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Frequently, when people think of extending range, they immediately think of using amplifiers (I suppose it's only natural; you have an amplifier for your home stereo, why not an amplifier for your network?). Good amplifiers that work in the microwave range have several nontrivial technical obstacles to overcome:
• Amplifiers blindly amplify everything that they're tuned to, both signal and noise. A greater signal won't help you if the noise in the band is increased as well, because the signal will just get lost (like shouting to your friends at a concert).
• 802.11b radio communications are half duplex; they send or receive, but never both at the same time. An amplifier attached to the antenna line will have to detect automatically when the radio is sending and quickly switch the amp on. When it's finished, it has to quickly cut it off again. Any latency in this switching could actually impair communications or, worse, damage the radio card.
• Amplifiers can help a bit on receive by adding some pre-emphasis, but they are really meant for transmitting. This means that if you only have an amp on one end of a link, the other end may be able to hear you, but you may not hear them. To make amps effective, you'll need them on both ends of the link.
• All amplifiers require power to operate. This means adding a DC injector to your antenna feed line or using an external adapter. This further drives up the cost of your node and makes yet another device that you have to provide power for.
As a result, amplifiers that work well with 802.11b gear are expensive ($400+) and difficult to come by. But do you really need them? Using standard gear and high gain antennas, you can extend a point-to-point link to 25+ miles without amplifiers. Your money is probably better spent on high-quality directional antennas and cabling, and possibly even adding another node for further saturation.
As far as U.S. federal law is concerned, you'll have to read the Part 15 (see Appendix A) and draw your own conclusions. Hire a lawyer if you're really paranoid. Tim Pozar (of the BAWUG) has made some interesting observations about the Part 15 rules regarding 2.4GHz emissions; check out his commentary online at
http://www.lns.com/papers/FCCPart15_and_the_ISM_2.4G_Band.index.
In short, the amount of power you can legally run (and the gain of your antenna) is limited, depending on how you use it. Fixed point-to-point links are allotted the most power, while omnidirectional point-to-multipoint configurations are the most restricted. Unless you use amplifiers, you probably aren't likely to run into the FCC limits, because standard client cards don't put out nearly enough power. But don't just take my word for it, because I am not a lawyer (besides, the person responsible for making sure that your rig is legal is you, the operator!)
I do believe that the intent behind the rules is to limit interference in the band, which is something we should all fight to make happen. Noise is everyone's enemy. To that end, try to use the least amount of power necessary to keep your link going, and use the most directional antennas that will work for your application. Be a good neighbor, and you may find that you enjoy your neighborhood more.