[Cu-wireless] A bit of confusion....

David Young dyoung at onthejob.net
Sat Aug 18 19:10:14 CDT 2001

You will be able to get something back from the access point, sometimes.

Consider an ideal omnidirectional radio source---i.e., one that radiates
with equal strength in all directions.  Say that its strength is 10
watts. About .00008 watt passes through a one-square centimeter target
held facing the source from 1 meter away.  At 2 meters, .00002 watt passes
through the target. At 3 meters, .00001 watt passes through. However,
.00002 watts pass through a two-square centimeter target at 3 meters,
and through a 1-square meter target at 3 meters, nearly .09 watts pass
through. Imagine that these targets are able to concentrate all the
radiation that falls on them at a detector.  Then a large antenna will
concentrate more radiation from a source than some very small antennas
nearer the source.

Some directional antennas consist of a parabolic dish several inches
wide, and a detector at the "focal point" of the dish. In detecting a
far-away access point's signal, clearly a receiver attached to such a
parabolic dish has an advantage over a PC Card with its minute antennas.


On Thu, Aug 16, 2001 at 12:30:08AM -0600, Numbski wrote:
> I'm a member of the infant "Mile High Wireless" group in the Denver/Colorado Springs area.  I'm originally from St. Louis though (Collinsville, IL in fact...), and I have a bit of confusion that I need clarified:
> I'm lost about how connections are made with long range antennae.  For argument's sake, a reasonably powered Omni-Directional antenna can provide a coverage area of 1 mile radius (I've seen schematics of a 10db gain omni, and I have no idea what kind of range that would provide).  Now, there's an access point hooked to that omni.  I have a directional antenna that can get me up to 25db gain.  I want to connect to that access point from several miles out, clearly out of the coverage area of that access point.  Clearly without question I can SEND radio signals TO the access point, but I won't be able to get anything back....correct?  Where I'm confused is that with all the wireless groups I've seen on the net, I see these multiple mile directional connections from access points, but I don't see how that's possible unless the access point has directionals pointing back at the users, and that would become very costly, very fast.
> So which is it?
> Please reply directly.  Thank you.
> Numbski

David Young                   On the Job Consulting
dyoung at onthejob.net     Urbana, IL * (217) 278-3933

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