Value chain · CLM-0988
In plain terms
The rule that radio astronomers hold the satellite to is a specific international report, and its limit near the satellite's frequency is 87 dB, about five hundred million times, below the noise the 1975 transmitter design would put on the ground. The rule also says nothing about noise just outside the protected bands, which is where most of a wideband transmitter's noise would fall.
The claim as recorded
The radio astronomy protection criterion the 1978-1981 programme documents compare the SPS against is CCIR Report 224-4, and its harmful-interference thresholds for continuum observations are -255 dB(W/m2 Hz) at 1420 MHz, -247 at 2700 MHz (the band nearest the SPS fundamental), -241 at 5000 MHz (nearest the second harmonic), -240 at 10.65 GHz and -233 at 15.35 GHz. Against a transmitter noise density of -160 dBW/m2/Hz at the earth's surface that is a gap of 80 to 95 dB from 1420 MHz to 10.65 GHz and 73 dB at 15.35 GHz, and a radio astronomer at the workshop adds that the standard "would allow infinite power at 1 Hz outside the band edge", so the band-edge structure of the criterion does not fit a wideband high-power source.
Evidence behind this: T3-proceedings carrying a reprinted primary instrument (a CCIR report) and a radio astronomer's reading of it. The CCIR table is the criterion itself, not a secondary's account of it.
Scope and limits
A THRESHOLD FOR AN ISOTROPIC RECEIVING ANTENNA AND A 2000 s INTEGRATION; the workshop's own VLA paper (PDF pp.141-148) puts tolerable levels 20 to 35 dB above these for an interferometer, with the two internal statements of that margin disagreeing (17 or 14 dB decorrelation at 25 MHz). The gap of 73 to 95 dB is to the register's -160 dBW/m2/Hz single-satellite floor from the 1975 design (CLM-0959), not to any later transmitter figure.
What it assumes
No assumptions are recorded against this claim.
Where it comes from
Table I of CCIR Report 224-4 as reprinted at PDF p.203, raw: nominal 1420 MHz, centre 1413.5, -255; 2700 MHz, centre 2695.0, -247; 5000 MHz, centre 4995.0, -241 dB(W/m2 Hz), with the table running from 20 MHz to 235 GHz; Table II gives stricter spectral-line figures, for example -230 at the 4830 MHz formaldehyde line. Erickson, PDF p.129, raw: "Frequency (GHz): 1.4, 2.5, 5, 10, 15 / Power Flux Spectral Density dB(w/m2-Hz): -255, -247, -241, -240, -233"; PDF p.130: "We foresee special difficulties with SPS in that the standards would allow infinite power at 1 Hz outside the band edge. SPS would generate extremely strong out-of-band signals which are not proscribed by existing standards, and which may be impractical to reject completely with filters." Report 224-4 Section 9 (PDF p.206) defines three categories of harmful interference, the third being low-level interference "particularly harmful" because it cannot be recognised and removed.
Basis: dB(W/m2 Hz) harmful-interference threshold, continuum observations, 2000 s integration
Related records
- Answers question
- QST-001 not published in this release
Cite this
energyaperture.com/c/clm-0988
CLM-0988, Energy Aperture, as of 1980.
Connected records
Other published records linked to this one. A list, not a judgement.
- Also from SRC-516
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