Answer to Question #366 Submitted to "Ask the Experts"

Q

Are living quarters immediately below roof-top cellular telephone antenna/transmitters hazardous?

A

There is very little radiofrequency (RF) energy exposure to people inside a building from a cellular base station located on its roof. There are several reasons for this. First, the transmitters operate at low power levels. Second, the antennas are normally mounted near the edges of the roof and are aimed away from the building. Third, most cellular transmitters use "high gain" or panel antennas. Such antennas transmit most of their energy in a narrow beam (in the vertical direction) from their front surfaces, away from the building. They radiate very little energy downwards towards the roof or backwards from their rear surfaces. Finally, building materials absorb a significant fraction of the RF energy passing through them. As a result, the RF signal levels at any location inside the building are invariably low and far below safety limits. The situation might be different in some locations on the roof itself. RF signal levels close to (within a few feet) and directly in front of cellular base station antennas can easily exceed safety limits. Some precautions are needed to prevent people from walking directly in front of the antennas while they are transmitting. This applies also to paging and other systems that use rooftop antennas, some of which transmit at higher power levels than many cellular base stations. Kenneth R. Foster, Ph.D.