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Walkie-talkie interference with Macs, Apple displays

Walkie-talkie interference with Macs, Apple displays

Yesterday we reported that a set of Motorola Talkabout T5420 handsets activated the touch-sensitive power panel on a reader's 15 inch Apple Studio Display. Today Randy Smith offers some additional insight on why the power pad - also used on the Power Macintosh G4 Cube and other Apple products - is susceptible to radio transfer signals, and could actually be damaged by them.

"The walkie-talkies in the article yesterday are Motorola FRS (Family Radio Service) transceivers and operate in the 400Mhz range (around 460mhz). At these frequencies the wiring in computers and TV sets can act as antennas. The higher the frequency the short an antenna has to be to be resonant. Depending on the power level of the transmission this can cause all kinds of problem with frequency dependent devices - such as monitors, mice, keyboards and the like.

"The frequencies of the two devices can mix and cause problems by adding to or subtracting from the frequencies the device is expecting. This could cause the screen to distort and could also lead to false mouse movements and clicks and well as false keyboard entries.

"This not a Mac-exclusive problem. Any computer or TV could be affected by stray RF (Radio Frequency) energy. While this should not damage the unit I would take care when transmitting around such equipment. Radio Shack sells RF chokes to stop RF from affect such equipment. They can snap on to the wires or the wire can be wrapped around them. This stops the RF from propagating down the wiring. If you are using radio equipment around your computer all wire going into and out of your computer should have these "chokes" on them. Also using the lowest power setting on the radio you can well help things as well. If the radio can use an external antenna it should be place well away from the computer. It is not really the radio but the RF coming from the antenna that is the problem."

Smith also suggests an amateur radio Web site that explains methods for separating radio and computer signals.

Feedback on this issue? Drop us a line at late-breakers@macfixit.com.

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