Value chain · CLM-1086
In plain terms
The number 2.45 GHz has a birthplace: a 1975 study for NASA that swept frequency from 1 to 5 GHz against cost, found a broad flat region near 2 GHz, and picked the industrial band sitting in it. The atmosphere was checked separately and found nearly transparent below 3 GHz.
The claim as recorded
The 2.45 GHz downlink was selected in the 1975 Raytheon study for NASA Lewis, as that study's own stated output, on a parametric capital-cost sweep over 1 to 5 GHz at 5 dB taper and 90 per cent beam efficiency with converter cost and weight written as functions of frequency, and on propagation work concluding the atmosphere is "minimal for frequencies below 3 GHz (2 percent attenuation nominally and 4 percent in most severe cloud and rain conditions)". Its selection paragraph: "The DC-RF converter characteristics and the system efficiency and cost factors have been shown to be favorable in a broad range near 2 GHz so that a choice of the USA industrial band of 2.4-2.5 GHz centered at 2.45 GHz appears to be straightforward. The effect on other users of the spectrum can be significant for any choice, but the 2.45 GHz selection appears to have minimal impact as discussed in an earlier section."
Evidence behind this: T3-the programme's own 1975 contractor trade study: a parametric cost sweep held as plots and a stated selection paragraph, transcribed from a render because the text layer is degraded.
Scope and limits
A 1975 PARAMETRIC RESULT WITH ITS FORMULAS ON A DEGRADED PAGE: the cost-versus-frequency figures are held as plots (1 to 5 GHz on the axis) and their minima are not read off here; "favorable in a broad range near 2 GHz" is the study's characterisation, not a number. The interference clause points to Section 10, which is CLM-0959, and that section's troposcatter criterion is the one CLM-0959's limits say is 89 dB looser than the 1978 lineage's. Tube availability is not a stated reason; converter cost and weight as functions of frequency are.
What it assumes
The 1975 cost and weight relations for amplitron and klystron converters, and 1975 transportation and power-source cost ranges (100 to 600 $/kg, 200 to 1000 $/kW), which the study states as its parametric inputs.
Where it comes from
PDF p.103 / 12-22, render read (extract/derived/SRC-451/render/p0103@2.0.png): "12.2.6 FREQUENCY SELECTION. Frequency selection perhaps is the most important output of this study since device development is intimately related to the choice, and system development can be severely impacted by difficulties in radio frequency interference and allocation." then the two sentences quoted in the claim; text layer renders "ba[U+00B7]1d" and "pe~haps is the most impo~:lt", so all three are TRANSCRIBED. PDF p.94 / 12-13, read at the render (the text layer garbles the sentence to "po..,i.:er are va riei:;"): "A beam taper of 5 dB and a beam collection efficiency" of 90 percent "were selected to exhibit trends of capital cost as frequency and power are varied"; costs "in 1975 dollars". PDF p.93 / 12-12 gives amplitron and klystron cost ($/kW) and weight (kg/kW) as linear functions of f in GHz and a rectenna cost rising with f; the formulas are in a degraded text layer and are not transcribed here. Vol II PDF p.43 / 3-1, NORM, the "minimal for frequencies below 3 GHz" sentence; p.50 / 3-8, NORM: "it is concluded that atmospheric attenuation due to molecular absorption and heavy rain is tolerable at frequencies below 3 GHz."; p.23 / 1-5, NORM: "For the atmosphere at frequencies below 3 GHz: a. Absorption and scattering effects are small except for wet hail." and RAW "For the ionosphere at frequencies above 1 GHz:" with absorption "negligible". Basis: GHz; capital cost per kW versus frequency, 1975 dollars; per cent atmospheric transmission
Related records
- Answers question
- QST-017 not published in this release
Cite this
energyaperture.com/c/clm-1086
CLM-1086, Energy Aperture, as of 1975-12.
Connected records
Other published records linked to this one. A list, not a judgement.
- 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.