Thinking outside the sphere Initial Comments on DRI Application for Wakeby Road Cell Tower September 26, 2017 The Cape Cod Commission ( Commission ) is hearing an application for DRI review of a proposed wireless communication facility with new tower at a location of Wakeby Road on an unnumbered parcel between parcels at 810 and 882 Wakeby Road. The Commission has engaged Isotrope to conduct a technical review of the application under the terms of the DRI Technical Bulletin 97-001 for wireless towers as revised. Summary of Observations Recommending the applicant resolve the following o 700 MHz coverage maps are absent o Verification of signal threshold and type is missing (RSRP for 700 MHz?) o Drive Test not normalized to RSRP o No verification of tree canopy height o No coverage analysis at tree canopy plus ten feet o FAA clearance report is not sufficient; file FAA Form 7460 o Intermediate coverage analysis at midpoint between tree canopy-plus-ten and proposed 140 ft antenna height is not required by Technical Bulletin, but recommended in this case Commission could consider alternative tower designs if more antenna concealment is needed See narrative for exact recommendations. Coverage Analysis The applicant s coverage analysis is provided in Tab 10. It has some shortcomings. Isotrope, LLC 503 Main Street Medfield, MA 02052 508 359 8833
700 MHz Coverage Maps Missing First, the analysis provided by the applicant is based on its 1900 MHz PCS license. 1900 MHz wireless coverage is more severely affected by vegetation and other obstructions than the 700 MHz service. 700 MHz service is typically used to provide broad coverage from each cell site, and the 1900 MHz coverage is uses as a fill-in service closer to the cell site. Users near the cell site can be shifted to the 1900 MHz service to make room for the users between cell sites who need the 700 MHz service. Based on the foregoing, the most appropriate representation of the applicant s coverage (existing and proposed) would be with its 700 MHz service. The applicant should provide computer modeling of existing, proposed and existing-plus-proposed coverage at 700 MHz. T-Mobile is presently aggressively building out its expanded 700 MHz services using new 700 MHz licenses nationwide. If the existing facilities do not have 700 MHz service today, that should not prevent the Commission from evaluating the applicant s intended design objective of deploying 700 MHz in the near future. Explicit Statement about Coverage Thresholds Used The coverage analysis uses two signal strength thresholds, -114 dbm for in-vehicle and -97 dbm for in-building service. Current nationwide metrics suggest that about 3/4 of all wireless data traffic is to/from indoor users. The in-building threshold is important in developed areas. We assume, but require the applicant s confirmation, that the customary LTE metric for signal strength RSRP is depicted in the computer-estimated coverage maps. When the applicant submits 700 MHz coverage maps, we seek verification of the in-building threshold it is using for 700 MHz, it could be a different threshold than for 1900 MHz. CW Test Normalization Is Incomplete The applicant also conducted a CW Drive Test of coverage from two heights at the proposed site. There are both a 1900 MHz test and a 700 MHz test. We plan to rely on the 700 MHz test to assess coverage needs, including tower height. 2
The CW Drive Test, however, is not normalized to reflect RSRP. Instead, the output power of the test transmitter was normalized to the output power of a typical base station transmitter, without any adjustment for the differences between raw transmitted power and RSRP. This could make the projected coverage from the proposed tower look greater than it really will be. We suggest the applicant modify its CW Drive test results to reflect normalized RSRP coverage. This will enable a more direct, apples-to-apples, comparison between the 700 MHz computerestimated coverage and the 700 MHz CW Drive Test coverage. Ensure that the in-building service threshold used in the 700 MHz computer-estimated coverage maps is also included among the signal levels in the normalized 700 MHz CW Drive Test maps. FAA Clearances The applicant provides in its Tab 14 a copy of an FCC database search for FAA airport clearances. This database (TOWAIR) investigates the notification slope clearances from runways in Federal Aviation Rules at 14 CFR 77.13 as referenced by the FCC in 47 CFR 17.7. These slope clearances are thresholds for notifying the FAA of proposed construction. These thresholds are conservatively based on a proposed tower s overall elevation versus its distances from runways, typically of public airports. The TOWAIR database indicates the proposed 145 foot tower is not tall enough to exceed the notification slope to the nearby Cape Cod Airfield. The database makes no mention of Air Station Cape Cod, perhaps because it is not listed as a public airport. One cannot be certain that Air Station Cape Cod was considered in the TOWAIR analysis. Also, in 14 CFR 77, the FAA reserves the right to request notification under other circumstances than simply those related to the regular notification slopes. For these reasons, we entered the tower information in an FAA database and obtained the following result (graphic, next page). 3
