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As an alternative, you can punch the holes by laying the platform flat on a table surface, and
gently tapping a thin wire brad through the wood with a hammer. However, you can easily
split the wood this way (especially on platform materials like an ice cream spoon or a popsicle
stick).

Patience is a virtue when mounting the paperclips. Work the paperclip into the material slowly
with a gentle twisting and pressing force and everything should be fine.




Step 3: Creating Your Dipole
Take the longest wire (the one that is 4.52 inches long) and form it to match the template in
Figure 2-15. This template is printed to scale. After bending the paperclip as described here,
lay it on top of this diagram to ensure the correct dimensions
Take your needle-nosed pliers and make a line on the nose at the point where it is 0.16 inches
(4 mm) thick. Clamp the largest wire with the pliers and make a bend that starts 1.3 inches
from one end,. Slowly wrap the paper clip wire around the needle nose, creating a fishhook that
is 0.16 inches wide (4 mm).
Carefully press the longest end of the fishhook through the first appropriate hole on your
platform. Work the wire into the hole, until the second end comes up to its appropriate hole.
Ease that second wire through so that its end just pokes through on the other side of the
platform.


5.35 cm

4 mm

2.62 cm 2.72 cm
1 mm

FIGURE 2-15: Radiating dipole paperclip dimensions”note that figure is not drawn to scale.
51
Chapter 2 ” Building a Classic Paperclip Antenna




FIGURE 2-16: Inserting the driven element/paperclip.

Take the long protruding end of the wire and carefully create the second bent end, bringing the
two ends extremely close together (about 1 mm or 0.04 inches), and create your radiating
dipole. (See Figure 2-16.)

Step 4: Preparing the Pigtail for Attachment
Take your wire cutter and simply snip off the large standard N connector on the end of the
pigtail. This is where a factory-built antenna would be connected to the pigtail or jumper cable
(as described in Chapter 1). Since we are soldering the antenna directly to the pigtail, the con-
nector is not needed.

Be careful not to snip off the smaller end of the pigtail, which needs to be attached to your lap-
top wireless card.



Strip off about three-fourths of the outer insulating jacket and the inner dielectric insulation
surrounding the core conductor.
You will need about 1/4 inch of the central core free, to create a soldered connection to one end
of the dipole. And you will twist about 3/4 inch of the outer shield into a tight coil in order to
solder it to the other end of the dipole. (See Figure 2-17.)
52 Part I ” Building Antennas




FIGURE 2-17: Pigtail cable ready for soldering.


Step 5: Soldering the Pigtail to the Dipole
Put the bent paperclip dipole in a stable grip, either in a small tabletop vice, or in a pair of vise grips.

Don™t touch the paperclip or the solder iron while you work on this, both will be very hot. Be sure
to wear eye protection because splattering solder can cause serious eye damage. Also, the solder
resin causes some fumes that can damage your lungs, so make sure your workspace is ventilated
to avoid any unhealthy buildup of vapors.

Carefully solder the core conductor and the shield to either end of the bent dipole radiator
(as shown in Figures 2-18 and 2-19).

Both sides of the paperclip need to be soldered to the pigtail, but they must not touch each other
or the antenna will be useless. When you choose a mounting platform, plan ahead to prevent
the ends from touching.


Step 6: Securing the Pigtail
Run the pigtail cable alongside the wooden platform (as shown in Figure 2-20). Use small
drops of glue or some tape to fix the first inch of insulation firmly to the wooden platform.
Zip ties or plastic bundle-ties also work great. Just don™t use anything made of metal or antenna
characteristics could change.
53
Chapter 2 ” Building a Classic Paperclip Antenna




FIGURE 2-18: Soldering the pigtail center conductor to the paperclip.




FIGURE 2-19: Soldering the pigtail shield to the other side of the paperclip.
54 Part I ” Building Antennas




FIGURE 2-20: Cable management on your tiny antenna.




Do not use metal twist-ties to secure the pigtail. Twist-ties are often used to bundle cables
together in consumer electronics, especially with wireless networking gear. The metal
inside the twist-tie may adversely affect the antenna properties. Use a nonconducting
plastic or glue for best results.


This will guarantee that the fragile soldered connections do not need to bear the weight
of the antenna, and will help prevent breakage when the antenna is moved relative to the
laptop.



Step 7: Inserting the Antenna Elements
Insert the remaining three wires in their appropriate locations as “elements.” The prongs
don™t need to be centered on the platform, but it is best to center them in relationship to
each other. (See Figure 2-21.)
Touch each wire with a drop of glue where it passes through the platform, just to hold
the wires in place. (See Figure 2-22.)
55
Chapter 2 ” Building a Classic Paperclip Antenna




FIGURE 2-21: Inserting the reflector and focus elements.




FIGURE 2-22: Applying glue to hold things in place.
56 Part I ” Building Antennas


Mounting and Testing Your Paperclip Antenna
Now let™s take this baby out for a spin!

