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Creating a Long Distance Point to Point Wireless Link


Overview

The purpose of this website is to demonstrate how to create a long distance wireless link between two geographically seperate locations using affordable and readily available components. There are many reasons why such a link may be desirable to the reader, whether you are connecting two offices networks together or perhaps just creating a link to your friend down the road DIYWireless.net will attempt to create a clear picture of how its all done. Basic wireless networking for a local area network within a home or office is outside of the scope of this site and you might consider visiting our sister site DIYWireless.com as it contains a wealth of information that will serve as an excellent starting point and assumes you have no previous wireless networking experience. DIYWireless.net assumes that you have a degree of computer literacy and knowledge of wireless networking.

Although we shall focus on linking two locations together using directional antennas linking multiple locations together using omnidirectional antennas is very similar and the knowledge you gain from linking two sites can be applied to more complicated set ups. The equipment required for each location consists of a suitably prepared router, an antenna which will be mounted outside the building and a cable to join the two together. The routers we will use for our demonstration link are Linksys WRT54GL's and they have had their standard firmware replaced with DD-WRT, an open source freely available stock firmware replacement for many readily available off the shelf routers. It is quite possible to do a long distance link using an off the shelf router with standard firmware and many of the configuration options described on this website can be directly applied to the standard firmware of whatever router you choose, assuming it supports WDS and WEP encryption and has an aerial that can be removed to accept a cable to an external antenna. We have chosen the Linksys with DD-WRT because it is a proven combination that works well and runs reliably.

So how far will it go?

The range of your wireless link is determined by many very variable factors. With clear line of sight and no interfering factors such as background noise, trees and buildings the setup we describe here will work very reliably with end points 5-10km apart. Of course it will work just as well if you only need to go a few metres. I have seen one work reliably in all weather conditions with a link 25km long.

Determine if your locations are suitable for linking with wireless

The ideal conditions for linking multiple locations together wirelessly are often frustrating to achieve. We will be using the 2.4Ghz free wireless spectrum and there are many factors that will determine if the link is even possible.

Line of Sight is an important factor. The important factor. If you are unable to see one end of the link from the other it is likely that the link will not work, depending of course on what is in the way. 2.4Ghz wireless will not go through mountains, hills or large obstacles such as buildings. With every object the signal must pass through its strength is diminished and what is left may be completely unusable. Landforms such as mountains will stop your signal dead in its tracks, dont even bother if there is a landform in the way. Vegetation will also reduce your signal markedly. If the link is a short one, say less than a kilometre you might get away with a few trees in the way however when it rains they will hold moisture which may stop your link from working until they dry out. In the very least tree's can cause problems. Very dense vegetation will stop your link in its tracks. A successfull wireless link requires you to be able to see one antenna from the other, even if you need a telescope to do so.

Background noise can be caused by many different devices. There are many things that use the 2.4ghz spectrum, cordless phones, remote controlled toys, other wireless networks and even doorbells can provide interference that can degrade your links performance. Avoiding interference from other networks is not too difficult unless you are in a very densely populated area. Simply do a scan with your router and choose a channel that has very few networks using it. If you suspect that there is interference from other devices choose a different channel for your link and monitor its performance to determine if there is any difference.

So, having determined that your locations are suitable for linking together wirelessly the next step is to prepare and install the hardware required and make the link work. If you have decided to use off the shelf routers you can skip the Reflashing the Routers section and jump straight into configuring them. It is strongly recommended that you configure and test the routers on the work bench before installing them as having them geographically close to together will greatly simplify debugging them if they dont work correctly first time.