Control links and bands
The link from your hands to the aircraft is two separate agreements: the RF protocol between radio and receiver, and the serial protocol between receiver and flight controller. Confusing them is the most common source of "it should work and it does not".
Two links, not one
"ELRS" and "CRSF" are frequently listed side by side as if they were alternatives. They are not. They describe different halves of the path a stick movement takes.
The RF link protocol is the agreement between your radio and the receiver on the aircraft: ExpressLRS, TBS Crossfire, TBS Tracer, ImmersionRC Ghost, FrSky ACCST D16, FrSky ACCESS. Both ends must run the same one, and there is no adapter. This is a hard gate.
The serial protocol is the agreement between the receiver and the flight controller, over a wire inside the aircraft: CRSF, SBUS, F.Port, IBUS, GHST, SRXL2, PPM. CRSF is what both Crossfire and ExpressLRS receivers speak to a flight controller, which is exactly why it is not an alternative to ELRS: it is the wire format an ELRS receiver uses. This one is nearly always satisfiable, because almost every modern flight controller supports CRSF and SBUS.
Buildlas records these as two separate properties and checks them with two separate rules, so the hard question and the easy one are not presented to you as one decision.
- Receiver Serial ProtocolsExpressLRS documentation · Project documentation · read 2026-07-27
- Crossfire and ELRS RC SystemsArduPilot documentation · Project documentation · read 2026-07-27
- FPV Drone Receiver Protocols: SBUS, CRSF, F.Port and IBUSUAVMODEL · Editorial · read 2026-07-27
Matching protocol is not enough: the band matters too
ExpressLRS exists at 2.4 GHz and at 900 MHz, and each only works with hardware on the same frequency. A 2.4 GHz ELRS radio cannot bind a 900 MHz ELRS receiver. Same protocol, same project, still incompatible.
This is why the planner checks the band as a rule of its own, and why a radio that transmits on several bands is recorded as a set rather than a single value: a dual-band radio genuinely does bind hardware on either.
- How to Choose an ExpressLRS ReceiverOscar Liang · Editorial · read 2026-07-27
The bands
Where each one is used, and what it is good at.
| Band | Region | Character |
|---|---|---|
| 2.4 GHz | Everywhere | Shorter range for a given power, smallest antennas, most hardware choice. |
| 868 MHz | EU | The European 900 MHz band. Longer range, better penetration, larger antennas. |
| 915 MHz | US and much of the rest of the world | The same idea as 868, on a frequency that is not legal to transmit on in the EU. |
- How to Choose an ExpressLRS ReceiverOscar Liang · Editorial · read 2026-07-27
- 868 MHz Listen-Before-Talk discussionExpressLRS on GitHub · Project documentation · read 2026-07-27
Why 868 MHz hardware needs Listen-Before-Talk
The European 868 MHz band carries a duty-cycle restriction: a transmitter may only occupy the channel for a small fraction of the time. ExpressLRS hardware for this band uses Listen-Before-Talk firmware, which checks the channel is clear before transmitting, in order to operate within those rules rather than under the raw duty cycle cap.
This is a firmware property rather than a hardware one, which is why it is a thing to check on the product you are buying rather than something you can read off the frequency alone.
- 868 MHz Listen-Before-Talk discussionExpressLRS on GitHub · Project documentation · read 2026-07-27
See this against real products
The planner reads these same properties off every product in the catalog and tells you what each pairing does with your build.