Homing In
The Art and Science of Radio Direction Finding (RDF)
Provided by Joe Moell, ham radio callsign KØOV. (That's K-zero-O-V)
Latest RDF News Headlines
The 25th annual CQ Worldwide Foxhunting Weekend (CQ WW FW) was May 13-14, 2023 but if your club didn't hold a hunt then, it's not too late! Start the fun now by reading the announcement at this site and my articles in the February and April 2023 issues of CQ Magazine. After that, plan a mobile or on-foot hunt for a weekend in the near future. This annual event is an ideal time for ham clubs and non-club groups around the country to enjoy this fast-growing sport. For clubs that participated in this year's CQ WW FW, the next thing to do (besides planning another hunt, of course) is send the results and photos to me for the follow-up article. Get the report form here.
The May 2023 issue of CQ Amateur Radio Magazine is now online and mailed to print subscribers. In it, my Homing In column has tales of transmitter hunters' encounters with law enforcement through the decades. Some ham radio stores may also have the February 2023 issue, in which my column has stories of mobile and on-foot foxhunts during 2022, including the annual CQ Worldwide Foxhunting Weekend. My column on radio direction finding appears in CQ Magazine four times per year. CQ Magazine is available by subscription and printed issues are sold in Amateur Radio stores. CQ is also available by subscription in digital form, viewable on PC, Mac, iPad, iPhone and Android. I welcome your input for future articles and columns, so please continue to send me your news of mobile and on-foot transmitter hunt activities.
Results and photos of the annual "Antennas In The Park" two-meter transmitter hunt and barbecue at Hillcrest Park in Fullerton on May 13 and the on-foot two-meter transmitter hunting session and barbecue at Morley Field in Balboa Park, San Diego are now in this site. The next southern California on-foot hunt will be announced here soon. Many of these sessions feature workshops for building measuring-tape two-meter yagis and active attenuators. For earliest notification of these events, you can join the southern California ARDF mailing list.
Eastern Texas hosted the 22nd USA Radio-Orienteering Championships from April 19 - 23, 2023. The site was Cooper Lake State Park near Sulfur Springs. The schedule included a practice and training day followed by foxoring, sprint and classic events on eighty meters and two meters. There is more information and a link to official results here. You can also read about the last USA Championships in Triangle, Virginia during April, 2022. USA's ARDF Championships are open to anyone of any age who can safely navigate in the woods with hand-held radio gear for several kilometers. An Amateur Radio license is not a requirement. Notice the new name for these championships. There's more about that here.
Team USA is now forming for the 21st IARU World Championships, which will take place in Liberec, Czech Republic from August 27 through September 2, 2023. There will be separate classic ARDF events on separate days for national teams on eighty meters and two meters, plus competitions in sprints and foxoring. If you are interested in traveling to Liberec as a competitor, guest, or team official, it's important that you contact the Team USA Selection Committee right away, as our Letter of Intent must be submitted soon. Read more about it here.
Central Michigan will be the site of the next USA championships of on-foot transmitter hunting. The 23rd USA Radio-Orienteering Championships will take place during October 2024 in venues near Chelsea, MI. A full week of activities is being planned, including two days of training and two days of practice, followed by competitions in sprint, foxoring and classics on two meters and eighty meters. Exact dates will be announced soon. Get more information here.
Even though it had the fewest members since 1998, ARDF Team USA brought home gold again at the 20th World ARDF Championships in Borovets, Bulgaria, August 28 through September 3, 2022. Originally scheduled for 2020, these championships were postponed twice and then relocated from Serbia to Bulgaria due to economic considerations resulting from COVID and the war in Europe. Two dozen persons had been invited to be on ARDF Team USA for these championships but most dropped out due to COVID and the last-minute changes. Get more details and a link to complete results in this site.
