Attachment RAD HAZ

This document pretains to SES-LIC-20040122-00070 for License on a Satellite Earth Station filing.

IBFS_SESLIC2004012200070_353518

                           RADIATION HAZARD STUDY
                                         For
                          AvL Technologies Model 2400 SNG

This analysis predicts the radiation levels around a proposed earth station complex,
comprised of one or more aperture (reflector) type antennas. This report is
developed in accordance with the prediction methods contained in OET Bulletin No.
65, "Evaluating Compliance with FCC Guidelines for Human Exposure to Radio
Frequency Electromagnetic Fields," Edition 97-01, pp 26-30. The maximum level of
non-ionizing radiation to which employees may be exposed is limited to a power
density level of 5 milliwatts per square centimeter (5 mW/cm2) averaged over any 6
minute period in a controlled environment and the maximum level of non-ionizing
radiation to which the general public is exposed is limited to a power density level of
1 milliwatt per square centimeter (1 mW/cm2 ) averaged over any 30 minute period
in a uncontrolled environment. Note that the worse-case radiation hazards exist
along the beam axis. Under normal circumstances, it is highly unlikely that the
antenna axis will be aligned with any occupied area since that would represent a
blockage to the desired signals, thus rendering the link unusable.


Earth Station Technical Parameter Table
Antenna Actual Diameter                                   2.4        meters
Antenna Surface Area                                      4.5        sq. meters
Antenna Isotropic Gain                                    49.0       dBi
Number of Identical Adjacent Antennas*                    0
Nominal Antenna Efficiency (ε)                            62%
Nominal Frequency                                         14250      MHz
Nominal Wavelength (λ)                                    0.0211     meters
Maximum Transmit Power / Carrier                          368        Watts
Number of Carriers                                        1
Total Transmit Power                                      368        Watts
W/G Loss from Transmitter to Feed                         1.2        dB
Total Feed Input Power                                    280        Watts
Near Field Limit       Rnf = D²/4λ =                       68        meters
Far Field Limit        Rff = 0.6 D²/λ =                   164        meters
Transition Region      Rnf to Rff
*The Radiation Levels will be increased directly by the number of antennas indicated,
on the assumption that all antennas may illuminate the same area.

In the following sections, the power density in the above regions, as well as other
critically important areas will be calculated and evaluated. The calculations are done
in the order discussed in OET Bulletin 65. In addition to the input parameters above,
input cells are provided below for the user to evaluate the power density at specific
distances or angles.


1.0        At the Antenna Surface

The power density at the reflector surface can be calculated from the expression:

PDrefl =      4P/A =                                               24.82 mW/cm²             (1)
Where:        P = total power at feed, milliwatts
              A = Total area of reflector, sq. cm

In the normal range of transmit powers for satellite antennas, the power densities at
or around the reflector surface is expected to exceed safe levels. This area will not
be accessible to the general public. Operators and technicians should receive training
specifying this area as a high exposure area. Procedures must be established that
will assure that all transmitters are rerouted or turned off before access by
maintenance personnel to this area is possible.


2.0        On-Axis Near Field Region

The geometrical limits of the radiated power in the near field approximate a
cylindrical volume with a diameter equal to that of the antenna. In the near field, the
power density is neither uniform nor does its value vary uniformly with distance from
the antenna. For the purpose of considering radiation hazard it is assumed that the
on-axis flux density is at its maximum value throughout the length of this region.
The length of this region, i.e., the distance from the antenna to the end of the near
field, is computed as Rnf above.

The maximum power density in the near field is given by:

                  PDnf = (16 ε P)/( π D²) =                            0 mW/cm²        (2)
                                                       From 0 to       68 meters
Evaluation
 Uncontrolled Environment:                          Complies to FCC Limits
 Controlled Environment:                            Complies to FCC Limits


3.0        On-Axis Transition Region

The transition region is located between the near and far field regions. As stated in
Bulletin 65, the power density begins to vary inversely with distance in the transition
region. The maximum power density in the transition region will not exceed that
calculated for the near field region, and the transition region begins at that value.
The maximum value for a given distance within the transition region may be
computed for the point of interest according to:

PDt =         (PDnf)(Rnf)/R = dependent on R                                   (3)
where:        PDnf = near field power density
              Rnf = near field distance
              R = distance to point of interest
              For:                                                  68 < R <   164 meters

We use Eq (3) to determine the safe on-axis distances required for the two
occupancy conditions:


Evaluation:

Uncontrolled Environment Safe Operating Distance,(meters), Rsafeu:                           0
Controlled Environment Safe Operating Distance,(meters), Rsafec:                             0



