Value chain · CLM-1048
In plain terms
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.
The claim as recorded
Raytheon measured an oven magnetron at 81.7 per cent overall efficiency, probable error +/-1 per cent, with no external filament power at 601 mA, 7462 V, 4484 W in and a computed 3008 gauss (B/B0 = 7.62), by series water calorimetry through the load and anode jacket balancing DC input to +0.58 per cent; it derives 94.8 per cent circuit efficiency, 86 per cent electronic efficiency and "at least 87.5%" DC-to-RF conversion after 50 W of cathode back-heating, against a theoretical 93.8 per cent at the field used and a 915 MHz magnetron's 93 per cent, calling the shortfall a "missing" 6 per cent that "is not a new discovery"; the 1981 report cites it as 82 +/- 1 per cent at B/B0 of eight, says its importance "is not the high efficiency, but rather that the efficiency is considerably lower than theoretical", and projects the SPS tube at a minimum of 85 and a maximum of 90 per cent at 20 kV, 3.2 kW or 5.0 kW for a 0.56 kW dissipation limit.
Evidence behind this: T3-tube developer's measurement by water calorimetry with a stated probable error.
Scope and limits
One tube type at 7.5 kV and 600 mA, twice its normal oven current, stripped of its magnets in a solenoid; the tube in the noise tests ran at 61.5 per cent at 3.5 kV (SRC-559 Table 4-1). The 85 and 90 per cent are projections for an unbuilt 20 kV design; the source's own list of unresolved issues puts "the sources of inefficiency" second. The 1980 introduction prints 81.5 and 87 where the body prints 81.7 and 87.5.
What it assumes
No assumptions are recorded against this claim.
Where it comes from
Table 6-1 (PDF 96 / 6-5), render read: "601 7462 4484 3008 3589 803 4392 4457 81.7 +0.0058 ... *B/Bo = 7.62". PDF p.99 / 6-8, render read: "The combined circuit efficiency ... was found to be 94.8%. The corresponding electronic efficiency of the tube would therefore be 81.7/94.8 or 86% ... the conversion efficiency of DC power into microwave power is at least 87.5% ... The Vh/V0 ratio was 16.4, which would indicate a theoretical efficiency of 93.8% ..." "a commercially available magnetron operating at 915 MHz and with about the same Vh/V0 ratio exhibits a DC power to rf power conversion efficiency of 93%. This 'missing' 6% of conversion efficiency in the microwave oven magnetron is not a new discovery". PDF p.145 / 8-3, render read: "A probable error of +/-1% of the 81.7% efficiency measurement resulted." SRC-560 PDF p.37 / 1-11, render read: "82 +1% overall efficiency from a microwave oven magnetron by operating it at a B/B0 ratio of eight ... the importance of this finding is not the high efficiency, but rather that the efficiency is considerably lower than theoretical". Table 7-3 (PDF 157), render read: "7 Minimum Efficiency at 20 kV 85% Present Design Capability ... 9 Maximum Efficiency at 20 kV 90% Inherent Capability of Crossed Field Device Much Development Needed".
Basis: per cent, DC in to RF out by water calorimetry
Related records
- Answers question
- QST-002 not published in this releaseQST-017 not published in this release
Cite this
energyaperture.com/c/clm-1048
CLM-1048, Energy Aperture, as of 1980-05.
Connected records
Other published records linked to this one. A list, not a judgement.
- Also from SRC-559
- CLM-1044In 1980 the quiet oven magnetron was already beyond the instrument's reach: at least 155 decibels below carrier per hertz away from the...CLM-1045Raytheon's own numbers had the klystron just failing the interference limit at the band edge and the magnetron clearing it by 45 decibels...CLM-1047The 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...CLM-1049The 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...CLM-1050The interference limit Raytheon measured its tubes against is given as a CCIR requirement but never traced to a CCIR document, and one page...
- Also from SRC-560
- CLM-1043With the heater off and a tuning circuit on the cathode, one hand-picked oven magnetron was as quiet as the instrument could measure: about...CLM-1045Raytheon's own numbers had the klystron just failing the interference limit at the band edge and the magnetron clearing it by 45 decibels...CLM-1046The number Raytheon wrote into the design table for the satellite tube was about fifty times noisier than its best laboratory reading...CLM-1047The 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...CLM-1049The 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...CLM-1050The interference limit Raytheon measured its tubes against is given as a CCIR requirement but never traced to a CCIR document, and one page...