Radio history: from crystals and channels to 2.4 GHz.

Radio history in RC car racing has two strands that need to be kept apart. One is the law: which frequencies each country's regulator allows for models. The other is the racing rules: how bodies such as IFMAR and ROAR handled transmitters at their events. Both changed when spread-spectrum 2.4 GHz systems arrived. Much of the dated material below comes from Model Aviation, the magazine of the Academy of Model Aeronautics, whose articles were written for aircraft modellers; where a date applies only to aircraft, the page says so.

The fixed-channel era

The earliest radio detail found for a commercial RC car comes from David Palmeter's account of the Testors Mustang announced in 1966: it used three 27 MHz channels so that three cars could race at once. That rests on his reading of a 1966 trade announcement and is unconfirmed beyond his site.

Model Aviation (Bob Underwood, September 1999) describes the radios of the time. It names AM, FM, PCM and PPM as the modulation types in use, and says 27 MHz sets were legal for either air or surface use but were exposed to interference from Citizens Band radio. When car radios moved between AM, FM and PCM was not found.

United States: 72 MHz for aircraft, 75 MHz for surface models

The same Model Aviation article says 72 MHz frequencies were assigned for model aircraft in 1982 and that a similar set of 75 MHz frequencies was put into service for surface models; it gives the surface set no year of its own, so its 1982 date rests on that pairing. The FCC's own rule of that time was not read, so this rests on the magazine. The article gives further dates that it states for aircraft frequencies, not for cars:

• March 1987: seven modeller frequencies shared with commercial users phased out;
• by 1991: all of the then-current 72 MHz model frequencies in service;
• 1 March 1993: transmitters bought after this date had to be narrowband;
• 1 March 1998: older wideband transmitters stopped being legal, with a receiver rule following from 1 March 1999.

The bands still appear in the US rules read for this site. 47 CFR 95.763 lists six shared channels in the 26 to 28 MHz band, fifty in the 72 MHz band and thirty in the 75 MHz band (75.41 to 75.99 MHz). In the 5 October 2017 edition of 47 CFR 95.731, read on a mirror, the 72 MHz band is for model aircraft only, the 75 MHz band for model surface craft only, and the 26 to 28 MHz band for any kind of device; the current edition of that section was not read. Under 47 CFR 95.305 these services need no individual licence. This is US law only; other countries' rules are on radio rules by country.

Europe: 40 MHz for model control, 2001

CEPT decision ERC/DEC/(01)12, adopted on 12 March 2001 and still active (last updated 10 June 2022), harmonises four frequencies from 40.665 to 40.695 MHz for short range devices used for model control and exempts them from individual licensing. No earlier European or UK regulator history for model frequencies was looked up for this site.

2.4 GHz arrives, around late 2005

Wikipedia calls Spektrum, developed by Paul Beard, the original application of 2.4 GHz spread-spectrum radio to radio-controlled models, using a direct-sequence method it calls Digital Spectrum Modulation (DSM). That "original" label is Wikipedia's description of a maker's system, and it is the closest the sources come to naming a first 2.4 GHz system.

Whether the first production system was for cars or for aircraft is told two ways:

• Surface first: Model Aviation (Steve Kaluf, March 2007) says Spektrum's first production 2.4 GHz spread-spectrum system was for surface use, about 18 months before the review, which places it around late 2005, with the first park-flyer aircraft system following about six months later. The years are worked out from the article's relative dates.
• Aircraft in late 2005: Fly RC (15 February 2007) dates Spektrum's aircraft DSM system, the DX6 transmitter with the AR6000 receiver, to late 2005, and does not mention a surface system.

Model Aviation (David Buxton, February 2015) describes how two makers' approaches developed, without giving years. Spektrum's first system used direct sequence only (DSM), later adding frequency hopping as DSM2 and then DSMX. Futaba's first 2.4 GHz radios used frequency hopping and later added direct sequence as FASST.

How the racing rules changed

Racing rules are each body's own and are not law. The dated rule books read show both kinds of radio side by side, and the transmitter impound giving way:

• IFMAR electric off-road rules (13 November 2019): allow fixed-frequency sets and 2.4 GHz DSM/DSS systems where the organising country permits them, and say the transmitter impound can be dropped with 2.4 GHz transmitters if all IFMAR officials, organisers and team managers agree.
• IFMAR 1/8 IC off-road rules (2024): still allow either 2.4 GHz DSM/DSS systems or standard crystal transmitters, on frequencies the host country's authority permits.
• IFMAR 1/10 IC track rules (2024): say that with what the rule calls 99 percent of drivers on 2.4 GHz systems no radio impound is needed, though the race director can reinstate it after complaints from at least three countries.
• ROAR rule book update (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 car.

Gaps

• The FCC's own texts for the 27 MHz, 72 MHz and 75 MHz allocations and their dates were not read.
• No regulator history for the United Kingdom's 27 MHz and 40 MHz model bands was looked up.
• The year 2.4 GHz systems were first allowed at an IFMAR World Championship was not found.

Today's radio rules by regulator are on radio equipment rules, and the equipment itself on radios and receivers.