Radios and receivers: the control link, as rules and projects describe it.

Racing rules on the control link

The FAI (F9U, 2025 edition)

The FAI's F9 Drone Sports volume, 2025 edition (effective 1 May 2025), article C.1.4, allows any 2.4 GHz spread-spectrum radio-control system. Frequencies and power must comply with the host country's regulations. Organisers may list other authorised equipment, naming 868 MHz and 915 MHz modules as examples, whose output must be the lower of 100 mW or the host country's limit. The FAI's rule defers to national radio law rather than replacing it. The 2026 edition was not read; its effective date is reported as 1 January 2026 and as 1 June 2026.

The radio is also part of the FAI's safety arrangement. Each F9U pilot has a mandatory helper beside them who, in an emergency, may switch off the pilot's transmitter to trigger the model's fail-safe, which must stop the motors.

Earlier FAI texts

• 2019 edition (effective 1 May 2019, C.1.4): any 2.4 GHz spread-spectrum equipment, with frequencies and power only as authorised in the organiser's country. The organiser could authorise other equipment, the rule naming 868 MHz and 915 MHz TBS Crossfire modules, and publish a list at least one month before the event. Using non-authorised equipment could bring penalties up to disqualification.
• 2024 World Drone Racing Championship Sporting Rules (June 2024, art. 2.4): TBS Crossfire 868/915 MHz or other 900 MHz modules authorised, the radio module set to 100 mW at most, and a note that 433 MHz was not authorised in China.

MultiGP

MultiGP, an organiser, allows "any control link" in its Pro Spec class, on its class page and Pro Spec page (read 30 October 2026; its Rule Book was not read). That is a class rule for MultiGP races, and national radio law still applies.

Control-link systems, as their makers describe them

The statements below are each project's or maker's own. They were not tested for this site, and none is presented as meeting any country's radio rules.

ExpressLRS

The ExpressLRS project's GitHub README (read 30 October 2026) describes it as an open-source radio link for radio control, licensed under GPL-3.0, and says it is designed to be the best FPV racing link (the project's own claim). It supports 900 MHz, 2.4 GHz and a dual-band link, with stated maximum packet rates of 200 Hz on 900 MHz and 1000 Hz on 2.4 GHz when used with EdgeTX. The project says it is based on Semtech SX127x and SX1280 LoRa radios with Espressif or STM32 processors, and that it does not manufacture any hardware. Its receivers can output CRSF, SBUS, SUMD, HoTT, MAVLink and PWM.

TBS Crossfire

Team BlackSheep's Crossfire manual (version 2, file dated 9 August 2022) describes Crossfire as a long-range, two-way remote-control system. It claims use of the 868 MHz short-range-device band in Europe (860 to 885 MHz) and the 915 MHz ISM band in America (902 to 927 MHz under the FCC; 915 to 928 MHz in Australia).

The manual itself says the system is capable of transmissions and output power that may not be allowed in a given country, and that users must follow local radio-frequency law. It adds that radio-controlled aircraft generally must be controlled within sight. That is the maker's statement; whether any use is allowed is for the national regulator.

The CRSF protocol, and a disagreement

The TBS manual describes CRSF as TBS's own radio-to-transmitter protocol, with telemetry from version 2 and a version 3 introduced with Crossfire firmware 6.03. It describes the older PPM signal as high latency with no telemetry.

Whether CRSF is open is unclear. A reseller's pages, seen as a search summary, call it a proprietary TBS protocol, while ExpressLRS, an open-source project, lists CRSF among the protocols it supports. No official TBS protocol specification was found, so the question is unresolved here.

Radios (handsets) and their firmware

EdgeTX describes itself on its About page as open-source firmware for remote-control transmitters used in hobby RC flying, started on 6 May 2021 as a fork of OpenTX with the aim of a more optimised, touch-enabled interface. It says it is firmware, not hardware.

DJI claims its O4 Air Unit works with its own FPV Remote Controller 3 or 2. Its original Digital FPV system, announced on 31 July 2019, also included an FPV remote controller alongside the goggles, air unit and camera.

What regulators say about control bands

• Europe (CEPT): ERC Recommendation 70-03 (an active recommendation, read on 30 October 2026) lists model-control frequencies under the standard EN 300 220 at 26.99 to 27.20 MHz, 34.995 to 35.225 MHz and 40.66 to 40.70 MHz. CEPT's explanatory paper (file dated 14 February 2018) says hobby drones mostly use 2400 to 2483.5 MHz and 5725 to 5875 MHz, with other options at 433 MHz and 863 to 870 MHz, all licence-exempt general authorisations.
• Canada (Transport Canada, aviation guidance, not radio law): the Aeronautical Information Manual, RPA chapter (effective 19 March 2026), section 3.2.1.2, says most small drones use 2.4 GHz, which it describes as a part of the spectrum that needs no licence to transmit and is crowded.
• United States (FCC): the FCC's fact sheet of 7 January 2026 names "ground control stations and UAS controllers" and "data transmission devices" among the drone critical components covered by its December 2025 Covered List additions.

Power limits and licensing differ by regulator and are set out, one regulator at a time, on radio rules by country and radio equipment rules. This site does not advise on choosing, setting or changing any transmitter's frequency or power.