HomeMy WebLinkAboutUP16-0005 - RF Exposure StudyAT&T Mobility • Proposed Base Station (Site No. CVU0331)
Royal Oaks Drive • Oroville, California
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Statement of Hammett & Edison, Inc., Consulting Engineers
The firm of Hammett & Edison, Inc., Consulting Engineers, has been retained on behalf of
AT&T Mobility, a personal wireless telecommunications carrier, to evaluate the base station (Site No.
CVU0331) proposed to be located along Royal Oaks Drive in Oroville, California, for compliance
with appropriate guidelines limiting human exposure to radio frequency (“RF”) electromagnetic fields.
Executive Summary
AT&T proposes to install directional panel antennas on a tall pole to be sited along Royal
Oaks Drive, near Kelly Ridge Road, in Oroville. The proposed operation will comply with
the FCC guidelines limiting public exposure to RF energy.
Prevailing Exposure Standards
The U.S. Congress requires that the Federal Communications Commission (“FCC”) evaluate its
actions for possible significant impact on the environment. A summary of the FCC’s exposure limits
is shown in Figure 1. These limits apply for continuous exposures and are intended to provide a
prudent margin of safety for all persons, regardless of age, gender, size, or health. The most restrictive
FCC limit for exposures of unlimited duration to radio frequency energy for several personal wireless
services are as follows:
Wireless Service Frequency Band Occupational Limit Public Limit
Microwave (Point-to-Point) 5,000–80,000 MHz 5.00 mW/cm2 1.00 mW/cm2
BRS (Broadband Radio) 2,600 5.00 1.00
WCS (Wireless Communication) 2,300 5.00 1.00
AWS (Advanced Wireless) 2,100 5.00 1.00
PCS (Personal Communication) 1,950 5.00 1.00
Cellular 870 2.90 0.58
SMR (Specialized Mobile Radio) 855 2.85 0.57
700 MHz 700 2.40 0.48
[most restrictive frequency range] 30–300 1.00 0.20
General Facility Requirements
Base stations typically consist of two distinct parts: the electronic transceivers (also called “radios” or
“channels”) that are connected to the traditional wired telephone lines, and the passive antennas that
send the wireless signals created by the radios out to be received by individual subscriber units. The
transceivers are often located at ground level and are connected to the antennas by coaxial cables. A
small antenna for reception of GPS signals is also required, mounted with a clear view of the sky.
Because of the short wavelength of the frequencies assigned by the FCC for wireless services, the
antennas require line-of-sight paths for their signals to propagate well and so are installed at some
AT&T Mobility • Proposed Base Station (Site No. CVU0331)
Royal Oaks Drive • Oroville, California
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height above ground. The antennas are designed to concentrate their energy toward the horizon, with
very little energy wasted toward the sky or the ground. This means that it is generally not possible for
exposure conditions to approach the maximum permissible exposure limits without being physically
very near the antennas.
Computer Modeling Method
The FCC provides direction for determining compliance in its Office of Engineering and Technology
Bulletin No. 65, “Evaluating Compliance with FCC-Specified Guidelines for Human Exposure to
Radio Frequency Radiation,” dated August 1997. Figure 2 describes the calculation methodologies,
reflecting the facts that a directional antenna’s radiation pattern is not fully formed at locations very
close by (the “near-field” effect) and that at greater distances the power level from an energy source
decreases with the square of the distance from it (the “inverse square law”). The conservative nature
of this method for evaluating exposure conditions has been verified by numerous field tests.
Site and Facility Description
Based upon information provided by AT&T, including zoning drawings by Diamond Engineering
Services, dated November 11, 2014, it is proposed to install twelve Andrew Model SBNHH-1D65C
directional panel antennas on a new 80-foot pole, configured to resemble a pine tree, to be sited about
50 feet northwest of the water tank located along Royal Oaks Drive, east of Kelly Ridge Road, in
Oroville. The antennas would be mounted with up to 6° downtilt at an effective height of about
76 feet above ground and would be oriented in groups of four toward 80°T, 200°T, and 330°T, to
provide service in all directions. The maximum effective radiated power in any direction would be
17,900 watts, representing simultaneous operation at 3,520 watts for WCS, 4,240 watts for AWS,
6,480 watts for PCS, 1,000 watts for cellular, and 2,660 watts for 700 MHz service. There are
reported no other wireless telecommunications base stations at the site or nearby.
Study Results
For a person anywhere at ground, the maximum RF exposure level due to the proposed AT&T
operation is calculated to be 0.025 mW/cm2, which is 2.6% of the applicable public exposure limit.
The maximum calculated level for a person on top of the nearby water tank is 3.2% of the public limit.
The maximum calculated level at the second-floor elevation of any nearby residence* is 1.5% of the
public exposure limit. It should be noted that these results include several “worst-case” assumptions
and therefore are expected to overstate actual power density levels from the proposed operation.
* Located at least 170 feet away, based on photographs from Google Maps.
