Place a transmitter and receiver in the 2D scene and read the coverage map in the sandbox, and predict — before you read it off the screen — the free-space path loss at a given distance, the received power that leaves, and how much a concrete wall in the path takes away.
In free space the signal spreads over an ever-larger sphere, so power falls as 1/d² — the free-space path loss FSPL = 20·log10(4πd/λ) rises by 6 dB every time the distance doubles, and by 20 dB every decade. Whatever leaves the transmitter at Ptx arrives at Ptx − FSPL, minus whatever the walls in the way absorb. Reading those numbers off a real 2D scene is how you know whether a link will close before you build it.
Open the sandbox and pick the Open field (no walls) preset — one ray, pure free-space path loss, the reference case. Set the frequency band to 2.4 GHz and the transmit power to Ptx = 20 dBm, then drag the receiver until the distance readout shows 100 m. Each step names the one thing to change; leave everything else alone.
Preset -> Open field (no walls) Frequency -> 2.4 GHz
Ptx -> 20 dBm Distance d -> 100 m (add a wall only in Step 3)
Watch the distance readout, the received-power readout in dBm, and the material table — every number you predict is printed there.
With the receiver at d = 100 m and the band at 2.4 GHz, the wavelength is λ = c/f ≈ 0.125 m. Predict the free-space path loss FSPL = 20·log10(4πd/λ), then read the coverage-map readout.
The path loss is FSPL = 80.05 dB at 100 m — and it is a clean anchor: FSPL at 1 m is 40.05 dB, and every decade of distance adds 20 dB, so 100 m is 40.05 + 40 = 80.05 dB.
Still d = 100 m, 2.4 GHz, Ptx = 20 dBm. In free space the received power is simply Ptx − FSPL. Predict it in dBm, then read the received-power readout.
The received-power readout is Ptx - FSPL = 20 - 80.05 = -60.05 dBm — this is exactly how the demo computes it: whatever leaves the transmitter arrives that much weaker after the free-space spread.
Add one wall straight across the line of sight and set its material to Concrete. The demo charges the wall's own penetration loss on any ray that crosses it. Predict how many dB the concrete wall takes away, then read the material table and the drop in the received-power readout.
The concrete wall costs 18 dB — the material table's penetration loss for concrete — so the received power drops from -60.05 dBm to about -78.05 dBm. A single concrete wall alone can be the difference between a link that closes and one that does not.
Everything above is waiting in the sandbox. Sweep the frequency and watch the whole coverage map dim, drag walls of different materials across the path and watch the shadow deepen, and add reflectors to see multipath rays bounce round corners and fill a room the line of sight never reaches.
- Read the free-space path loss at 100 m, FSPL = 80.05 dB at 2.4 GHz
- Found the received power, Ptx - FSPL = 20 - 80.05 = -60.05 dBm
- Watched a concrete wall take away 18 dB, dropping the receiver to about -78.05 dBm
- Every value you predicted is the demo's own path-loss arithmetic, not a picture