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In the schematic map above, the red target is the proposed tower site. Airports are to the right and left, with approach rectangles (ASCC and Barnstable Municipal). The other two gray areas with blue hashmarks (runways) are smaller airstrips. The schematic map shows the proposed tower is neatly positioned between the two main airports and their approach zones. Notification slopes for both airports are satisfied. However, the FAA requests a notification in an abundance of caution to ensure that radio frequency navigational aids will not be affected by the emissions of the proposed tower. We recommend the applicant file an FAA Form 7460 Notification of Proposed Construction of objects affecting navigable airspace. Technical Bulletin This section briefly touches on key points in the Technical Bulletin. Alternative Existing Structures A preliminary scan of orthophotography and other GIS resources at Isotrope did not identify any tall structures within a mile of the proposed facility. With respect to the camouflage requirement in section IV.B. of the Technical Bulletin, the applicant proposes a fully exposed three-faced antenna-boom mount for each of up to four wireless carriers. Screening and/or Camouflage If the present and potential future visibility of the proposed tower is negligible, then perhaps the remoteness and vegetation surrounding the site serves as the camouflage (screening) from the general public. If not, the Commission could consider seeking additional architectural treatment to disguise the structure (e.g faux tree/water tower/clock tower/concealed-antenna monopole, etc.). Technical Bulletin dimensional requirements, at section V.A., require full camouflage/concealment for structures that exceed the height of the zoning district. Limitations of Concealed-Antenna Monopoles Carriers are requiring more vertical real estate on new concealed-antenna monopoles. More vertical space is needed to address the current design approach to put the radio heads near the 5
antennas, and to address some carriers needs to support more antennas. They tend to avoid this style of new pole to preserve their flexibility to add antennas and radio heads. Tower Height The applicant is seeking variances from the Town of Barnstable, including a height variance. The Technical Bulletin limits tower heights to ten feet above the average tree canopy. We did not find any assessment of the existing tree canopy height. The Bulletin calls for a demonstration that the proposed height is required. The application only contains T-Mobile coverage estimates from the proposed height and a drive test at the proposed height and 20 feet less. The applicant should prepare coverage analyses with the proposed T-Mobile facility at the 10-feet-above-tree-canopy height and at the point halfway between that and the proposed antenna height of 140 feet. Tree canopy height should not be guessed, but evaluated by a professional. Model coverage at 700 MHz. Regional Policy Plan Minimum Performance Standard LU2.2 requires a demonstration of the commitment of two or more co-locators into the design of the facility. The Commission is aware from experience that it is not always possible to propose a new tower with at least two committed carriers at the outset. The proposal is designed to accommodate the facilities of additional carriers. The proposal is also in a location that is distant from existing towers and existing overlay district locations. Based on the foregoing, it is likely that other carriers in the not-too-distant-future will find the proposed tower as useful to their network objectives as it will be for T-Mobile. The optimal height of a tower at the Site is determined largely by 1) the coverage improvements in the three adjoining towns obtained by T-Mobile at the finally established height, 2) the remaining space available to any carriers who would join the tower, and 3) the relative differences in visual impact, if any, at heights other than the proposed height. 6
Tree-Growth Preservation Technical Bulletin Section V.B. encourages dense tree-growth to help screen new towers from view. The applicant s proposal includes preservation of some of the surrounding wooded spaces. RF Exposure Compliance The application does not contain an analysis of compliance with FCC 47 CFR 1.1307 relating to human exposure of the general population to the emissions of the facility. While we do not anticipate an issue, it is customary for the Commission to receive a copy of the Routine Evaluation that the FCC requires the applicant to perform and maintain in the applicant s records. If the applicant is seeking the ability to add carriers to the tower without further DRI review, Section VIII Modifications of the Technical Bulletin requires the applicant to provide a pro forma analysis of the combined emissions of the total number of carriers for which approval is sought. Noise The applicant s noise analysis is solely focused on the noise from the generator, which tests briefly once a week and runs continuously during power outages. This might be considered an intermittent noise source not unlike a resident mowing a lawn. Automatic testing is generally scheduled for business hours to minimize the nuisance. This could be made a condition of any approval. The applicant s noise analysis assumes free space propagation of sound (no attenuation due to vegetation, terrain or other obstacles). The calculation predicts a 55.6 dba sound level at the nearest property line. The Technical Bulleting sets 50 db(a) as the threshold for compliance. The actual level experienced at the nearest point on the property will be less than this safe-side estimate and probably very close to the threshold. It might be sufficient to require the applicant to measure the noise level after construction to verify compliance, or simply to waive the requirement for temporary operation of the generator. 7
Other equipment at a single-tenant cell site is typically not as noisy as a generator and is not likely to even be audible at the property line. One thing to address is whether the permittee has by-right authority to add wireless carriers in the future. If so, then some provision to ensure continued compliance with the noise regulation should be imposed for the combination of all facilities operating at the site. David Maxson, WCP 8