Getting the static out

Question: I like to listen to my clock-radio while using my computer. The radio is located about four feet from the CPU, separated by air and wood, and about six inches above the monitor.

Problem: The static is excruciating, especially when my computer is booting up. The problem occurs with all stations.

Static occurs when the CPU is on and other components are off and seems loudest during booting up. Do you have any suggestions? — F.D.

Answer: There are two possible ways the radio is suffering interference, either “conducted” or “radiated,” according to Jim Nelson, senior project engineer at Illinois-based Oneac, a company that makes products that provide protection against power and data-line disturbances.

Conducted means the interfering radio frequency noise is flowing out of the power cord of the PC and up the power cord of the radio.

Radiated means the interfering radio frequency noise is being emitted directly from the PC or cables connected to it through the air, just like a radio station.

“It’s true that a PC sends a much weaker signal than any radio station. It is infinitely closer, as far as the radio is concerned, so the noise wins,” said Nelson.

First, try a battery-operated radio in the same location and tune it to your regular station. If the interference goes away, the problem is most likely conducted interference, though this is no guarantee. The portable radio may just be better filtered.

If you think the problem is conducted, plug the radio into a different electrical circuit than the one the computer is on. Or try using a line filter on the PC and radio. Look for transformer-based Uninterruptible Power Supplies (UPS) that filter out noise and protect against surges. (“Oneac makes them,” said Nelson.)

Look for one that has built-in filters for Radio Frequency Interference/Electro-Magnetic Interference (RFI/EMI) and that has high isolation rating in db (db stands for decibels).

If the problem seems to be radiated interference, first try repositioning or re-orienting both pieces of equipment and their cords.

Some radios use the power cord as the antenna. The cables coming out of the PC can work as antennas, too. A device at the end of the wire doesn’t need to be in use, or even on, for the cord to be a problem.

Turn the PC and radio on so you can hear the interference. Start disconnecting the cords from the back of the PC one at a time to see if one in particular is causing the problem.

The interference may be caused by several sources. So the interference may diminish slightly if one cord is removed. You can’t pull the power cord, but it may be the source, so don’t forget it when you try some of the following suggestions provided by Nelson.

• If there are screws on any of the connectors, make sure they are tight, as some shielded cables require them for good grounding.
• If you suspect some of the cables going to your printer or serial device are unshielded, buy replacements that say shielded wire is used.
• If any cables are longer than they need to be, bundle and tie them up.
  Don’t roll them into a coil. Weave them back and forth as tightly as possible and tie or tape them.
• Ferrite cores or beads in a cable can help at certain frequencies. These look like a small cylindrical lump near the connector. Your monitor’s video cable probably has one.
  Snap-on versions can be bought at places like RadioShack. Try them on the cables that you suspect.
  They work best nearest the source (the PC main box), though sometimes sliding them up and down the cable changes the effect. If the hole in the bead is large enough, loop the cable more than once to increase effectiveness.
• Sometimes, long slots or breaks in the metal PC cabinet can act as an antenna. Make sure the PC cover is seated properly and screwed on tight, if you have ever taken it off.

If there are still long openings in the box, try to seal them with aluminum foil tape sold at heating and air conditioning suppliers.

Do not put the tape near electrical connections or use it where it could fall on something that has power running through if it came unstuck. Also, be sure not to cover openings used for ventilation. The tape trick is a last resort.

“It’s rare that this is the source, but I’ve seen it work,” said Nelson.

Here’s a site that has more information:www.fcc.gov/cib/Publications/tvibook.html.