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SF64153S RF Exposure Study 03112021
T-Mobile West LLC • Proposed Base Station (Site No. SF64153S) 10889 North De Anza Boulevard • Cupertino, California B8QA Page 1 of 4 ©2021 Statement of Hammett & Edison, Inc., Consulting Engineers The firm of Hammett & Edison, Inc., Consulting Engineers, has been retained by T-Mobile West LLC, a personal wireless telecommunications carrier, to evaluate the base station (Site No. SF64153S) proposed to be located at 10889 North De Anza Boulevard in Cupertino, California, for compliance with appropriate guidelines limiting human exposure to radio frequency (“RF”) electromagnetic fields. Executive Summary T-Mobile proposes to install directional panel antennas above the Cupertino Hotel, located at 10889 North De Anza Boulevard in Cupertino. The proposed operation will comply with the FCC guidelines limiting public exposure to RF energy; certain mitigation measures are recommended to comply with FCC occupational guidelines. 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 limit for exposures of unlimited duration at several wireless service bands are as follows: Transmit “Uncontrolled” Occupational Limit Wireless Service Band Frequency Public Limit (5 times Public) Microwave (point-to-point) 1–80 GHz 1.0 mW/cm2 5.0 mW/cm2 Millimeter-wave 24–47 1.0 5.0 Part 15 (WiFi & other unlicensed) 2–6 1.0 5.0 CBRS (Citizens Broadband Radio) 3,550 MHz 1.0 5.0 BRS (Broadband Radio) 2,490 1.0 5.0 WCS (Wireless Communication) 2,305 1.0 5.0 AWS (Advanced Wireless) 2,110 1.0 5.0 PCS (Personal Communication) 1,930 1.0 5.0 Cellular 869 0.58 2.9 SMR (Specialized Mobile Radio) 854 0.57 2.85 700 MHz 716 0.48 2.4 600 MHz 617 0.41 2.05 [most restrictive frequency range] 30–300 0.20 1.0 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. T-Mobile West LLC • Proposed Base Station (Site No. SF64153S) 10889 North De Anza Boulevard • Cupertino, California B8QA Page 2 of 4 ©2021 The transceivers are often located at ground level and are connected to the antennas by coaxial cables. 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 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”). This methodology is an industry standard for evaluating RF exposure conditions and has been demonstrated through numerous field tests to be a conservative prediction of exposure levels. Site and Facility Description Based upon information provided by T-Mobile, including construction drawings by SureSite Consulting Group, LLC, dated February 10, 2021, it is proposed to remove all of the existing Sprint antennas and to install nine directional panel antennas – three each Ericsson Model AIR6449, Ericsson Model AIR32, and RFS Model APXVAALL18 – behind view screens above the roof of the four-story Cupertino Hotel, located at 10889 North De Anza Boulevard in Cupertino. The antennas would employ up to 11° downtilt, would be mounted at an effective height of about 45 feet above ground, 7½ feet above the roof, and would be oriented in identical groups of three toward 0°T, 90°T, and 270°T. The maximum effective radiated power in any direction would be 73,380 watts, representing simultaneous operation at 58,900 watts for BRS, 4,400 watts for AWS, 6,990 watts for PCS, 700 watts for 700 MHz, and 2,390 watts for 600 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 T-Mobile operation is calculated to be 0.31 mW/cm2, which is 32% of the applicable public exposure limit. The maximum calculated level at the second-floor elevation of any nearby building* is 44% of the * Located at least 70 feet away, based on photographs from Google Maps. T-Mobile West LLC • Proposed Base Station (Site No. SF64153S) 10889 North De Anza Boulevard • Cupertino, California B8QA Page 3 of 4 ©2021 public exposure limit. The maximum calculated level at the top-floor elevation of any nearby residence† is 27% 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. Levels are calculated to exceed the applicable public exposure limit on the roof of the subject building in front of the antennas, as shown in Figure 3. Recommended Mitigation Measures It is recommended that the roof access hatch be kept locked, so that the T-Mobile antennas are not accessible to unauthorized persons. To prevent occupational exposures in excess of the FCC guidelines, it is recommended that appropriate RF safety training, to include review of personal monitor use and lockout/tagout procedures, be provided to all authorized personnel who have access to the roof, including employees and contractors