RF simulation: the two models
Everything about a run that involves the air passes through one layer, and that layer can decide reception two different ways. Which one is active changes what a result means, so it is stamped into every saved run.
A concrete case: two repeaters relay the same flood within a millisecond of each other, and a third node hears both at similar strength. Calculated mode sums each transmission into the other's noise and both fail. A real SX1262 usually recovers the stronger one, and waveform mode shows that, because the chirps are synthesised, summed, and handed to a real demodulator that locks onto the stronger frame. When "did it collide" is the question, the mode is part of the answer.
Which to use#
Calculated is the default and the right choice for anything large - a national network, a coverage raster, a sweep across seeds. It is the mode most questions should be asked in.
Waveform answers what arithmetic cannot: whether two overlapping transmissions capture or collide, what a partial overlap actually costs, and what a receiver would hear if an SDR were attached to it.
| Calculated | Waveform | |
|---|---|---|
| verdict from | link-budget SNR | a decoded frame |
| concurrent transmissions | summed into the noise, in dBm | summed coherently, as samples |
| capture effect | none | emerges from the physics |
| partial overlap | counted as full-length interference | costs what it actually costs |
| cost, 300-node burst | 46 ms | 1.0 to 2.3 s |
What calculated gets wrong, and in which direction#
Two known biases, and they pull opposite ways:
- Any overlap counts as full-length interference, however briefly it clipped the packet. Pessimistic under partial collisions.
- There is no capture. A strong signal is destroyed by a weak overlap that a real chip would ignore.
Measured against waveform mode on a dense 60-node burst with six simultaneous senders: roughly half the collision-affected pairs decode under the waveform that calculated calls lost. In a contended scenario, calculated understates delivery.
That is a reason to compare two runs in the same mode rather than to distrust the mode. It is also why the mode is stamped into every saved run - two runs under different models are not comparable.
Switching#
Configuration → RF Simulation, or the rf.mode verb. It applies on a whole-transmission boundary, so a run can be switched while it plays without cutting a frame in half. The status bar names the active mode.
Where to go next#
- The RF chain - the physics both modes share: path loss, terrain, summation, noise.
- The waveform - the sample-accurate path in full, including the SDR observer and the carrier-sense detector.
- What it does not do - the error budget for each mode.