Re: [gentoo-user] looking for wireless technology

[Stroller <stroller@stellar.eclipse.co.uk>]

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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