LoRa link planner: terrain profile & link budget
Put two stations on the map, choose their radios and see whether they can hear each other over real terrain: line of sight, Fresnel zone, diffraction loss and the link margin both ways.
Map
Click the map to place the chosen station, or drag a marker. The coordinates below follow. With a keyboard, type the coordinates in the station fields below.
Result
Enter the stations and press “Check the link”.
Inputs changed — press “Check the link” to recalculate.
- Distance
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- Path
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- Free-space loss
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- Diffraction loss
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- Receiver sensitivity
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- A → B received
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- B → A received
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- Ground
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How it is calculated
The server samples the terrain every 30 m along the great circle between the stations and raises it by the Earth's bulge for k = 4/3. The ends of the profile are the antenna tips.
Path loss is free-space loss plus diffraction over the terrain: the highest edge by the ITU-R P.526 knife-edge formula and one more edge on each side of it (the Deygout method), added without a correction, which errs on the pessimistic side.
FSPL = 20·log10(4πd/λ) · Prx = EIRP − FSPL − Ldiffraction + Grx − Lcable
Receiver sensitivity is that of an SX1262: thermal noise for the bandwidth, a 6.5 dB noise figure and the demodulator limit of the spreading factor (−7.5 dB at SF7 to −20 dB at SF12). The margin is the received power above that. With 10 dB or more both ways the link is likely; from 0 to 10 dB it is marginal.
The power check below each station uses the ERP calculator rules for EU868. They are the EU-wide limits: some countries do not open every sub-band, so check your own regulator.
Frequently asked questions
How accurate is the result?
It is an estimate for planning. The terrain is a surface model, so forests and buildings count as solid ground, and the diffraction loss over several ridges is taken on the pessimistic side. Rain, vegetation in leaf, antenna patterns and local noise are not modelled. A "likely" link with 10 dB or more to spare usually works; a marginal one needs a test on site.
What is the Fresnel zone and why does it matter?
The radio path is not a thin line but an ellipse around it. When terrain enters the first Fresnel zone the signal weakens even with a clear line of sight. Keeping at least 60% of it clear gives close to free-space loss.
Why must both directions work?
A mesh node has to hear the other one and be heard back. If one station transmits with more power or has a better antenna, the stronger direction does not help: the verdict follows the weaker one.
Where do the terrain heights come from?
From the Copernicus DEM GLO-30, a 30 m elevation model of the whole world. The planner samples it every 30 m along the great circle between the stations and adds the curvature of the Earth for a standard atmosphere (k = 4/3).
This calculation is approximate and is not a guarantee of coverage. Terrain: produced using Copernicus WorldDEM-30 © DLR e.V. 2010-2014 and © Airbus Defence and Space GmbH 2014-2018 provided under COPERNICUS by the European Union and ESA; all rights reserved. Points in tiles the data set does not cover (open sea) are taken as sea level.