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08 February 2012

Answer to Question #2060 Submitted to "Ask the Experts"

Category: Cell Phones

The following question was answered by an expert in the appropriate field:

Hospitals do not allow cell phone use due to potential interference. Last weekend I was in a hospital where the top of the hospital building was studded with cell tower antennas. Why is it that cell phones would cause interference, but cell tower antennas would not?

It's a question of signal strength. Interference has been observed only very close to transmitting antennas where there is strong signal strength. Interference has been observed in some medical electronics due to hand-held cell phones. Roof-top antennas are some distance away from any susceptible electronics. In addition to proximity, the directionality of the antennas is important. Most rooftop antennas have strong gain in the forward direction—towards the horizon—and very low gain in the vertical direction. Finally, there are layers of building materials shielding the interior areas from the rooftop antennas. Proximity, directionality, shielding—all go towards reducing the signal strength inside a building due to the antennas on the roof so that interference is not generally an issue. This does not mean that you cannot receive the signals from the roof top antennas inside the building; it simply means that the received signals are not strong enough to cause interference. Gary H. Zeman, ScD, CHP

Answer posted on 29 May 2002. The information and material posted on this website is intended as general reference information only. Specific facts and circumstances may alter the concepts and applications of materials and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice specific to whatever facts and circumstances are presented in any given situation. Answers are correct at the time they are posted on the Website. Be advised that over time, some requirements could change, new data could be made available, or Internet links could change. For answers that have been posted for several months or longer, please check the current status of the posted information prior to using the responses for specific applications.