Scope and limits

THIS IS A 1978 MODELLED ASSESSMENT IN A PRELIMINARY DRAFT, NOT A MEASUREMENT, AND IT DISCLAIMS ITS OWN COMPARISON. The exceedance is stated for one converter model set and rests on assumed antenna gains and assumed bandwidths that the report itself calls uncertain. IT MAY NOT BE QUOTED AS ESTABLISHING THAT ANY SPS DESIGN EXCEEDS ANY PROTECTION LIMIT. AND THE DOCUMENT'S OWN APPENDIX DISOWNS THE FIGURE THIS RECORD RESTS ON, IN A STATED DIRECTION AND MAGNITUDE. Appendix I, "Notes on the SPS Noise Calculation of R-31", opens: "Two frequency-dependent effects neglected in the noise calculation of R-31 will, if included, substantially alter the noise spectrum obtained." Both verified first-hand on registration of this limit. EFFECT ONE, BEAM SCANNING, CUTS AGAINST THE INTERFERENCE CASE: the report's own section 6.6.1 gives the slotted waveguide radiator "a frequency scanning sensitivity of 1 arc minute per 612 Hz frequency deviation. This indicates that a deviation of 300 kHz will scan the main lobe off the earth", and "At any given location in the beam's scan path there would be particular narrow frequency ranges where noise could be observed possibly as intense as that calculated below, but most of the spectrum would be much quieter." EFFECT TWO, COHERENCE, CUTS BOTH WAYS: against R-31's -160 dBW/M2Hz at band centre, the appendix computes -183 for out-of-band with tubes independent, "Corrected for 11.5 dB illumination taper it is -178 dBW/M2-Hz, or 18 dB less noisy than the report's result", and -151.4 for in-band and coherent. Net, verbatim: "The net effect of considering the frequency dependence of coherence is to increase the predicted noise density near the carrier by about 9 dB, and decrease the predicted noise far from the carrier by about 18 dB." SO THE EXCEEDANCE SURVIVES NEAR THE CARRIER, WHERE THE CORRECTION IS +9 dB, AND WEAKENS FAR FROM IT, WHERE IT IS -18 dB AND THE MAIN LOBE HAS SCANNED OFF THE EARTH BEYOND 300 kHz. A reader taking Figure B at face value across the whole plotted span is taking a figure the same document says is wrong. THE AXIS QUESTION IS SETTLED BY THE APPENDIX TEXT AND NOT BY READING THE PLOT: the appendix states its own results in dBW/M2Hz, per hertz, so the noise quantity IS bandwidth-referenced by construction - which is what XC01 needed and it comes from prose rather than from a position on a 1978 scan. Its protection reference is CCIR Report 224-3 of 1974, superseded by the ITU-R RA.769 series; the comparison against RA.769-2 (SRC-648) is CLM-1315, which bounds the carrier-value gap at 87 dB at 2695 MHz and does not establish an in-band exceedance. The 10 MHz radio-astronomy bandwidth is this report's own assumption, not a figure taken from the protection standard - so it does not close the reference-bandwidth question that XC01 needs closed; it records what one 1978 draft assumed, FOR THE HARMONICS FIGURE. A REPORTED BUT UNVERIFIED LEAD, NOT PART OF THIS RECORD: the drafting stream reports Figure B's vertical axis as dB(W/m2Hz), which would be bandwidth-referenced by construction and would bear directly on XC01. That plot has NOT been rendered for this record and the axis label is not recorded as established. If it holds it belongs in its own record with the reading treated as a position on a 1978 scan and not a printed number. THE FIGURE THIS RECORD RESTS ON COMES FROM A DOCUMENT THE ARCHIVE DOES NOT HOLD, ESTABLISHED 2026-09-15. SRC-111's Figures B and C are drawn from its reference R-31: "Microwave Power Transmission Studies", Volumes I-IV, December 1975, contract NAS3-17834, NASA-CR-134886, Raytheon ER75-4368 - named independently by Brown in SRC-353 as his reference 8, so two held documents agree on the identifier. It is not held. So the sideband and harmonic findings rest on a 1978 preliminary draft's rendering of a 