Amateur radio direction finding
| Amateur radio direction finding | |
|---|---|
| Abbreviation | ARDF; also called radio orienteering (the ARRL's preferred term) |
| What it is | An on-foot sport combining direction finding with orienteering |
| Rules | IARU ARDF rules (Region 1 rules, Part B, 2025 version) |
| Bands | 3.5 MHz (3.510–3.600 MHz) and 144 MHz (144.500–144.900 MHz) |
| Competition | |
| Formats | Classic (both bands), Sprint and Foxoring (80 meters) |
| Classic cycle | Five transmitters, one minute each, plus a continuous finish beacon |
| Categories | M19, M21, M40, M50, M60, M70; W19, W21, W35, W45, W55, W65 |
| Latest World Championships | 22nd, Birštonas, Lithuania, August 2025 |
| In the US | |
| Organized by | ARRL ARDF Committee |
| National championships | Held each year; the 25th were near Mount Hood, Oregon, in August 2026 |
Amateur radio direction finding (ARDF) is an organized sport in which competitors run or walk through woods and fields with a map, a compass and a small receiver, finding hidden radio transmitters against the clock. It is the athletic, international form of fox hunting, and it is run under rules set by the International Amateur Radio Union (IARU), with regional and world championships. In the US the sport is increasingly called radio orienteering, the name the ARRL's ARDF committee now officially favors, because it is more descriptive and is less easily confused with hunting a transmitter by car.[1]
Classic competition
The classic event is the oldest format. On each band the organizers hide five transmitters, the foxes, plus a finish beacon. On the 80-meter band the foxes send a keyed carrier in the 3.510 to 3.600 MHz range at 1 to 5 watts; on the 2-meter band they send a tone-modulated signal between 144.500 and 144.900 MHz with a fraction of a watt to 1 watt.[2] All five share one frequency and take turns on a five-minute cycle, each sending a short Morse code identifier for one minute: MOE, MOI, MOS, MOH and MO5. The finish beacon sends MO continuously on its own frequency.[2]
Competitors must find the transmitters their category requires, in any order, and punch a control at each one. Depending on the category, a course has three to five transmitters plus the beacon and an effective length of about 4 to 12 kilometers.[2] Fastest time wins, with a time limit for finishing. At championships, two groups of categories switch bands on the second day, so everyone competes on both.[2]
Other formats
- Sprint is a short, fast event on 80 meters. Competitors find two loops of five low-power transmitters, one loop keyed slowly and the other quickly, each loop sharing a one-minute cycle of 12 seconds per transmitter. The course is planned for a winning time of about 15 minutes.[2]
- Foxoring is closer to traditional orienteering. Competitors receive a map showing approximately where each transmitter is, and the transmitters, also on 80 meters, run continuously but so weakly, about 10 milliwatts, that they must be clearly audible about 30 meters away but not at 250 meters.[2] The map gets the runner close; the receiver finds the last few meters.
Categories and championships
Competitors are grouped by gender and age. The open categories are M21 and W21. M19 and W19 are for juniors through the year they turn 19, and the older categories begin at 40 for men (M40 to M70) and at 35 for women (W35 to W65), counted by the calendar year in which the competitor reaches that age.[2]
The IARU ARDF rules are maintained by the IARU Region 1 ARDF Working Group and serve as the basis for championships in other regions. World Championships are held about every two years. Recent ones were held in Borovets, Bulgaria (2022), Liberec, Czechia (2023), and Birštonas, Lithuania (2025).[3] A separate World Youth ARDF Championships has been held since 2017; the eighth was set for Veszprém, Hungary, in July 2026.[3] Each IARU region also holds its own championships.
Radio orienteering in the United States
The ARRL's ARDF Committee administers the sport in the US and helps clubs and orienteering groups set up events.[1] The USA Radio Orienteering Championships are held each year and help choose Team USA for the World Championships.[1] The 25th USA championships, held together with the 13th IARU Region 2 championships, took place near Mount Hood, Oregon, in August 2026.[1] Team USA members pay their own way to international events.[1] At Liberec in 2023 the team won an individual silver medal in foxoring and team bronze medals.[4]
Equipment is simple. The 80-meter receivers use a small ferrite-rod loop with a sense antenna, and the 2-meter ones a small handheld Yagi; the fox hunting article describes them. For organizers, the SignalSlinger is a 5-watt, open-source 80-meter fox transmitter built for radio orienteering that supports classic, sprint and foxoring events. Its code is published on GitHub, and kits have been offered through the Backwoods Orienteering Klub, making it easier for a club to own a full set of foxes.[1]
See also
References
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 Amateur Radio Direction Finding, ARRL.
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 Rules for Championships in Amateur Radio Direction Finding, Part B (2025), IARU Region 1 ARDF Working Group, 2025.
- ↑ 3.0 3.1 Past ARDF Events, IARU Region 1.
- ↑ USA Radio Orienteering Team Brings Home Silver and Bronze Medals, ARRL, September 2023.