Answer to Question #455 Submitted to "Ask the Experts"

Q

What are the health issues with satellite dishes? We are looking for authoritative statements on the state of research that can be shared with others. Our interest is in both transmitting dishes and receiving dishes (the latter both institutional and home). Any help would be appreciated.

A

Satellite dishes are used both for transmitting and receiving signals. Most of the dishes that you see near people's houses are only used for receiving broadcasts from satellites—there are no radiation exposure issues at all. A variety of dishes are used to transmit signals to satellites. Nearly all of them are low-powered units and the RF signal levels, even in the main beams of the antennas, are well below recommended limits. Moreover, the beams are highly collimated, i.e., the beams are cylindrical in shape, as in a flashlight beam, and levels of public exposure to RF energy outside of the main beams are invariably very far below the limits. Some satellite dishes are used to transmit significant power to satellites for rebroadcast—these typically are very large dishes, tens of feet across. While they may handle considerable levels of RF energy, the signal strength in their beams is not necessarily high (since the beams are very large). Moreover, their beams are also very highly collimated and levels of public exposure are invariably very far below recommended limits. In short, there is little or no possibility that an ordinary person might be exposed to RF energy from satellite dishes that exceeds or even comes close to recommended exposure limits such as those of the FCC. These limits are designed to avoid exposures that are likely to be hazardous, with a very large safety margin. There has been some public controversy over whether there are hazards from exposure to RF energy at levels far below recommended limits. Such questions are always very hard to answer definitively. Expert groups that have examined the matter have concluded that there are no identifiable hazards at low exposure levels (i.e. below recommended limits) but they also point out that the scientific data are difficult to interpret and unclear in many respects. However, the exposure that a person can receive from a satellite dish is so low, the chances of any significant health effects would seem to be very slim indeed. Sources of information for a layperson are the COMAR Web site, which has a report on RF exposures from cell base stations (which operate in a similar frequency range as satellite dishes), the WHO EMF Web site, and John Moulder's FAQ sheet on cell base stations and possible health risks of RF energy.



Kenneth R. Foster

Professor, Bioengineering University of Pennsylvania