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
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
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