'''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 {/regexpicons/emoticons/emoticon-face1.png :)}) 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.



(http://lists.bawug.org/pipermail/wireless/2003-February/010661.html Here's a link) to some other suggestions - follow the "Next Message" links for more.



!! What is a Fresnel Zone?



'''The space around the [LoS] along a link.'''



{http://www.westcon.co.za/images/fresnel.gif Fresnel Zone}



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  (http://gbppr.dyndns.org/fresnel.main.cgi fresnel zone calculator) 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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