Will Switching to Digital (DMR) Radios Fix Our Building's Dead Zones?

No. Switching from analogue FM to digital DMR will make your audio cleaner in the areas you already cover, but it buys you only about 2-3 dB of extra link budget — and a single reinforced-concrete floor slab costs you 15-20 dB. If your radios go silent in the basement carpark or on the upper floors today, they will still go silent after the upgrade, just more abruptly. Dead zones are a path-loss problem, and path loss is solved with a repeater and distributed antennas, not with a different modulation scheme.

I am asked this two or three times a month, usually after a vendor has quoted a fleet replacement as the answer to a coverage complaint.

Does a digital radio signal penetrate concrete better than an analogue one?

No, and this is the most common misconception in the market. Propagation is governed by frequency and geometry — wavelength, distance, and what is physically in the way. A 450 MHz carrier attenuates through a 200 mm reinforced-concrete slab by the same amount whether it carries analogue FM or a 4FSK DMR waveform. Modulation is what you write onto the carrier; it does not change how the carrier behaves passing through rebar.

The claim that "digital punches through concrete" conflates two things: penetration (physics, unchanged) and intelligibility at low signal levels (processing, genuinely improved). Digital gives you the second, not the first.

How much extra coverage does DMR actually give you?

A real but small amount. The figures, for UHF portables in the 400-470 MHz band:

• Analogue FM portable receiver sensitivity: typically −119 dBm at 12 dB SINAD

• DMR digital portable receiver sensitivity: typically −116 to −119 dBm at 5% BER (verify against the radio datasheet; varies by model)

• Practical gain from forward error correction at the coverage edge: roughly 2-3 dB

• Loss through one reinforced-concrete floor slab: 15-20 dB (first traversal ~25-28 dB)

• Loss through a basement or shear wall: 20-30 dB

• Design threshold for reliable in-building DMR voice: −95 dBm at the portable

• Fade margin: 10 dB minimum for standard commercial, 15 dB for mission-critical

The arithmetic answers the question. Two to three decibels does not buy you one more floor, and it will not get you from the ground-floor lobby down to B3. It is a fraction of a single slab.

The digital advantage is real at the boundary. Analogue degrades gracefully — hiss, then more hiss, then unusable mush — and an experienced user can still pull a message out of a noisy signal. DMR holds full clarity down to its error-correction limit and then drops out completely. That is the cliff effect. Digital gives you a slightly larger area of clean audio with a much sharper edge to it, which is why staff often call a digital system "worse" after a swap: the marginal areas that used to be scratchy-but-workable are now silent.

Why doesn't more transmit power fix it either?

Because the uplink is almost always the limiting path, and the upgrade does not touch it. A base repeater typically runs 25-40 W (44-46 dBm). A body-worn portable runs 4-5 W (36-37 dBm), and loses another 3 dB to body loss with the radio on the hip. That is a built-in asymmetry of 10 dB or more: the guard in the B2 carpark hears the control room perfectly and the control room cannot hear him at all.

Digital portables change neither number, and a higher-power repeater only widens the imbalance. The fix is to shorten the uplink path by putting an antenna near the user, which is what a distributed antenna system does — see our explainer on what a DAS is and whether your building needs one and the underlying figures in how much signal is lost through each concrete floor slab.

When is a fleet upgrade to DMR still worth doing?

On its own merits, not as a coverage fix. DMR Tier II gives you two talkpaths per 12.5 kHz channel, effectively doubling channel capacity on a busy site — that matters in a mall or on a construction site where guards, cleaning and M&E all compete for airtime. You also get individual and group calling, text and status messaging, GPS reporting, lone-worker and emergency alerting, and better battery life from the TDMA duty cycle. Those are good reasons to go digital.

Just do not buy it expecting the basement to come alive. If your survey shows areas below −95 dBm, the deficit is tens of decibels and only infrastructure closes it: an on-site repeater with distributed antennas, or a bi-directional amplifier fed from an off-air donor. Any repeater or booster installed in Singapore also needs an IMDA station licence and type-approved equipment — the radios themselves are the easy part of the compliance picture.

Related questions

Does a DMR system need a different DAS design than an analogue one? Largely no. The passive distribution — coax, couplers, taps, antennas — is identical, because it is broadband and modulation-agnostic. What changes is the acceptance criterion: you test an analogue system to 12 dB SINAD and a digital one to 5% BER or a DAQ score, so the pass thresholds on the survey sheet differ.

How do we prove whether we have a coverage problem or a radio problem? Run a grid survey with a calibrated test set and record received level per cell. If levels sit above −95 dBm with margin and the audio is still poor, it is an equipment or interference problem. If they are below threshold, no radio on the market will fix it.

How Suneast approaches this

We survey before we quote. For in-building coverage work in Singapore we run a grid-based measurement across the affected floors, record actual received levels in dBm against a −95 dBm threshold with a 10 dB fade margin (15 dB where the system supports emergency response), and produce a link budget covering both downlink and uplink with the limiting path identified. If the survey shows a fleet upgrade will not close the gap, we say so rather than sell it. Where a DAS is warranted we design the antenna placement and coupler schedule to a stated 95% area coverage target, and handle the IMDA licensing and type-approval for the repeater or BDA as part of the works.