Overview
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About ARDF
On-foot ARDF, also known as Radio Orienteering or Radio-‘O’, has been popular in a number of countries for many years, particularly in Central and Eastern Europe. The more formal competitions, at both national and international level, conform to rules set by the International Amateur Radio Union (IARU) and use the 2m or 80m Amateur Radio bands. It is a combination of radio direction finding and foot orienteering. Five beacons are located in a wooded site and transmit for one minute, in sequence, on the same frequency.
Getting Started
Interested in IARU style ARDF but have no equipment? ON7YD 80m micro transmitter A micro power transmitter for 80m or 2m is an ideal starting point for your ARDF experience, simple enough to build on prototype board, for those with basic homebrew skills. Powered by a 9v PP3 battery, it provides a useful signal source when building receivers, and can be used for short-range ARDF. The micro transmitters schematics are reproduced from the web site of ON7YD
RSGB Events
The Radio Society of Great Britain (RSGB) is the national organization for amateur radio enthusiasts in the UK, founded in 1913. It represents, promotes, and protects the interests of licensed radio amateurs, fostering the science and practice of wireless communication. RSGB site links RSGB Home page : https://rsgb.org/main/ ARDF committee : https://rsgb.org/main/about-us/committees/ardf-committee/ ARDF site links Home page : https://ardf.thersgb.org/ Events : https://ardf.thersgb.org/events.html Results : https://ardf.thersgb.org/results.html
80m 10 channel TX
Photo above shows the transmitter enclosed in a Sistema 200ml food box for a good degree of weather protection. This 80m ARDF transmitter was designed to be multi purpose, suitable for Classic (1W minimum) , Sprint (300mW-1W) and FoxOring formats. Compact and lightweight and easy to deploy. Low component count. Multipurpose socket for charging/syncro/tune-up. Internal ATU for matching to a short wire antenna. The battery pack is mounted below the pcb.
80m 3watt TX : ATX80
CLASSIC 80M TRANSMITTER FOR RADIO ORIENTEERING The 80m TX described here is the well known ON7YD ATX-80 and timer combined on one PCB and fitted in a standard folded aluminium enclosure.( regrettably no longer manufactured !) For a full description of this popular design visit the ON7YD web site Hardware Changes (from original ON7D) Tactile button added, wired in parallel with the sync socket. Used for manual changing of the callsign ‘TUNE’ header added.
80m Short Wire Antenna
Experiments with foxOring micro transmitters using antenna 2m long or less, showed that a very short tuned, resonant antenna could be usefully detected over far greater distance than expected. As a result, various options to match a simple 5m wire antenna were investigated. At 80m, any antenna using a wire length of 8m or less , has a high input reactance with a very low radiation resistance. The ‘L’ match network used is similar to that published by AA3SJ.
80m Tiny Bug
The authors version on the ON7YD low power ARDF transmitter. To be used as a signal source or for ARDF training. Schematic: BOM: above: PP3 battery box is fixed to the back of the PCB. Antenna and ground wire added, ready to hang from a tree branch for a mini ARDF hunt or for training. Download Gerber Files : https://drive.google.com/drive/folders/10j0-jX6sPyb-9hk9q5eC4sXTpdA01c0c?usp=drive_link Reference ON7YD website: https://www.qsl.net/on7yd/ardfbrew.htm
80m Simple Receiver
A SIMPLE 80m DC RECEIVER FOR ARDF This receiver has a VXO using a ceramic resonator. The VXO is very stable, and the frequency can be pulled down to 3.51MHz using a variable capacitor. It can therefore cover the whole frequency band used in international ARDF events - 3.51MHz to 3.60MHz. However - Important - Ceramic resistors are very variable in their suitable for a VXO. Please see my post on VXOs before attempting this project.
VXO Notes
VXO using a ceramic resonator for an 80m ARDF receiver. You can find numerous articles on VXOs using ceramic resonators, but when adopting this technology on a project to build multiple receivers a few pitfalls were discovered, not knowingly discussed elsewhere. Skip to the summary at the end of this page, if you don’t want a long read ! An ARDF receiver will use a VFO to tune between 3.51Mhz to 3.
2m Receiver : ROX2-T
This receiver is based on an original design by OK2BWN in which the IF amplifier, detector and audio amplifier is provided in a single TDA1083 IC. above: SCHEMATIC: VERSION 5.3 The TDA1083 is a one chip AM/FM radio widely used in consumer radios until the early 2000’s. The TDA1083 and many pi-compatible variants have been around for a very long time so ICs should not be too difficult to obtain or salvage.
2m Receiver : ROX2-K
A receiver suitable for both AM Radio orienteering and the end game of FM foxhunts. (updated 24/05/2026) above: SCHEMATIC: VERSION B (open in new tab or save-as for larger image) The SA605 makes for a simple AM receiver. It contains a mixer good to 500 MHz, an onboard local-oscillator (LO) transistor, 80 dB of stable IF gain, and an FM-quadrature detector. This application does not use the FM detector; instead, the received signal-strength indicator (RSSI) serves to demodulate the AM signal’s sidebands.
2m Yagi : 3 ele WB2HOL
WB2HOL 3 ELE YAGI The WB2HOL yagi is a popular choice for ARDF. A link to the original design can be found at the end of this post. This page describes a construction methods for a stand-alone antenna where the receiver is connected by a coax feed. Alternatives for a collapsible and integrated antenna+receiver unit are described in a separate post. ALTERNATIVE CONSTRUCTION The WB2HOL yagi uses 4-way pipe connectors used to support the elements, but these are not generally available in the UK.
2m Yagi : 2 element
Receiver Integrated and Collapsible YAGI Overview A 3 element yagi is generally excepted as the best compromise between gain, beam width and handling size, but is still relatively large, so the attraction of a smaller option remains. The 2 element HB9CV is a popular alternative but has mechanical complexity which can make it difficult for the home constructor to build. The HB9CV is commercially available ready built, but built with the stiff aluminium tubing, so not ideal for carrying through dense forest undergrowth.