RF Design & Link Budget
Edit on GitHubFree-space path loss, link budget math and realistic range expectations for 410-525 MHz
RF Design & Link Budget
Overview
The Aegis-Beacon uses the SX1262 transceiver in CW (Continuous Wave) mode for emergency beacon transmissions. The signal is detectable by any AM-mode receiver on the same frequency.
Frequency Range
| Parameter | Value |
|---|---|
| Operating Band | 410-525 MHz |
| Default Frequency | 433.500 MHz |
| Frequency Steps | 100 kHz |
| Max Frequencies | 10 per cycle |
Link Budget Analysis
TX Parameters (SX1262 + E22 PA)
| Parameter | Value |
|---|---|
| Output Power | +22 dBm (RadioLib) / +30 dBm (E22 PA) |
| Antenna Gain | 0 dBi (wire) / 2 dBi (whip) |
| Feedline Loss | 0 dB (direct) |
RX Parameters (Typical Scanner)
| Parameter | Value |
|---|---|
| Sensitivity | -120 dBm (AM mode) |
| Antenna Gain | 2 dBi (whip) |
| Noise Floor | -110 dBm |
Free Space Path Loss
FSPL(dB) = 20*log10(d) + 20*log10(f) + 32.45
Where:
d = distance in km
f = frequency in MHzExample: 433.5 MHz, 5 km
FSPL = 20*log10(5) + 20*log10(433.5) + 32.45
= 13.98 + 52.74 + 32.45
= 99.17 dBLink Margin
Link Margin = TX Power + TX Antenna - FSPL + RX Antenna - RX Sensitivity
With E22 PA (+30 dBm):
= 30 + 0 - 99.17 + 2 - (-120)
= 52.83 dB (excellent margin)
With RadioLib (+22 dBm):
= 22 + 0 - 99.17 + 2 - (-120)
= 44.83 dB (good margin)Maximum Range Estimates
| Condition | Range |
|---|---|
| Line of Sight (LOS) | 15+ km |
| Mountain terrain | 5-10 km |
| Urban/suburban | 1-3 km |
| Through snow | 3-9 dB loss at 1m depth |
| Through foliage | 5-10 dB loss |
Warning
Range estimates assume clear line of sight. Real-world performance depends on terrain, obstacles, and antenna quality.
Antenna Considerations
Quarter-Wave Lengths
| Frequency | Length |
|---|---|
| 433.5 MHz | 17.3 cm |
| 462 MHz | 16.2 cm |
| 868 MHz | 8.6 cm |
Best Practices
- Vertical orientation for omni-directional coverage
- Keep antenna away from battery and metal enclosure walls
- Ground plane (copper foil) improves gain by ~3 dBi
- E22 SMA connector — use quality 433 MHz whip antenna
CW Signal Characteristics
Modulation
- Type: CW (Continuous Wave) — on/off keying
- Detection: Any AM-mode receiver
- Bandwidth: ~500 Hz (narrow)
- Audible: Yes, through earpiece/speaker
Comparison with Other Modes
| Mode | Bandwidth | Sensitivity | Audible |
|---|---|---|---|
| CW (Aegis) | ~500 Hz | -120 dBm | Yes |
| FSK | ~125 kHz | -130 dBm | No |
| OOK | ~10 kHz | -115 dBm | Yes |
Note
CW mode is chosen for maximum compatibility. Any AM-mode receiver can detect the signal without special software.