Value chain · CLM-1315
In plain terms
The 1975 estimate of the satellite's radio noise, taken at its own frequency, is about a hundred million times above today's threshold for spoiling radio astronomy. The noise in the astronomy band itself would be lower, by an amount nobody has yet read from the 1975 study.
The claim as recorded
The 1975 Raytheon SPS noise density of -160 dBW/m2/Hz at the 2.45 GHz carrier is 87 dB above RA.769-2's continuum threshold for 2695 MHz (-247 dB(W/(m2 Hz))) and 81 dB above that for 4995 MHz (-241). The gap is 102 and 96 dB if the -15 dB GSO adjustment applies. The comparison is a bound, not a finding about the radio-astronomy bands: -160 is the carrier value, and the 1975 level inside 2690-2700 MHz is not in any held record as read.
Evidence behind this: T3, the weaker of its sources: the 2003 ITU recommendation is T1 (SRC-648); the 1975 and 1978 reports that give the noise levels are T3 (SRC-451, SRC-111). The comparison and its arithmetic are ours; neither source makes it.
Scope and limits
The -160 is a 1975 modelled estimate at the carrier, not an in-band or a measured level (CLM-0959 limits). CLM-0918 records that the 1978 appendix revises the estimate +9 dB near the carrier and -18 dB far from it, and that frequency scanning moves the beam off the earth beyond 300 kHz. The level inside the RA bands needs a read of SRC-451 Vol II section 4 and Vol IV. These are thresholds of detrimental interference, not regulatory limits, and no SBSP out-of-band emission level is given in RA.769-2.
What it assumes
The SPS satellite is in GSO, so the -15 dB adjustment applies (RA.769-2 section 2.1, p.6); the side lobe is 0 dBi.
Where it comes from
-160 - (-247) = 87; -160 - (-241) = 81; -160 - (-255) = 95 (1413.5 MHz); with GSO -15: -160 - (-262) = 102 and -160 - (-256) = 96; with 10 h: -160 - (-253.3) = 93.3. Against SRC-111 Appendix I's far-from-carrier -178 (CLM-0918): -178 - (-247) = 69. RA.769-2 values from Table 1, p.9. The 1975 IRR isotropic radio-astronomy line in CLM-0959 is -249, 2 dB stricter than RA.769-2 at 2695 MHz; its frequency is unverified.
Basis: dB(W/(m2 Hz)) at the earth's surface, 0 dBi side lobe, 2000 s
Related records
- Answers question
- QST-017 not published in this release
Cite this
energyaperture.com/c/clm-1315
CLM-1315, Energy Aperture, as of 2003.
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-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...
- 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-648
- CLM-1314The international radio-astronomy standard says how weak a stray signal must be before it spoils a sensitive observation. In the...