Hardware Reference
In-Depth Information
RFI, sometimes you can add a filter to the transmitter that suppresses spurious emissions.
Unfortunately, problems sometimes persist until the transmitter is either switched off or
moved some distance away from the affected computer.
Note
If you depend on wireless Ethernet (Wi-Fi) networks, keep in mind that the popular 2.4GHz
band used by 802.11b, 802.11g, and 802.11n networks is in the same general frequency band
as Bluetooth and 2.4GHz cordless phones, so there's plenty of potential for interference.
To avoid interference from other 802.11-based networks, use a program such as inSSIDer
(
http://www.metageek.net/products/inssider/
)to view the frequencies used by other nearby
802.11-based networks, and choose the least-crowded channel from 1, 6, or 11. (The other
channels overlap substantially with each other.) To avoid conflicts with cordless phones, use
cordless phones that operate on frequencies other than 2.4GHz. To learn more about avoid
conflicts with Bluetooth devices, see “
Bluetooth
,
” in
Chapter 17
.
Dust and Pollutants
Dirt,smoke,dust,andotherpollutantsarebadforyoursystem.Thepower-supplyfancar-
ries airborne particles through your system, and they collect inside. If your system is used
in an extremely harsh environment, you might want to investigate some of the industrial
systems on the market designed for harsh conditions.
Manycompaniesmakespecialhardenedversionsoftheirsystemsforharshenvironments.
Industrial systems typically use a different cooling system from the one used in regular
PCs. A large cooling fan is used to pressurize the case rather than depressurize it. The air
pumped into the case passes through a filter unit that must be cleaned and changed peri-
odically. The system is pressurized so that no contaminated air can flow into it; air flows
only outward. The only way air can enter is through the fan and filter system.
These systems also might have special keyboards impervious to liquids and dirt. Some
flat-membrane keyboards are difficult to type on, but are extremely rugged; others re-
semble the standard types of keyboards but have a thin, plastic membrane that covers all
the keys. You can add this membrane to normal types of keyboards to seal them from the
environment.
A relatively new breed of humidifier can cause problems with computer equipment. This
type of humidifier uses ultrasonics to generate a mist of water sprayed into the air. The
extra humidity helpscureproblems withstatic electricity resulting fromadryclimate, but
the airborne water contaminants can cause many problems. If you use one of these sys-
tems, you might notice a white, ash-like deposit forming on components. The deposit is
the result of abrasive and corrosive minerals suspended in the vaporized water. If these
depositscollectonthesystemcomponents,theycancauseallkindsofproblems.Theonly
