Value chain · CLM-1003
In plain terms
For a transmitter built from millions of small solid-state amplifiers instead of tubes, the 1980 study worked its noise budget down to the ground and found about 27 decibels of headroom against the limit it used; it also noted that for such a large array the second harmonic's grating lobes miss the earth altogether, so the worry moves to the third harmonic, and that a separate frequency allocation for harmonics might be needed.
The claim as recorded
Raytheon's 1980 solid-state transmitter study sets its amplifier noise goal at -156 dBW/Hz relative to carrier, non-coherent between subarrays, and derives from it a noise density at the earth of -217 dBW/m2/Hz for a 2 GW transmitter (-181 dBW/m2 per 4 kHz) against a "CCIR requirement" it states as -154 dBW/m2 per 4 kHz, a 27 dB headroom that incoherent addition of 500 such systems would consume; it estimates the coherent residual harmonic power density at the earth as -66 dBW/m2 at the third harmonic "and less at higher harmonics", and states that "since grating lobes for the second harmonics do not intersect the earth, it is not considered a fundamental requirement to contend with"; and its summary of issues reads "frequency allocation needs at harmonics should be considered or consider spread spectrum and active suppression". Its parameter table fixes the transmit frequency at 2.450 GHz and three pilot frequencies at 2.301, 2.550 and 2.799 GHz.
Evidence behind this: T3-contractor study; goals and constraints stated for a design, with the derivation of one shown as a table.
Scope and limits
THE -154 dBW/m2 PER 4 kHz IS NOT CCIR REPORT 224-4's RADIO-ASTRONOMY THRESHOLD (CLM-0988) AND THE DOCUMENT DOES NOT SAY WHICH LIMIT IT IS; the same figure appears as a standing constraint in the magnetron work (SRC-560) and is a programme-wide design limit of unstated origin. The grating-lobe statement depends on the solid-state design's element spacing and is not general.
What it assumes
Non-coherent noise between subarrays; the -154 figure is used as a bare constraint without naming which CCIR instrument it comes from (probed: CCIR, ITU, ISM, radio astronomy - none in the document beyond that line).
Where it comes from
PDF p.146, Table 5.4-1 "Transmitter Noise Goals", raw: total transmitter power (2 GW) +93 dBW; amplifier noise relative to carrier -156 dBW/Hz; GT (0.1 m element) +9 dB; GR (1 m reference) +29 dB; LP (D = 3.71e7 m) -192 dB; "Noise Density At Earth -217 dBW/m2/Hz"; "CCIR Requirement (-154 dBW/m2/4 kHz)"; "-181 dBW/m2/4 kHz". Arithmetic: 93 - 156 + 9 + 29 - 192 = -217; -217 + 10 log(4000) = -181; -181 to -154 is 27 dB = 10 log(500). Same page, normalised: "The residual harmonic power density that may be coherent over the total transmitting array periodically as estimated at the earth is -66 dBW/m2 at the third and less at higher harmonics... Since grating lobes for the second harmonics do not intersect the earth, it is not considered a fundamental requirement to contend with." PDF p.12, Table 2.1-1, normalised: "FREQUENCY ALLOCATION NEEDS AT HARMONICS SHOULD BE CONSIDERED OR CONSIDER SPREAD SPECTRUM AND ACTIVE SUPPRESSION." PDF p.92, Table 3-1: "FREQUENCY (TRANSMIT) = 2.450 GHz; FREQUENCIES (PILOT) = 2.301 GHz, 2.550, 2.799"; "ELECTROMAGNETIC INTERFERENCE - 154 dBW/m2/4 kHz".
Basis: dBW/Hz relative to carrier; dBW/m2/Hz and dBW/m2 per 4 kHz at the earth; GHz of pilot
Related records
- Answers question
- QST-001 not published in this release
Cite this
energyaperture.com/c/clm-1003
CLM-1003, Energy Aperture, as of 1980.
Connected records
Other published records linked to this one. A list, not a judgement.