Page 797 - (ISC)² CISSP Certified Information Systems Security Professional Official Study Guide

The standard straight or pole antenna is an omnidirectional antenna
that can send and receive signals in all directions perpendicular to the

line of the antenna itself. This is the type of antenna found on most
base stations and some client devices. This type of antenna is
sometimes also called a base antenna or a rubber duck antenna (due to
the fact that most are covered in a flexible rubber coating).

Most other types of antennas are directional, meaning they focus their
sending and receiving capabilities in one primary direction. Some

examples of directional antennas include Yagi, cantenna, panel, and
parabolic. A Yagi antenna is similar in structure to that of traditional
roof TV antennas. Yagi antennas are crafted from a straight bar with
cross sections to catch specific radio frequencies in the direction of the
main bar. Cantennas are constructed from tubes with one sealed end.
They focus along the direction of the open end of the tube. Some of the
first cantennas were crafted from Pringles cans. Panel antennas are
flat devices that focus from only one side of the panel. Parabolic

antennas are used to focus signals from very long distances or weak
sources.

Adjusting Power Level Controls

Some wireless access points provide a physical or logical adjustment of
the antenna power levels. Power level controls are typically set by the

manufacturer to a setting that is suitable for most situations. However,
if after performing site surveys and adjusting antenna placement,
wireless signals are still not satisfactory, power level adjustment might
be necessary. However, keep in mind that changing channels, avoiding
reflective and signal-scattering surfaces, and reducing interference can

often be more significant in terms of improving connectivity reliability.
When adjusting power levels, make minor adjustments instead of

attempting to maximize or minimize the setting. Also, take note of the
initial/default setting so you can return to that setting if desired. After
each power level adjustment, reset/reboot the wireless access point
before re-performing site survey and quality tests. Sometimes
lowering the power level can improve performance. It is important to

keep in mind that some wireless access points are capable of providing
higher power levels than are allowed by regulations in countries where