I’ve always wanted to build a cantenna just to do it. My problem has always been that I don’t have a wireless card that supports an external antenna and I never wanted to spend the money to buy one. The other day I ripped apart this old Atheros PCMCIA card I had and found that it wouldn’t be too difficult to solder a pigtail straight onto the board.
That’s the wifi card. You can tell on the left side that I removed that part of the cover. This is a Blitzz Super G BWP 712 Atheros PCMCIA card. A friend gave this to me a few years ago when I needed an Atheros card to try my hand at WEP cracking. Since then I’ve acquired a few more cards so I figured I’d take this one apart to see if I would be able to attach an external antenna connector.
Here’s a pretty good shot of the entire PCB that is exposed. On the left side it looks like there is an port for some sort of pigtail. I really have no idea what type of port that is or what pigtail I would need for that. I don’t even know if I can buy one. On the right side there are a few exposed solder pads. It looks like the manufacturer included a place on the PCB for another port but they decided not to put one there. Right after that port appears to be either a tiny resistor or capacitor. I’m not really sure how to tell on these little parts. My best guess is that I should be able to solder a cable onto those pads for an external connector. Here is another picture with some crude labels explaining what I have in mind:
After realizing that my soldering iron isn’t sharp enough to desolder that capacitor/resistor I had to come up with a new solution. That solution was to just cut the trace after the component that leads to the antenna. I just scratched away at the trace with a knife until it was broken. Here is a shot of what that looks like.
The next step is to prepare the pigtail connector for soldering. I had to chop off the small end with some shears in order to get at the actual cable. Once the connector was removed, I had to carefully strip away the clear outside insulation to get at the braided ground cable. I de-braided the cable and separated it into two sections on opposite sides of the cable. Then I had to strip away a small section of the inside insulation to get at the actual signal wire. Here is a photo of what this looks like.
This next part was the most difficult. I had to solder those cables to the tiny traces on the circuit board. I ended up having to scratch away some of the coating on the antenna trace in order to solder the signal wire. Those tiny little solder pads were just way too small, and also too close to the ground pads. I didn’t want to create a short. I scratched off some of the coating on the trace before it reached the pads in order to give myself more room to solder.
Now that the wifi card was prepped and ready, the only thing left to do was prepare the can. For this section of the project I used http://www.turnpoint.net/wireless/cantennahowto.html as my reference. I pretty much just followed that guide 100% to build the actual cantenna. All of the measurements I used were derived from that website.
The first thing I did was cut a length of coat hanger to as close to 1.21″ as I could. Then, I soldered it to the male side of the “N” connector mount. This is the antenna.
Now the first mistake I made was attaching this to the can as-is. The reason this was bad is because the sides of the can touched the antenna probe. This caused a short. Ground was tied straight to the signal. In order to prevent this from happening, I wrapped some table around the base of the probe.
Now that the mount is ready to rock it was time to mount it. I used a sharpie to mark the five points where the holes needed to be. Then I used my Dremel to drill the holes in the outside of the can. Once the holes were drilled, I stuck four screws through the outside holes. I put the heads of the screws on the inside of the can so that it would be easier to screw the nuts on later. Once the mount was fitted on, I attached the nuts and presto, I had myself a spiffy new cantenna.
You can see that I used a Borden Eggnog can for my cantenna. It was the longest can I found at my local Fry’s grocery store that was about 3.5″ in diameter. The exact measurements of this can are: 3 3/8″ diameter with a length of 7.5″. According to the reference I used this should work just fine.
I attached everything together and plugged it into my laptop. It doesn’t look like the cantenna is as effective as I had hoped. Kismet shows typically between a 3-8db improvement on most networks in my area. There are so many variables of things that I could have done wrong for this project that it would be difficult to figure out how to make it better. I consider this project completed until I get myself a wireless card with an external antenna port. Once I have that I will be able to eliminate the card or my awesome soldering job as potential problems. I’ll be able to just focus on getting the antenna tuned correctly.