Originally Posted On: https://www.marconitech.com/how-to-choose-antenna-locations-for-an-fdny-arcs-system-in-nyc-steel-towers/
What You'll Need Before Picking Antenna Locations
Gather this before you set foot in the building. Missing one item usually means a second site visit, and in an NYC high-rise that means another round of building management paperwork.
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Approved floor plans and risers: Current architectural and structural drawings for every floor, plus the stair and shaft layouts. Old drawings lie, so confirm them against what's actually built.
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FDNY ARCS requirements: The current Fire Code and Rules provisions for your building, and any notes from your fire protection consultant or the FDNY Fire Alarm Inspection Unit.
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Portable radio: An FDNY-compatible handheld, or a test radio on the same channel plan, for walking stairwells and checking signal.
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Signal measurement gear: A handheld signal meter or spectrum analyzer, and a way to log readings floor by floor.
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Access credentials: Roof access, mechanical rooms, the fire command center, and every stairwell. Line these up with the building engineer ahead of time.
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Equipment specs: Datasheets for your repeater and console. Know your unit, whether that's the RC-108A with active antenna monitoring (UL Listed for 2524A) or the dual-channel VC-121N with TB9400, before you place a single antenna.
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Marking tools: A tablet or printed plans, a marker, a camera, and a tape measure for cable run lengths.
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Skills: Basic RF knowledge, the ability to read shop drawings, and familiarity with how steel and concrete block radio signals.
Time required: Plan on one to two days for the walkthrough of a typical high-rise, plus another day or so to mark up drawings. Larger towers take longer.
Short on any of this? Call Marconi Technologies' 24/7 line at (212) 376-4548 or email office@marconitech.com and ask for an engineering consultation before you start.
Most failed ARCS inspections in NYC don't come down to bad equipment. They come down to where somebody put the antennas. A single misplaced antenna in a stairwell can leave a dead pocket that a portable radio will find in about ten seconds, and the FDNY inspector will find it just as fast.
If you're running life safety for a steel high-rise in Midtown or the Financial District, you already know the problem. Steel frames, concrete cores, and fire-rated shafts swallow radio signals whole. A properly designed fdny arcs system has to push a clean signal through all of that, floor after floor, and it has to do it the first time you call for acceptance testing.
Placement is where the work gets won or lost. Get it right and the repeater, console, and monitoring all fall into line. Get it wrong and you're paying for a second visit, a delayed sign-off, and some uncomfortable conversations with ownership.
What You'll Achieve and What You Need Before You Start (FDNY ARCS System Prerequisites)
A fire safety director in a 52-story Midtown tower walks the 31st floor with an FDNY inspector. The radio test fails in the stair shaft. Not the lobby. Not the roof. The stair. Poorly placed antennas caused it — the fix meant opening finished ceilings.
Choosing locations correctly the first time prevents that. Here's what to line up before a single antenna gets mounted.
What a Passing Antenna Layout Looks Like in an NYC High-Rise
A passing layout gives clear, two-way radio coverage in every stairwell, the fire command center, and the elevator lobbies. The FDNY ARCS system has to hold that signal through steel and concrete, floor after floor. Dead spots in a stair shaft are the classic failure. So is a layer of coverage that drops when a fire door closes.
Materials, Drawings, and Approvals to Gather First
Pull these together before design starts:
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Current floor plans showing every stair, shaft, and mechanical room
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Riser diagrams and the fire command center layout
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The fire alarm shop drawings, since a fire alarm arc tie-in must be mapped from the start
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Roof access plans and structural notes for the donor antenna
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Your FDNY filing details and permit status
Skip one, and you'll redo work. That's the honest answer.
Step 1: Map Your Building's Steel, Concrete, and Dead Zones
Antenna placement starts with a survey, not a drawing. Before anyone picks a spot for the FDNY arcs system, someone has to find where radio signal dies inside the tower. In NYC steel-frame high-rises, that's usually the core, the stairwells, and the lower levels.