AT&T Mobility • Proposed Base Station (Site No. CVU0331)
Royal Oaks Drive • Oroville, California
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No Recommended Mitigation Measures
Due to their mounting locations, the AT&T antennas would not be accessible to the general public,
and so no mitigation measures are necessary to comply with the FCC public exposure guidelines. It is
presumed that AT&T will, as an FCC licensee, take adequate steps to ensure that its employees or
contractors receive appropriate training and comply with FCC occupational exposure guidelines
whenever work is required near the antennas themselves.
Conclusion
Based on the information and analysis above, it is the undersigned’s professional opinion that
operation of the base station proposed by AT&T Mobility along Royal Oaks Drive at Kelly Ridge
Road in Oroville, California, will comply with the prevailing standards for limiting public exposure to
radio frequency energy and, therefore, will not for this reason cause a significant impact on the
environment. The highest calculated level in publicly accessible areas is much less than the prevailing
standards allow for exposures of unlimited duration. This finding is consistent with measurements of
actual exposure conditions taken at other operating base stations.
Authorship
The undersigned author of this statement is a qualified Professional Engineer, holding California
Registration Nos. E-20309, which expires on March 31, 2015. This work has been carried out under
her direction, and all statements are true and correct of her own knowledge except, where noted, when
data has been supplied by others, which data she believes to be correct.
_________________________________
Andrea L. Bright, P.E.
707/996-5200
January 13, 2015
FCC Radio Frequency Protection Guide
FCC Guidelines
Figure 1
Frequency (MHz)
1000
100
10
1
0.1
0.1 1 10 100 103 104 105
Occupational Exposure
Public Exposure
PCS
CellFM
Po
w
e
r
De
n
s
i
t
y
(m
W
/
c
m
2 )
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 FCC adopted the limits from Report No. 86, “Biological
Effects and Exposure Criteria for Radiofrequency Electromagnetic Fields,” published in 1986 by the
Congressionally chartered National Council on Radiation Protection and Measurements (“NCRP”).
Separate limits apply for occupational and public exposure conditions, with the latter limits generally
five times more restrictive. The more recent standard, developed by the Institute of Electrical and
Electronics Engineers and approved as American National Standard ANSI/IEEE C95.1-2006, “Safety
Levels with Respect to Human Exposure to Radio Frequency Electromagnetic Fields, 3 kHz to
300 GHz,” includes similar limits. These limits 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.
As shown in the table and chart below, separate limits apply for occupational and public exposure
conditions, with the latter limits (in italics and/or dashed) up to five times more restrictive:
Frequency Electromagnetic Fields (f is frequency of emission in MHz)
Applicable
Range
(MHz)
Electric
Field Strength
(V/m)
Magnetic
Field Strength
(A/m)
Equivalent Far-Field
Power Density
(mW/cm2)
0.3 – 1.34 614 614 1.63 1.63 100 100
1.34 – 3.0 614 823.8/ f 1.63 2.19/ f 100 180/ f2
3.0 – 30 1842/ f 823.8/ f 4.89/ f 2.19/ f 900/ f2 180/ f2
30 – 300 61.4 27.5 0.163 0.0729 1.0 0.2
300 – 1,500 3.54 f 1.59 f f /106 f /238 f/300 f/1500
1,500 – 100,000 137 61.4 0.364 0.163 5.0 1.0
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, and higher
levels also are allowed for exposures to small areas, such that the spatially averaged levels do not
exceed the limits. However, neither of these allowances is incorporated in the conservative calculation
formulas in the FCC Office of Engineering and Technology Bulletin No. 65 (August 1997) for
projecting field levels. Hammett & Edison has built those formulas into a proprietary program that
calculates, at each location on an arbitrary rectangular grid, the total expected power density from any
number of individual radio sources. The program allows for the description of buildings and uneven
terrain, if required to obtain more accurate projections.
RFR.CALC™ Calculation Methodology
Assessment by Calculation of Compliance with FCC Exposure Guidelines
Methodology
Figure 2
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 permissible 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.
Near Field.
Prediction methods have been developed for the near field zone of panel (directional) and whip
(omnidirectional) antennas, typical at wireless telecommunications base stations, as well as dish
(aperture) antennas, typically used for microwave links. The antenna patterns are not fully formed in
the near field at these antennas, and the FCC Office of Engineering and Technology Bulletin No. 65
(August 1997) gives suitable formulas for calculating power density within such zones.
For a panel or whip antenna, power density S = 180
BW
0.1 Pnet
D2 h , in mW/cm2,
and for an aperture antenna, maximum power density Smax = 0.1 16 Pnet
h2 , in mW/cm2,
where BW = half-power beamwidth of the antenna, in degrees, and
Pnet = net power input to the antenna, in watts,
D= distance from antenna, in meters,
h= aperture height of the antenna, in meters, and
= aperture efficiency (unitless, typically 0.5-0.8).
The factor of 0.1 in the numerators converts to the desired units of power density.
Far Field.
OET-65 gives this formula for calculating power density in the far field of an individual RF source:
power density S = 2.56 1.64 100 RFF2 ERP
4 D2 , in mW/cm2,
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 formula 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.