Why indoor range is different
A radio datasheet range is measured in open conditions: clear line of sight, no buildings, no interference and an ideal antenna. An indoor site is the opposite. The signal has to pass through walls, floors, doors, furniture, racking and people, and it has to compete with electrical noise.
The result is that a radio advertised at “5 miles” may cover one floor of a concrete building, while a radio advertised at “2 miles” may cover an open warehouse aisle. The box number is an upper bound, not a site prediction.
There is a second difference that buyers notice later: indoor coverage is not uniform. A handheld may work in the corridor outside the plant room and fail inside it, or work at the lift lobby and fail in the stair core two metres away. The signal is not a circle on a floor plan; it is a pattern of paths, reflections and shadowed corners.
The four losses
Most indoor failures come from four sources:
- Walls. Concrete, brick and metal-framed walls absorb or reflect energy. A reinforced concrete wall can cost 10–20 dB or more.
- Floors and ceilings. A concrete slab between floors is a major loss. A repeater on the roof may not reach the basement through it.
- Metal. Racking, containers, steel cladding, lifts and foil-backed insulation create reflections and dead spots.
- Bodies and furniture. People, stock and partitions absorb signal, especially at UHF.
The practical consequence: coverage is not uniform. It is a patchwork that changes when the stock, partitions or building work changes.
A link budget you can sketch on one page
You do not need a full propagation model to understand why a radio fails in a room. A first-order link budget is enough to show where the energy goes.
The free-space path loss at 450 MHz is roughly:
| Distance | Free-space path loss |
|---|---|
| 10 m | 45 dB |
| 30 m | 55 dB |
| 100 m | 66 dB |
| 300 m | 75 dB |
| 1 km | 86 dB |
The numbers come from the standard free-space formula, and they assume no obstructions. A handheld transmitter might deliver 4 W (36 dBm) into an antenna with 2 dBi gain, so the radiated power is about 38 dBm. With a receiver antenna gain of 2 dBi, the received power at 100 m in free space is roughly:
36 dBm + 2 dBi − 66 dB + 2 dBi = −26 dBm
That is a very strong signal. Now add a reinforced concrete wall at 15 dB, a floor at 18 dB and 10 dB of margin for bodies and fading:
−26 dBm − 15 − 18 − 10 = −69 dBm
Still usable. But if the path is 300 m instead of 100 m, and passes two reinforced concrete walls at 30 dB each before reaching a stair core, the same calculation lands near or below the receiver’s sensitivity limit even before the 10 dB margin. That is why a radio can be loud and clear in one room and dead two rooms away.
Two rules follow from the arithmetic:
- A 3 dB change is small. Doubling transmit power adds 3 dB. One reinforced concrete wall can take 15 dB, which is roughly a 30-fold power increase to recover. Power is not a substitute for a path.
- Cable loss is real. At 450 MHz, thin coax can lose 20 dB or more per 100 m, while a low-loss cable loses a fraction of that. A repeater on the roof with a long thin cable run may deliver less power to the antenna than expected.
The exact figures depend on frequency, materials and geometry, but the lesson is stable: plan the path, then the power.
How building materials change the plan
Indoor attenuation varies widely. Use these as planning values, not exact predictions:
| Material | Typical loss at UHF | Planning implication |
|---|---|---|
| Drywall / stud partition | 2–4 dB | Several partitions are tolerable |
| Brick wall | 6–10 dB | A few walls cut the usable range |
| Concrete wall, unreinforced | 10–15 dB | One wall can halve the practical coverage |
| Reinforced concrete | 15–30 dB | Treat as a major boundary |
| Metal-framed wall / steel cladding | 20–30 dB | Dead spots behind it |
| Metallised or tinted glass | 10–20 dB | Common in modern office façades |
| Fire door, closed | 5–10 dB | Corridor coverage changes when doors close |
| Dense racking with stock | 10–20 dB per rack line | Aisle-by-aisle coverage varies |
| Concrete floor slab | 15–25 dB | Vertical coverage is expensive |
The design response is different for each:
- Drywall offices can often be covered by one antenna per zone, with power chosen to avoid overshooting into other zones.
- Concrete and reinforced walls need antennas on the correct side of the wall, not a stronger radio on the wrong side.
- Metal cladding and racking need antennas placed along aisles or at the rack ends, because reflections create nulls.
- Fire doors and stair cores need coverage tested with the doors closed; a corridor that works during a survey with doors propped open may fail in a real evacuation.
- Metallised glass can turn an exterior-facing office into a shielded box; check coverage near windows before assuming an outdoor antenna will reach inside.
Antenna choices: ceiling omni, directional and leaky feeder
An indoor antenna system is not one product. The choice follows the geometry of the building.
| Antenna / system | Best for | Strengths | Limitations |
|---|---|---|---|
| Ceiling-mounted omni | Open floors, corridors, retail | Even coverage, simple install | Ceiling height and obstructions matter |
| Directional panel / Yagi | Long corridors, warehouses, point-to-point | Gain in one direction | Needs aiming and clear line of sight |
| Leaky feeder | Tunnels, car parks, stair risers, long service ducts | Coverage along the cable route | Higher cost, careful installation |
| Passive DAS | Small to medium buildings | No active electronics, predictable | Splitter loss, cable loss, limited size |
| Active / fibre DAS | Large buildings, campuses, high-rise | Long runs, many antennas, monitoring | Higher cost and complexity |
| Portable repeater | Events, temporary sites, short projects | Rapid deployment, no fixed cabling | Limited power and antenna height |
A passive distributed antenna system is the usual starting point for a hotel or an office building. The repeater feeds a splitter, then a chain of taps and antennas. Each splitter and each metre of coax takes a share of the power, so the design has to balance the antenna count against the loss. Adding more antennas does not always improve coverage if the last antenna receives too little power.
