Value chain · CLM-0959
In plain terms
The original 1975 calculation found the satellite's radio noise would be fine for ordinary and troposcatter radio links and a problem only for radio astronomy. The 1978 review that redrew its chart swapped the two "fine" limit lines for stricter ones and then listed troposcatter as a problem. The disagreement is over which limit to apply, not over the arithmetic.
The claim as recorded
The 1975 Raytheon study computes the SPS noise power density at the earth's surface at the carrier as -160 dBW/m2/Hz for both amplitron and klystron converters - 7 GW radiated from a 1 km antenna at 2.45 GHz - and plots it against four IRR limits, not two: regular service -118 dBW/Hz, troposcatter -132 dBW/m2/Hz, radio astronomy isotropic -249 and radio astronomy with a 60 dB antenna -309 dBW/m2/Hz. Its conclusion, verbatim as transcribed from a letterspaced page: "no problem exists with regular and troposcatter commercial regulations. A selection of 2.45 GHz is demonstrated to be reasonably good." SRC-111's Figure B, drawn from this, kept the two radio-astronomy lines and replaced R-31's two commercial criteria with ITU ones - the troposcatter line assuming a 40 dB antenna - and SRC-111's Point II then names troposcatter among the services whose protections the sidebands would exceed. The primary says the opposite on its own criterion.
Evidence behind this: T3-primary-report, and the primary behind two held secondaries: SRC-111's Figure B and SRC-450's Figure 1-13 are both drawn from this section, so this is the document the register had been reading at one remove.
Scope and limits
THE TROPOSCATTER VERDICT DEPENDS ENTIRELY ON WHICH CRITERION IS APPLIED, AND THE TWO DIFFER BY 89 dB. This study tested troposcatter at -132 dBW/m2/Hz. SRC-450 - and the IRR lineage SRC-111 cites - uses -168 dBW at the receiver terminals in any 4 kHz band, which SRC-450 converts to about -185 dBW/m2 in 4 kHz on boresight, roughly -221 dBW/m2/Hz. Same -160 floor; it passes one criterion and fails the other. So SRC-111's listing is not an arithmetic error but a criteria choice, and this record does not settle which criterion governs. The -160 is a 1975 estimate "assuming certain noise and filter characteristics (since such high efficiency, high power level devices have yet to be constructed and tested)" - SRC-450's own words about this figure. Vol IV's text layer is letterspaced on the conclusion page, so that sentence is transcribed and confirmed by squashed match rather than quoted raw.
What it assumes
No assumptions are recorded against this claim.
Where it comes from
Vol IV Section 10.1. The -160 figure is computed on PDF p.55 in the line "-31.5 + 33.7 - 162 = 160 dBw/m2/Hz", where the result is printed without its minus sign - the klystron line two paragraphs down carries it and Figure 10-2 plots -160; a reading hazard for anyone quoting the amplitron line. The conclusion sentence matches only at the squashed level on PDF p.57, where the text layer renders "anq tropcscatter" for "and troposcatter"; "A selection of 2.45 GHz is demonstrated to be reasonably good" matches at the normalised level on the same page. SRC-111's Appendix I records that R-31 gives -160 dBW/M2Hz at band centre - an exact match, so the redraw is faithful in axis and floor. The four IRR limits are from the section's own reference 10-1. SRC-111 read directly, not through another record: its Figure B caption block (PDF p.19) names the limit lines it plots - CCIR 74 Report 387-2 line-of-sight, ITU regulations 470NF, 470NI and "470NGA (TROPOSPHERIC SCATTER, 40 db ANTENNA ASSUMED)", and CCIR Report 224-3 Annex 1 radio astronomy - so its troposcatter line is an ITU criterion with an assumed 40 dB antenna, not R-31's -132 dBW/m2/Hz; Point II (PDF p.20) lists "Radio Astronomy, Deep Space Research and Tropospheric Scatter Communications Systems" as provided specific protections that might be violated.
Basis: 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-0959
CLM-0959, Energy Aperture, as of 1975.
Connected records
Other published records linked to this one. A list, not a judgement.
- Also from SRC-111
- CLM-0918The 1978 study of what a solar power satellite would do to the radio spectrum found two things. Its transmitter NOISE would exceed what...CLM-0919In 1978 there was no rule allowing a solar power satellite to transmit power, and the industrial band everyone assumed it would use permits...CLM-0920The 1978 study says a solar power satellite cannot keep its beam entirely on the receiving station - the physics of beams forbids it - so...CLM-0921The 1978 report says the power density a solar power satellite apparently needs to make economic sense was thought to be about the same as...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-1315The 1975 estimate of the satellite's radio noise, taken at its own frequency, is about a hundred million times above today's threshold for...
- 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-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...CLM-0972If you take a 1975 estimate of how fast people could build structure in space, checked against one Skylab task, and apply it to the 1978...More on the source page.