RSSI Explained
Edit on GitHubWhat the RSSI number in SEARCH mode means, how the threshold works, and how to interpret the hit log.
RSSI Explained
RSSI is the number the beacon shows while scanning. It is the raw signal-strength readout, and SEARCH mode’s whole job is built on it.
What RSSI measures
RSSI is the receiver’s estimate of the incoming signal power, in dBm. The SX1262 measures it during each receive window.
| RSSI | Meaning |
|---|---|
| -40 to -70 dBm | Strong signal (nearby) |
| -70 to -90 dBm | Moderate |
| -90 to -105 dBm | Weak but possibly audible |
| -110 to -120 dBm | Near the noise floor; likely nothing |
The threshold
SEARCH mode compares each reading against a configured threshold (default -90 dBm). Above threshold = a hit; below = quiet. The threshold is a trade-off:
- Too high (e.g. -70): only very strong signals count; you miss distant beacons.
- Too low (e.g. -110): noise counts; the scan logs false hits.
The dwell window
The beacon listens on each frequency for the dwell time (default 400 ms) and records the peak RSSI in that window. A brief transmission is still caught if it overlaps the window.
Reading the hit log
The RTC RAM hit log stores the last 20 detections with frequency, RSSI, and a classification:
- STRONG: typically -60 dBm or better
- MEDIUM: roughly -60 to -80 dBm
- WEAK: roughly -80 to -105 dBm
Audio correspondence
The SEARCH audio pitch maps directly to RSSI: quiet = silence (DAC parked), weak = 440 Hz rising, strong = up to 2200 Hz. The pitch change is your real-time proximity sensor.
Troubleshooting with RSSI
- Floor reading around -110 to -90 with no signal: normal.
- A steady strong reading on one frequency with no transmitter: local interference; see the interference page.
- RSSI stuck at one value across all frequencies: the radio is not actually receiving; check the antenna and the SX1262 wiring.