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Some of the projects in this book can be performed using stand-alone wireless networks, espe-
cially if you are experimenting or just “playing around.” At a minimum, you should have a com-
puter with wireless capability. Ideally, this computer is a laptop. Laptops with 300 MHz
processors can now be found used for just a few hundred dollars on eBay.
If you will be sharing Internet access or setting up an in-home network, a high-speed connec-
tion is practically a must. On the other hand, if you just want to build an in-home network, all
you need is two computers.
About the only strong requirement for this book is the desire to obtain wireless equipment.
Each chapter will describe which components you will be working with.
You will also need tools. Tools are mentioned at the beginning of each chapter. You can expect to use
common tools such as screwdrivers, wire cutters and strippers, crimping tools, and soldering irons.
Wi-Fi security is an ever-present concern. As you will see in Chapter 5, “Gearing Up for War
Driving,” finding a wireless network is not difficult. If you do not secure your network, anyone
within range can eavesdrop on your network and possibly gain access to your files. It™s like let-
ting them in the front door. Basic steps to secure your network are to enable the built-in
encryption capabilities of your wireless devices, using WEP. If you plan to share your connec-
tion with others, make sure you install a personal firewall on your computer.
part
Building
Antennas

in this part
Chapter 1
Building Your Own Wi-Fi
Antenna Cable

Chapter 2
Building a Classic Paperclip
Antenna

Chapter 3
Building a Directional Tin
Can Antenna

Chapter 4
Modifying Your Access Point
with a High-Gain Antenna
chapter
Building Your
Own Wi-Fi
Antenna Cable
T
hink back to the olden days, say three or four years ago, when
computers were tied to the desk with a phone line or network cord.
in this chapter
Surfing the Web, reading e-mail, or checking your PetCam meant
plugging in, jacking in, or getting wired. Now just about any device can be
Understanding
“unwired” to use a wireless network. You still need electricity though, so
Wi-Fi and radio
batteries or power cords are still in the picture. At least for a little while.
frequencies
Ironically, wireless seems to use twice as many cables as wired connections.
This wireless paradox arrives in the form of extra power cords, antenna
Learning about
cables, pigtail jumper cables, and Ethernet patch cables.
coaxial cables
One critical component to a successful wireless project is the antenna cable,
used to extend the reach of the radio to the antenna. This chapter will show
Making your own
how to build an antenna cable for use with many of the projects in this
coax cable
book. You can purchase this type of cable in pre-defined lengths from
connector
online sources. However, building your own antenna cable is easy and can
take less than 5 minutes.
Selecting a pigtail
The instructions in this chapter apply to a Wi-Fi coaxial antenna
cable (also called coax). The steps in this chapter can be adjusted
to apply to any type of coaxial cable, like that used in cable tele-
visions.


You will need the following items:
¤ Wi-Fi network device with an external connector (client adapter or
access point)
¤ Wi-Fi pigtail cable, if using a wireless client adapter
¤ Coaxial cable, preferably Times Microwave LMR-400
¤ Coaxial cable cutters
¤ Crimp tool, ratcheting style
¤ Crimp tool “die” with hex sizes .429, .128, and .100
4 Part I ” Building Antennas


¤ Long-nosed pliers
¤ Small wire cutters
¤ Single-sided razor blade
¤ Scissors
¤ Type-N connectors, reverse-polarity male
¤ Digital multimeter or electrical continuity tester
¤ Known-good coax cable for comparison testing
Some of these items are specific to building an antenna cable (crimp tools, connectors, and so
on). Don™t worry if they are unfamiliar to you. All will become clear as the chapter progresses.



About Wi-Fi
If you want to understand what is going on with a wireless network, you first need to know
some of the basics of wireless communication and radio transmission.
Wireless networking is accomplished by sending a signal from one computer to another over
radio waves. The most common form of wireless computing today uses the IEEE 802.11b
standard. This popular standard, also called Wi-Fi or Wireless Fidelity, is now supported directly
by newer laptops and PDAs, and most computer accessory manufacturers. It™s so popular that
“big box” electronics chain stores carry widely used wireless hardware and networking products.

Wi-Fi is the root of a logo and branding program created by the Wi-Fi Alliance. A product that
uses the Wi-Fi logo has been certified by the Wi-Fi Alliance to fulfill certain guidelines for inter-
operability. Logo certification programs like this one are created and promoted to assure users
that products will work together in the marketplace. So, if you buy a Proxim wireless client
adapter with the Wi-Fi logo branding, and a Linksys access point with the same logo on the
product, they should work together.

