What is Signal Strength Testing

IFC Section 510.5.3 defines exactly what is required for acceptance testing of a building, and can be used to determine whether a building passes or fails a benchmark test. Each floor of the building must be divided into a grid of 20 test areas of approximately equal size, and a radio test shall be conducted in the approximate center of each grid. In addition to the 20 test locations, critical areas may be added here as defined by the AHJ. To pass, you must meet a signal strength of -95 dBm over 95% of the grids (IFC 2015) or a DAQ of 3.0 over 95% of the grids (IFC 2018 and 2021).

DAQ (Delivered Audio Quality) is a judgement call, and although there are tools that exist to convert BER (bit error rate) into a DAQ score, we are expecting this DAQ score from a calibrated radio of the latest brand and model or a BER score from calibrated test equipment. Not all field-deployed radios will be the latest brand and model and depending on how close the building is to a fail threshold, passing on DAQ alone may still prohibit communication in the building during an emergency.

Signal strength testing, also referred to as ERRCS testing, alone is simply a measure of power and does not give us details on signal quality (signal to noise ratio or bit error rate). However, it is important to know where we stand in relation to minimum signal strength usable by a portable. Current P25 Phase II systems may function perfectly down to -115 dBm downlink signal strength. If we take two different buildings that each have a DAQ of 5 everywhere inside, but building 1 has an average signal strength of -75 dBm while building 2 has an average signal strength of -110 dBm, then we would have two very different opinions on where these buildings stand for whether or not an ERRC System is required.

Building 1 has great DAQ and great signal strength, so there is no reason to put in a BDA. Building 2 has great DAQ, but poor signal strength. Depending on which code, a BDA may not be enforced. However, all testing is done under ideal conditions. Let’s look at a real life scenario: a portable radio with a damaged antenna (5dB of loss) and an emergency responder wearing turnout gear with the radio under a rescue coat (3dB of loss), our two scenarios change. Building 1 will have an average signal strength of -83 dBm for this first responder, while Building 2 will have an average signal strength of -118 dBm. This first responder will be able to communicate just fine in Building 1, but may not be able to communicate at all in Building 2.

At ERRCS Design & Testing, we want to ensure all parts of this system are understood by our clients. There is the code compliance issue with IFC Section 510 (2015, 2018, and 2021), NFPA 72 2013, NFPA 1221 (2016 and 2019), and any state codes. There is also the approval required for a BDA by the FCC Licensee, as it is their frequencies that we will be re-broadcasting. In addition, there is also the safety of first responders inside the building that must be addressed.

We look forward to working with you and educating you on testing for public safety radio communication and interpreting the results to comply with your local codes.