A building’s emergency responder communications system can meet 99% coverage in critical areas and 95% everywhere else, pass every individual radio test at commissioning, and still drop a firefighter’s transmission at the worst possible moment. The cause is the near-far problem, and the 2027 edition of NFPA 1225 changes how the code treats it. The 2022 edition told designers to minimize near-far conditions. The 2027 edition requires systems that use signal boosters to be designed to handle them.
Last month’s overview, NFPA 1225-2027: Major ERCES Changes to Watch, covered six changes to the new edition that owners, designers, contractors, and AHJs should have on their radar. We said we would start the detailed posts with near-far, because it illustrates the theme running through the whole edition: a system has to perform under the conditions responders create, not the conditions a test procedure finds convenient.
This post explains what near-far is, why it happens, what the new language requires, and how to design a system that meets it.
What Is the Near-Far Problem?
Two firefighters are working inside a high-rise. One is standing a few feet from an ERCES antenna in a corridor. The other is at the far end of a different floor, behind heavy construction, near the edge of what the antenna system covers. Each has good coverage. Tested alone, each passes.
Now both key up at the same moment on different channels, one on a fireground tactical channel and the other on dispatch. The near radio drives a very strong signal into the system. The far radio’s signal arrives very weak. When the two reach the signal booster together, the strong one can cause the weak one to be lost.
Neither radio did anything wrong, and neither location has a coverage gap. The failure appears only when both transmit together, which is exactly what happens when an incident is at its busiest.
Why the Difference Is So Large
“Strong” and “weak” understate it. A rough uplink budget for the two firefighters shows the scale:
| Near radio | Far radio | |
| Portable transmit power | 5 W (+37 dBm) | 5 W (+37 dBm) |
| Path loss, radio to nearest antenna | about 40 dB (a few feet) | about 85 dB (distance, walls) |
| DAS loss, antenna to booster | about 25 dB | about 35 dB |
| Signal at booster uplink input | about -28 dBm | about -83 dBm |
Illustrative values only. Actual figures depend on the building, the antenna layout, and the radios.
In this example the near radio arrives at the booster 55 dB stronger than the far radio. That is roughly 300,000 times more power, and spreads of 50 to 70 dB are common in real buildings. The booster has to pass both signals at the same time.
How the Booster Turns That Into a Failure
Every signal booster has a limit on how much uplink power it can put out before it distorts or exceeds its FCC limits. Automatic gain control (AGC) enforces that limit by turning the gain down when the input gets too strong.
In a wideband (Class B) booster, AGC typically responds to the total power across the whole passband and reduces gain for everything in that passband together. If the near radio is hot enough that the booster cuts its uplink gain by 15 dB, the far radio loses the same 15 dB. If the far radio was only 10 dB above what the donor site needs, it is now below it. The dispatcher or incident commander hears nothing, or hears it broken.
That is the whole mechanism: one radio’s strong signal takes away gain that another radio needed.
Why Different Channels?
The scenario specifies different channels for a reason. Two radios on the same channel is a separate problem. FM receivers lock onto the stronger signal (the capture effect), and a repeater can only pass one talker at a time. That happens with or without an ERCES and is handled through radio discipline, not system design. Near-far is the case where both transmissions should get through and the booster stops one of them.
What NFPA 1225-2022 Required
The 2022 edition already recognized the problem. Section 18.3.4 required ERCES designs to minimize near-far conditions and to provide sufficient distribution antenna density to address them.
That was sound engineering direction, but it set no performance threshold. A system could meet the coverage percentages and pass individual audio quality tests without anyone demonstrating how it behaves when strong and weak uplink signals reach the booster at the same time.
What Changed in NFPA 1225-2027
The 2027 edition keeps the requirement to minimize near-far conditions and adds a specific one. Section 18.3.4.3 requires an ERCES that uses a signal booster to be designed to support two radios transmitting simultaneously on different talk paths or channels, one producing the strongest signal and the other the weakest signal arriving at the booster.
The shift is from “minimize” to “support.” The code now defines a worst-case operating condition the system must handle. Coverage percentages establish where communications must work. This requirement addresses whether they work when more than one person is talking.
Annex A.18.3.4.3 recommends near-far testing before commissioning. It describes evaluating the strongest and weakest uplink conditions and simulating simultaneous transmissions to confirm the booster can support both. It also discusses how AGC characteristics, antenna-system balancing, antenna placement, and uplink dynamic range affect near-far performance. Annex material is advisory, so the test itself is a recommendation rather than a mandated acceptance test. As discussed below, that distinction may matter less in practice than it does on paper.
