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7 <br /> A . <br /> ' ' <br /> 3910.3A <br /> 10/ 19/83 <br /> 34. EVALUATION OF HAZARDS. / <br /> a. Equipment. There are two general types of instruments available for <br /> RF radiation evaluations; those that measure power density and those that <br /> measure field intensity (or field strength). Power density meters are more <br /> commonly used in health hazards evaluations largely because of their <br /> portability and direct reading capability. Field intensity meters, although <br /> less portable, are particularly valuable in the detection and measurement of <br /> low levels of RF radiation. <br /> ( 1) Power Density Devices currently in use are broadband isotropic <br /> systems consisting of a meter and probe(s) that provide near and far field <br /> power density measurements regardless of polarization and direction of the <br /> incident RF energy. They integrate pulsed or CW signals into an average power <br /> density reading in mW/cm . Probes are available to provide a dynamic range <br /> of 0.02 to 100 mW/cm2 across frequencies ranging from 500 KHz to 18 GHz. <br /> These instruments are lightweight, easy to use, and reasonably accurate. They <br /> have two distinct limitations; ( 1) they cannot be calibrated in the field and <br /> must be returned for factory calibration, and (2) their probes are subject to <br /> peak power burnout even when the instrument is turned off. <br /> (2) Field Intensity Devices, which usually consist of an assortment <br /> of calibrated antennas coupled to an interference analyzer, are extremely <br /> accurate and sensitive over a wide dynamic range. They have certain <br /> disadvantages that limit their use in routine health hazards evaluations. <br /> They are bulky, nonportable, and require special training for proper use. <br /> Their antennas are highly directional and field intensity measurements made <br /> with these systems may not be completely representative of the exposure <br /> potential that exists at the point of measurement. Nonetheless, they remain <br /> the best devices for evaluation of far field low level RF energy, particularly <br /> in the low frequencies; e.g. ,< 500 KHz. <br /> b. Procedures. The following procedures are intended as guidelines ; <br /> conditions at the survey site may suggest or require modifying them. Survey <br /> equipment manuals should be consulted for complete operating instructions. <br /> ( 1) RF measurements are no better than the calibration of the survey <br /> equipment used to make the measurements. As a minimum, survey meters must be • <br /> calibrated annually. The power density meters currently in use must be <br /> returned to the manufacturer for calibration. <br /> (2) An RF source should be approached from a known safe distance <br /> with the detector initially set on its maximum range. This is to avoid <br /> unnecessary personnel exposure and, in the case of power density meters, to <br /> avoid peak power burnout of the probe. <br /> (3) All RF measurements should be made in close coordination with <br /> operating personnel so that the exact conditions under which measurements are <br /> made are known to all concerned. <br /> Page 26 Chap 3 <br /> Par 34 <br />