Building a Simple Pringles Cantenna - Wifi Shenanigans (Part Four)

A few years back I read this guide and decided I'd give it a shot. My construction was essentially the same. The only difference is instead of running a pigtail to a copper wire inside, I just put a wireless USB dongle in it to see how that worked. It turned out pretty well. I haven't measured any numbers with it, but I get a few more bars on APs when I point it down towards the financial district. This also has the advantage of just running a really long usb extension cable, rather than using a pigtail, which normally results in signal loss.

Here's the parts list:

Pringles can (including lid)
5 5/8" long 1/8" diameter threaded rod
2 - 1/8" nylon nuts
5 - 1" dia. Washer
Some cardboard
Some Pipe that will slide over the threaded rod.
USB wifi dongle (or an N-type connector, pigtail and wirelss card)

and of course your around the house tools:
Scissors
Hot Glue
Hack Saw
Probably Other Stuff

The idea is pretty simple. Resonance occurs at 1/4 the wavelength. This happens for antennas, musical instruments and anything that has waves. This resonance will help the wifi adapter pick up signals, thus increasing signal strength. Also, the metallic coating and bottom of the can tend to reflect the signal back into it.

Resonator Construction:
The idea here is that we will put a washer at every 1/4 wavelength so the space between resonates and we'll fit a full wavelength inside the can. So now we need to calculate the spacing.

Things we know:
Speed of wave (in this case speed of light) = wavelength * frequency

299,792,458 m/s = w * 2,437,000,000 hertz (frequency of channel 6) w = .123m

So one wavelength is 12.3cm. 1/4 of that is 3.075cm, which is the spacing for our washers. In construction, get as close to this spacing as possible for maximum performance.

Cut four 3.075cm lengths of pipe to act as spacers. Go ahead and measure to 12.3cm though and make your marks since the width of the saw should be fairly close to the width of the washers. Place the lid on the cardboard and cut out a piece the same size as the lid and poke a hole in the center of each. The purpose here is to hold the collector in the middle of the can. Assembly should look like this:

Collector Construction

Take some hot glue around the ends and between the parts to make sure it won't fall apart.

Now take the can and cut a slit for the USB dongle 3 3/8" from the bottom of the can. This number is the sweet spot for the transmitter. Push the dongle up to roughly the middle of the can, maybe a bit above or below. Don't glue this yet since you may want to play with it to find the depth it works best.

Once this is done, test it out. You should see, at the very least, a small increase in signal strength. Good luck and have fun building. Feel free to comment this with suggestions and feedback on my blog.