# Betaflight RSSI and Link Quality Explained: dBm, LQ, and Range Testing Guide
Understanding your radio link health in real time is one of the most important skills an FPV pilot can develop. RSSI and Link Quality (LQ) are the primary metrics that tell you how strong your control signal is — and when you are about to failsafe. This guide explains what these numbers mean, how to configure them in Betaflight OSD, and how to interpret them during flight to avoid losing your drone.
## RSSI vs Link Quality: What Is the Difference?
Many pilots confuse RSSI and LQ, but they measure fundamentally different things:
| Metric | Measures | Units | Scale | Protocol Support |
|—|—|—|—|—|
| RSSI (Received Signal Strength Indicator) | Raw signal power at receiver antenna | dBm or percentage | 0-100% (or -130 to 0 dBm) | All protocols |
| LQ (Link Quality) | Percentage of valid data packets received | Percentage | 0-100% | ExpressLRS, TBS Crossfire, Tracer |
| RQly (RF Quality) | Signal-to-noise ratio and bit error rate | Percentage | 0-100% | TBS Crossfire |
| RSSI dBm | Absolute signal strength in decibel-milliwatts | dBm | -130 to 0 dBm | ExpressLRS, Crossfire (with LUA) |
**Key insight:** RSSI tells you signal strength. LQ tells you whether that signal is actually usable. You can have strong RSSI with terrible LQ if there is heavy interference. Conversely, ExpressLRS can maintain 100% LQ at RSSI levels that would have already failsafed older protocols.
## How RSSI and LQ Relate to Range
### ExpressLRS (LQ-Based)
ExpressLRS uses **LQ as the primary range indicator**, with RSSI dBm as a secondary sanity check:
| LQ Value | Link Status | Action |
|—|—|—|
| 100 (Mode 2:1) | Perfect link, maximum data rate | Normal flying |
| 90-99 | Minor packet loss, still solid | Continue flying, note for long range |
| 80-89 | Noticeable loss, near sensitivity limit | Turn back if pushing range limits |
| 70-79 | Degraded link, control latency increasing | Turn back immediately |
| Below 70 | Critical — failsafe imminent | Land or risk failsafe |
ExpressLRS displays LQ in a unique way: it is often shown as `RSSI` in the OSD but actually represents LQ scaled to 0-100. In Mode 2:1 (500Hz), the raw value is 2:1 ratio, so 200:100 = 100% LQ.
### TBS Crossfire (RSSI + LQ)
Crossfire provides both RSSI (0-100%) and LQ (0-100%, also called RQly):
– **RSSI above 50%** with LQ at 100%: Strong link
– **RSSI 30-50%** with LQ at 100%: Still fine for most flying
– **RSSI below 30%** with LQ dropping: Turn back
– **LQ below 70%**: Failsafe imminent regardless of RSSI
### FrSky (RSSI Only)
Older FrSky ACCST receivers report RSSI only (0-100%, or raw values like 45-100 in SBUS). There is no LQ metric. A failsafe typically occurs at RSSI values around 38-42 (raw SBUS) or 35-40%:
| RSSI (FrSky %) | Status |
|—|—|
| 70-100% | Strong signal |
| 50-70% | Moderate — fly with caution |
| 38-50% | Weak — turn back |
| Below 38% | Critical — failsafe imminent |
## Configuring RSSI/LQ in Betaflight OSD
### Step 1: Set the RSSI Channel
In Betaflight Configurator, go to the **Receiver** tab:
– **RSSI Channel**: Set to “Auto” if using CRSF (Crossfire/ELRS) or set to the AUX channel carrying RSSI (often AUX8 or AUX12) for SBUS receivers
– For FrSky: Set RSSI Channel to the correct AUX channel (e.g., AUX8 = 12 in the dropdown)
### Step 2: Configure RSSI Scaling (FrSky/SBUS Only)
If using FrSky or any SBUS receiver with analog RSSI:
“`
set rssi_scale = 100
set rssi_invert = OFF
“`
Test by turning off your radio (with props off!) — RSSI should drop from near 100% to 0%.
### Step 3: Add RSSI and LQ to OSD
Go to the **OSD** tab and enable:
– **RSSI Value** — shows numeric percentage or dBm
– **RSSI dBm** — shows dBm value (for ExpressLRS/Crossfire)
– **Link Quality** — shows LQ percentage (ExpressLRS/Crossfire only)
– **Warnings** — enable “RSSI Low” alarm at your chosen threshold
### Step 4: Set RSSI Warning Threshold
In the OSD tab, set the **RSSI Alarm** value:
| Protocol | Recommended RSSI Alarm |
|—|—|
| ExpressLRS | Use LQ alarm instead (LQ < 80) |
| TBS Crossfire | RSSI < 30% or LQ < 80% |
| FrSky ACCST | RSSI < 45% |
## Understanding dBm Values
dBm (decibel-milliwatts) is a logarithmic scale. Every 6 dBm drop roughly doubles the distance or halves the signal strength:
| dBm Value | Signal Interpretation | Typical Distance (250mW ELRS) |
|---|---|---|
| -20 to -40 dBm | Extremely close range (<10m) | Bench testing |
| -50 to -70 dBm | Normal flying range | 50-500m |
| -80 to -90 dBm | Extended range | 1-5 km |
| -95 to -100 dBm | Near sensitivity limit | 5-10 km |
| -105 to -110 dBm | Below sensitivity — LQ drops | 10+ km (packet loss) |
## Practical Range Testing
### Bench Test (No Props, USB Power OK)
1. Set your radio to **Range Test / Low Power mode** (0.01mW on ELRS, 0.1mW on Crossfire)
2. Walk away from the quad while watching RSSI in OSD/Goggles
3. Note the distance where LQ drops below 90% or RSSI drops below 50%
4. Full-power range is roughly **30-100x** the range test distance
### In-Flight Monitoring
- On ExpressLRS: Watch LQ first. If LQ stays at 100%, your link is perfect regardless of dBm.
- On Crossfire: Watch both RSSI and LQ. RSSI under 50% is fine if LQ is 100%.
- Set up audio warnings in your radio (EdgeTX/OpenTX) for critical values.
## Recommended Receivers and Radio Gear
A reliable radio link starts with quality hardware. UAVModel carries a full lineup of **ExpressLRS receivers, TBS Crossfire modules, and high-gain antennas** for every build size. Visit [uavmodel.com](https://uavmodel.com) to find receivers with true diversity and reliable LQ reporting.