AHJ Specifications Review
The first step in the design of a two-way radio communications enhancement system is a review of the technical specifications and the AHJ requirements for the proposed system. The following questions need to be answered:
- What channels need to be covered? Fire only? Fire and police? Other agencies?
- Where are the radio repeaters located?
- Are there any radio repeater backup sites that need to be included in the BDA design?
- What are the permit, documentation, inspection, and testing requirements?
- What are the service and inspection requirements?
- Any specific monitoring requirements, or follow NFPA / IFC?
- Are there any other specific requirements?
Initial Survey and System Planning
An initial survey is required to determine if the signal enhancement is required. If it is, the next step is to measure the in-building signal levels to identify those areas needing signal enhancement. Typically, only part of the building will need coverage enhancement, such as below-grade levels and lower floors in a high rise. Upper floors may not require enhancement or only require partial enhancement in the middle of the building or the side of the building facing away from the radio repeater donor site.
The building must be sufficiently complete for the initial survey. All floors, walls, and the roof should be constructed. We typically survey the site just before electrical rough-in wiring starts. If the survey is completed too early, an inaccurate reading will result and if it is done too late, the necessary electrical work and wiring to install the radio signal enhancement system is more difficult.
The survey will be done by a qualified and FCC GROL (General Radiotelephone Operator License) licenses BDA technician using a handheld radio with calibrated RSSI (received signal strength indications) programmed with the frequency channel information of the desired radio coverage. The technician will move through the building and note signal readings from the basement to the roof, taking careful note of readings in critical areas such as machine rooms, stairways, and other areas that may inhibit radio coverage. Lastly, the direction of the repeater antenna is verified so as to determine the location and orientation of the roof donor antenna.
Using the information gathered from the site survey, the BDA system will be designed to augment existing radio coverage as necessary, filling in weak signal areas so final overall coverage is near 100%. Antennas will be prescribed for areas with weak signals and provide coverage which overlaps from adjacent areas and floor. After this, system diagrams will be created with a riser diagram, antenna locations, cable paths, donor antenna location and direction, along with grounding, monitoring and supervision, and other connections.