The IEEE 802.11b Wi-Fi standard supports a maximum speed of 11 megabits per second
(Mbps). The true throughput is actually something more like 6 Mbps, and can drop to less than 3
Mbps with encryption enabled. Newer standards like 802.11a and the increasingly popular
802.11g support higher speeds up to 54 Mbps. So why is 802.11b so popular? Because it was first
and it was cheap. Even 3 Mbps is still much faster than you normally need to use the Internet.

A megabit is one million binary digits (bits) of data. Network speed is almost always measured in
bits per second (bps). It takes 8 bits to make a byte. Bytes are used mostly to measure file size (as
in files on a hard disk). A megabyte is about 8 million bits of data. Don™t confuse the term
megabyte for megabit or you will come out 8 million bits ahead.

The 802.11a standard, which operates in the 5 GHz frequency band, is much faster than
802.11b, but never caught on, partly because of the high cost initially and partly because of the
actual throughput in the real-world conditions of a deployed wireless network.
5
Chapter 1 ” Building Your Own Wi-Fi Antenna Cable


The fast and inexpensive 802.11g standard (which uses the same 2.4 GHz band as 802.11b) is
rapidly moving to unseat 802.11b from the top of the heap. The very cool thing about “g” is the
built-in backwards compatibility with 802.11b. That means any “b” product can connect to a
“g” access point. This compatibility makes 802.11g an easy upgrade without tossing out your
old client hardware.

Because of the compatibility with 802.11b and 802.11g, there is no great hurry to push the myr-
iad of funky wireless products to the new “g” standard. Most manufacturers have support for
basic wireless infrastructure using 802.11b and 802.11g with access points and client adapter.

Wi-Fi 802.11b really shines when you look at the host of wireless products available. Not only
are there the basic wireless networking devices, like adapters, base stations, and bridges, there
are also new products that were unthinkable a few years ago. Wireless disk drive arrays, presen-
tation gateways, audiovisual media adapters, printer adapters, Wi-Fi cameras, hotspot con-
trollers, and wireless broadband and video phones dominate the consumer arena. And the
enterprise market is not far behind.
We™ve been tossing out the terms wireless, gigahertz (GHz), and frequency. Next, we™ll discuss
how Wi-Fi uses wireless radio waves, also called RF, to communicate amongst the devices in a
wireless network.


About RF
Entire books, libraries, and people™s careers are devoted to understanding more about radio fre-
quencies (RF) and electromagnetism. The basics are covered here to help make your projects a
success.
Wi-Fi wireless products use microwave radio frequencies for over-the-air transmissions.
Microwave RF is very similar to the radio used in your car, only at much higher frequencies.

For a downloadable PDF of the spectrum assignments in the United States, visit
www.ntia.doc.gov and look under “Publications” for the “Spectrum Wall Chart.” The chart is
a few years old, but most of the information is accurate. And it™s suitable for framing.
For frequency spectrum assignments covering most of Europe, check out the European
Radiocommunications Office at www.ero.dk and look under the CEPT National Frequency
Tables. The ERO “Report 25” document also covers much of this information in a single report
file. To find this deeply buried document, search the Web for ERO Report 25.

Visualizing the radio frequency signals helps to understand the behavior of the electromagnetic
(EM) spectrum. Imagine dropping a rock in a pond. Waves are created in concentric circles com-
ing from the point where the rock was dropped. These waves are just like radio waves, except at a
very low frequency of perhaps 10 waves per second, which are called cycles per second or hertz.
Now imagine a cross-section of those waves. Perhaps the rock was dropped in a fish tank and
the waves are visible from the side. The wave would look similar to that shown in Figure 1-1.
The electromagnetic spectrum spans frequencies from subaudible sound of 1 hertz all the way
through radio and visible light to beyond X-rays and cosmic rays at a frequency of 10 followed by
6 Part I ” Building Antennas




FIGURE 1-1: Waves viewed from the side.

24 zeros. The frequency of an FM car radio operates at about 100 million hertz, or 1 megahertz
(MHz). For example, 103.1 MHz FM is a radio station in Los Angeles. Wi-Fi operates at about
2,400 MHz or 2.4 GHz. Table 1-1 shows a frequency chart to help you understand the scale.

Microwave ovens also operate at 2.4 GHz, but at much higher power than Wi-Fi gear. One-
tenth of a watt (0.1 W) is typical for a Wi-Fi device, versus 1,000 watt for a microwave oven.
That™s a difference of over 10,000 times the power! Still, to be safe, always observe caution and
minimize unnecessary exposure when working with RF.


