Overview
Docs
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
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.
80m 10 channel Transmitter
Please note: The ICS525-01 used in this transmitter is no longer manufactured. and may become increasing difficult to source. 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.
Simple DC 80m RX
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.
2m ARDF RX, ROX-2T
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. 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. The equivalent TA7613AP is used in this project.
2m Tape Yagi
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 some alternative construction methods, and integration with a 2m receiver enclosure. COAX FEED The WB2HOL yagi uses 4-way pipe connectors used to support the elements, but these are not generally available in the UK After several failed attempts to use T-piece connectors and various pipe clips to support the elements the author finally opted to use a 2-hole-fixing plastic saddle clip, designed for the Marley 21.