ELRS Configuration — Bind Phrase, FCC vs LBT

calendar Jul 13, 2026 · 3 min read · fpv elrs expressLRS radio link bind fcc lbt  ·
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ExpressLRS (ELRS) is an open-source RC link protocol known for ultra-low latency and long range. Two critical settings must match between transmitter module (TX) and receiver (RX): regulatory domain and bind phrase.

Regulatory Domain: FCC vs LBT (ELRS/CE)

ELRS firmware is compiled for a specific radio regulatory domain that determines how it hops frequencies and what transmission behavior is allowed.

DomainUsed inBehavior
FCCUSA, Canada, most of the AmericasFull frequency hopping, no listen-before-talk
LBTEU, UK, Australia, Lithuania 🇱🇹Listen-Before-Talk — checks channel before TX
CESynonym for LBT in many contextsSame as LBT; ELRS uses "LBT" in firmware

LBT (Listen Before Talk) adds a brief channel check before each transmission to comply with EU spectrum regulations. This adds a small amount of latency compared to FCC mode.

Why They Must Match

TX and RX must be flashed with the same regulatory domain. A FCC TX will not bind to an LBT RX, and vice versa. They operate on different channel sequences and timing assumptions.

Mismatched domains = no link, even at close range.

If you import a module from the USA and use it in the EU, reflash both TX and RX to LBT firmware.

Checking Your Domain

In ELRS Configurator (during a flash or update):

  • Look for the Regulatory Domain dropdown — it will show FCC_915, EU_868, ISM_2400, EU_CE_2400 etc.
  • 2.4 GHz has two builds: ISM_2400 (no LBT) and EU_CE_2400 (with LBT, for EU/CE use).

For both 900 MHz and 2.4 GHz the domain matters: TX and RX must run the same domain to link.

Bind Phrase

The bind phrase is a user-chosen passphrase that TX and RX hash into the same UID. It replaces traditional button-press binding.

  • TX module and RX must use the same bind phrase.
  • It is usually set when flashing, but can also be changed later without reflashing (e.g. via the WiFi web UI / runtime options).
  • It is optional: firmware built without a phrase uses traditional bind (bind mode on RX + Bind in the TX Lua).

Setup:

  1. Open ELRS Configurator
  2. Select your hardware target
  3. Enter your chosen bind phrase in the Binding Phrase field
  4. Select regulatory domain
  5. Flash both TX module and all receivers with identical settings
1# Example bind phrase (use something unique to you)
2MY_UNIQUE_PHRASE_2024

The phrase is hashed — it doesn't need to be secret, just consistent.

Packet Rate & Telemetry

After binding, set your preferred packet rate and telemetry ratio on the TX module LUA script (run from your radio's tools menu).

Packet rateLatencyRange trade-off
50 Hz~20 msBest range
150 Hz~6.7 msGood balance
250 Hz~4 msLow latency, shorter range
500 Hz~2 msLowest latency
F1000 / D500~1 msRace mode, very short range

For cinematic and general flying: 150 Hz is a solid default. For racing: 250 Hz or higher.

Telemetry ratio (1:n) controls how often the RX sends data back. Higher ratio = less TX time for telemetry = better link budget on RX → TX path.

Common ELRS Issues

SymptomLikely cause
No bind after flashingDifferent bind phrase or regulatory domain
Intermittent link dropsAntenna orientation; TX and RX domains differ
Telemetry not workingTelemetry ratio set to Off; wrong serial port
RSSI shows but no controlUART not configured in Betaflight; CRSF not set as receiver type

In Betaflight CLI:

1set serialrx_provider = CRSF
2set serialrx_inverted = OFF
3save

Assign the UART connected to the ELRS RX as Serial RX in the Ports tab.

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