On May 27, 2004, at 12:35 PM, John Kelsey wrote:
Does anyone know whether the low-power nature of wireless LANs protects them from eavesdropping by satellite? Is there some simple reference that would easily let me figure out whether transmitters at a given power are in danger of eavesdropping by satellite?If you assume a perfect vacuum (and note that the athmosphere is fairly opaque at 2.4 Ghz) and perfect antenna's etc - then the specific detectivity needed in space suggests a not unresonably sized (m2's) and cold antenna (below 180k) by very resonably NEP which is commercially available. Given the noise from the earth background (assuming a black body radiator) at 2.4, the Sun and the likelyhood that that largish antenna catches a fair chunk of exactly that then you are at the edge of what would be realistic. However with some clever tricks and processing, like a phase array, you certainly should be able to at least detect that short (1-2mseconds) 100Khz wide 2.4Ghz transmisison at 0.1 watt is happening - assuming you know where to look. Listening in over a country-sized swath over a prologned periods of time is an entirely different story. Given that you then need to be at least 3-4 order's of magnitude better - and that you only get at best square root when increase the easy things like detector size etc, at best - my guess would be that some flying or earthbound is a heck of a lot cheaper and more realistic.
There are some good papers on Lidar and Radar detections of clouds in the 3Ghz range at 12km which should give you more of an idea of the spatial resolution you could accomplish. When looking at these - bear in mind that the 2-3kWatt used is reflected by the ice particles - so what gets back is 30-40dBZ less - and that you can use a phased locked loop amplifier easily.
Dw
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