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%(.. d f ¡ , RFRCALC Tal Calculation Methodology Assessment by Calculation of Compliance with FCC Exposure Guidelines The U.S. Congress required (1996 Telecom Act) the Federal Communications Commission ("FCC") to adopt a nationwide human exposure standard to ensure that its licensees do not, cumulatively, have a significant impact on the environment. The maximum pennissible exposure limits adopted by the FCC (see Figure 1) apply for continuous exposures from all sources and are intended to provide a prudent margin of safety for all persons, regardless of age, gender, size, or health. Higher levels are allowed for short periods of time, such that total exposure levels averaged over six or thirty minutes, for occupational or public settings, respectively, do not exceed the limits. L ~ Near Field. Prediction methods have been developed for the near field zone of panel (directional) and whip (omnidirectional) antennas, typical at wireless telecommunications cell sites. The near field zone is defined by the distance, D, from an émtenna beyond which the manufacturer's published, far field antenna patterns will be fully fonned; the near field may exist for increasing D until some or all of three conditions have been met: 2h2 1) D >T 2) D > 5h 3) D > 1.6^- where h = aperture height of the antenna, in meters, and ^- = wavelength of the transmitted signal, in meters. The FCC Office of Engineering and Technology Bulletin No. 65 (August 1997) gives this fonnula for calculating power density in the near field zone about an individual RF source: S 180 0.1 x Pnet W 2 power density = no-- X D h' in m /em, °aw 7t x x where Saw = half-power beamwidth of antenna, in degrees, and P net = net power input to the antenna, in watts. The factor of 0.1 in the numerator converts to the desired units of power density. This fonnula has been built into a proprietary program that calculates distances to FCC public and occupational limits. Far Field. OET-65 gives this fonnula for calculating power density in the far field of an individual RF source: Power density S = 2.56 x 1.64 x 100 x RFF2 x ERP . mW¡ 2 4 x 7t x D2 ' In em , where ERP = total ERP (all polarizations), in kilowatts, RFF = relative field factor at the direction to the actual point of calculation, and D = distance from the center of radiation to the point of calculation, in meters. The factor of 2.56 accounts for the increase in power density due to ground reflection, assuming a reflection coefficient of 1.6 (1.6 x 1.6 = 2.56). The factor of 1.64 is the gain of a half-wave dipole relative to an isotropic radiator. The factor of 100 in the numerator converts to the desired units of power density. This fonnula has been built into a proprietary program that calculates, at each location on an arbitrary rectangular grid, the total expected power density from any number of individual radiation sources. The program also allows for the description of uneven terrain in the vicinity, to obtain more accurate projections. ~;::œg HAMMETT & EDISON, INc. .r¿:, .~;::- CO!\:SULTI."iG ENGINEERS ~ ~~;::~, SA:>; FRA,\:CISCO Methodology Figure 2