RC Telemetry — RSSI, LQ, and SNR Explained

calendar Jul 13, 2026 · 4 min read · fpv elrs telemetry rssi lq snr link-quality range  ·
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Modern RC links send telemetry back from the receiver to the transmitter and OSD. Three numbers dominate: RSSI, LQ, and SNR. They measure the same link from different angles — and knowing which one to watch prevents both false alarms and missed warnings.

What Each Metric Measures

flowchart LR
    TX([Transmitter]) -->|RF signal| RX([Receiver])
    RX -->|Telemetry| TX

    subgraph "What telemetry reports"
        RSSI["RSSI (dBm)<br/>Raw signal strength<br/>at the receiver antenna"]
        LQ["LQ (%)<br/>Packet success rate<br/>over last 100 packets"]
        SNR["SNR (dB)<br/>Signal vs noise floor<br/>how much margin exists"]
    end

RSSI — Received Signal Strength Indicator

Measured in dBm (decibels relative to 1 milliwatt). More negative = weaker signal.

  • −50 dBm — excellent, very close range
  • −90 dBm — usable but approaching sensitivity limit
  • −105 dBm — near noise floor; link may struggle

RSSI tells you signal power but not whether that power is usable. A strong signal in a high-noise environment (interference) can have excellent RSSI but terrible LQ.

LQ — Link Quality (ELRS-specific)

The percentage of expected packets that were successfully received in the last 100 packet slots. This is the most reliable indicator of actual link health for ELRS.

  • 100% — every packet received; link is clean
  • 70–99% — some packet loss; quad may feel slightly less responsive
  • Below 70% — serious issues; consider landing
  • 0% — link lost

LQ dropping before RSSI drops significantly is a warning sign of interference — the signal is present but corrupted.

SNR — Signal to Noise Ratio

How far above the noise floor the signal sits. Measured in dB.

  • Positive SNR (> 5 dB) — clean link; signal clearly above noise
  • Near zero SNR — signal barely distinguishable from noise; link unreliable
  • Negative SNR — receiver is working below the noise floor using spread-spectrum techniques (ELRS is designed to work here)

ELRS can maintain a link at negative SNR values because of its spread-spectrum modulation — this is normal and expected.

ELRS-Specific Behaviour

{ "type": "line", "data": { "labels": ["100m","200m","400m","700m","1km","1.5km","2km","3km","4km","5km"], "datasets": [ { "label": "RSSI (dBm, approx 2.4GHz 250mW)", "data": [-60,-66,-72,-78,-82,-86,-89,-93,-96,-99], "borderColor": "rgba(59,130,246,1)", "backgroundColor": "transparent", "borderWidth": 2.5, "pointRadius": 3, "tension": 0.3, "fill": false, "yAxisID": "y" }, { "label": "LQ % (typical, 150Hz, good conditions)", "data": [100,100,100,100,99,97,93,85,72,55], "borderColor": "rgba(34,197,94,1)", "backgroundColor": "transparent", "borderWidth": 2.5, "pointRadius": 3, "tension": 0.3, "fill": false, "yAxisID": "y2" } ] }, "options": { "responsive": true, "interaction": { "mode": "index", "intersect": false }, "plugins": { "title": { "display": true, "text": "ELRS 2.4GHz — Approximate RSSI and LQ vs Distance (250mW, open field)" }, "legend": { "position": "bottom" } }, "scales": { "y": { "type": "linear", "position": "left", "min": -110, "max": -50, "title": { "display": true, "text": "RSSI (dBm)" } }, "y2": { "type": "linear", "position": "right", "min": 0, "max": 100, "title": { "display": true, "text": "LQ (%)" }, "grid": { "drawOnChartArea": false } } } } }

Values are approximate and vary with antenna orientation, interference, and environment.

What to Watch on OSD

For most flying, watch LQ — it tells you directly what percentage of control packets are getting through. RSSI is useful for range reference but doesn't change until you're already far out.

Recommended OSD warnings:

  • LQ < 70% — yellow warning
  • LQ < 50% — red warning, land now
  • RSSI < −100 dBm — getting close to sensitivity limit

In Betaflight OSD setup, enable LINK QUALITY and RSSI VALUE. Also add RSSI dBm VALUE for the raw power reading.

FrSky / Legacy Systems

Older FrSky links (D16, D8) report RSSI as an analogue 0–100 scale rather than dBm. A reading of 50+ is comfortable; below 30 warrants landing.

FrSky does not have LQ in the ELRS sense — it uses RSSI as the primary indicator. The absence of LQ makes it harder to detect interference-induced packet loss at close range.

Telemetry Ratio (ELRS)

ELRS telemetry is sent from RX → TX on a subset of available time slots. The ratio (e.g., 1:16) means one telemetry packet per 16 RC packets.

Higher ratio = less telemetry bandwidth = fresher, more responsive RC control at the cost of slower telemetry updates. For most flying, 1:16 or 1:8 is fine. For close-range practice, 1:4 gives faster telemetry without meaningful range impact.

Set in the ELRS LUA script on the transmitter: Telemetry Ratio.

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