Frequency versus Wavelength
Frequency and wavelength are inseparably related to each other. As frequency increases, wave-
length decreases and vice versa.

Frequency: The rate at which a radio signal oscillates from positive to negative.
Wavelength: The length of a complete cycle of the radio signal oscillation.


Table 1-1 Frequency Ranges
Range Abbreviation Cycles Per Second Application

Hertz Hz 1 Ripples in a pond, ocean waves
Kilohertz kHz 1,000 AM radio, CB radio
Megahertz MHz 1,000,000 FM radio, television, cordless
phones, 2-way radios, older
cell phones
Gigahertz GHz 1,000,000,000 Wi-Fi, satellite, microwave
ovens, cordless phones, newer
cell phones, GPS
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Chapter 1 ” Building Your Own Wi-Fi Antenna Cable




FIGURE 1-2: Dimensions of a Wi-Fi channel 6 (2.437 GHz) radio wave.


Wavelength is, of course, a length measurement, usually represented in metric (meters, cen-
timeters, and so on). And frequency is a count of the number of waves occurring during a set
time, usually per second. Cycles per second is represented as Hertz (Hz).
Figure 1-2 shows a Wi-Fi radio wave for channel 6 (2.437 GHz). The dimensions are impor-
tant to note, because the physical properties of the wave define antenna, cable, and power
requirements. Wavelength is critical for antenna design and selection as we will cover in the
next chapter.
Wi-Fi signals operating at a frequency of 2.4 GHz have an average wavelength of about
12 cm. Since the wavelength is so short, antennas can be physically very small. A common
design for antennas is to make them 1/4 of a wavelength or less in length, which is barely more
than an inch long. That™s why Wi-Fi antennas can perform so well even though they are physi-
cally very small. As a comparison, a car radio antenna is much longer to get a decent signal
because FM radio signals are an average of 10 feet long.
Wavelength and antenna length go together. To oversimplify, the longer the antenna, the more
of the signal it can grab out of the air. Also, antenna length should be in whole, halves, quarters,
eighths, and so on of the intended wavelength for best signal reception. The highest reception
qualities come from a full wavelength antenna.

Perform this simple math formula to find wavelength: 300 / frequency in megahertz. The answer
will be the wavelength in meters. So, 300 / 2437 0.12 meters or 12 cm.




Unlicensed 2.4 GHz Wi-Fi
Wi-Fi makes use of the internationally recognized unlicensed frequency band at about 2.4 GHz.
The IEEE standards body created 802.11b and defined the “channels” and frequencies for use by
manufacturers worldwide. Different countries accepted the standard and allowed the use of
devices in this frequency range with few restrictions.The word unlicensed as it applies to Wi-Fi
specifically means that products can be installed and used without prior approval from the local
governing body. That™s the Federal Communications Commission (FCC) for users in the United
States. Radio systems that operate in “licensed” bands require an application and permission
8 Part I ” Building Antennas


procedure before turning on or using a radio system. For example, FM radio stations require per-
mission from the FCC before broadcasting.
Certain other unlicensed products have been in use for some time: CB radios, walkie-talkies or
consumer two-way radios, cordless phones, and many other radio products operate in unli-
censed bands.
Unlicensed is not equivalent to unregulated, though. There are still rules that need to be fol-
lowed to stay legal, especially regarding power output. This is covered in Chapter 2.

In the United States, 802.11b usage is regulated by the FCC. The FCC laws define maximum
power output, among other more specific regulations. In addition, the FCC approves products
for use in the U.S. market. Manufacturers must submit their product for testing and authoriza-
tion. The FCC then grants an “FCC ID” for the product. Anyone can look up an FCC ID from the
Web site at www.fcc.gov (look under Search, for “FCC ID Number” searches). This can help you
track down the true manufacturer of a Wi-Fi radio product, despite the label or brand.


Wi-Fi Channels
As defined in 802.11b, Wi-Fi consists of 14 channels worldwide. Only channels 1 to 11 are
available in North America. Channels in other countries vary. Table 1-2 shows each channel
and frequency, and the countries with approval to use that channel. (The lucky ones in Japan
can use all 14!)
What is not easily shown in Table 1-2 is channel separation.To make the channel numbering
scheme work with different radio technologies, the IEEE community defined these 802.11b
channels with significant overlap. For example, channel 6 is centered on 2.437 GHz, but it
extends in both directions by 11 MHz (0.011 GHz). That means channel 6 uses 2.426 GHz



