November 2001
Beginner
144 pages
3h 41m
English
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Power Amps and the Law
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 ...
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