Wide Area Coverage
A coverage survey answers three questions before money is spent: how far the signal reaches, how many repeaters are needed and where, and where the budget should go. It is a link budget calculated in advance and a walk or drive test measured afterwards against a written criterion.
"How many kilometres will it reach?" is the first question every buyer asks and the one question that cannot be answered. The same radio covers fifteen kilometres across a plain, one kilometre in a city, and twenty metres from a basement. What determines range is not the device but how much the signal loses along the way.
A coverage survey is the work of calculating that loss before installation and measuring it afterwards.
Three questions, each of which has a cost attached to getting it wrong.
Where does it stop working? The point at which the signal falls below what the receiver can decode.
How many repeaters, and where? If the whole area must be covered, how many transmitting positions are needed and where they should be.
Where should the money go? The same budget can buy antenna height, higher power, or a second repeater. These are not equivalent.
A purchase made without answering them ends the same way every time: "it doesn't work down here", and a second installation budget.
A link budget is simple arithmetic on a chain of gains and losses, in decibels, from transmitter to receiver.
Transmit power — 4 to 5 W for a handset (about 36–37 dBm), 25 to 50 W for a mobile, up to 25–50 W for a repeater.
Feeder loss — the cable from the repeater to the antenna. Specified per 100 metres at the operating frequency; thin cable on a long rooftop run can consume several decibels, which is a large fraction of what you paid for.
Antenna gain at both ends. Gain is not free power; it is directionality. A 6 dBi omnidirectional antenna achieves its gain by flattening the pattern, which is excellent across a yard and poor across floors of a building.
Path loss — the dominant term and the hardest. In free space it rises with the square of distance and with frequency. In the real world it also includes buildings, terrain, vegetation and the human body holding the radio.
Receiver sensitivity — the weakest signal the receiver can decode, typically around −119 dBm analogue and better for digital at equivalent audio quality.
Sum the gains, subtract the losses, and compare against sensitivity. Keep a fade margin — commonly 10 to 20 dB — because signals vary with weather, movement, vehicles, stock levels and where the user is standing. A design with no margin works on the day of testing and fails on ordinary days.
The radio horizon in kilometres is roughly 4.12 × √h, h in metres, at each end. A handset held at 1.5 m sees about 5 km. A repeater antenna at 20 m sees about 18 km. Together, the geometric limit is around 23 km.
That is why raising the antenna beats increasing power almost every time. Going from 25 W to 50 W is 3 dB. Going from a 10 m mast to a 25 m mast changes the horizon by kilometres and, more importantly, clears obstructions that no amount of power gets through. When a budget conversation reaches "should we buy the higher-power repeater", the better question is usually "can we get the antenna higher".
Calculation predicts; it does not verify. Real sites contain reflections, absorption and structures no model captured.
Walk test — indoor and pedestrian areas, recording received signal level and voice quality at defined points. It must include the places that will be complained about later: basements, plant rooms, lift cars, stairwells, loading docks, the far corner of the yard.
Drive test — vehicle-based, logging signal against position along the routes the operation actually uses.
Talk test — two people, real equipment, real accessories, in the real environment. Instrument readings do not capture whether a message is intelligible over a running machine, and intelligibility is what was actually bought.
Test under realistic conditions. A warehouse surveyed empty is not the warehouse. A construction site surveyed at foundation stage is not the site it will be in a year.
This is where most projects lose the argument, because "good coverage" was never defined.
A criterion that can be tested and settled:
> Portable-to-repeater coverage shall be provided in all areas listed in Annex A, including levels B1 and B2, all stairwells and the loading dock, at a received signal level not less than −100 dBm, measured at a minimum of five points per area at 1.5 m above floor level, with at least 95 percent of measured points passing. Voice quality shall be not less than DAQ 3.4 at all passing points. Results shall be recorded and submitted as a coverage report.
Every element there exists to close a specific dispute: which areas, what level, measured how, how many points, what counts as passing, and what gets handed over. A contract without this is not enforceable in the only respect that matters.
Some areas will never be reached from a single site, and no antenna or power increase changes that. The options, in increasing cost:
The survey is what tells you which of these you need, and that is the point of doing it before rather than after.
A survey that costs a small percentage of the installation removes the failure mode that costs the whole installation again.
The question has no answer as asked. The same handset reaches fifteen kilometres across flat open ground, one kilometre in a city and twenty metres in a basement. Range is a property of the path, not of the device, which is why a survey measures the path rather than reading a datasheet.
No. Doubling power is a 3 dB gain, and in free space path loss rises with distance squared, so it buys roughly 40 percent more distance in ideal conditions and considerably less in real ones. Raising the antenna a few metres usually delivers more than any power increase available to you.
Approximately 4.12 × √h kilometres, where h is antenna height in metres, applied at both ends of the link and added together. A 20 metre mast gives about 18 km of horizon before terrain is considered. It is an upper bound set by geometry, not a prediction of usable coverage.
As a measurable criterion: named areas, a minimum received signal level or a defined voice-quality score, a stated percentage of test points that must pass, and the test method. Without that, 'good coverage' is a matter of opinion after installation, and the argument has no way to end.
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