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LOS IS A LINE OF DIRECT VISIBILITY BETWEEN TWO POINTS.
If at point A you can see point B, you have line of sight between
those points. Long distance wireless links require this. For the best
reason, microwave radiation is highly directional, But just seeing
isn't always enough, you must also have a good fresnel zone.
HOW CAN I CONFIRM LINE OF SIGHT BETWEEN TWO NODES?
BY SIGHT.
Someone on-list suggested using a bright torch (Dolphin brand ) at
night to shine toward the node to indicate where you are, and get the
person at the node to tell you if they can see your torch light.
It really helps during antenna work to have someone in direct voice
communication on each side available to move the antenna direction
(not necessary for omnidirectional antennae, since omnis don't improve
with different facing). Mobile phones, CBs or ham radios help a lot in
this area.
Here\'s a link [1] to some other suggestions - follow the "Next
Message" links for more.
WHAT IS A FRESNEL ZONE?
THE SPACE AROUND THE LOS [2] ALONG A LINK.
Good question. It's not even completely clear to me why you need it,
but it goes something like this. You need more than just a line to get
a good link, you need space around this line too. The closer you are
to each side of the link, the less space you need, so if you start on
one side, as you get towards the middle, you need more and more space,
until you get to the middle, which needs the most space. Imagine two
cones with the flat parts stuck together, thats what a fresnel zone
looks like. If trees or buildings or anything is in this zone, you may
get a poor link, or none at all. You can use an online fresnel zone
calculator [3] to work out the size of a fresnel zone.
If you are in an area with a lot of tall trees, you can attempt to
breach the divide by attaching an antenna to a mast that rises above
the treeline, or attach your antenna to the branch of a tall tree.
Depending on council requirements, you might need to watch the height
of any devices you try to erect in your backyard, as neighbours will
often complain. Councils love to fine people, and antennae can fall
over in strong weather conditions.
In no way do I suggest arranging the antenna or local trees to fall
on your neighbours, but if it helps you get a clear zone and strong
signal...
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Back to TheEvolvingFAQ [4]
Links:
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[1]
http://lists.bawug.org/pipermail/wireless/2003-February/010661.html
[2] http://melbournewireless.org.au/?LOS
[3] http://gbppr.dyndns.org/fresnel.main.cgi
[4] http://melbournewireless.org.au/?TheEvolvingFAQ
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