Table 1-2 802.11b Specified Channels
Channel Center Frequency (GHz) Countries

1 2.412 USA, Europe, Japan
2 2.417 USA, Europe, Japan
3 2.422 USA, Europe, Japan
4 2.427 USA, Europe, Japan
5 2.432 USA, Europe, Japan
6 2.437 USA, Europe, Japan
7 2.442 USA, Europe, Japan
8 2.447 USA, Europe, Japan
9 2.452 USA, Europe, Japan
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Chapter 1 ” Building Your Own Wi-Fi Antenna Cable


Channel Center Frequency (GHz) Countries

10 2.457 USA, Europe, Japan, France, Spain
11 2.462 USA, Europe, Japan, France, Spain
12 2.467 Europe, Japan, France
13 2.472 Europe, Japan, France
14 2.484 Japan



to 2.448 GHz, which, as shown in Table 1-2, means it uses frequencies already assigned to
channels 4, 5, 6, 7, and 8. Clearly, Wi-Fi devices using channels 6 and 7 would not operate
together in harmony because of the interference.
To ensure trouble-free operation, with little interference from any other Wi-Fi devices, the
channels need to be separated.
In the United States, channels 1, 6, and 11 are the sweet-spots for maximum usage with
the least interference. In Europe, the recommended channels are 1, 7, and 13, and in
Japan, the channels are 1, 7, and 14. For this very reason, most products come with one of
these channels as the default setting, and most Wi-Fi hotspots are set to one of these three
channels.

Recently, users have been squeezing these nonoverlapping channels down to minimal-overlapping
channels 1, 4, 8, and 11. This opens up significantly more options for Wi-Fi device and access point
placement. There are possible downsides due to the increased interference, but it™s worth testing if
your setup needs a lot of devices in a small space.

Now you would have a basic understanding of how Wi-Fi works in a physical and logical
sense. There™s lots more to Wi-Fi technology and specifications, but that™s all you need to know
about the theory for now. Next, we™ll get down to the specifics about building your own Wi-Fi
projects.



Parts of a Wi-Fi Project
Every Wi-Fi project contains specific primary components to make the system work properly.
These are broken down into five simple components:

Data signal (Ethernet, computer interface, USB, and so on)
Data to RF converter
Radio transceiver
Transmission line
Antenna system
10 Part I ” Building Antennas




Data Source
Antenna System
Radio Transceiver Transmission Line
Data to RF Converter
(computer, etc)




FIGURE 1-3: Parts of a Wi-Fi project.


Figure 1-3 shows the breakdown. The data to RF converter and radio transceiver are nearly
always in the same appliance, and even on the same circuit board as on a PC card.


Data Signaling
The data signal is the digital signal with which every Wi-Fi access point or client project will
interface. In some cases, the data will come from a computer via PC card slot or USB cable. In
others it may be an Ethernet camera or the network itself.
The data signal is usually based on the Internet protocol, TCP/IP. TCP/IP is a protocol used to
transmit data between computers on normal, wired networks. Wi-Fi is meant to convert
TCP/IP traffic into radio waves and back.


Wi-Fi Devices
The category of Wi-Fi devices consists of the digital data to RF converter and the radio
transceiver. Most often, these two items are in the same product. In this book, projects will
not break down these two components; we™re describing them separately here for clarity. For
example, cable and antenna modifications to a wireless access point are covered in several
chapters throughout the book. Wi-Fi devices have two jobs: convert the data from the com-
puter into a radio signal, and transmit and receive radio signals to and from the data con-
verter. They come in several forms that can be broken down into the following four major
groups:

Wireless Access Point: Attached to an Ethernet network, an access point provides a wired
network gateway to wireless clients. An access point is the essential component for set-
ting up a typical wireless network.
Wireless Client Adapter: Connected or installed in a computer, a client adapter provides
wireless connectivity to a wireless access point and then to a wired network. This can be
inserted into a desktop computer, a laptop, a USB adapter, or any other computer interface.
Wireless-to-Ethernet Bridge: Provides a direct connection between a wireless and wired
(Ethernet) network without the need of a computer interface. It usually acts as a client
connecting to an access point.
Specialized Components: These include dedicated wireless networking devices, audiovisual
devices, music streaming devices, digital picture frames, wireless scanners, wireless print-
ers, and many more to come.
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Chapter 1 ” Building Your Own Wi-Fi Antenna Cable


A radio transceiver is merely a transmitter and receiver in one unit. Your car radio is a receiver. An
AM or FM radio station uses a transmitter. A CB radio is a transceiver. Wi-Fi devices are
transceivers constantly sending and receiving radio signals when in use.

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