How many repeaters do I need to cover a large warehouse?

Almost every warehouse enquiry I get opens with this question, and almost every time the honest answer is: fewer than you think, and that is not the number that decides whether your radios work.

Let me show you the arithmetic, because it settles the point quickly.

Take a typical single-storey logistics warehouse in Tuas or Jurong: roughly 30,000 m² of floor plate, 12 m clear height, dense pallet racking, concrete tilt-up walls, steel roof deck. Assume a 40 W UHF DMR repeater at 450 MHz, mounted in the ELV room, feeding a single omni antenna at high level near the centre of the roof structure.

Downlink from the repeater: +46 dBm at the transmitter, less about 3 dB through the duplexer and jumpers, less 1.8 dB down 40 m of 1/2" coax, plus 2 dBi from the omni. That is roughly +43 dBm EIRP at the antenna. Free-space path loss at 450 MHz over 150 m is about 69 dB. Dense pallet racking is the real variable — measured clutter loss in a fully loaded steel-racked aisle typically runs 15 to 25 dB depending on load and aisle orientation. Take the pessimistic 25 dB, and subtract another 3 dB body loss for a radio worn on the hip.

That lands you at roughly −54 dBm at the portable. The design threshold for reliable DMR voice is −95 dBm. You have over 40 dB of margin on the downlink.

The uplink is the path that usually limits an in-building design, so check it rather than assume. A 4 W portable transmits +36 dBm, loses the same 3 dB body loss and the same 25 dB clutter and 69 dB path loss, arriving at about −61 dBm at the antenna. Add the 2 dBi antenna gain, subtract the feeder and duplexer losses, and the repeater receiver sees around −64 dBm against a −119 dBm sensitivity figure. Also comfortable.

So on a link budget, one repeater covers the building several times over. Which tells you the question is wrong.

What actually causes warehouse radio failures

In fifteen years of remediating warehouse systems in Singapore, I have almost never found a site that failed because the repeater lacked power. The failures cluster into four causes, and none of them are solved by buying a second repeater.

The first is shadowing. RF does not care about your average coverage figure — it cares about the worst location. Cold rooms and freezer chambers with insulated metal panel construction routinely add 30 to 40 dB. Battery charging rooms, sprinkler pump rooms, and ground-floor offices tucked under a mezzanine slab are similarly opaque. So are lift cars and reinforced concrete stairwells. A single roof-mounted antenna will not reach into any of those, no matter how much power you put behind it.

The fix is antennas, not repeaters. You take the same 40 W repeater, split its output through a directional coupler network, and drop antennas into the shadowed zones — one inside the cold room, one in the charging room, one in the mezzanine office corridor. Each antenna needs only enough power to cover a 20 to 30 m radius, so the per-port levels are modest and the distribution is cheap compared to a second repeater plus a second licence plus the frequency coordination that comes with it.

The second cause is noise floor. Warehouses are electrically filthy environments. VSD-driven conveyors, forklift battery chargers, and LED high-bay drivers all raise the UHF noise floor, sometimes by 10 to 15 dB. That degrades the uplink specifically, which is why the symptom is always "they can hear the office but the office cannot hear them." No amount of downlink power fixes this. You fix it by finding the emitter and by siting the receive antenna away from it.

The third is capacity, not coverage. DMR Tier II gives you two timeslots per 12.5 kHz channel. If you have 60 pickers, a yard team, and a supervisor group all sharing one channel, users will experience busy tones and clipped calls and report it as "the radio does not work." That genuinely does call for a second repeater — but for traffic, not for range.

The fourth is topology. Two blocks separated by more than about 200 m, or a multi-storey ramp-up facility with several suspended slabs, are two coverage problems, not one. Reinforced concrete slabs typically cost you 20 to 30 dB per floor at UHF, so vertical coverage does not come free the way horizontal coverage does.

The rule I work to

For a single-storey warehouse up to about 30,000 m², plan on one repeater and budget for a distributed antenna system sized to the shadowed zones. Count the zones, not the square metres. A typical site of that size needs one repeater and somewhere between six and fourteen antennas, fed from the ELV riser through staged directional couplers so every antenna port lands within about 3 dB of its neighbours.

Add a second repeater only when you can name the reason: a second building, a second slab, or a traffic count that overflows two timeslots.

None of this is decidable from a floor area figure alone. It needs a walk-through with a service monitor, a look at the racking layout and load, and a check of what plant runs near the proposed antenna position.

How Suneast approaches this

Suneast designs and installs in-building two-way radio coverage systems in Singapore, including warehouse and logistics facilities. We work from the client's CAD floorplan to produce a link budget, an antenna placement plan, and a floor-by-floor coupler and tap schedule that a contractor can build directly and a consultant can audit line by line. We conduct on-site RF survey and post-installation coverage verification against a stated design threshold, and we handle the IMDA station licensing that a repeater installation requires. Where a site turns out not to need a second repeater, we say so.