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