AS THE WIRELESS UNIVERSE EXPANDS, WEIRD NEW CASES of electromagnetic interference are surfacing. On Feb. 27, immediately after WFAA-TV in Dallas began its first transmission of high-definition television, 12 pocket-size heart-monitoring devices used by patients at nearby Baylor University Medical Center went on the blink. The devices relay electrocardiogram signals to a central station, where nurses monitor the patterns on computer screens. The nurses became alarmed when screens they were watching repeatedly went blank. Troubleshooters quickly traced the problem to the HDTV signals, which occupied the same slice of radio spectrum as some of the older heart monitors used at the hospital.

No patients were affected, and WFAA halted broadcasts while the hospital replaced the old monitors. But more incidents of this sort seem likely as HDTV and other forms of wireless digital communications proliferate. Last year, equipment at a cable-TV facility in Virginia was thrown out of whack by emissions from microwave ovens at a fast-food restaurant. Cell-phone signals have also been known to cause interference at cable-TV facilities as well as disrupting antilock brakes and other electronic systems in cars.

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