like the NT99 of 1941 allowed operations at 50 cm, or 600 MHz, leading to a series of new radar sets. These saw less use as the introduction of production-quality
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the heat. In the micropup, glass portions maintained the vacuum in the low-heat sections of the tube, and the active area, in the middle, was made of copper with metal fins that were brazed to the outside of the cylinder to improve heat dissipation, resulting in a design that looks somewhat like the cyclinders in an air-cooled aviation engine. The much greater heat handling allowed the tubes to operate at much higher power levels.
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two glass tubes. The rod ran out through the end of glass enclosure and acted as the grid electrode connection. The cathode was supported by a glass disk inside the anode, with wires running the opposite direction and out through the second glass tube. A second wire on this end connected to the cathode heater. The anode, which was exposed outside of the tube, was connected to directly.
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place the components closer together. This allowed the operating frequencies to be increased, and could operate at the same power levels as the VT90 at 600 MHz, leading to a series of radars operating at this frequency. The NT99 also introduced a new oxide coated cathode which greatly improved the electron emission and led to higher efficiency overall.
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GEC continued improving the design, with the next major version being the NT99 (known to the military as the CV92) which appeared in mid-1941. This greatly reduced the length of the glass tube and metal post holding the grid, resulting in a stronger design, allowing it to use a larger cathode and to
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Key to the micropup design is the development of methods to seal glass directly to metal, allowing the construction of mixed-material vacuume chambers. Previously, tubes were all-glass and the need to limit heating of the glass led to very large designs known as doorknobs or acorns which spread out
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The first models, the VT90s, could be operated at very short wavelengths (for the era), as low as 25 cm, or 1,200 MHz, but only at very low power levels of a few hundred watts per pulse. At 50 cm, 600 MHz, this was improved to the kilowatt range, and at 1.5 m, 200 MHz
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The active section of the tube was similar to other designs of the era. The grid was a wire mesh cylinder, known alternatively as a "squirrel cage" or "parrot cage", was positioned just inside the anode and supported by a metal rod running out one end of the tube and held in position by one of the
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to travel from the cathode to the anode, and this results in a maximum frequency that the tube can operate at. The micropup's large physical dimensions would normally result in a low-frequency tube, but this was overcome by operating at very high
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There is a dependance between the physical size of the tube that puts a limit on the minimum time it takes for the
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was able to produce significant power at much higher frequencies, as radar systems developed during the war.
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applications, the 1.5 m band became widely used in early-war
British sets, including their
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they reached 10 kW. As power level is more important for basic
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Technical and
Military Imperatives: A Radar History of World War 2
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The
Development of Radar Equipments for the Royal Navy, 1935–45
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Although widely used in "metre-band" radar systems, the
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sets. A 50 cm radar set using micropup was used by
48:-frequency radars that outperformed the best micropups.
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made a version known as the 4C28 that they used in the
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for use at very high frequencies such as those used in
170:, Technical Manual TM 11-673, June 1953, pp. 114–116
168:Generation and Transmission of Microwave Energy
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73:to speed up the motion of the electrons.
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166:United States Department of the Army
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151:"High-frequence Space Charge Tubes"
96:anti-aircraft radars, and several
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28:(valve) developed by the British
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83:Airborne Interception radars
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104:to track movements of the
30:General Electric Company
24:is a style of triode
200:F.A. Kingsley (ed.),
87:Air-Sea Vessel radars
44:the same year led to
183:, CRC Press, 1999,
42:cavity magnetrons
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52:Description
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222:Categories
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179:L. Brown,
131:References
98:Royal Navy
66:electrons
46:microwave
120:system.
106:Bismarck
71:voltages
22:micropup
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118:SHORAN
233:Radar
154:(PDF)
79:radar
38:radar
206:ISBN
185:ISBN
92:and
20:, a
114:RCA
16:In
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