Attachment Rad Hazard Study

This document pretains to SES-MOD-20101210-01526 for Modification on a Satellite Earth Station filing.

IBFS_SESMOD2010121001526_856327

                 Radiation Hazard Analysis for the
                    Harris MCS Earth station
                        Melbourne, Florida
This report analyzes the non-ionizing radiation levels for a 6.3-meter earth station system
located at the Harris MCS facility in Melbourne, Florida. The analysis and calculations
performed in this report comply with the methods described in the FCC Office of
Engineering and Technology Bulletin No. 65 first published in 1985 and revised in 1997
in Edition 97-01. The radiation safety limits used in the analysis are in conformance with
the FCC R&O 96-326, Bulletin No. 65 and the FCC R&O specifies that there are two
separate tiers of exposures limits that are dependant on the situation in which the
exposure takes place and/or the status of the individuals who are subject to the exposure.

The Maximum Permissible Exposure (MPE) limits for persons in a General
Population/Uncontrolled environment are shown in Table 1. The General
population/Uncontrolled MPE is a function of the transmit frequency and is for an
exposure period of thirty minutes or less.

The MPW limits for persons in an Occupational/Controlled environment are shown in
Table 2. The Occupational MPE is a function of transmit frequency and is for an
exposure period of six minutes or less.

The purpose of the analysis described in this report is to determine the power flux density
levels of the earth station in the far-field, near-field, transition region, between the sub-
reflector or main reflector surface, at the main reflector surface, and between the antenna
edge and the ground and to compare these levels to the specified MPEs.


          Frequency Range (MHz                          Power Density (mW/cm2)
                  30-300                                            0.2
                 300-1500                              Frequency (MHz)*(0.8/1200)
               1500-100,000                                         1.0
            Table 1. Limits for General Population/Uncontrolled Exposure (MPE)


          Frequency Range (MHz                           Power Density (mW/cm2)
                  30-300                                            1.0
                 300-1500                               Frequency (MHz)*(4.0/1200)
               1500-100,000                                         5.0
                Table 2. Limits for Occupational/Controlled Exposure (MPE)


     Parameter              Symbol           Formula             Value              Units
  Antenna Diameter              D              Input               6.3                m
                                                  2
Antenna Surface Area         Asurface          πD /4              31.2               m2
Sub-reflector Diameter         Dsr             Input             .7112                m
 Area of Sub-reflector         Asr            πDsr2/4             .397               m2
      Frequency                 F              Input            14125               MHz
     Wavelength                 λ              300/F              0.02                m
   Transmit Power               P              Input              250                W
 Antenna Gain (dBi)            Ges             Input              57.5               dBi
                                                 Ges/10
Antenna Gain (factor)           G             10               562341.3             N/A
          Pi                    π            Constant         3.1415927             N/A
  Antenna Efficiency            η           Gλ2/(π D)2          .64757              N/A
                          Table 3. Variables used in calculations


1. Far Field Radiation
The distance to the beginning of the far field region ( Rff ) can be expressed by the
equation:

WHERE:

        Rff =    0.6 D2               D = 6.3         Antenna Diameter (meters)
                   λ                  λ = 0.02        Wavelength


        Rff = 0.6 x (6.3)2 =    1121.2 meters
               0.02


The maximum main beam power density in the far field can be determined from the
following equation:

Sff =     G P__                           G = 562341.3     Antenna Gain (factor)
         4 π (Rff)2                       P = 250          Transmit Power




Sff =     (562341.3)*(250)__ =      8.90 W/m2 or 0.890 mW/cm2
             4π (1121.2) 2


2. Near Field Radiation
The extent of the near field can be described by the equation:

WHERE:

Rnf =       __D2__                      Rnf = Extent of near-field
              4λ                        D = Antenna diameter
                                        λ = Wavelength



Rnf =       ___(6.3)2__     =     467.2 meters
              4 * 0.02

The maximum value of the near field on-axis (main beam) power density is given by the
equation:

WHERE:

Snf =       __16 η P__                  S = Maximum near-field power density
               π D2                     η = Efficiency of aperture (percentage)
                                        P = Power into feed (Watts)
                                        D = Antenna Diameter (meters)



Snf =       __16 * (.64757) * 250_ =     20.77 W/m2 or 2.077 mW/cm2
              3.1415927 ∗ (6.3)2



3. Transition Region
On-axis power density will decrease with distance in the transition region. The power
density can be expressed by the equation:
                                       WHERE:

        S        =        S(nf) R(nf)            S = Power Density
                               R                 S(nf) = Power Density in (near field)
                                                 R(nf) = Extent of near field
                                                 R = Distance to point of interest