1975 study, and the study itself has not been seen. That is a limit on how far this record can be pushed, not a reason to doubt the quotation: what SRC-111 SAYS is verified; what R-31 COMPUTED is not checkable here. THE DOCUMENT IS NOW HELD, 2026-09-15, AND THIS FIELD'S STATEMENT THAT IT IS NOT IS SUPERSEDED. R-31 was acquired as SRC-451, all four volumes, 803 pages, open on NTRS at no cost. R-31's CONTRACT NUMBER IS WRONG BY ONE DIGIT: it reads NAS3-17834 and the title pages read NAS 3-17835, so a search on the cited number finds nothing. This record is not yet checkable against it - the volumes are located, not read - and the sideband and harmonic content is most likely in Vol II section 4 and Vol IV on a marker count. Until someone reads those sections, what SRC-111 SAYS remains verified and what R-31 COMPUTED remains unchecked; the difference now is that checking it is a reading task rather than an acquisition one. FIGURE A IS NOW HELD AND READ, AND IT DOES NOT CARRY THE DISTANCES THIS RECORD READS AGAINST IT. ESTABLISHED 2026-09-15, VERIFIED FIRST-HAND. SRC-111's Figure A is SRC-450's Figure 1-9, "SPS 10-dB taper array pattern", PDF p.24 - identified by matching SRC-111's own figure text against it, both carrying km RADIUS AT EQUATOR, 10 m SUBARRAY, 1 min ARC ATTITUDE CONTROL, GRATING LOBES and % FAILURES. ITS AXES ARE GAIN IN dBi AND dB RELATIVE TO PEAK, AGAINST ANGLE FROM BORESIGHT IN DEGREES, with a secondary top scale in km radius at equator. THERE IS NO POWER-DENSITY AXIS. Power density appears only as four horizontal reference lines - 10 mW/cm2 OSHA, 1 mW/cm2 OVEN, 0.1 mW/cm2 LeRC-JSC, 0.01 mW/cm2 EE. SO ANY DISTANCE FOR A THRESHOLD OTHER THAN THOSE FOUR LINES REQUIRES A POWER BUDGET TO TURN GAIN INTO POWER DENSITY, AND SRC-439'S THRESHOLDS ARE FIELD STRENGTHS FROM MILITARY STANDARDS - 194 V/m, 135 dB uV/m, 100 dB uV/m - WHICH ARE NOT ON THIS FIGURE AT ALL. THE CORRECT AND WEAKER STATEMENT IS THAT THE FIGURE SUPPORTS THE GEOMETRY AND THAT THE SPECIFIC DISTANCES ARE DERIVED RATHER THAN READ. The geometry does check: 500 to 1000 km sits at roughly 0.8 to 1.6 degrees on the top scale, which is the grating-lobe region the figure labels and Dickinson's text treats as the whole problem, and 15 km sits near the 0.01 mW/cm2 line. What remains unchecked is the conversion, which neither SRC-111 nor SRC-439 shows. THE LINEAGE CONVERGES, ESTABLISHED 2026-09-15 FROM THE REFERENCE LIST. SRC-450's Figure 1-13, "SPS noise PSFD at the ground (after Ref. 4)", PDF p.35, carries the same content as SRC-111's Figure B - klystron and amplitron noise against the deep-space, line-of-sight and radio-astronomy limit lines, with the 2.69-2.70 and 4.99-5.00 GHz astronomy windows and the 2/f0 and 3/f0 harmonic marks. Dickinson's Ref. 4 is "NASA CR-134886, ER75-4368, Microwave Power Transmission System Studies, 4-volumes, NASA Lewis Research Center, Dec. 1975", verified at PDF p.103 - the same document as SRC-111's R-31, which is SRC-451. So both held renderings of this record's sideband and harmonic content derive from one primary source, and that source is now held. There is no fourth link in the chain. What remains is the read of SRC-451 Vol II section 4 and Vol IV that nobody has yet done. QUALIFIED 2026-09-17 BY THE PRIMARY, CLM-0959 AND CLM-0960: THE TROPOSCATTER LISTING IN POINT II IS A CRITERIA CHOICE, NOT THIS REPORT'S ARITHMETIC.** R-31 tested the same -160 dBW/m2/Hz floor against a troposcatter limit of -132 dBW/m2/Hz and concluded no problem exists with troposcatter regulations; the criterion this report's lineage applies is about -221 dBW/m2/Hz, 89 dB stricter, and the same floor fails it. And R-31 states that the fourth harmonic of all three tubes clears radio astronomy; this report's Figure C is faithful to R-31's data and does not say otherwise, whatever later readers took from it.