Now, for those of you who do not want to make their own antenna, the best ones are at Fab-Corp (www.fab-corp.com). I will be adding more antenna guides. Soon to come are the best guides or Pringle antennas (below), omni directional antennas, Yagi antennas, and many a few more.
Ok this is a rip of another guide. I know that, but the reason I've converted it to this format is for easier reading and because I intend to translate it. -- The one I'm gonna use is : http://www.oreillynet.com/cs/weblog/view/wlg/448
How to make your own wardriving antenna :
Like many would-be
802.11b hackers, I'm increasingly obsessed with
pushing more bits further and faster for less
cost (I believe the unofficial goal of our
community wireless project is to provide
infinite bandwidth everywhere for free. Of
course, there are problems with approaching
infinity, but it's still fun to try!)
The work that Andrew
Clapp and others have done is helping to
demystify the ancient black magic of Resonance
(i.e. antenna building). And so, over last
weekend, some friends and I decided to give it a
go for ourselves.
Anything you do with your gear is YOUR
RESPONSIBILITY. This is a stupid idea that
will probably ruin your radio, set your house on
fire, bring the FCC to your door, ruin your
crops, and send famine and pestilence across the
land. And as the operator, it is YOUR
RESPONSIBILITY to not take the word of some
raving lunatic on the web with funny colored
hair, and find things out for yourself. Your
mileage will vary. I'm probably lying. You have
Anyway, our first run
was a direct rip-off of Andrew Clapp's terrific original
design (knowing next to nothing about
antenna construction, it's helpful to start off
with a working known good.) By using PVC,
all-thread, washers, some cheap copper tubing, a
Pringles can, and some scrap cardboard, we were
able to make a prototype shotgun yagi in a
matter of hours. Having a couple of other
excited alpha geeks around can help move
construction projects along very quickly.
Once this was up and
running, we looked at the design, and of course
speculated about ways to optimize it. While a
directional antenna showing between 12 and 15db
gain is impressive, it's also pretty large,
physically. We realized that, if we were
careful, we could fit a full wavelength inside
the Pringles can itself (at a reduced total
gain), but make the entire antenna much more
In about 45 minutes, we
had the collector rod built, the locknuts on,
and the whole thing in place. The result: A
Pringles can that pulls about 12db!
5 5/8" long, 1/8" OD
nylon lock nuts
1" washers, 1/8" ID
aluminum tubing, 1/4" ID
connector to match your radio pigtail
1/2" piece of 12 gauge solid copper
tall Pringles can
plastic disc, 3" across
Of course, buying in
bulk helps alot. You probably won't be able to
find a 6" piece of all-thread; buy the
standard size (usually one or two feet) and a
10-pack of washers and nuts while you're at it.
Then, you'll have enough for two, for about $10.
Pipe cutter (or hacksaw or dremel tool, in a pinch)
Heavy duty cutters (or dremel again, to cut the all-thread)
Something sharp to pierce the plastic (like an awl or a drill bit)
Hot glue gun
about an hour
and cut four pieces of tubing, about 1.2"
(1 15/64"). Where did I get this number?
First figure out the wavelength at the bottom of
the frequency range we're using (2.412 GHz,
or channel 1). This will be the longest that the
pipe should be:
W = 3.0 * 10^8 * (1 / 2.412) * 10^-9
W = (3.0 / 2.412) * 10^-1
W = 0.124 Meters
W = 4.88 inches
be cutting the pipe to quarter wavelength, so:
1/4 W = 4.88 / 4
1/4 W = 1.22"
figure out what the shortest we'll ever use is (2.462
Ghz, or channel 11 in the US):
W = 3.0 * 10^8 * (1 / 2.462) * 10^-9
W = (3.0 / 2.462) * 10^-1
W = 0.122 Meters
W = 4.80 inches
1/4 W = 1.20"
speaking, what's the difference between the
shortest pipe and the longest pipe length? about
0.02", or less than 1/32".
That's probably about the size of the pipe
cutter blade you're using. So, just shoot for
1.2", and you'll get it close enough.
Cut the all-thread to
exactly 5 5/8". The washers we used
are about 1/16" thick, so that should leave
just enough room for the pipe, washers, and
Pierce a hole in the
center of the Pringles can lid big enough for
the all-thread to pass through. Now is probably
a good time to start eating Pringles (we found
it better for all concerned to just toss the
things; Salt & Vinegar Pringles get to be
almost caustic after the first fifteen or so.)
Cut a 3"
plastic disc, just big enough to fit snugly
inside the can. We found another Pringles lid,
with the outer ridge trimmed off, to be ideal.
Poke a hole in the center of it, and slip it
over one of the lengths of pipe.
Now, assemble the pipe.
