Tech Tip
Chapter 4 Wireless Technology
153
electrical power lines, radar, motors, fl uorescent lights, and such. The list is ever
increasing. There are thousands of products that produce electromagnetic waves.
The FCC regulates the electromagnetic spectrum and dictates the frequency
that is to be used for each group of devices. Even with all these regulations,
equipment fails and produces undesirable frequencies that can interfere with a
regulated frequency. If you move the tuner of an AM radio across the various
stations, you will hear an excellent example of interference.
AM radio is an old technology that was susceptible to radio interference. FM radio is an
improvement over AM radio because it is less susceptible to radio interference.
Virtually any type of electrical equipment can produce radio interference
even if it is not assigned to the radio frequency spectrum assigned to wireless
LAN communications. For example, some other sources of radio interference
that could corrupt data packets are fl uorescent lighting, electric motors, electrical
control systems, welding equipment, portable radios, and such. While not
intended to produce radio interference in the assigned wireless spectrum,
a defective piece of equipment can produce electrical radio harmonics. The
harmonic signal is a multiple of an original signal. For example, a radio frequency
of 12,000 can also produce signals of 24,000, 36,000, 48,000, and so on. This
means that harmonic frequencies produced by other areas of the electromagnetic
spectrum can cause interference with the wireless network.
Another major factor is proximity to the source of the signal. If radio
interference is in close proximity to the wireless network system, it need not be
at the same frequency. Close proximity and a powerful signal can disrupt the
wireless communication. Radio signals can also refl ect or bounce off surrounding
materials, usually metallic surfaces, Figure 4-5. The refl ected signal is an exact
copy of the original signal. The refl ected signal does not always disrupt the
original signal. At times, it actually increases the strength of the original signal
Figure 4-5.
A reflected radio
signal can combine
with the intended
radio signal and
either disrupt the
intended signal or
enhance it.
Reflective surface
Reflected signal Original signal
Original signal