On Thursday (05/09/2002 at 10:00PM -0500), Mike Bresnahan wrote: > NEWBIE ALERT > > I'm very new to this wireless stuff and have never played with radio > equipment beyond Citizen's Band (CB radio), but I know enough to have a > couple questions about the range of 802.11b. > > What little I have read about 802.11b and its counterparts (e.g. bluetooth > wireless) discusses effective ranges of 10-100 meters. My limited > experience with my Linksys Prism2.5 card confirms this range. How is it > that people on this list are discussing ranges upwards of 23 miles? Perhaps > the stuff I have been reading assumes very small antennae? > > After seeing the coverage maps of the Twin Cities displayed at the meeting, > I'm left with some confusion. What good is it to put up a big antennae > backed by a big amplifier and coat a very large area with 802.11b? Can > people with ordinary WLAN cards in their laptops actually communicate with > the access point? I can understand how they might be able to recieve data, > but how can they hope to transmit over such a large distance with their > wimpy amplifier and antennae? Do you need a big antennae only on one end to > make it work? Mike, This is exactly the kind of problem we want to watch out for. Adding an amplifier (if even legal) to only one end of a link, will generally make that link asymetric or unbalanced. The condition you describe is the result-- the node can hear the AP over a huge area but the AP cannot hear the node. In a duplex (ie, two-way, bidirectional) system like 802.11b, this does absolutely no good. All it does is splatter the area with signal from the AP that is not useable beyond the distance that the node can transmit back-- yielding nothing but interference for other users in the same general area. Adding a "bidirectional" amplifier (ie, a transmit power amplifier and a receive preamplifier) at one end doesn't really do much better because the preamplifier will never be able to recover the signal from the node that is lost in the noise over the same distance. Adding any kind of amplifier to these systems and then using omni antennas is just going to cause grief for everyone. The people that are talking about 20+ mile paths are hopefully using directional antennas at both ends and keeping their signal to a relatively narrow beamwidth. This approach is acceptable because you are not flooding huge areas with signal that nobody needs. Keep thinking wireless *LANs*. The "L" is for local. Connecting a bunch of LANs into a bigger WAN, using routing and backbone links is the right way to do this, I believe. Spewing whopping great signals from mountain tops (which we don't have) is not... -- Chris Elmquist mailto:chrise at pobox.com http://www.pobox.com/~chrise