RadioWiki · Tools · Off-grid

🛰️ Meshtastic presets & airtime

What LongFast actually means: SF/BW/CR, the frequency slot for any channel name, airtime per message and hop cost.

Modem preset

Spreading factor

Bandwidth

Coding rate

Region

Frequency slot

Primary channel nameThe slot comes from a hash of this name - a renamed channel lands on a different frequency

Slot: 20 of 104
Frequency: 906.875 MHz

Nodes only hear each other on the same preset and slot. Most of the US is on LongFast slot 20 (906.875 MHz); if a group tells you to use “MediumFast slot 45” this is where that number comes from.

Airtime

Message lengthbytesText bytes; a typical chat line is 20-60, a position packet ~30Hop limit

Raw data rate: 1.07 kbps
One transmission: 682.0 ms; 40 B + 16 B header
Channel time for the mesh: 2.73 s; 4 relays worst case
Sensitivity (approx): -131.5 dBm; lower is better
Msgs/hour at 10% duty: 131; before the channel saturates

Slower presets reach farther (each step of SF adds ~2.5 dB) but every message costs the whole mesh airtime, and each hop repeats it. Busy metros are moving to Medium Fast for that reason; rural Oklahoma with a handful of nodes is fine on Long Fast. Firmware caps a node’s own airtime near 10%.