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THEORETICAL RF FIELD CALCULATIONS - GROUND LEVELS <br /> These calculations are based on what are called"worst-case"estimates. That is,the estimates <br /> assume 100% use of all transmitters simultaneously. Additionally, the calculations make the <br /> assumption that the transmitters are directed along the same azimuth,and that the surrounding area <br /> is a flat plain. The resultant values are thus conservative in that they over predict actual resultant <br /> power densities. <br /> The calculations are based on the following information: <br /> 1. Effective Radiated Power [ERP]. <br /> 2. Antenna height (centerline, above ground level [AGL]). <br /> 3. Antenna vertical radiation patterns;the source of the negative gain[G]values. "Directional' <br /> antennas are designed to focus the RF signal,resulting in"patterns"of signal loss and gain. <br /> Antenna vertical radiation patterns display the loss of signal strength relative to the direction <br /> of propagation due to elevation angle changes. The gain is expressed as"G a". <br /> Note: G is a unitless factor usually expressed in decibels [dB]; where G= 10(dW10). <br /> For example: for G =3, dB = 10(3110) =2; for G =-3, dB = 10 t"`01 =0.5. <br /> To determine the magnitude of the RF field, the power density [S] from an isotropic RF <br /> source is calculated,making use of the power density formula: <br /> S = P • G Where: P Power to antenna(watts) <br /> 4 7[ RZ G —+ Gain of antenna <br /> R Distance(range)from antenna source to point of <br /> intersection with the ground (feet) <br /> R' _ (Height)' +(Horizontal distance)' <br /> Since P • G = EIRP (Effective Isotropic Radiated Power)for broadcast antennas,the equation <br /> can be presented in the following form: <br /> S = EIRP <br /> 471W <br /> In the situation of off-axis power density calculations,apply the negative elevation gain [G E] value <br /> from the vertical radiation patterns with the following formula: <br /> S = EIRP • GE <br /> 4 7[ R2 <br /> 427 Amherst Street,Unit#11 <br /> Nashua,NH 03063 <br /> Page-3- <br />