DMR Radio Systems
UHF around 400-470 MHz has a wavelength near 70 cm, short enough to diffract through doorways, stairwells and racking that block longer waves. That makes it the default band indoors: buildings, warehouses, plants, hospitals and campuses. In open terrain the advantage reverses.
The question "UHF or VHF?" gets answered on habit more often than on physics, and the wrong answer is expensive because it is discovered after installation. The physics is not complicated, and it decides most cases on its own.
A radio wave in the UHF band used by professional radio — roughly 400 to 470 MHz — is about 65 to 75 centimetres long. A VHF wave at 150 MHz is two metres.
That difference matters because radio waves interact with objects according to how the object's size compares with the wavelength. An opening much smaller than the wavelength behaves like a wall. An opening comparable to the wavelength lets energy through and bends it around the edges.
A doorway, a stairwell, the gap between two pallet racks, a lift lobby, the space between a machine and the ceiling — these are all in the range of tens of centimetres to a couple of metres. To a 70 cm wave they are passages. To a 2 m wave they are largely obstacles.
Everything else about the UHF-versus-VHF choice follows from this.
A concrete floor slab with steel reinforcement is a serious attenuator at any frequency. Signal between floors mostly does not travel through the slab; it travels through the vertical openings — stair cores, lift shafts, service risers, atria — and those are exactly the geometry UHF handles and VHF does not.
In practice a UHF handset in a hotel or office building reaches several floors from one repeater position, while the same power in VHF is confined to the floor it is on and the corridor it can see. This is why hotels, hospitals, shopping centres and office towers are UHF sites almost without exception.
Where the building is deep as well as tall, one repeater stops being enough. That is not a band problem, it is a distribution problem, and the answer is a distributed antenna system or leaky feeder rather than a change of frequency.
A high-bay warehouse is one of the more hostile radio environments in ordinary commerce, and it is hostile in an unobvious way. The building is often a steel shed — highly reflective — filled with metal racking in regular rows, which produces strong multipath and standing-wave patterns. Coverage measured when the building is empty bears little relation to coverage when it is full, and stock levels change weekly.
UHF is the right band here for the diffraction reason, but the design lesson is different: a warehouse must be surveyed loaded, not empty, and the antenna position chosen so that aisles are illuminated along their length rather than across it. Forklift-mounted mobiles behave differently from handsets on belts, and both need testing.
Production halls combine everything difficult: metal structure, heavy machinery in the path, high ambient noise, and often an explosive atmosphere zone where certified equipment is mandatory.
UHF handles the structure. The noise is handled by accessories — heavy-duty headsets, bone-conduction or in-ear sets under hearing protection — and by digital voice, where DMR's error correction keeps speech intelligible at signal levels that would leave analogue audio buried in hiss.
Sites with a mix of buildings, outdoor areas and underground levels are the common case for facilities and security teams. UHF covers the buildings; the outdoor spans between them are short enough that UHF's range disadvantage does not bite; and the underground levels get a repeater or a feeder.
The typical failure here is not the band. It is a channel plan that puts security, cleaning, technical and reception on one channel, so everyone hears everything and nobody hears what matters. That is a programming problem, and it is cheap to fix before delivery and irritating to fix afterwards.
Be equally clear about the reverse. UHF loses to VHF when:
For those environments the argument runs the other direction, and it is set out in when to choose VHF.
Mixed operations — a farm with sheds, a port with terminal buildings — sometimes need both bands. That is a legitimate outcome, not a failure of planning, and it is resolved with a gateway rather than by making one band do work it cannot.
A specification that produces a working system names the outcome, not just the hardware:
Get those right and the band choice is the easy part.
Because the wavelength is close to the size of the openings a signal has to get through. At 450 MHz a wave is about 67 cm long, which diffracts around door frames, through stairwells and between racking. At 150 MHz the wave is two metres and treats those same openings as walls. It is geometry, not power.
In open terrain, yes — noticeably. Over flat ground with nothing in the way, VHF carries further for the same power. But almost no commercial site is flat empty ground, and once buildings, machinery or racking are in the path UHF delivers more usable coverage even though the theoretical range is lower.
Professional UHF bands are licensed by the BTK, and frequencies are assigned per organisation and per site. Licence-free alternatives exist in the PMR446 band with strictly limited power and no repeaters, which suits a shop floor and nothing larger. Licensing is part of the project, not an afterthought.
Usually not. Gain is achieved by flattening the radiation pattern, which helps across a car park and hurts across floors of a building. Indoors the answers are a repeater in the right place, a distributed antenna system, or leaky feeder — putting the signal where it is needed rather than shouting harder from where it is not.
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