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
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 computerinto a radio signal, and
transmit and receive radio signals to and from the data
converter.
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 setting
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 printers,
and many more to come.
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.
Transmission Lines
When you work with Wi-Fi products, you will find
that the transmission line is nearly always a
coaxial cable.
Internal transmission lines may be of very small diameter, high
loss cable. But usually the cable
run is less than a few inches, so line loss is not much of a
factor. See Figure 1-4 for an
internal view of a transmission line for the Linksys WAP11, a
popular 802.11b wireless access
point.
An RF transmission line transfers RF energy from
the transmitter to the antenna while both losing and radiating
as little as possible. Radiation should be left to the antenna
system. It also transfers RF energy from the antenna to the
receiver in the same fashion.
Antenna System
The antenna system is where the rubber hits the
road, so to speak. The antenna emits the electromagnetic
radio frequency signal out of the Wi-Fi device.
Antenna systems will be covered in
Chapter 2 while building a simple antenna for a
laptop PC card.
At this point, what you need to know is that the
antenna is where you want to send as much signal as possible.
The transmission line should be designed to be as short as
possible with the least line loss to pass power to the antenna.
Once the RF signal leaves the antenna, it immediately begins to
lose power. (Really, as soon as it leaves the transceiver it
begins to lose power.) The design of the antenna can redirect
the amount of power available to shape the beam pattern as
needed, much like a flashlight reflecting a tiny light bulb into
a bright light.
Now that you know more about Wi-Fi projects in
general, we can start to focus on the project for this chapter:
building an antenna cable. Before you pick up your tools,
though, you need to understand how coaxial cable works, which is
the subject of the next section.