Walk the Stairwells and Risers with a Portable Radio
Grab a portable radio and walk every stair, floor by floor. Don't skip the ones nobody uses. Log each dead spot (a spot where the signal drops or garbles) against the floor plan.
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Start at the lobby and test in the stairwell nearest the fire command station.
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Climb one floor at a time. Mark every spot where talk-back fails.
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Check the riser shafts, mechanical floors, and cellar levels. Concrete and steel stack the worst losses there.
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Repeat in the opposite stair. Results often differ.
Keep the notes. They'll feed your antenna layout and the paperwork later. Teams comparing FDNY approved ARCS companies should ask how each one uses survey data to place antennas, because a good layout depends on it.
It also helps to know how the system ties into the ARC fire alarm panel and console, since that shapes where the repeater and risers can physically run.
Skip this walk and you're guessing. Guessing fails inspections.
Step 2: Place Antennas to Cover Stairwells, Elevator Lobbies, and Fire Command Center
Where does a signal actually die in a steel tower? Almost always in the stairwells, behind the concrete core. Any arc system FDNY layout has to solve those spots first.
Start at the Fire Command Center.
It's the anchor. Firefighters will hold their radios there for the whole operation, so coverage must be clean at every desk and panel. Then work outward.
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Stairwells: Put an antenna on every stair, at a minimum on the lobby level and roughly every 10 floors. Steel and fire-rated doors eat signal fast.
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Elevator lobbies: Cover the fire service elevator lobby on each floor you serve. Don't assume the stair antenna reaches through the core.
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Command center: Mount one inside the room itself, not in the corridor outside.
Here's what most people miss: the FDNY ARC system is judged on the radio in the responder's hand, not on a drawing. A repeater can be perfect and the test still fails if one landing is dead. (It happens more than you'd think.)
Before drilling anything, run a propagation study. A manufacturer-backed team such as Arc Fire Services can model the steel frame — flag weak floors early. Walk every stair with a portable afterward. Fix gaps now, not at inspection.
Step 3: Position the Repeater, Dedicated Radio Console, and Antenna Monitoring Points
A steel-and-concrete core in an NYC tower can swallow 20 to 30 dB of radio signal before it reaches a stairwell. That number drives every placement call in an FDNY auxiliary radio communication system design.
Start with the repeater. Put it in the fire command center or a rated equipment room, never a shared closet. Mount the dedicated radio console where the fire safety director can reach it in seconds.
Choosing Between Rooftop and Interior Antenna Runs for FDNY ARCS Compliance
Rooftop antennas give the cleanest line of sight. But they leave a long cable run through risers, and every foot adds loss. Interior runs keep cable short and protect it from weather. They also fight the steel layer around the core.
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Rooftop: best for the upper floors and the donor path. Watch for mechanical clutter and cooling towers nearby.
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Interior: best for lower levels, cellars, and stairwells. Keep it inside rated enclosures.
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Monitoring points: place one at every antenna, because a silent failure is the one that fails inspection.
Which one wins? Most NYC towers need both, and the survey decides the split.
Walk the full route with the installer before anything gets drilled. Not after.
Step 4: Avoid Common Antenna Placement Mistakes That Fail FDNY Inspections
Myth: more antennas mean better coverage. Wrong. In NYC steel towers, extra antennas often create the very dead spots that sink a test. A retired inspector sees it constantly, and it's rarely the radio that fails.
A properly engineered arcs system depends on antenna spots chosen with intent, not guesswork. The FDNY's arcs system fails most often on placement, not hardware.
Check your layout against these common mistakes before the inspector does:
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Antennas hugging steel columns or shaft walls. Metal shadow kills the signal in the next room.
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Skipping stairwell and elevator lobby coverage. Firefighters live in those spaces during a response.
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Ignoring the cable path. A long coax run with too many splitters eats your signal budget before it reaches the antenna.
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No antenna monitoring. A cut or damaged antenna goes unnoticed until the test.
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Mounting in spots the contractor can't reach later. Maintenance access counts.
But here's the thing. A walk test on a bare floor won't match an occupied one (furniture, partitions, and tenant buildouts change everything). Re-test after fit-out.