Arducon is a new Arduino-based transmitter controller designed by NZØI and WB8WFK specifically for ARDF on both two meters and 80 meters. It can be remotely controlled via DTMF and features transmit sequences for all ARDF events including classic, foxoring and sprint. A novel modulator board will convert the two-meter FM carrier from a handi-talkie into AM in compliance with IARU rules. Plans and user manual are online and in CQ Magazine for December 2021. Circuit boards have been built and tested.
Learn about international-rules on-foot hunting (ARDF, radio-orienteering) and how the sport is organized
Obtain RDF equipment for two-meter hunting on foot 
Attend a southern California on-foot transmitter hunt
Participate in national and world championship hunts
Learn about mobile transmitter hunting (T-Hunting) and the equipment that hunters use
Attend a southern California two-meter mobile T-hunt
Buy or build a two-meter "fox" transmitter
Learn about 80-meter transmitter hunting
More and more hams and orienteers are discovering the fun of tracking down hidden transmitters out in the woods. It's a worldwide sport with opportunities for friendly competition at home and abroad. A ham radio license isn't a requirement, but it makes it lots more fun. Learn the basics and get the international hunt rules at the "International Style Transmitter Hunting Comes to the Americas" page of this site.
The Southern California T-Hunts for Beginners page has has information about three monthly mobile hidden transmitter hunts in the Orange County area where first-timers are especially welcomed and encouraged. On two of them, there are usually some clues to help everyone eventually find the transmitter and on one, you can compare bearings with other hunters on a separate frequency. Mount some RDF gear on your vehicle and come on out!
Easy-to-use apps for Apple and Android tablets and phones can simplify bearing plotting and triangulation over short and long distances. They are useful for both on-foot and mobile transmitter hunting. Bearings can be entered manually or with the internal device compass. Some apps allow entering bearings taken by other hunters or networing with them during the hunt. One new app has an RS-232 interface to Doppler RDF sets. Read all about Foxhunt Pro, SigTrax Plus and Map-n-Compass apps in this updated compilation of Homing In columns.
Mobile hidden transmitter hunters have regularly prowled the streets in search of the elusive sources of unusual signals for more than four decades. Equipment has evolved, but the adventure and intrigue remain the same. Read "T-Hunting Then and Now -- From Gooney Birds to GPS" in this site for stories of classic mobile T-hunts in the Los Angeles area. Some of them, but not all, could be done again today. Then to find out what it's like nowadays, and to help get your club started in this activity, read "Transmitter Hunting, Southern California Style."
When it's your turn to hide the transmitter, what will you use? It depends on the range and duration of the hunt, as well as whether or not the transmitter must be unattended and automatic. It's important to match your foxbox and its location to the level of proficiency of the hunters. There are many options, and you can read about them in the Foxboxes for Mobile and On-foot Transmitter Hunts page in this site.
For three decades, international-rules radio-orienteering competitions have had two major competition days. Each participant must compete on the two-meter band and the 80-meter band. The 2012 USA and World ARDF Championships included competitions in two new events: sprints and foxoring. The sprint is a shortened form of the five-fox 80-meter ARDF run that's intended to be a demonstration for the public. Foxoring is a combination of classic orienteering and direction-finding on 80 meters. More information about these new events can be found here.
For over twenty years, I have used a special cubical quad for mobile transmitter hunting on two meters. From inside the vehicle, I can select the signal polarization. Find out why this is important, why I like this antenna and how to make one for yourself in a classic Homing In column titled "Build a Multiple-Polarization Quad."
The Agrelo DFjr Doppler RDF set has been out of production for over ten years, but there is still a great deal of interest in it. DFjr was the first inexpensive plug-and-play Doppler set designed for interface to computer mapping systems and APRS. For those who own one or are considering buying a used one, the DFjr page on this site has a downloadable manual, my 73 Magazine review, antenna system improvements, and frequently asked questions about this product.
What's "Homing In?"
Homing In refers to the process of tracking down the source of a radio or other electromagnetic signal using radio direction finding (RDF) equipment.