1. After you have soldered the pigtail to the antenna and secured it with tape, connect the
pigtail to your wireless card.
2. Mount the antenna and try it out.
3. If you have glued a clothespin or clamp to the wooden platform, you can clip it to vari-
ous objects, so that the antenna itself is either vertically or horizontally polarized.
4. Position and aim the antenna in search of the strongest signal.
5. Observe (and learn about) the link quality differences with the antenna in each
position.

Wireless networking software should come with some program or component used to measure
signal strength on your computer. In Windows XP, the Wireless Network Connection Status
dialog displays a Signal Strength bar graph. The more green bars that light up in the display,
the stronger the signal.




FIGURE 2-23: Signal strength survey in progress.
57
Chapter 2 ” Building a Classic Paperclip Antenna


You can also use the software that came with the wireless adapter. This software will have some
form of signal strength meter. Figure 2-23 shows the signal strength meter for an Engenius
Wi-Fi adapter.
Use your “signal strength meter” to see what happens to the signal strength as you vary where
the antenna is positioned and how it is oriented. You can adjust and re-orient the antenna for
the best connection.

Other software can be used to measure signal strength. See Chapter 6 for details on using
NetStumbler as a signal measurement tool.




Hitting the Road with Your Paperclip Antenna
Paperclip antennas are the ultimate cheap tool for connecting to Wi-Fi signals. They™re not the
most efficient, but they might be the most fun.
Your new, lightweight, budget-conscious paperclip antenna will expand the receptivity of the
antenna that comes with your wireless network adapter. As noted in the beginning of this
chapter, you can expect a gain of up to 9 dBi, which is probably two to three times better than
your laptop card.
With this type of antenna, your laptop should work better in fringe coverage areas. You can
probably use your laptop an additional 100 to 200 feet from the wireless access point.
Experiment with this new range by taking your laptop to a part of your network that doesn™t
usually have good signal quality. Attach your new paperclip Yagi and see how the signal
strength changes. By pointing away from the access point, it should go down. Also, you can
hold the antenna sideways or upright to change antenna polarization. This simple act can
change your signal strength by 20 percent or more.



Summary
You now have a nice little gadget that will boost your Wi-Fi signal when the wimpy internal
antenna just won™t bring in the signal. By walking around with your new antenna, you should
be starting to understand how radio waves move through the air. You saw that just by rotating
the antenna from horizontal to vertical and pointing it in different directions drastically affects
the signal strength.
By creating this simple antenna, you have entered the realm of microwave RF engineering.
The device you built in this chapter would have been unthinkable a short time ago when these
microwave radio frequencies were reserved for military and scientific use.
Read on to the next chapter. We expand on the concept of homebrew by introducing the
waveguide antenna”a very powerful, highly focused antenna that can be built using an empty
coffee can and some ingenuity. (Plus knowing where to drill!)
chapter
Building a
Directional Tin Can
Antenna
I
n Chapter 1, you learned how to make a Wi-Fi antenna cable that
can be used to connect an external antenna to your Wi-Fi card or
in this chapter
access point. It is now time to build an antenna and put the cable from
Chapter 1 to good use. While there are many commercial antennas
Understanding
available on the market today, they can be expensive. And hey, let™s face
waveguides
it, attaching a commercial antenna to your Wi-Fi network will not turn
heads like making your own will.
Finding and
There are several different types of antennas that you can build. The
preparing the can
most famous Wi-Fi antennas are made from either a coffee can or a
Pringles potato chip can. In this chapter, you will learn how to build
Building the
your own antenna from a regular, metal coffee can. You will be able to
radiating element
build it quickly and cheaply. As an added bonus, you will have lots of
coffee, which will come in handy in staying awake for the other projects
in this book. Constructing the
can antenna
Here are the items you will need for this chapter™s project:
¤ The coaxial cable you built in Chapter 1
Using antenna
¤ Metal can about 4 inches in diameter and 5 „2 inches long simulation software
1

(100 mm“135 mm)
¤ Type N-Connector
¤ Long-nosed pliers
¤ Small wire cutters
¤ Single-sided razor blade
¤ Scissors
¤ Hammer
¤ Drill
¤ Soldering iron and solder
¤ Copper embossing material (optional)
60 Part I ” Building Antennas


Types of Can Antennas
There are two popular types of homebrew Wi-Fi can antennas, the Pringles can antenna and
the tin can antenna. They both have the same means to an end”increase signal strength in one
direction”but they differ radically in operation and construction.
The Pringles can antenna is actually a Yagi antenna with a Pringles can covering used to mount
the antenna components. You may recall from Chapter 2 that a Yagi antenna uses a single ele-
ment as a radiator, with additional metallic elements. A single reflector element and multiple
director elements help to shape the beam into a directional pattern.
In fact, the Pringles can isn™t really a can, it™s just a cylindrical cardboard container. Figure 3-1
shows the internal components of the Pringles can antenna. The primary components are the
radiator and the beam-shaping elements. All other components serve to hold the antenna
together in the correct position for best efficiency.
While the Pringles can is merely a shell, the tin can is the actual antenna on a tin can antenna.
This is because the tin can antenna is a “waveguide” antenna (see Figure 3-2). That is, the size,
shape, and electrical conductivity of the tin can act upon the radio frequency signals. When you
place a small radiator in the right location, the dimensions of the can itself will shape the beam
and light up the sky.




