Radios, receivers and transponders: what the racing rules say.

Two kinds of transmitter in the rules

IFMAR's rule books name two kinds of transmitter: "2.4GHz DSM/DSS systems" and crystal-controlled fixed-frequency transmitters (1/8 IC off-road 2024, 3.25; 1/10 IC track 2024, 2.14.3; electric off-road 2019, 2.19). Either may be used only on frequencies permitted in the organising country. The 1/8 IC off-road book (3.25) allows only frequencies of the host country's competent body, and others only with the organiser's approval.

The rules do not define how 2.4 GHz systems work. The AMA's magazine Model Aviation (David Buxton, February 2015), writing about aircraft radios that use the same kind of systems, describes them as using frequency hopping (FHSS), direct sequence (DSSS) or both. It reports that Futaba began with FHSS and added DSSS as FASST, and that Spektrum began with DSSS-only DSM, added hopping in DSM2 and then DSMX; it also names JR DMSS, Hitec AFHSS and Airtronics FHSS-x, and says receivers discard data packets that fail an error check. These are makers' system names as trade press reports them; this site makes no claim about how any of them performs.

Rules on transmitters at an event

IFMAR

• Electric Off Road (2019), 4.2: all transmitters must be inspected and approved before use.
• Electric Off Road (2019), 2.19: a driver using a fixed-frequency or 2.4 GHz system cannot ask for a delay for radio problems.
• Electric Off Road (2019), 1.13: with 2.4 GHz transmitters the transmitter impound can be dropped if all IFMAR officials, organisers and team managers agree; transmitters may then be switched on only when racing or under technical inspection, and the impound can be reinstated at any time.
• 1/10 IC track (2024), 2.14: with what the rule calls 99 percent of drivers on 2.4 GHz systems no radio impound is needed, but radios may be switched on only for the heat running and the next group warming up, with maintenance in a designated area far from the rostrum. The race director can reinstate impound after complaints from at least three countries.
• 1/8 IC track (2023) and 1/8 IC off-road (2024): transmitters are limited to the maker's recommended voltage, and external transmitter battery packs are not permitted.
• 1/8 IC off-road (2024): drivers coming down from the rostrum must hand their radio to their mechanic before going to their marshal post, on pain of a penalty.

EFRA

• Appendix 3 (2026), A 4.5: the organiser may inspect any car, its components and its transmitter at any time during the event.
• General Rules (2024), 5.3.10: mobile phones may not be used on the rostrum, pit lane or track, nor may other transmitting devices, except the drivers' radios, the driver-to-mechanic radio equipment that rule 8.6.2.b allows at certain classes, and those the organiser needs.
• General Rules (2024), 8.6: where transmitter impound is not compulsory, there must be a place next to the rostrum where drivers leave their transmitters while they marshal (8.6.7), and driver-to-mechanic radio equipment, which some classes allow, may not be carried while marshalling (8.6.2.b).

ROAR

ROAR's rule book update of 18 October 2024 deleted rule 8.15.10, which had banned turning radios on in the pits; rule 8.14.3.9 still prohibits using a radio during a race if it affects another driver's vehicle. ROAR's current rule book was not read.

Radio between driver and pit crew

The rule books differ here, each for its own events:

• IFMAR 1/10 IC track (2024) allows driver-to-mechanic radio only on designated public service bands at no more than 500 mW, through a single earpiece and within local radio rules; 2.4 GHz equipment is not allowed for this.
• IFMAR electric off-road (2019, 2.19) bans driver-to-pit radio communication that gives an advantage during heats and finals.
• EFRA Appendix 3 (2026, A 5.10) bans radio or other driver-to-pit communication deemed an advantage during any heat or final at 1/12, 1/10 track and 1/10 off-road electric events.
• EFRA General Rules (2024, 8.6.2.b) allow driver-to-mechanic radio at certain classes, only on designated public service bands at no more than 500 mW, through a single earpiece and within local radio rules, with no 2.4 GHz equipment; the rule does not list the classes.

Receivers and servos

• EFRA Appendix 3, A 4.1 and 4.2: the receiver may operate steering and motor management; using it to capture signals from sensors in the car is banned.
• IFMAR electric off-road (2019), 4.5: the receiver may have only two devices connected (normally the steering servo and the speed controller) plus an optional separate battery; and (4.2) a car may have at most two control devices.
• IFMAR 1/8 IC track (2023), 5.27: more than two servos are not allowed.
• IFMAR 1/8 IC track (2023), 5.11: the aerial must be flexible enough to bend completely under the weight of the car upside down, and a metal aerial must have its free end protected.
• Signals from the car: EFRA (A 4.4) allows no signals from the car other than the official lap-counting transponder's; IFMAR (electric off-road 2019, 4.5) bans any radio or wireless signal from the car to an outside receiver during a race that gives the driver a competitive advantage.

Transponders

Laps are counted by a transponder carried in the car. How timing works at a meeting is on timing and transponders; the equipment rules are:

• EFRA Appendix 3, A 5.1, 5.2 and 12.6: cars must allow a transponder to be fitted in a suitable position and orientation; organisers may hand out timing equipment, which the driver fits and removes; a driver using a personal transponder is entirely responsible for it working. A separate battery supply for timing equipment is allowed (A 4.1). All minimum weights apply with a personal transponder fitted (A 12.19), and GT12 uses only personal transponders (C 1.24).
• IFMAR electric off-road (2019), 1.15 and 2.18: automatic lap counting names the MyLaps system "or IFMAR approved equivalent", run in duplicate with two loops. A driver may use an IFMAR-approved personal transponder if the lap counting officials agree, but missed laps with a transponder not specified by the decoder maker are the driver's responsibility. A car starting without a transponder, or with the wrong one, is not counted, and no heat is re-run for transponder failure.
• IFMAR 1/8 IC off-road (2024), 3.9: every competitor uses their own AMB/MyLaps-compatible personal transponder, fitted to the body shell or chassis, and secure fitting is the driver's responsibility.
• IFMAR 1/8 IC track (2023) and 1/10 IC track (2024), 4.6: in qualifying a car without a transponder is not counted; in finals a manual back-up count is used; no heat or final is re-run for a missing or failed transponder.

The law comes first

IFMAR's rule books leave frequencies to what the host country permits. Which frequencies a car radio may use is set by each country's regulator and is on radio equipment rules and radio rules by country. A body's rule never makes a transmitter lawful; the regulator's rule decides.