Does a Channelized (Class A) Booster Solve It?
Mostly, and the reason matters. Under FCC rules, a Class A booster has no passband wider than 75 kHz, which in practice means a separate filter for each channel. When each filter has its own AGC, a loud radio on one channel can only turn down the gain on its own channel. The far radio on a different channel keeps its full gain. That is the structural fix for near-far, and it is why channelized boosters are the stronger choice where near-far risk is high.
Three caveats apply:
- Shared AGC. Some products group several channels into one filter or one AGC block. Within that group the booster behaves like a small Class B booster, and near-far comes back. Read the specification for how AGC is applied, not just the Class A label.
- The front end. The low-noise amplifier ahead of the channel filters sees every signal in the band. A strong enough signal can push it into compression before channel filtering happens. Front-end design and antenna placement still matter.
- Channel plans change. Trunked and simulcast systems assign voice channels dynamically and add channels over time. A channelized booster has to be programmed for every channel the radio system can use, and reprogrammed when that system changes.
Class B boosters are not ruled out by the 2027 language. They can meet it, but only if the system is designed so that the strongest and weakest signals both fit within the booster’s dynamic range without triggering gain reduction that pushes the weak signal below what the donor site needs. That is a design problem, and it has to be solved on paper first.
How to Design for Near-Far
The variable that matters is the spread between the strongest and weakest uplink signals at the booster. Every effective mitigation either shrinks that spread or keeps AGC acting on one signal from affecting another.
- Use more antennas at lower power. A denser layout shortens the distance from the worst-case location to the nearest antenna, which raises the weakest signal. Avoiding high-gain hot spots near heavily traveled paths lowers the strongest. Both narrow the spread.
- Balance the uplink paths. An antenna on a short cable run near the head end delivers far more uplink signal than one at the end of a long run. Coupler and splitter choices, or added attenuation on short runs, equalize those losses so a radio next to any antenna arrives at the booster at a similar level.
- Use per-remote gain control in fiber DAS. Where the system uses fiber-fed remotes that each set their own uplink gain, a loud radio near one remote does not pull down the others. Confirm how AGC is applied end to end, because the combined signal at the head end still has to fit the booster.
- Choose channelized boosters where the risk is high. Large floor plates, dense antenna layouts along primary response routes, and buildings with long distribution runs are good candidates.
- Run the numbers. Build the uplink link budget for the best-case and worst-case locations, then compare it to the booster’s AGC threshold and dynamic range and to the input level the donor site requires. If worst-case gain reduction drops the weak signal below that level, change the design before installation, not after.
How Compliance Will Be Shown
Section 18.3.4.3 is mandatory, but the code does not prescribe a test for it. That raises a practical question on every project: how does a designer demonstrate that a system is designed to support the strongest and weakest radios at once?
In our view, two answers will converge. Plan reviewers will ask to see the near-far analysis in the design submittal, meaning the uplink link budget for the strongest and weakest locations and the booster’s AGC behavior. And AHJs will likely treat the Annex procedure as the de facto acceptance test, because it is the only procedure the standard describes. Designers who plan for that test from the start will have an easier review than those who first encounter it at commissioning.
It is also worth noting that the 2027 Annex on qualified personnel, covered in our overview, lists near-far conditions among the knowledge expected of the people who design, install, and test these systems.
When Does This Apply in California?
Our overview covered the adoption timeline in detail. The short version: California’s current code is in effect through December 31, 2028, and January 1, 2029, is the earliest likely date for NFPA 1225-2027 to become part of the statewide code.
It can reach your project sooner. Many AHJs publish ERCES criteria that reference the current edition of NFPA 1225 rather than a fixed year, and those can pick up the near-far requirement as soon as the new edition is published. Confirm the applicable requirements with the AHJ for each project.
Our advice is to design for the 2027 requirement now. The RF problem is the same under either edition, a system installed today will be in service for many years, and adding near-far performance after installation costs far more than building it in.
The Bottom Line
Coverage tells you where a radio will work. Near-far determines whether it works when someone else is talking too. NFPA 1225-2027 makes that second question part of the requirement, and the time to answer it is during design.
IBWS designs ERCES for near-far from the first link budget, and we can perform near-far testing before commissioning on new or existing systems. If you have a project in design, or a system that tests well but has had unexplained dropouts during drills, contact us at in-buildingwireless.com.