Friday, November 20, 2009

Desperate Times call for… Engineering-Part II

I’ve had plenty of setbacks… You don’t know how glad I am to be able to live up to my promise of writing this entry. It really did take forever for me to get this all together without internet. Namely the N-type female chassis mount connector took me a long time to find, as I outlined in the last entry. Tanner’s Electronics thankfully had all the stuff I needed, but before that I had spent days going to different places and trying to find an N-type connector. No one I talked to even knew what it was. The closest I got was an f-type connector used for coaxial connections, which mind you, won’t work for this particular project. Anyway, enough complaining about my mishaps.

Kudos to anyone who can tell me what time it is from that binary clock (the square thing with all the blue lights)

Isn’t it beautiful? If you notice, I even used wall tacks to hold in the N-Connector. Not such a good idea as you’ll see in a second but I was just eager to test this thing. The trickiest part was getting a hole through the can. Never mind butchering the solder a couple of times, as I’ve never soldered anything in my life. Getting the hole through the can proved to be tough without a drill, nail, or anything.

Poor thing never stood a chance

Thank you, Kyle, for showing me how to solder! Once I soldered the #12 copper wire onto the connector, punched holes through the can, and mounted the wire inside, it was time to test it. Here’s a chart of what my Wi-Fi situation looks like without the cantenna.

So I can see 2 access points and both are pretty poor signal. Each have a -91 and -86 RSSI (Received Signal Strength Indication) reading, which would amount to poor bandwidth and probably dropped connections every so often. Apogee is a local service provider, and admittedly we have service now that it’s been 3 weeks since the lightning hit, but given that, my signal strength is pretty poor and I can’t live with poor signal strength. Now let me plug in my cantenna....

Wow! Simply plugging in the can shows me all the world I was missing out on… This image shows a long period of time before I eventually wired everything up. You can see that at 1:10 PM, as soon as I hooked up the cantenna to the wireless USB card, I was inundated with access points. Now, opposed to the 1 or 2 I was receiving signal from earlier, I now have a plethora of options!

If all I have to do is plug in the can to see all these, what happens when I point the can in a certain direction? Afterall, it is a waveguide antenna. Out there you see plenty of campus buildings, a football field, and most importantly, more radio waves! Well you don’t see them per se but believe me, they're there.

My roommate needs to do laundry... I guess I do too though

My wall tacks then proceeded to fall off the can… thus destroying my cantenna. I’m no civil engineer, but I’d say tacks make for a pretty shoddy construction job. The image above is my “improved” can which is bound by soldering the N-connector to the can and duct taping it for reinforcement… I call it the McCormick Cantenna MkII

This is what the can looks like on the inside. There are actually several complex math equations used to determine where you need to puncture the can and how long the #12 copper wire needs to be. To save you the headache, and to avoid admitting I don’t know how to do the math, I used an online calculator to figure out where these need to be. Given the diameter of the can was 3.125 inches across, I needed to puncture the can 2.9 inches up from the bottom. Ideally my can could have been a bit longer to compensate for the length of the wavelength I’m trying to guide since Wi-Fi operates at a frequency of about 2.4 GHz.
To fully test this, I would like to find a big open field, and set up my access point as far away from my can as possible and see what my signal strength can be. Cantennas and waveguide antennas in general can increase the range of your Wi-Fi connectivity by up to a kilometer or in some cases many kilometers. Industrial level antennas can provide wi-fi from the base of a mountain to those users on top of the mountain! Perhaps range testing of my cantenna can be for another entry ;)