Why 433 MHz
Edit on GitHubThe reasoning behind the beacon's band choice: license-free operation, universal receivers, propagation, and the trade-offs.
Why 433 MHz
The single most important design decision in the project is the band. This page is the honest reasoning, including what 433 MHz costs.
The case for 433 MHz
| Reason | Detail |
|---|---|
| License-free in Europe | CEPT harmonized ISM band (see ISM Band Explained) |
| Universal receivers | Scanners, SDRs, handhelds and other beacons all cover it |
| The antenna is practical | Quarter wave is 17 cm: fits a handheld device (see Quarter Wave Antenna) |
| The hardware is cheap | The SX1262 modules for this band cost a few euros |
| Low-band advantage | Better propagation through foliage and terrain than 868 MHz |
The trade-offs
| Cost | Why it is acceptable |
|---|---|
| Power limited to 10 mW ERP | The beacon is a rescue device; emergency use overrides (see Emergency Use Legal) |
| Shared with consumer devices | The band is crowded in cities (see Urban RF Environment) |
| Legally a gray area at higher power | Solved by the amateur license (see Amateur License Process) |
| Not satellite-linked | The beacon is line-of-sight; that is the honest design |
The comparison
| Alternative | Why not |
|---|---|
| 868 MHz | Higher ISM power (500 mW) but worse propagation, fewer cheap modules, and US-incompatible |
| 2.4 GHz | WiFi/Bluetooth band: crowded, short range, poor in foliage |
| Satellite PLB | The commercial comparison page covers it: reliable but expensive and closed |
| Amateur 70 cm | Excellent but requires a license for the unlicensed builder |
The result
433 MHz is the only band that is license-free for receivers everywhere, cheap to build for, and usable for the beacon’s mission. Every constraint it imposes is a constraint the project documents and works within, rather than hides.
Related pages
- Frequency Compatibility for the full band data
- ISM Band Explained for the legal frame
- Commercial PLB vs DIY for the market comparison