of T-Mobile and of the property owner. No work within 36 feet of the antennas, such as might occur during certain maintenance activities, should be allowed while the pertinent antennas are in operation, unless other measures can be demonstrated to ensure that occupational protection requirements are met. It is recommended that boundary lines be marked on the roof with blue and yellow paint to identify areas within which exposure levels are calculated to exceed the public and occupational FCC limits, respectively, as shown in Figure 3. It is recommended that explanatory signs‡ be posted at the roof access hatch, at the boundary lines, and on the screens in front of the antennas, readily visible from any angle of approach to persons who might need to work within that distance. Conclusion Based on the information and analysis above, it is the undersigned’s professional opinion that operation of the base station proposed by T-Mobile West LLC at 10889 North De Anza Boulevard in Cupertino, California, can comply with the prevailing standards for limiting human exposure to radio frequency energy and, therefore, need 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. Locking the roof access hatch is recommended to establish compliance with public exposure limits; training authorized personnel, marking roof areas, and posting explanatory signs are recommended to establish compliance with occupational exposure limits. † Located at least 250 feet away, based on photographs from Google Maps. ‡ Signs should comply with OET-65 color, symbol, and content recommendations. Contact information should be provided (e.g., a telephone number) to arrange for access to restricted areas. The selection of language(s) is not an engineering matter, and guidance from the landlord, local zoning or health authority, or appropriate professionals may be required. T-Mobile West LLC • Proposed Base Station (Site No. SF64153S) 10889 North De Anza Boulevard • Cupertino, California B8QA Page 4 of 4 ©2021 Authorship The undersigned author of this statement is a qualified Professional Engineer, holding California Registration Nos. E-13026 and M-20676, which expire on June 30, 2021. This work has been carried out under his direction, and all statements are true and correct of his own knowledge except, where noted, when data has been supplied by others, which data he believes to be correct. William F. Hammett, P.E. 707/996-5200 March 11, 2021 FCC Radio Frequency Protection Guide FCC Guidelines Figure 1 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 Frequency (MHz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© 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 θ BW × 0.1 × Pnet π× D× h , in mW/cm2, and for an aperture antenna, maximum power density Smax = 0.1 × 16 × η × Pnet π × h 2 , in mW/cm2, where qBW = half-power beamwidth of antenna, in degrees, Pnet = net power input to antenna, in watts, D = distance from antenna, in meters, h = aperture height of antenna, in meters, and h = 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 × RFF 2 × ERP 4 × π × D2 , in mW/cm2, where ERP = total ERP (all polarizations), in kilowatts, RFF = three-dimensional relative field factor toward point of calculation, and D = distance from antenna effective height to 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 is used in a computer program capable of calculating, at thousands of locations on an arbitrary grid, the total expected power density from any number of individual radio frequency sources. The program also allows for the inclusion of uneven terrain in the vicinity, as well as any number of nearby buildingsRIYDU\LQJKHLJKWV, to obtain more accurate projections. T-Mobile West LLC • Proposed Base Station (Site No. SF64153S) 10889 North De Anza Boulevard • Cupertino, California Calculated RF Exposure Levels on Roof B8QA Figure 3 Recommended Mitigation Measures 2021c Shaded color Boundary marking Sign type Legend:Exceeds Occupational - Yellow CAUTION N/A blank Less Than Public - Green INFORMATION Exceeds 10x Occupational - Orange WARNING Exceeds Public - Blue NOTICE • Lock roof access hatch • Mark boundaries as shown • Post explanatory signs • Provide training Notes: See text. Base image from Google Maps. Calculations performed according to OET Bulletin 65, August 1997. No r t h FEET 25 0 25 50 Calculations performed according to OET Bulletin No. 65, August 1997. Colors shown represent percent of applicable FCC public limit. [blank] <100%>100%>500%>5000% roof access hatch T-Mobile antenna groups