At the beginning of the transition region, i.e. at a distance of 496.1 meters, the power
density equals:

        S        =        2.077 x 467.2 =        2.077 mW/cm2
                             467.2


At the beginning of the far-field region, i.e. at a distance of 1121.2 meters, the power
density equals:

       S       =       2.077 x 467.2 =         0.866 mW/cm2
                           1121.2

4. Region between Main Reflector and Subreflector
Transmissions from the feed assembly are directly toward the subreflector surface, and are
reflected back toward the main reflector. The most common feed assemblies are waveguide
flanges, horns or subreflectors. The energy between the subreflector and the reflector surfaces
can be calculated by determining the power density at the subreflector surface. This can be
determined from the following equation.

WHERE:

Ssr    =        P                      S =     Power density
               π r2                    P =     Power into feed
                                       r =     radius of subreflector (m)

Ssr    =          250         =        629.3 W/m2      =       62.9 mW/ cm2
                            2
               3.14 x .3556


5. Region within Antenna
The maximum power density between the main reflector and the feed is taken as the
power density at the main reflector. This can be described from the equation.

WHERE:

S      =        P                      S =     Power density
               π r2                    P =     Power into feed
                                       r =     radius of reflector

S      =            250        =       8.02 W/m2       =       0..802 mW/ cm2
               3.14 x 3.152


6. Between Antenna and Ground
As suggested by OET Bulletin 65, Edition 97-01 (August 1997) the level of RF fields in
the off-axis vicinity of the aperture antenna may be estimated by the use of the
specification for maximum allowable gain for antenna side-lobes not within the plane of
the Geo-stationary orbit, as follows:

                   32- {25 log10 (θ)} dBi            for       1° ≤ θ ≤ 48°

                   and:         -10dBi         for         48° < θ ≤ 180°

Therefore, at the minimum elevation angle of 24˚ a value of -2.5 dBi is utilized for the
side-lobe gain at all vicinities to the beginning of the Far Field power density where:

       Sff     =        PG               S =   Power density
                       4 π D2            P =   Power into feed
                                         D=    Distance from feed to ground
                                         G=    Antenna Gain Factor - 10-2.5/10 = .566


       Sff     =        250 x 2.367            = 30.61 W/m2 = 3.061 mW/ cm2
                      4 x 3.14 x 3.152




7. Summary of calculations


              Region           Radiation Level                 Hazard Assessment
                                   mW/cm2
Far-Field                      0.890 mW/cm2                 Satisfies FCC MPE
Near-Field                     2.077 mW/cm2                 See Note 1
Transition Region              0.866 mW/cm2                 Satisfies FCC MPE
Between sub and Main Reflector 62.9 mW/cm2                  See Note 2
Reflector Surface              0.802 mW/cm2                 Satisfies FCC MPE
Between antenna and ground     3.061 mW/cm2                 See Note 1
Table 4. Summary of Expected Radiation Levels for Uncontrolled Environment



              Region           Radiation Level                 Hazard Assessment
                                   mW/cm2
Far-Field                      0.890 mW/cm2                 Satisfies FCC MPE
Near-Field                     2.077 mW/cm2                 Satisfies FCC MPE
Transition Region              0.866 mW/cm2                 Satisfies FCC MPE
Between sub and Main Reflector 62.9 mW/cm2                  See Note 2
Reflector Surface              0.802 mW/cm2                 Satisfies FCC MPE
Between antenna and ground     3.061 mW/cm2                 Satisfies FCC MPE
Table 5. Summary of Expected Radiation Levels for Controlled Environment


Note 1: The Near-Field region of the Uncontrolled Environment has limited public
activity due to its land usage. It contains unused open fields without pedestrian traffic,
rain water retention ponds and passing vehicular movement. An 8’ fence having a
minimum12m distance from the antenna is erected to restrict public access. The
Controlled Environment is contained behind the fenced area where professional satellite
engineers may pass but do not linger.


Note 2: Region between the subreflector and feed does not meet the MPE. However, the
area is inaccessible unless standing in the antenna. If access to subreflector is required,
Standard operating procedures require the amplifier be de-enegized and power removed.

8. Conclusion
Based on the prior analysis it is concluded that all levels of radiation within the areas
occupied by the public and earth station personnel are below FCC guidelines of 5.0
mW/cm2. To further minimize the possibility of RF exposure to the public the earth
station is secured within a fenced-in area that is security controlled with limited access.
Additionally the transmitter will be shut down whenever maintenance personnel are
within the secured area.



Document Created: 2009-08-18 11:57:47
Document Modified: 2009-08-18 11:57:47

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