FIGURE 3-1: The popular Pringles can Yagi antenna and the insides.
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Chapter 3 ” Building a Directional Tin Can Antenna




FIGURE 3-2: The tin can waveguide antenna.



A waveguide is a type of radio frequency (RF) transmission path. Where low-frequency systems
can use copper wires, like that used in your car radio, high-frequency RF will sometimes use
waveguides to route high-power, high-frequency signals. Military radar systems often use
waveguide transmission lines.


Understanding Waveguides
A waveguide is a type of transmission line, like coaxial cable (see Figure 3-3). But, unlike coax-
ial cables, waveguides can carry microwave frequencies with almost no loss. RF energy as high
as 60 GHz or higher travel easily through a waveguide conduit. A waveguide is constructed
from metal in a very specific size and shape, usually rectangular. It is also very costly to manu-
facture, install, and can be difficult to maintain. Because it™s made from metal, and must be of
exact dimensions, waveguide transmission lines are very rigid.
Waveguides exploit a very interesting aspect of electromagnetic RF energy: The duality of elec-
tromagnetism. Electromagnetic energy is composed of an electric field and a magnetic field
(hence the name). In a coaxial wire, these fields are present along the center conductor and
reflected from the outer shield. In a waveguide, these two fields travel along the waveguide
62 Part I ” Building Antennas


90-Degree
Rectangular Circular
Connector




Slotted Waveguide
Antenna
FIGURE 3-3: Examples of various waveguides.



without the need for a center conductor. The inner surface of the waveguide essentially directs
the signal through the empty space of the interior itself.
Waveguide theory breaks apart all of the elements of radio frequency transmission. The details
are quite complicated and can fill volumes. For this book, the important thing to note about
waveguides is that size and shape of the waveguide itself is important, and placement of the
radiator inside the waveguide is important.
Constructing a waveguide transmission line is difficult. To use a waveguide antenna, however,
is a snap. You only need a short portion of the waveguide path to make an antenna. And Wi-Fi
frequencies dictate a size and shape that is easily available at any grocery store.


Sizing a Waveguide Antenna
As you know, a waveguide needs to be of specific dimensions. The waveguide antenna, there-
fore, must be the correct size for the frequency you are working with. In this case, you are
working with Wi-Fi operating in the 2.4 GHz band.
Let™s size this antenna for the middle of the band at channel 6, which has a frequency of 2.437
GHz (see the frequencies in Table 1-2 in Chapter 1). With proper construction, this antenna
should operate well across all Wi-Fi frequencies from channels 1 to 14.
To ensure a can that™s sized well, it should follow the dimensions shown in Figure 3-4.
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Chapter 3 ” Building a Directional Tin Can Antenna


123 mm
100 mm




Radiator




Radiator
Offset
FIGURE 3-4: Dimensions for a waveguide can antenna.


The dimensions for the can antenna built in this chapter are:

Diameter: ideally 100 mm plus or minus 10 percent (90“110 mm)
Length: about 123 mm or a full wavelength, plus or minus 10 percent
Wedge-shaped radiating element: 24 mm (about 1/5 of a wavelength)
Radiator offset: 27 mm (about 7/32 of a wavelength)

To calculate wavelength, use the formula wavelength in millimeters = 300 divided by the frequency
in gigahertz. So, the wavelength for channel 6 is 300 / 2.437 = 123 mm.




Finding the Right Can
For this project, you can use just about any smallish coffee can. There are a couple of things you
have to keep in mind: it has to be a metal can and it should be close to the dimensions noted in
the previous section. Remarkably, Maxwell House and Folgers Coffee cans are the exact
dimensions needed for this project. The ounces (or grams) measurements vary somewhat from
11.5 oz. (368 g) to 13 oz. (326 g) because they are measuring weight. But the can dimensions
are identical for these two brands and probably many more.
To find the right can, go to your local grocery store with a measuring tape or ruler and measure
the cans on the shelf. The store personnel might look at you funny. Just tell them you are buying
some coffee to make your Internet access go further.
64 Part I ” Building Antennas


In choosing your coffee, remember that one can make many cups of coffee to drink. You really
have two choices; you can dump the coffee or keep a pot of coffee ready at all times for the
other projects in this book. For this chapter, we used an 11.5 oz. Maxwell House coffee can.



Preparing the Can
It™s time to get the can ready to be converted into a directional antenna. You can do this in two
steps: preparation and cleaning.


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