Dummies, Wireless

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Part I: Wireless Networking Fundamentals
products, but there’s a minor trend away from using detachable antennas in
802.11a products because of a potential conflict in the frequency channels
allocated to 802.11a. This situation potentially thwarts misuse but also robs
those deploying access points of their ability to choose optimal antennas.
Industry Standards
One of the most significant factors that has led to the explosive growth of
personal computers and their effect on our daily lives has been the emergence
of industry standards. Although many millions of personal computers
are in use now around the world, only three families of operating system software
run virtually all these computers: Windows, Mac OS, and Unix (including
Linux). Most personal computers used in the home employ one of the
Microsoft Windows or Apple Macintosh operating systems. The existence
of this huge installed base of potential customers has enabled hundreds of
hardware and software companies to thrive by producing products that interoperate
with one or more of these industry-standard operating systems.
Computer hardware manufacturers recognize the benefits of building their
products to industry standards. To encourage the adoption and growth of
wireless networking, many companies that are otherwise competitors have
worked together to develop a family of wireless networking industry standards
that build on and interoperate with existing networking standards. As a result,
reasonably priced wireless networking equipment is widely available from
many manufacturers. Feel safe buying equipment from any of these manufacturers
because they’re all designed to work together, with one important
caveat: You need to make sure your gear can all “speak” using the same version
of Wi-Fi. The four major flavors of this wireless networking technology
for LAN applications are IEEE 802.11a, 802.11b, 802.11g, and 802.11n — two
of these, 802.11g and n are the current (and future) versions. You just have to
Understanding antenna gain
Antenna gain is usually expressed in dBi units
(which indicate, in decibels, the amount of gain
an antenna has). An antenna with a 4 dBi gain
increases the output power (the effective
isotropic radiated power, or EIRP) of the radio by
4 dBm. The FCC permits IEEE 802.11 radios to
have a maximum EIRP of 36 dBm when the
device is using an omnidirectional antenna.
The antennas included with wireless home networking
equipment are typically omnidirectional
detachable dipole antennas with gains of 2 dBi
to 5 dBi. Some manufacturers offer optional
high-gain antennas. (Note: The maximum EIRP
output permitted in Japan is 100 mW; and the
maximum output in Europe is only 10 mW.)