6.3 HUMAN-MADE RF SOURCES

Human-made RF sources support communications, navigation, sensing, industrial processing, medical treatment, scientific research, and consumer applications. Their emissions differ widely in operating frequency, power, modulation, duty cycle, and operating characteristics, which can span many orders of magnitude, from milliwatt wireless sensors to high-power broadcasting, radar, and industrial heating systems. Still, transmitter power alone is seldom a reliable indicator of human exposure. Antenna characteristics, operating frequency, duty cycle, distance, source–body coupling, and the surrounding environment must also be considered, as well as the distance between the source and the human.

This section introduces the power quantities used to describe and compare RF transmitters. Appendix D provides a more detailed survey of representative source categories, their operating frequency ranges, and typical power ratings. Again, it should be noted that none of these source-power quantities directly states a person’s exposure. They form only a part of source characterization. Exposure assessment determines the external electric and magnetic fields, or the incident power density, at the person’s location, taking account of factors such as distance, radiation pattern, beam direction, operating frequency, duty cycle, reflections, and shielding. RF dosimetry then determines the resulting internal fields and absorbed-power or absorbed-energy quantities. Transmitter power should therefore be treated as one input to the assessment, rather than as a measure of exposure.