Problem: I'd like to extend the range at which I can use my wireless router
Solution Difficulty: Moderate
If your not the type to play around with computer with computer hardware you may be wondering what a cantenna is. Simply put it's a form of wave-guide antenna that focuses a radio signal and extends the range at which you can receive it. The science behind it is fairly simple but I will spare you the lecture and will proceed to the project.
So why do you build a cantenna? For starters it's a great way to track down rogue wireless access points within a building. Because of the direction nature of the cantenna, you can easily figure out which way the signal is coming from and by using the overall signal strength, track it down. Another nifty advantage is that you can set up a peer-to-peer connection between two wireless computers over a much further distance. And last of course, is that you can easily poach wireless connectivity off anyone in the vicinity.
To construct a waveguide / cantenna you need a few specialty items that you'll have to order. The first is what's called an N-Type connector and the second is a pigtail. The N-Type connector is what holds the antenna element, which is a small copper rod that picks up the signal. The other end of the connector is where you attach the pigtail, which is a short piece of wire that connects to your wireless card. Pigtails come in various lengths and types, so you'll need to figure out which pigtail connector you need. Luckily someone has gone through the trouble of categorizing the various types. Then you'll need to order the pieces. I recommend Fleeman Anderson and Bird. Though they charge quite a bit for shipping, they do offer the complete N connector plus pigtail of your choice for a fair price.
Once you have these items you can move on toward finding your can. Using the following website I was able to calculate the approximate diameter of the can that I needed. The smaller the diameter the longer the can needs to be. Obviously there are certain practical limitations here, but as I found out they didn't really matter that much. I tried two cans, a larger coffee can and a smaller sloppy Joe can. I obtained similar results with both, so I'd wager you could use about anything that's remotely close.
I did however find out that the length of the copper element inside the can matters a great deal. Though you can use any piece of copper, it's best to use something around 12 gauge. The best off the shelf part to use is scrap piece of household grounding wire. The important thing is that once the wire is inserted into the N connector that it is as close to 1.21" long as possible. I cut mine to the approximate length and then used a sanding block to fine tune the antenna. When I was satisfied with the length I soldered the copper wire in place. Oddly enough I found that the antenna worked almost as well if I just put a little piece of electrical tape around it. The overall length was by far the most important thing.
The next thing you'll want to do is drill a hole in the can so you can insert the connector. You can use this website to calculate exactly how far from the back of the can the hole needs to be. Mark it with a sharpie and start drilling. The only problem I had here was that my cordless drill will not take a drill bit large enough to make the hole. I had to use the largest possible bit to "round out" the hole. After a few minutes I managed to make the hole large enough to slip the connector inside.
Finally, you'll want to secure your connector with some screws, or tape, or anything that will hold it in place. You can think attach the pigtail and start surveying for wireless signals. I used some wire ties (or zip ties) to secure the can to the top of a tripod so I didn't have to hold the can. This worked pretty well, though I'd go for something a little more permanent if I found a waveguide setup that I liked. Once you have the cantenna affixed to your liking your ready to crank up the software and take a peek.
For Windows users the best utility to use is NetStumbler, which by the way works perfectly well with a regular wireless antenna also. NetStumbler will listen for active hotspots and give you an approximate reading on the signal strength and noise of each hotspot it finds. This is a great tool for figuring out which antenna configuration works best since you get an easy to see chart as well as the ability to save your logged data. One thing you may need to do first is to unbind TCP/IP from your wireless card so you don't accidentally "lock on" and connect to any signals you spot, and second remove any reference to access point SSID. You can turn off auto-reconnect while you’re at it as well, which you can usually do from the config tab in network settings and also inside the NetStumbler app.
If you live in a fairly dense neighborhood you should spot several access points within the first minute. If you aren't seeing anything you may have a loose connection or something could be blocking your antenna. Anything metal, very dense, or of an electronic nature will interfere with your signal. I found that with my tripod I could raise the cantenna up as high as possible for the best results. I also found that I could tweak the angle of the can to obtain better reception.
So what did I find? Within the first minute of turning on NetStumbler I found four or five hotspots. Some of them were WEP encrypted, but most were wide open. As I found out in reading about wireless APs, WEP is a very weak encryption and is intended for privacy, not security. Any bad guy with a Linux box and a cantenna could crack into your network with little trouble, so it's important to use multiple layers of security. It's also probably not a nice thing if you leech bandwidth from your neighbors, so unless you have a real need (and your neighbor’s permission); don't arbitrarily connect to people's networks.
You may be wondering why you'd even bother to build a waveguide if your not going to use it to connect to networks. First off it's kinda fun to just play around with and to see how many distant signals you can pick up. However if your not the experimenting type there is another, must more useful reason to build a cantenna. It gives you greater control over your wireless network. Waveguides can also be employed as wireless access point antennas. Like the cantenna receiver, the transmitting antennas can be pointed directionally, to push your wireless signal further in one direction than in another. This is great if your access point sit at the far end of your house and you want to connect from the other side of the building. A simple waveguide with help "push" more of the signal in that direction. They can also prevent your signal from "leaking" out in the other direction.
As you can see the cantenna / waveguide can be used for a lot of things, and it's fairly easy to build. Have fun and always remember that when you have a wifi connection anyone could be listening.
This article contributed by ERSWeb
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