Answer to Question #11743 Submitted to "Ask the Experts"

Category: Micro/Radio Waves, Radar & Powerlines — Satellite Dishes

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

Q

I have a microwave dish (6 watts [W], 5 gigahertz [GHz]) at my store. I didn't know that my friend connected the power supply to it. I stood near it (60 centimeters [cm]) for about four hours, but the dish was turned toward the ground. Will there be any effect on my body?

A

In this situation, there should be no concern for any adverse health effects.

While not specifically defined in your question, it appears you have a highly directional antenna transmitting within the Federal Communications Commission (FCC) unlicensed 5 GHz band. In 1997, the Institute of Electrical and Electronics Engineers (IEEE) created the first wireless local area network (WLAN) standard referred to as "802.11" after the name of the group formed to oversee its development. Since then, there have been needs for faster and faster communication speeds, along with different frequency allotments to minimize interference. The family of wireless standards today include 802.11a, 802.11b/g/n, and 802.11ac.

Standard 802.11 requires these 5 GHz units to be equipped with transmit power control (TPC; sometimes called dynamic power control [DPC]). TPC is a mechanism used in radio communications to reduce the power (typically 6 decibels [dB] down, or to 25%) of a radio transmitter in response to an input signal or a condition (e.g., a command signal is issued by a controller when the received signal falls below a predetermined threshold).

You state the dish was facing the ground. This is similar to placing a floodlight on the surface of an absorbing material (without the excessive heat factor!) and noticing some light in the area, but light that is certainly nowhere near the brightness of the main beam. In addition, the TPC would recognize the failure to receive incoming signals and would reduce the transmit power to the minimum necessary to search for and attempt to maintain a link. With this reduced power, any released energy that was NOT absorbed by the ground surface but was reflected back to the surrounding areas would be extremely low. At 5 GHz, most of the energy reaching you would be dissipated in the first millimeter (mm) of your skin. When we factor in the low transmit power and its shallow penetration in the skin, the total absorbed energy you were exposed to would undoubtedly be below the specific absorption rate (SAR) limits of 1.6 watts per kilogram (W kg-1) for partial-body exposure. Thus, there should be no concern for any adverse health effects.

For further information about radiofrequency (RF) exposure standards, visit the International Committee on Electromagnetic Safety (ICES; formerly the IEEE Standards Coordinating Committee 28) at http://www.ices-emfsafety.org.

Donald L. Haes, Jr., CHP, CLSO

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