Hardware Reference
In-Depth Information
• Power-line noise problems increase with the resistance of the circuit, which is a function of
wire size and length. So, to decrease resistance, avoid extension cords unless absolutely
necessary, and then use only heavy-duty extension cords.
• Inevitably, you will want to plug in other equipment later. Plan ahead to avoid the temptation to
connect too many items to a single outlet. If possible, provide a separate power circuit for non-
computer-related devices.
Air conditioners, coffee makers, copy machines, laser printers, space heaters, vacuum cleaners, and
power tools are some of the worst corrupters of a PC system's power. Any of these items can draw
an excessive amount of current and wreak havoc with a PC system on the same electrical circuit. I've
seen offices in which all the computers begin to crash at about 9:05 a.m. daily, which is when all the
coffee makers are turned on!
Another major problem in some companies is partitioned offices. Many of these partitions are
prewired with their own electrical outlets and are plugged into one another in a sort of power-line
daisy-chain, similar to chaining power strips together. The person in the cubicle at the end of the
electrical daisy-chain is likely to have power problems.
Radio-Frequency Interference
Radio-frequency interference (RFI) is easily overlooked as a problem factor. The interference is
caused by any source of radio transmissions near a computer system. Living next door to a 50,000-
watt commercial radio station is one sure way to get RFI problems, but less-powerful transmitters
can cause problems, too. I know of many instances in which cordless telephones have caused
sporadic random keystrokes to appear, as though an invisible entity were typing on the keyboard. I
also have seen RFI cause a system to lock up. Solutions to RFI problems are more difficult to state
because every case must be handled differently. Sometimes, simply moving the system eliminates the
problem because radio signals can be directional in nature. At other times, you must invest in
specially shielded cables for external devices, such as the keyboard and the monitor. If the keyboard
or mouse is wireless, RFI can be especially problematic; the only solution might be to try a different
brand or model that operates on a different frequency.
One type of solution to an RFI noise problem with cables is to pass the cable through a toroidal iron
core, a doughnut-shaped piece of iron placed around a cable to suppress both the reception and
transmission of electromagnetic interference (EMI). Many monitors include a toroid (sometimes
spelled
torroid
) on the cable that connects to the computer. If you can isolate an RFI noise problem in
a particular cable, you often can solve the problem by passing the cable through a toroidal core.
Because the cable must pass through the center hole of the core, it often is difficult, if not impossible,
to add a toroid to a cable that already has end connectors installed.
RadioShack sells a special snap-together toroid designed specifically to be added to cables already
in use. This toroid looks like a thick-walled tube that has been sliced in half. You simply lay the
cable in the center of one of the halves and snap the other half over the first. This type of construction
makes adding the noise-suppression features of a toroid to virtually any existing cable easy.
The best, if not the easiest, way to eliminate an RFI problem is to correct it at the source. It is unlikely
that you'll be able to convince the commercial radio station near your office to shut down, but if you
are dealing with a small radio transmitter that is generating 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.