Leaky feeder is the practical answer for a car park ramp, a tunnel or a long stair riser where a single antenna cannot see the whole route. It radiates along its length, so the coverage follows the cable rather than a cone from a ceiling point.
A portable repeater is useful when the requirement is temporary: a renovation phase, an event, a seasonal site or a building where the permanent system is not ready. It can be deployed in hours, but it still needs an antenna position and a power source, and it is not a substitute for a designed permanent system.
Realistic distances by building type
| Environment | Typical handheld-to-handheld range | What decides it |
|---|---|---|
| Open-plan office | 50–150 m | Partitions, furniture, people |
| Hotel guest floor | One floor or one corridor | Concrete walls, fire doors |
| Warehouse aisle | 100–300 m, less across racking | Racking height, stock density |
| Basement / plant room | Often no reliable coverage | Concrete slab, equipment, ducts |
| Car park | 50–150 m | Concrete, ramps, vehicles |
| Stair core | One to three floors | Concrete, metal doors |
These are planning estimates, not guarantees. A site survey is the only way to know.
Why the basement always fails
The basement is usually below a concrete slab, surrounded by earth and concrete, and full of plant, ducts and metal. A rooftop repeater may cover the upper floors but not the basement. The signal has to go through the slab or through a service shaft, and both are lossy.
The usual fixes are:
- an indoor antenna in the basement, fed by the repeater;
- a local repeater closer to the basement;
- a leaky feeder or distributed antenna system for long tunnels and car parks.
Do not assume “one repeater covers the building”. The basement is the exception that proves the rule.
There is a second basement problem: the handheld-to-repeater path. A basement antenna may hear the handheld, but the handheld may not hear the basement antenna if the repeater output is split too many ways. Test both directions. A system that talks down but not up is not a working system.
When a repeater fixes it
A repeater helps when:
- the repeater antenna is above the clutter;
- the handheld can reach the repeater from the work area;
- the duplex pair and isolation are correct.
A repeater does not create coverage where the handheld cannot reach it. If the user is deep in a basement or behind a thick wall, the repeater on the roof may not hear them. In that case, the answer is an indoor antenna or a local repeater, not more power.
The duplexer deserves a note. A repeater transmits and receives at the same time on two frequencies, usually with a 5 MHz separation at UHF. The duplexer filters the transmitter so it does not desensitise the receiver, and the antenna system must provide enough isolation between the transmit and receive paths. If the isolation is insufficient, the repeater’s own signal deafens it, and the coverage collapses even though the antenna is in the right place. This is an installation and tuning issue, not a radio-model issue.
When you need indoor antennas
Plan an indoor antenna system when:
- the building has multiple floors or wings;
- there is a deep basement, car park or plant room;
- racking or metal structures create dead spots;
- the site needs even coverage, not just a strong signal in the lobby.
An indoor system is a small distributed antenna network fed by the repeater. The design goal is even coverage across the work areas, not maximum signal in one corridor.
A simple design sequence:
- Mark the coverage zones on the floor plan: public areas, back-of-house, plant, basement, car park, stair cores.
- Estimate the loss from the repeater to each zone, including splitters and coax.
- Choose antenna positions at ceiling height or on cable trays, not inside cupboards.
- Balance the split so the nearest antenna is not overloaded and the farthest still has margin.
- Check the talk-back path from each zone to the nearest antenna.
- Leave 10–20 dB of margin for stock, people and building changes.
The margin matters. A system designed exactly at the threshold will fail when the warehouse fills with stock or the hotel opens a new partition wall.
Ranking the fixes by cost and impact
When coverage fails, the fixes are not equal. A practical order:
| Fix | Cost | Impact | When to use |
|---|---|---|---|
| Reposition a handheld or antenna | Low | Sometimes large | The problem is a local obstruction |
| Raise the antenna | Low–medium | Large | The antenna is below the clutter |
| Use a better antenna with gain | Low–medium | Moderate | The path is directional and clear |
| Reduce cable loss | Medium | Moderate–large | Long coax runs are eating the power |
| Add an indoor antenna | Medium | Large in the target zone | The zone is shadowed from the main antenna |
| Add a local repeater | Medium–high | Large in a separated area | Basement, annexe, car park |
| Increase transmit power | Medium | Small–moderate (3 dB per doubling) | The link is marginal and every dB counts |
| Add capacity (second carrier) | High | Solves waiting, not coverage | The coverage is fine but the channel is busy |
The last row is the one that gets confused with coverage. A site where users cannot get a word in at shift change has a capacity problem, not a range problem. A second talk path or a second carrier fixes it; a higher antenna does not.
How to test before acceptance
Agree the test method before installation:
- Define the test points or route.
- Use the final programming and final antenna positions.
- Record signal level and audio quality at each point.
- Test talk-out and talk-in separately.
- Agree pass/fail thresholds in writing.
- Keep the result as a baseline for future changes.
For a multi-floor building, test each floor and the stair core. For a warehouse, walk every aisle. For a basement, test with the fire doors closed.
A defensible test also records the conditions: doors open or closed, stock level, HVAC running, lifts moving, people present. Coverage that works in an empty building at 07:00 may fail at 17:00 with a full floor of guests and a delivery truck at the loading dock.
If you want a first-pass recommendation, use the coverage planner. For the full coverage guide, read walkie-talkie range. For hotel and warehouse specifics, see hotel radios and warehouse radios.