Homing In is also the title of my regular column on RDF that ran for 15 years in 73 Amateur Radio Today magazine, then for ten years in CQ-VHF magazine and now appears quarterly in CQ-Plus digital magazine. At this Homing In site, you will find more about these columns, plus RDF articles that I have written for other publications, including Monitoring Times, CQ VHF and QST magazines. There is also information about my comprehensive book on the subject.
Radio direction finding is used to find sources of interference to any
form of wireless electronic communications, including broadcast and two-way
radio, television, and telephones. It is also used to track missing or stolen
cars and other property. Search and rescue workers use it to find persons in
distress. Emergency Locator Transmitters in downed aircraft are tracked with
RDF techniques.
Most of the information at this site pertains to RDF equipment and techniques for Amateur Radio (ham) operators. Hams use RDF to track jamming stations and stolen equipment, but more often, they use it just for fun. Hidden transmitter hunting has been done by hams for about seventy years and it is a growing activity. T-hunting refers specifically to hunts involving hams driving in RDF-equipped vehicles. A mobile T-hunt is best described as hide-and-seek for all ages with radio gear. When you set out on a T-hunt, you never know where you'll end up, and you have no idea what you're going to find. No form of ham radio contesting is more fun! Mobile T-hunting is done in cities and towns all over the USA, and elsewhere in the world. Depending on the frequency band and the nature of the hunt, the hunters use loop, yagi, quad, doppler and time-difference-of-arrival RDF antenna systems mounted on their vehicles. Click here for for general information about mobile T-hunting or click here for beginner-level T-hunts in southern California.
Mobile T-hunting is called foxhunting in some parts of the USA, but everywhere else in the world, the terms "foxhunting" and ARDF refer to another kind of RDF contest, done completely on foot in large woods and parks. It's a map-and-compass sport similar to orienteering, with about a half-dozen "fox" transmitters to find in a period of two hours or so. Someday this sport, which is also called foxtailing, fox-teering and radio-orienteering, may become an Olympic event. Meanwhile, it's a fun-filled activity for your hamfests and Scout Jamborees. Try it, and you may find yourself at the next annual national USA ARDF Championships. You might even become a member of ARDF Team USA, which has competed in five foxhunting World Championships. Click here for for general information about radio-orienteering or click here for beginner-level ARDF events in southern California.
Keep reading---you will find lots more about foxhunting, T-hunting, and other uses of RDF at this site.
What's at the Homing In Site?
Find your topic of interest below in the complete Table of Contents (or as some call it, the Site Map). Or you can Click here for the Site Search page.
Getting Started -- The basics
RDF Topics in Print -- Read all about it
Home-built RDF Projects -- Inexpensive and educational
Commercial RDF Equipment -- Getting the most from it
Follow-up and Support -- for readers of THRDFS and Homing In
Championship Radiosports -- Taking on the world
Results, stories and photos of ARDF sessions, large and small
Volunteer Opportunities -- Use your RDF skills to help researchers and protect wildlife
Other resources
Spending a few minutes at this Homing In site will give you a jump-start into the world of transmitter hunting. After that, you can find out how to get involved in mobile T-hunts in your area by visiting local T-hunt/foxhunt web sites and contacting nearby Homing In Correspondents listed on the links page. You'll find manufacturers and suppliers of RDF gear there, too.
Joe collaborated with Tom Curlee WB6UZZ to write TRANSMITTER HUNTING---Radio Direction Finding Simplified, a comprehensive text on RDF, and has written over 280 published articles on the subject, including his monthly Homing In columns that ran for 15 years in 73 Amateur Radio Today magazine, then for ten years in CQ-VHF magazine, for one year in CQ-Plus digital magazine and now appears four times per year in CQ Magazine. As a Technical Advisor to ARRL Headquarters, he authored a chapter on RDF for The ARRL Handbook and has made more than 100 presentations on transmitter hunting to clubs, conventions, classes and seminars. As time permits, he is available for private engineering consulting.
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Contact info:
Joe Moell
PO Box 2508
Fullerton, CA 92837
k0ov@homingin.com
This page updated 23 May 2023
