Value chain · CLM-0989
In plain terms
The same figure, minus 160, appears in two 1970s papers meaning two different things: in one it is the noise reaching the ground, in the other it is the noise of a single tube compared with its own signal, which after adding up ninety thousand tubes and the distance to the ground comes out 27 decibels lower. Anyone quoting "minus 160" has to say which.
The claim as recorded
Two different quantities carry the number -160 in the 1975-1979 literature and must not be conflated. In SRC-451 (1975), -160 dBW/m2/Hz is the noise density at the earth's surface, computed as -31.5 + 33.7 - 162. In Arndt and Leopold (1978), "-160 dB/Hz" is the assumed noise spectral density of a single klystron relative to its own carrier, which multiplied by 90,000 tubes gives -61.9 dBW/Hz at the antenna and -187.4 dBW/m2/Hz at the ground, compared there with a general S-band CCIR flux limit of -180 dBW/m2/Hz. A January 1979 National Academy of Sciences panel put the unfiltered noise of the earlier amplitron design at -153 dBW/m2/Hz at the surface and stated that "the harmful interference levels defined in the CCIR report lies some 80 to 90 dB below this level in the 2-3 GHz region".
Evidence behind this: T3-proceedings reprinting a 1978 conference paper and a 1979 Academy panel statement.
Scope and limits
THE REGISTER'S -160 (CLM-0959) IS THE AT-EARTH QUANTITY AND IS NOT AFFECTED; the hazard is a reader importing Arndt and Leopold's per-tube figure as if it were. The Academy panel's -153 is for the 1974 amplitron design of CR-2357 (about 100 satellites, 6 GW, near 3 GHz), a different reference point from the 1978 klystron system. The "-180 dBW/m2/Hz for S-band" is a general out-of-band flux limit, a third meaning of "the CCIR requirement" beside Report 224-4 (CLM-0988) and R-31's four IRR lines (CLM-0959). Recomputed from the page's own G_N (35.6 dB) and a 35,800 km range, the ground density is -188.4 dBW/m2/Hz, 1 dB from the printed -187.4; the page does not state its R.
What it assumes
The -187.4 at ground uses the paper's own antenna noise gain GN and 4 pi R^2 spreading, not shown in full on the page.
Where it comes from
PDF p.245, the cleaned reading confirmed at the render (the text layer prints "90, 1J'JO klystrons", "(72.000)" and "-61. g"): "Since there will be 90,000 klystrons in the antenna for the 5 GW system, the total power density generated within the antenna will be PN = (# of klystrons)(signal power/klystron)(Noise Spectral Density) = (90,000)(72,000)(-160 dB/Hz) = -61.9 dBW/Hz... The noise spectral density at the ground is PN-G = PN GN/4 pi R^2 = -187.4 dBW/m2/Hz." "The CCIR (International Radio Consultative Committee) requirements for power flux density at the earth's surface is -180 dBW/m2/Hz for S-band frequencies with an angle of arrival above 25 degrees." PDF p.236 (the passage continuing onto p.237), normalised: "Current tubes, according to the study, can achieve a noise power, in a 1 MHz band, 55 dB below the signal; with such tubes a broadband noise power of 43 dBW/MHz would be generated by the satellite... The unfiltered noise signal with current tube designs would be -153 dBW m2 Hz-1 at the earth's surface. The harmful interference levels defined in the CCIR report lies some 80 to 90 dB below this level in the 2-3 GHz region." "Even if adequate filters could be designed, the failure of a single one of the 10^6 filters could produce a noise level in excess of the harmful limits of CCIR 224-4." Arithmetic: 10 log(90,000 x 72,000) = 98.1 dBW; 98.1 - 160 = -61.9 dBW/Hz.
Basis: dB/Hz per tube relative to carrier; dBW/m2/Hz at the earth's surface
Related records
- Answers question
- QST-001 not published in this release
Cite this
energyaperture.com/c/clm-0989
CLM-0989, Energy Aperture, as of 1979.
Connected records
Other published records linked to this one. A list, not a judgement.
- Also from SRC-451
- CLM-0954The 1975 designers worked out how much their kilometre-wide antenna would bend, precisely so they could decide how good the beam-steering...CLM-0959The original 1975 calculation found the satellite's radio noise would be fine for ordinary and troposcatter radio links and a problem only...CLM-0960The 1975 study found the satellite's harmonics - the multiples of its transmit frequency - would trouble radio astronomy at the second and...CLM-0961Everything in the 1975 interference analysis is for one satellite. The study itself says that a hundred of them would raise the noise and...CLM-0965In 1973 an astronaut on Skylab put together two long poles from short sections in just over two hours, about six minutes per join. A 1975...CLM-0966In 1975 the antenna alone was expected to take one to two years to assemble in orbit with about fifty people, and robot arms were judged...CLM-0968The 1975 antenna study worked out how hot the middle of the transmitter gets depending on how efficient the tubes are and how tightly they...CLM-0969If the tubes are only 70 per cent efficient, the transmitter's own face is not big enough to get rid of the heat they make, even spread...More on the source page.
- Also from SRC-516
- CLM-0988The rule that radio astronomers hold the satellite to is a specific international report, and its limit near the satellite's frequency is...CLM-0990The extra twenty decibels of noise suppression for a fleet assumes a hundred satellites. The government's reference plan was sixty, which...CLM-0991In 1978 the frequency band the satellite was to use was an industrial free-for-all band in the West, where users must put up with each...CLM-0992The receiving field on the ground makes its own harmonics: the diodes that turn microwaves into electricity also generate signals at two...CLM-1091The people running the programme said 2.45 GHz was sensible and also said, in the same breath, that nobody international had agreed to it...CLM-1222The fourth paper the 1978 design cites for its beam limit also calls the limit a theory that had not been tested. The one experiment it...