4.0    On-Axis Far-Field Region

The on- axis power density in the far field region (PDff) varies inversely with the
square of the distance as follows:

         PDff = PG/(4 π R²) = dependent on R                                (4)
         where: P = total power at feed
                G = Numeric Antenna gain in the direction of interest
                relative to isotropic radiator
                R = distance to the point of interest
                For: R > Rff =                                              164 meters
                                                                             0 mW/cm² at
                 PDff =
                                                                            Rff

We use Eq (4) to determine the safe on-axis distances required for the two
occupancy conditions:

Evaluation:

Uncontrolled Environment Safe Operating Distance,(meters), Rsafeu :         See Section 3
Controlled Environment Safe Operating Distance,(meters), Rsafec :           See Section 3


5.0    Off-Axis Levels at the FarField Limit and Beyond

In the far field region, the power is distributed in a pattern of maxima and minima
(sidelobes) as a function of the off-axis angle between the antenna center line and
the point of interest. Off-axis power density in the far field can be estimated using
the antenna radiation patterns prescribed for the antenna in use. Usually this will
correspond to the antenna gain pattern envelope defined by the FCC or the ITU,
which takes the form of:

Goff = 32 - 25log(Θ)
for Θ from 1 to 48 degrees; -10 dBi from 48 to 180 degrees
(Applicable for commonly used satellite transmit antennas)

Considering that satellite antenna beams are aimed skyward, power density in the
far field will usually not be a problem except at low look angles. In these cases, the
off axis gain reduction may be used to further reduce the power density levels.

For example: At one (1) degree off axis At the far-field limit, we can calculate the
power density as:

Goff = 32 - 25log(1) = 32 - 0 dBi = 1585 numeric
   PD1 deg off-axis = PDff x 1585/G =                         0 mW/cm²                 (5)


6.0     Off-Axis power density in the Near Field and Transitional Regions

According to Bulletin 65, off-axis calculations in the near field may be performed as
follows: assuming that the point of interest is at least one antenna diameter
removed from the center of the main beam, the power density at that point is at
least a factor of 100 (20 dB) less than the value calculated for the equivalent on-axis
power density in the main beam. Therefore, for regions at least D meters away from
the center line of the dish, whether behind, below, or in front under of the antenna's
main beam, the power density exposure is at least 20 dB below the main beam level
as follows:

PDnf(off-axis) = PDnf /100 =               0 mW/cm² at D off axis (6)

See page 5 for the calculation of the distance vs elevation angle required to achieve
this rule for a given object height.


7.0     Region Between the Feed Horn and Sub-reflector

Transmissions from the feed horn are directed toward the subreflector surface, and
are confined within a conical shape defined by the feed horn. The energy between
the feed horn and subreflector is conceded to be in excess of any limits for maximum
permissible exposure. This area will not be accessible to the general public.
Operators and technicians should receive training specifying this area as a high
exposure area. Procedures must be established that will assure that all transmitters
are rerouted or turned off before access by maintenance personnel to this area is
possible.

Note 1:
Mitigation of the radiation level may take several forms. First, check the distance
from the antenna to the nearest potentially occupied area that the antenna could be
pointed toward, and compare to the distances appearing in Sections 2, 3 & 4. If
those distances lie within the potentially hazardous regions, then the most common
solution would be to take steps to insure that the antenna(s) are not capable of
being pointed at those areas while RF is being transmitted. This may be
accomplished by setting the tracking system to not allow the antenna be pointed
below certain elevation angles. Other techniques, such as shielding may also be used
effectively.


Evaluation of Safe Occupancy Area in Front of Antenna

The distance (S) from a vertical axis passing through the dish center to a safe off
axis location in front of the antenna can be determined based on the dish diameter
rule (Item 6.0). Assuming a flat terrain in front of the antenna, the relationship is:

S = (D/ sin α ) + (2h - D - 2)/(2 tan α)                                            (7)

Where:     α = minimum elevation angle of antenna
           D = dish diameter in meters
           h = maximum height of object to be cleared, meters

For distances equal or greater than determined by equation (7), the radiation hazard
will be below safe levels for all but the most powerful stations (> 4 kilowatts RF at
the feed).

For                      D=                2.4                meters
                         h=                2                  meters
Then:
                         α                 S
                         10                12.7               meters
                         15                  8.5              meters
                         20                  6.5              meters
                         25                  5.2              meters
                         30                  4.5              meters
                         5                  25.3              meters


Suitable fencing or other barrier should be provided to prevent casual occupancy of
the area in front of the antenna within the limits prescribed above at the lowest
elevation angle required.



Document Created: 2004-01-21 23:46:39
Document Modified: 2004-01-21 23:46:39

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