Value chain · CLM-1044
In plain terms
In 1980 the quiet oven magnetron was already beyond the instrument's reach: at least 155 decibels below carrier per hertz away from the carrier, quieter at low magnetic field and high current, unaffected by drive level. Close to the carrier its added phase noise was about 114 decibels down per kilohertz at 50 kilohertz.
The claim as recorded
Raytheon's May 1980 JPL report measures the oven magnetron directional amplifier's background noise as "at least 155 dB below the carrier" per Hz at more than 10 MHz from the carrier (tube #12, heater off, 15 W drive, 24 dB notch, 300 kHz bandwidth, 3.0 to 5.0 kV and 150 to 350 mA), limited by an analyser residual 103 dB below carrier in 300 kHz, finds it "increased with operating voltage", cleanest "at the lower values of magnetic field and at the higher current levels", and "independent of the level of rf drive and of the frequency of the rf drive"; measures added phase-modulation noise on a Hitachi 2M170 (heater off, 710 W, 61.5 per cent) at -114 dBc in a 1 kHz band 50 kHz from the carrier (instrument-limited), -110 at 10 kHz and -100 at 5 kHz; records that pre-contract measurements had reached "160 dB/Hz at noise frequencies removed by 50 MHz or more", and that later measurements with 35 dB more sensitivity gave "as high as 195 dB/Hz" on selected tubes.
Evidence behind this: T3-tube developer's report for JPL; instrument-limited floors, measured.
Scope and limits
Every background figure is an instrument floor, and the source says so ("still limited by the test arrangement", 4-2). The report's own summary states the close-in figure as "145 dB below the carrier at ... 50 kHz" (8-2), the per-Hz conversion of -114 dBc/kHz. The 195 is a statement about later work with no data in this report. The notch depth is printed 25 dB on p.40 and 24 dB in the figure caption (second reader, VER-1277).
What it assumes
No assumptions are recorded against this claim.
Where it comes from
PDF p.144 / 8-2, render read: "A noise spectral density that was at least 155 dB below the carrier was obtained in the normal operating range of voltage at frequencies removed from the carrier frequency by more than 10 MHz. Background noise increased with operating voltage ... independent of the level of rf drive and of the frequency of the rf drive". Fig. 4-2 (PDF 43 / 4-5), render read: "TUBE #12 PFIL = 0 Pd = 15 W FREQ. = 2450 MHz NOTCH FILTER 24 dB [BW = 300 KHz SCAN = 20 MHz/DIV] RESIDUAL NOISE LEVEL OF SPECTRUM ANALYZER 103 dB BELOW CARRIER". PDF p.42 / 4-4: "The cleanest spectra are seen to be at the lower values of magnetic field and at the higher current levels." PDF p.51 / 4-13, render read (the text layer prints "leve1" and "aa" for "level" and "as", and PDF p.40 prints "recordad"): "a noise level in a 1 kHz bandwidth that is 114 dB below the carrier. The noise contributed by the magnetron directional amplifier will be less than this value ... At 10 kHz ... 110 dB below the carrier level. At 5 kHz ... 100 dB". Table 4-1 (PDF 52), render read: "Hitachi 2M170 ... 20 Watts ... 710 Watts ... 3531 Volts ... 0.357 Amperes ... 61.5% ... 2437 MHz". PDF p.12 / 1-2, render read: "signal to noise ratios of as high as 160 dB/Hz at noise frequencies removed by 50 MHz or more from the carrier" (the text layer prints 180). PDF p.40 / 4-2, render read: "signal to background noise ratio measurements of as high as 195 dB/Hz have been recorded from selected microwave oven magnetrons."
Basis: dB below carrier per Hz and per kHz; 300 kHz and 1 kHz measurement bandwidths
Related records
- Answers question
- QST-017 not published in this release
Cite this
energyaperture.com/c/clm-1044
CLM-1044, 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-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-1048A cheap oven magnetron run cold and hard converted 81.7 per cent of its DC input to microwaves, measured carefully by heating water...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...