Do cellular DAS antenna spacing figures apply to a UHF two-way radio DAS?

No. Almost every per-antenna coverage figure published online — the widely repeated "1,250 square feet within a 20-foot radius" being the usual one — is a cellular DAS number derived at 1900 MHz or above. At 400–470 MHz, where DMR and analogue two-way radio live, one antenna covers roughly six times that floor area for the same delivered power. If you size a two-way radio DAS from cellular figures you will specify four to six times more antennas than the building needs, and pay for all of them. The error runs the other way too, and that direction is the dangerous one: a UHF spacing plan applied to a cellular or converged system will leave holes.

Why one antenna covers far more area at 450 MHz than at 1900 MHz

The frequency term in the path loss equation is the whole story. Path loss scales with the square of frequency, so moving from 1900 MHz down to 450 MHz recovers 20·log₁₀(1900/450) ≈ 12.5 dB at the same distance, before anything else in the building is considered. That is a large number in a link budget — larger than most people expect from what looks like a footnote in a specification.

Converting it into distance needs an indoor path loss exponent. In a typical office or hotel fit-out that sits around 3.0 to 3.5; taking 3.2, the 12.5 dB advantage translates to about 2.4 times the radius, and radius squared gives roughly six times the floor area. That is the arithmetic behind the six-times figure, and it is worth showing rather than asserting, because it is also the arithmetic that tells you when the ratio does not hold. In a heavily partitioned building where walls rather than distance dominate the loss, the exponent rises and the distance advantage shrinks — though UHF partly claws it back, since reinforced concrete and blockwork attenuate less at 450 MHz than they do at 1900 MHz.

The hard numbers a two-way radio DAS is actually designed around:

• 12.5 dB — the frequency term alone between 450 MHz and 1900 MHz at equal distance

• Roughly 2.4 times the radius and 6 times the floor area, at an indoor path loss exponent of 3.2

• 1/2" plenum coax: about 4.5 dB per 100 m at 450 MHz, roughly double that in the cellular bands (verify against the cable datasheet)

• −95 dBm design threshold at the portable, with 10 dB fade margin commercial and 15 dB mission-critical

• 4 W (36 dBm) UHF portable against a 0.2–0.25 W (23–24 dBm) mobile handset — about 12 dB of uplink difference

What figures should a UHF two-way radio DAS actually be designed to?

For UHF at 400–470 MHz, working design practice puts a single ceiling omni at roughly 1,000–1,500 m² in open-plan space and 400–700 m², or about 15–20 m spacing, through a partitioned office or hotel floor. Those are budgeting figures, not a design — they exist so a quantity surveyor can price a tender before survey, and they are stated the same way in our note on DAS antenna spacing per floor. Nothing replaces a measured survey, because the fit-out drives the layout far more than floor area does.

Compare 400–700 m² against the cellular figure of 1,250 sq ft, which is about 116 m². The gap is three-and-a-half to six times, which is exactly what the frequency arithmetic predicted. The consistency is the point: when the number you read online and the number the physics gives you differ by a factor of six, the number is from a different band.

Why you cannot simply reuse the cellular DAS hardware

This is where the mistake stops being a costing error and becomes an installation that does not work. Wideband DAS passives and ceiling antennas sold for cellular are typically specified 698–2700 MHz. They do not pass 400–470 MHz. Feed UHF into a 698–2700 MHz coupler and the loss is unspecified and usually severe; the antenna will not radiate efficiently at a wavelength it was never designed for. The coax and the riser route are reusable in principle, but the couplers, splitters and antennas generally are not — which is the substance of what we set out on sharing a building's existing telco DAS.

The reverse asymmetry matters on the uplink. A 4 W portable transmits roughly 12 dB harder than a mobile phone, so a UHF system that is downlink-comfortable can still be uplink-limited by a noisy repeater receiver rather than by antenna count — a different failure mode from the one cellular DAS design is tuned to avoid.

What about a converged DAS carrying both?

Engineer it at the highest band it must serve. A branch that is comfortable at 450 MHz can fail outright at 2100 MHz on identical hardware, because both the free-space term and the cable loss grow with frequency. That means the antenna count is set by the cellular requirement and the UHF service rides along with generous margin — acceptable, and usually cheaper than two parallel systems, provided every passive component is genuinely rated across the full 400–2700 MHz span and low-PIM where the cellular operators require it. Verify that against datasheets rather than a supplier's summary sheet.

Related questions

Is the "1,250 sq ft per DAS antenna" figure wrong? Not wrong, just cellular. It comes from consumer signal-booster material where the band is 700–2100 MHz and the source is an off-air donor. Applied to a 450 MHz two-way radio DAS it understates per-antenna coverage by roughly a factor of six.

Does rebar and concrete change the comparison? It narrows it. A 200 mm reinforced-concrete wall costs on the order of 15–25 dB at UHF and more at cellular frequencies, so heavy partitioning erodes the UHF distance advantage without eliminating it. In an open warehouse the six-times figure is close; in a cellular-plan hotel it is nearer three or four.

Can I use a cellular DAS design tool for a UHF system? Only if it lets you set the band, the path loss exponent and the component loss values yourself. Tools with fixed cellular defaults will return an antenna count several times higher than needed.

Suneast designs and builds in-building two-way radio coverage systems in Singapore at 400–470 MHz, with the link budget, coupler and tap schedule and per-floor antenna placement documented so a consultant can recompute them. We survey the building before quoting antenna counts, we specify passives rated for the band actually in use, and where a converged cellular and radio DAS is on the table we say plainly which band is setting the design and what it costs.