SRC-560

Satellite Power System (SPS) Magnetron Tube Assessment Study -- NASA CR-3383; Contract NAS8-33157; February 1981

Commissioned by Marshall Space Flight Center, Contract NAS8-33157. Who paid for a study is recorded because it bears on how its conclusions should be read, not because it makes them wrong.

Published claims resting on this source

• CLM-1043 With the heater off and a tuning circuit on the cathode, one hand-picked oven magnetron was as quiet as the instrument could measure: about 197 decibels below its carrier per hertz of bandwidth, 50 megahertz away from the carrier. Detuning the cathode circuit cost 20 decibels; turning the heater on swamped the display.
• CLM-1045 Raytheon's own numbers had the klystron just failing the interference limit at the band edge and the magnetron clearing it by 45 decibels, while conceding nobody had measured a klystron that close to its carrier and that near the carrier the klystron was slightly quieter.
• CLM-1046 The number Raytheon wrote into the design table for the satellite tube was about fifty times noisier than its best laboratory reading, because it did not yet know where the noise came from; the only work on that question was Raytheon's own unfunded research.
• CLM-1047 The oven magnetron's second harmonic came out about 70 decibels below its carrier, a tuned stub took another 40 off, and the antenna's own pattern was credited with 65 more, so Raytheon reckoned the whole satellite's second harmonic would arrive on the ground fifty decibels under the limit. The third, fourth and fifth were measured but never filtered, and the fifth was unexpectedly strong.
• CLM-1048 A cheap oven magnetron run cold and hard converted 81.7 per cent of its DC input to microwaves, measured carefully by heating water. Raytheon's point was that theory said 94 and a lower-frequency tube already did 93, so the 2.45 GHz tube was leaving six points on the table nobody had explained.
• CLM-1049 The fifty-year magnetron rests on a cathode that runs cool because the tube heats it only as much as it needs, on tube-life curves from 1950s transmitter valves, and on twelve radio-station valves that ran ten years without failing. No magnetron had been life-tested that way, and the test tubes Raytheon looked into poisoned themselves in under an hour.
• CLM-1050 The interference limit Raytheon measured its tubes against is given as a CCIR requirement but never traced to a CCIR document, and one page even gets its units wrong by a factor of a thousand.

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