On Nov 13, 2005, at 5:51 am, Willie Wong wrote:
If you have line-of-sight, you might be able to make do with a pair of directional antennae set up in the right way, and you might need a way of increasing the power output of the antennae. Any such modifications, however, is surely ILLEGAL in most civilized municipalities. The long-range wireless guys who have been doing stuff like this all have ham licenses, and are allowed quite a bit more power from their devices then us lowly consumers....
I think you're mistaken here. 802.11 is on an unregulated part of the frequency spectrum, so ham radio operators have no more rights when operating in it than the rest of us.
802.11 is perfectly achievable over distances of a kilometer, providing line of sight is available, and legally. The requirement is not to emit more than a certain signal strength (about 18dB or 20dB, I think) but signal strength is a product of transmitter power and amplification caused by the aerial. A very directional aerial amplifies the signal lots, but if you combine this with a low-power transmitter then you can still creep in under the legal signal strength.
One might ask, "but if I'm transmitting 20dB with a low-power directional aerial, that gives me the same range as 20dB using a non-directional aerial (like the rubber-jacketed kind that are supplied with wireless cards) at high-power" but this doesn't take into account receive attenuation. The directional aerial at the OTHER end will pick up the signal more clearly - it's listening in only one direction and effectively "amplifies" that signal for the receiver.
Instructions for building directional aerials are posted widely on the net, and the OP will be able to find them easily with a bit of searching (check out the Seattle Wireless & Guerilla Wireless websites) but it's harder to find wireless cards that will transmit at low enough power to make them (legally) useful. Last time I checked I could only find the expensive Cisco "Aeronet" (??) kit to be documented as being used in this way; I suspect there's not much available in Linux-compatible "54G" kit out there. When I looked at doing this line-of-sight was a bigger hurdle.
Stroller.
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