WiFi Antenna #1

Where I live there's still no high speed internet available as of 4/9/2014, but this is the only house on the road. Some people have DSL, we can't get it because it's not profitable enough to be worth running the wires for one customer. DSL is slow anyway, I want fiber optics, which is still being negotiated. I had this garden variety collinear USB WiFi setup which is supposed to work with my Raspberry Pi, but I'm still downloading stuff to get a driver working. I also had some 6 foot USB extension cords which sell for $3-4 at All Electronics. I plugged the collinear into an extension cord, plugged it into my laptop, clothespinned the collinear to a window curtain up high, and viola, signals. The nearest house is about 1/4 mile away so they're all weak, but there's one open AP out there.

Using a commercially-made USB antenna hopefully avoids all the usual issues with bulky, expensive coax, line losses, getting the antenna resonant. I should just need to give it more gain by making it directional. And set the Raspberry Pi up as a router since it runs on 2 watts. I designed the antenna using the PDF on this page which is what I wrote that for. So I printed out 2 copies and got busy. I didn't spend any money, this is made out of stuff that was kicking around.

This is some cheap plywood or paneling from the local Home Depot bargain bin years ago, cost 50 cents for a 2 x 4 foot piece originally. I cut out 4 pieces to match the 8½ x 11 paper. One corner is a little dinged up.
I use rubber cement (LePage's or Elmer's) for stuff like this, smear both surfaces lightly, let them dry, then put them together. I drilled holes where the focal point marks were so they didn't get lost.
I cut them out with a saber saw, use one or a jig saw, coping saw, band saw, whatever you've got. The object is to not spend money on this. Be careful here because there's no waste: you're going to keep both the outside and inside pieces.
The reflector is made from some 8 inch wide aluminum flashing that's been around for years. 6 inch wide would have been good enough.
After cutting out the plywood I peeled the paper back off. Then I made crude notches in the corners for my support posts. The cut plywood pieces are mounted to whole 8½ x 11 pieces with machine screws.
Here it's mostly put together and I'm starting to slide the aluminum in. The corner pieces are oak squares about 1-1/8, but pine would work OK. I cut them as accurately as I could, but I had trouble sliding in the flashing. So I cut shims to gain a little more spacing, but ended up taking them back out. Each corner is held by a sheetrock screw and I left those a little loose then tightened them up when I got done. Cutting a slight bevel on the corners of the flashing would help for sliding it in.
Here I've gotten the flashing slid into place finally. It took me a few tries and ended up being a sit-down job. I used clamps to hold the cut plywood pieces in place, then put in more machine screws. The pieces inside the curve went in first, then the flashing, then I pushed the outside pieces up tight against the inside and bolted them. I had to put the outer plywood pieces in before the flashing but I didn't bolt them until last. The focus point holes get extended through the top & bottom plywood pieces.
Rear view. It's all pretty crude, I didn't spend a lot of time or money on it. Most of the time I spent was figuring out how I could do it cheaply. I didn't go anywhere for supplies or spend any money.
The collinear in place through a hole drilled in the top plywood at the focal point. There's about 2 inches of wasted flashing width, 6 inch would be good enough. I was planning to take a plastic pill bottle, screw the lid to the bottom then drill a hole in the bottom to hold the free end of the collinear but this is good enough for now.

How does it work? Not as well as I hoped, but it turns out none of the software I've got gives me a good signal strength indicator either. The next attempt is to mount a mini-USB adapter ($7) at the focal point of an old Dish network satellite dish, but that adapter won't be here for another week.

Don't bother to build one of these unless you've got some insight as to why this one doesn't work better than it does. I usually model an antenna before I build it but that didn't work, or did it? This works almost as badly as the model predicted, I just didn't believe that. A foot of antenna height seems to make more improvement than this reflector. I think I figured out what direction the strongest AP is in, and I've gone back to watching it in airodump-ng with the collinear clothespinned to the window curtain again. Poking a random hole in a coffee can and sticking the collinear in would probably be better than this.

AB1JX / toys