Fix the layout on paper first. It's cheaper than fixing it after a failed inspection.
Step 5: Verify Coverage, Document the Layout, and Prepare for FDNY Acceptance Testing
A fire safety director in a Midtown tower walks the 31st floor with a portable radio, and the signal drops dead behind the elevator core. Nobody planned for that sector. Now the antenna layout goes back to the drawing board two weeks before the inspection.
Don't let that be you. Walk every floor with a handheld before anyone from the Department shows up. Test the stairwells, the mechanical rooms, and the lobby. A FDNY ARC system has to pass in the full body of the building, not just the spots that are easy to reach.
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Run coverage tests on each floor and log every weak spot.
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Adjust antenna placement or add a layer of coverage where the signal falls short.
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Finalize as-built and shop drawings that match what's actually on the ceiling.
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Schedule commissioning with a certified tech before the FDNY test date.
Equipment matters here too. The RC-108A adds active antenna monitoring (UL Listed for 2524A), so a cut or failed antenna gets flagged right away. The VC-121N pairs a dual-channel TB9400 repeater in a compact unit, which helps in tight riser closets. You can review the full line of arc fire alarm systems before you finalize the design.
Stuck on a failed test? Call the 24/7 line at (212) 376-4548 or email office@marconitech.com to book an engineering consultation.
How-To FAQ
How many antennas does an FDNY ARCS system need in a high-rise?
There's no fixed number. The count depends on floor plate size, steel density — how many stairwells and risers you have. In practice, plan for coverage in every stairwell, every elevator lobby, and the fire command center, then add antennas wherever your portable radio test drops out. Your engineer's propagation study settles the final count.
How long does antenna layout planning take?
Expect a few days of field work and a few weeks of design and drawings for a typical tower. The walk-through with a portable radio is the quick part. Shop drawings and approvals take longer, so start before your inspection window gets tight.
Can I put antennas in the stairwell enclosure itself?
Yes, but only where the installation keeps fire-rated assemblies intact and the antenna is protected and supervised. Seal every penetration properly. Sloppy firestopping is a classic reason inspectors write you up. Check your approved drawings before anyone drills.
What happens if an antenna cable gets cut or disconnected?
A system with antenna monitoring flags it as a trouble condition. Marconi Technologies' RC-108A uses active antenna monitoring — it is UL Listed for 2524A, so a broken run shows up on the panel instead of hiding until a real emergency. Without monitoring, you may not know a floor has gone dark.
Is a rooftop antenna enough for an FDNY ARCS system?
No. A rooftop antenna handles the link to outside radio sites. It does nothing for coverage inside steel and concrete. You still need interior antennas on the floors, stairwells, and lobbies, tied back to the repeater.
Who do I call if my coverage test fails?
Call your system manufacturer's support line before you move any antennas. Marconi Technologies runs 24/7 support at (212) 376-4548 and can be reached at office@marconitech.com to set up an engineering consultation. A quick call often finds a cable, splitter, or gain setting problem and saves you a second test round.
Antenna placement decides whether an FDNY ARCS system passes on the first visit or gets sent back with a deficiency list. Steel framing and concrete cores don't forgive guesswork. A fire safety director who walks the stairwells with a portable radio, marks the dead zones, and puts antennas where responders actually work will see the difference at acceptance testing.
Three points carry the most weight. Stairwells, elevator lobbies, and the fire command center come first, since that's where crews depend on the radio. Rooftop and interior runs should be picked on the building's real structure, not on habit. And the layout needs paperwork behind it: as-built and shop drawings that match what's on the walls.
Equipment choice matters too. The RC-108A, with active antenna monitoring and UL Listed for 2524A, flags a failed antenna run before an inspector does. The VC-121N, a dual-channel TB9400 unit, gives a compact repeater option for tighter risers.
Next step: pull your riser diagrams and stairwell test notes, then call Marconi Technologies' 24/7 line at (212) 376-4548 or email office@marconitech.com to schedule an engineering consultation. Do it before the inspection date is on the calendar.
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