Does a DMR digital radio system need a different in-building DAS design than an analogue system?

No. The passive part of a DAS (coax, couplers, splitters and antennas) does not know whether the signal on it is analogue FM or DMR, so antenna count, spacing and cable topology carry over unchanged. What changes is how much margin you need, how you survey and accept the system, and which active components you can reuse. Digital radio fails by cutting out rather than by getting noisy, so a design that was marginal but usable on analogue can become unusable on DMR.

Why is the passive DAS the same for DMR and analogue?

Both are narrowband UHF signals in the same 400-470 MHz range, each in a 12.5 kHz channel. Coax loss, coupler tap values, splitter losses and antenna gain are functions of frequency, not modulation. A layout that delivers -85 dBm at the worst point on analogue delivers -85 dBm on DMR.

Multipath is not a concern either. DMR uses 4FSK at 4800 symbols per second, so one symbol lasts about 208 microseconds. Indoor delay spread is typically tens to a few hundred nanoseconds, and 100 m of coax adds roughly 400-500 ns, so two overlapping DAS antennas fed from one source cannot cause inter-symbol interference. This is why a single-source DAS needs none of the delay engineering that simulcast systems do.

What actually changes when you move from analogue to DMR?

The failure mode changes. Analogue FM gets progressively noisier as signal drops, so users complain early and keep talking. DMR holds clean audio until bit errors overwhelm the vocoder, then the audio turns robotic and drops. The cliff sits only a few dB wide, which is why I design DMR to a fade margin rather than to the bare receiver sensitivity (see our article on the digital radio cliff effect).

Receiver sensitivity is similar. Portable datasheets typically quote around -119 dBm for 12 dB SINAD on analogue and a comparable figure for 5% bit error rate on digital; verify against the datasheet of the radios actually being bought. The practical difference is what happens just above that point, not the number itself.

The key figures I work to:

• Thermal noise in a 12.5 kHz channel: about -133 dBm before receiver noise figure.

• Design threshold for reliable DMR voice at the portable: -95 dBm.

• Fade margin: 10 dB minimum for commercial buildings, 15 dB for mission-critical areas.

• Uplink: a 4 W (36 dBm) portable against a 40 W (46 dBm) repeater makes the uplink the limiting path in most buildings.

Do I need to re-survey the building before switching to DMR?

Yes, and the survey method should change. A signal-level grid alone can pass a floor that still has audio problems, because digital is sensitive to a raised noise floor and co-channel interference in ways a level reading does not show. Measure bit error rate or DAQ alongside level, and test both directions, since the uplink fails first. The reasoning is covered in our piece on DAQ 3.0 versus a -95 dBm acceptance criterion.

Which active components can I reuse from an analogue system?

Passive parts can all be reused if rated for 380-520 MHz. Check active parts individually. A channel-selective BDA adds group delay, and DMR's two-slot TDMA structure has a short guard time between bursts, so confirm the vendor's quoted delay and DMR compatibility. Repeaters, BDAs and filters should also be confirmed for 12.5 kHz operation and for the radio vendor's DMR tier. Do not assume an old wideband booster is acceptable.

What do DMR and analogue share on licensing in Singapore?

The coverage design is unaffected, but an IMDA licence and type-approved equipment are required for the repeater or BDA either way. Confirm the channel plan and bandwidth with IMDA before ordering, since I have not verified a modulation-specific condition.

Related questions

Does DMR have better range than analogue? Not meaningfully on the same hardware. DMR's benefit is cleaner audio at moderate signal levels and two timeslots per channel, not extra range.

Can DMR and analogue radios share one DAS? Yes, if the repeater or BDA supports both modes. The passive network carries both, but plan margin for the weaker mode.

Will DMR fix my dead zones? No. A dead zone is a link-budget problem, and changing modulation does not add signal.

How Suneast approaches this

Suneast designs and installs in-building two-way radio coverage in Singapore, covering UHF DMR and analogue repeaters, BDAs and DAS. We survey in both directions, design to a stated fade margin, and test with level and bit error rate so the system passes on audio as well as signal. If you are migrating from analogue to DMR, we can re-survey an existing system and tell you whether it needs more antennas or only new radios.