Attachment Exhibit A

This document pretains to SES-MOD-20100216-00197 for Modification on a Satellite Earth Station filing.

IBFS_SESMOD2010021600197_800028

CapRock Communications, Inc. EXHIBIT A, Main Form Page 1 of 4 Radiation Hazard Study The study in this section analyzes the potential RF human exposure levels caused by the Electro Magnetic (EM) fields of a Seatel 9797 2.4m antenna operating with a maximum power at the flange of 20 Watts. The mathematical analysis performed below complies with the methods described in the FCC Office of Engineering and Technology (OET) Bulletin No. 65 (1985 rev. 1997) R&O 96-326.1 Maximum Permissible Exposure There are two separate levels of exposure limits. The first applies to persons in the general population who are in an uncontrolled environment. The second applies to trained personnel in a controlled environment. According to 47 C.F.R. § 1.1310, the Maximum Permissible Exposure (MPE) limits for frequencies above 1.5 GHz are as follows:  General Population / Uncontrolled Exposure 1.0 mW/cm2  Occupational / Controlled Exposure 5.0 mW/cm2 The purpose of this study is to determine the power flux density levels for the earth station under study as compared with the MPE limits. This comparison is done in each of the following regions: 1. Far-field region 2. Near-field region 3. Transition region 4. The region between the feed and the antenna surface 5. The main reflector region 6. The region between the antenna edge and the ground Input Parameters The following input parameters were used in the calculations: Parameter Value Unit Symbol Antenna Diameter 2.4 m D Antenna Transmit Gain 47 dBi G Transmit Frequency 14250 MHz f Antenna Feed Flange Diam. 13.0 cm d Power Input to the Antenna 20 Watts P 1 Evaluating Compliance with FCC Guideliness for Human Exposure to Radiofrequency Electromagnetic Fields, OET Bulletin 65 (Edition 97-01), Supplement B, FCC Office of Engineering & Technology, November 1997.

CapRock Communications, Inc. EXHIBIT A, Main Form Page 2 of 4 Calculated Parameters The following values were calculated using the above input parameters and the corresponding formula: Parameter Value Unit Symbol Formula Antenna Surface Area 4.52 m2 A πD2/4 Area of Antenna Flange 132.73 cm2 a πd2/4 Antenna Efficiency 0.39 η Gλ2/( π2D2) Gain Factor 50118.7 g 10G/10 Wavelength 0.0211 m λ 300/ f Behavior of EM Fields as a Function of Distance The behavior of the characteristics of EM fields varies depending on the distance from the radiating antenna. These characteristics are analyzed in three primary regions: the near-field region, the far-field region and the transition region. Of interest also are the region between the antenna main reflector and the subreflector, the region of the main reflector area and the region between the main reflector and ground. D Figure 1. EF Fields as a Function of Distance For parabolic aperture antennas with circular cross sections, such as the antenna under study, the near-field, far-field and transition region distances are calculated as follows: Near-Field Distance Rnf = D2/(4λ) = 68.400 m Distance to Far-Field Rff = 0.60D2/(λ) = 164.160 m

CapRock Communications, Inc. EXHIBIT A, Main Form Page 3 of 4 Distance of Transition Region Rt = Rnf = 68.400 m The distance in the transition region is between the near and far fields. Thus, Rnf ≤ Rt ≤ Rff . However, the power density in the transition region will not exceed the power density in the near-field. Therefore, for purposes of the present analysis, the distance of the transition region can equate the distance to the near-field. Power Flux Density Calculations The power flux density is considered to be at a maximum through the entire length of the near-field. This region is contained within a cylindrical volume with a diameter, D, equal to the diameter of the antenna. In the transition region and the far-field, the power density decreases inversely with the square of the distance. The following equations are used to calculate power density in these regions. Power Density in the Near-Field Snf = 16.0 η P/(πD2) = 0.691 mW/cm2 Power Density in the Far-Field Sff = GP/(4π Rff2) = 0.296 mW/cm2 Power Density in the Transition Region St = Snf Rnf /(Rt) = 0.691 mW/cm2 The region between the main reflector and the subreflector is confined to within a conical shape defined by the feed assembly. The most common feed assemblies are waveguide flanges. This energy is determined as follows: Power Density at the Feed Flange Sfa = 4P / a = 602.717 mW/cm2 The power density in the main reflector is determined similarly to the power density at the feed flange; except that the area of the reflector is used. Power Density at Main Reflector Ssurface = 4P / A = 1.768 mW/cm2 The power density between the reflector and ground, assuming uniform illumination of the reflector surface, is calculated as follows: Power Density b/w Reflector and Gnd Sg =P/A = 0.442 mW/cm2 Summary of Calculations Table 1 summarizes the calculated power flux density values for each region. In a controlled environment, the only region that exceeds FCC limitations is the region between the main reflector and the sub-reflector. This region is only accessible by trained technicians who, as a matter of procedure, turn off transmit power before performing any work in this area. Furthermore, the antenna is enclosed in a radom.

CapRock Communications, Inc. EXHIBIT A, Main Form Page 4 of 4 Controlled Environment Power Densities (mW/cm2) (5 mW/cm2) Far Field Calculation 0.296 Satisfies FCC MPE Near Field Calculation 0.691 Satisfies FCC MPE Transition Region 0.691 Satisfies FCC MPE Region b/w Main & Subreflector 602.717 Exceeds limitations Main Reflector Region 1.768 Satisfies FCC MPE Region b/w Main Reflector & Ground 0.442 Satisfies FCC MPE Table 1. Power Flux Density for Each Region In conclusion, the results show that the antenna, in a controlled environment, and under the proper mitigation procedures, meets the guidelines specified in § 1.1310 of the Regulations.


Document Created: 2010-02-15 15:51:34
Document Modified: 2010-02-15 15:51:34
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