[olug] Wireless LAN

[Eric Penne]

It does not have to be line of sight.  It helps but there can be stuff
in the way of the signal path.  

2 friends of mine set up a link between their houses 3 blocks apart. 
Doug has DSL and Joel had nothing (and this little piggy laughed about
his roadrunner all the way home. :) )  They tried putting the antennas
in the house on the DSL side and up high with a Yagi (directional)
antenna on the other.  No connection made us realize Doug has metal
siding and the signal was not even getting out of the house.  Putting
the antennas about 6 feet high on the outside of the house gave a solid
11Mbps connection.  802.11 autoswitches the speed depending on the
connection it gets.  The antennas on the DSL were pointing straight
into the neighbors house.

Looking for a more weatherproof solution they strung cat5 and power up
to the attic and put the antennas up there.  8 feet higher but going
through asphalt shingles (maybe 2 layers) and plywood produced zero
signal.  The only thing Doug got from that experiment was a networkable
attic and a large hole above his fridge (nobody was hurt). 

Some tips:
1.  Higher is not always better.
2.  The material you go through is very important. (Drywall is better
than glass)
3.  Don't walk in attics that have lots of insulation covering the
ceiling joices.
4.  make the cat5 run as long as possible and the antenna coax as short
as possible to reduce transmission losses from the base station.
5.  circular polarization works well in buildings.

circular polarization simplified.  Imagine the wave from you standing
behind the sending antenna.  The wave rotates clockwise.  You follow
the wave until it gets to the receiving antenna which is pointed toward
you.  The antenna is designed to recieve waves that only rotate this
way.

now imagine the wave bouncing off a wall.  You always follow the wave
toward the reciever.  Before hitting the wall the wave rotates
clockwise.  when it bounces off the wall the direction on the wave is
reversed so you need to switch sides to follow the wave.  (Rotate you
hand clockwise, now switch sides of your hand and your hand is rotating
counterclockwise.)  Now you are going away from the wall toward the
reciever and the wave is rotating counterclockwise.  the antenna is
designed for the other direction so it ignores this signal. This helps
get rid of ghosting effects like you hear on the radio and see on TV
and helps give you a stronger signal.

I've completely lost my train of thought and have discontinued my
ramblings.  Maybe next week on Geek Thoughts with Eric Penne, I will
remember my point and finish it.

Eric Penne

--- "Chad S. Lauritsen" <csl at perfectionlearning.com> wrote:
> Hi,
> 
> A while back there were some threads regarding 802.11 wireless
> networking. I
> have never played with it, but I had a question maybe some of you
> could answer.
> 
> Would it be possible for an apartment landlord to use it to provide
> high-speed
> internet to tenants? (To avoid retrofitting Cat-V in the walls.)
> Specifically, can it travel through the walls reliably
> enough to a central router connected via, say T1 access? Or does it
> really have
> to have a _visually_ non-obstructed line-of-sight?
> 
> Thanks,
> Chad
> 
> -- 
> Chad Lauritsen                          | 1000 N 2nd Ave
> System Administrator                    | Logan, IA 51546
> Perfection Learning Corporation         | 712-644-2831 Ext 223
> 
> 
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