You might have to use a file or dremel tool to
shave the tips of the thread, if you have
trouble getting the nuts on. The pipe is a
sandwich that goes on the all-thread like this:
Nut Lid Washer Pipe Washer Pipe Washer Pipe-with-Plastic Washer Pipe
Tighten down the nuts
to be snug, but don't overtighten (I bent the
tubing on our first try; aluminum bends VERY
easily.) Just get it snug. Congratulations, you
now you have the front collector.
now you should have eaten (or tossed) the actual
chips. Wipe out the can, and measure 3
3/8" up from the bottom of the can. Cut
a hole just big enough for the connector to pass
through. We found through trial and error that
this seems to be the "sweet spot" of
On the Pringles Salt
& Vinegar can, the N connector was directly
between Sodium and Protein.
the heavy copper wire, and solder it to the
connector. When inside the can, the wire should
be just below the midpoint of the can (ours
turned out to be about 1 1/16"). You
lose a few db by going longer, so cut it just
shy of the middle of the can
We were in a hurry, so
we used hot glue to hold the connector in place.
If you have a connector that uses a compression
nut and washer, and you're really careful about
cutting the hole, you could use that instead.
Now, insert the
collector assembly into the can, and close the
lid. The inside end of the pipe should NOT touch
the copper element; it should be just forward of
it. If it touches, your all-thread is probably
Now, just read FCC
Part 15.247, connect your pigtail, aim
carefully, and have fun!
Unfortunately, I don't
have access to any of the necessary equipment
(spectrum analyzer, power meter, or even an SWR
meter) to properly evaluate the characteristics
of the antenna. SWR in particular would be a
really good idea to measure, as we're not sure
how much power is feeding back into the circuit
(too much and you can easily blow your
transmitter.) With the extremely low power
output (15dbm) of the Orinoco cards, I don't
think this is too much of a danger, but
remember, anything you do with your equipment is
your responsibility, and at your own risk!
Without the proper
(multi-thousand dollar) tools, how were we able
to estimate antenna performance?
Using the Link Test
software that comes with the Orinoco silver
cards, you can see the signal and noise readings
(in db) of a received signal, and your test
partner's reception of your signal. As I happen
to be 0.6 mile LOS from ORA headquarters, with
very little noise on the channel between, we had
a fairly controlled testbed to experiment with.
We shot at the omni on the roof, and used the
access point at ORA as our link test partner.
To estimate antenna
performance, we started by connecting commercial
antennas of known gain, and taking readings.
Then, we connected our test antennas and
compared the results. We had the following at
two 10db, 180
degree sector panel antennas
one 11db, 120 degree sector panel antenna
one 24db parabolic dish
a couple of Pringles cans and some tin foil
Here were the average
received signal and noise readings from each, in
roughly the same position:
The test partner (AP
side) signal results were virtually the same.
Interestingly, even at only 0.6 mile, we saw
some thermal fade effect; as the evening turned
into night, we saw about 3db gain across the
board (it had been a particularly hot day:
almost 100 degrees. I don't know what the
relative humidity was, but it felt fairly dry.)
Yagis and dishes are
much more directional than sectors and omnis.
This bore out in the numbers, as the perceived
noise level was consistently lower with the more
directional antennas. This can help alot on long
distance shots, as not only will your perceived
signal be greater, the competing noise will seem
to be less. More directional antennas also help
keep noise down for your neighbors trying to
share the spectrum as well. Be a good neighbor
and use the most directional antennas that will
work for your application (yes, noise is
When trying to aim a
yagi (like our little can), keep in mind that
they have large side lobes that extend up to 45
degrees from the center of the can. Don't point
directly at where you're trying to go, aim
slightly to the left or the right. We also found
that elevating the antenna helped a bit as well.
When aiming the antenna, hold it behind the
connector, and SLOWLY sweep from left to right,
with the Link Test program running. When you get
the maximum signal, slowly raise the end of the
can to see if it makes a difference. Go slowly,
changing only one variable at a time.
Remember that the can
is polarized, so match the phase of the antenna
you're talking to (for example, if shooting at
an omni, be sure the element is on the bottom or
the top of the can, or you won't be able to see
it!) You can use this to your advantage to try
to eliminate some noise on a long distance link:
slowly turn both ends of the link from vertical
through horizontal, and stop at the point that
you see the most gain (and lowest noise.)
We haven't looked into
weatherproof housing for the can; sinking the
whole thing into some 3" PVC should do the
trick. Of course, at $10 for two, it might just
be more economical to replace them when they
Apparently, antennas of
comparable gain cost upwards of $150. Over a
clear line of sight, with short antenna cable
runs, a 12db to 12db can-to-can shot should be
able to carry an 11Mbps link well over ten
Rob Flickenger is the O'Reilly Network's Systems Administrator