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)

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JOTAScouting's annual Jamboree-On-The-Air (JOTA) was October 16-18, 2020.  JOTA is an ideal time to introduce young people to all aspects of ham radio, especially hidden transmitter hunting.  Only the transmitter hider has to have a ham license!  If your club included COVID-safe transmitter hunting in this year's JOTA, please e-mail me for possible use in an upcoming article.  For more information, see the Foxhunting for Scouts page at this site.

Radio-O Year 2020 hasn't been good for on-foot hidden transmitter hunting in southern California.  Just as spring was about to usher in the usual Amateur Radio Direction Finding season, the COVID-19 pandemic struck.  Cities and counties cancelled permits for activities in parks, so the annual Antennas-In-The-Park session in Fullerton during May could not be held.  Then just as we thought that park gathering prohibitions would be relaxed somewhat, widespread wildfires broke out.  State and national forests were closed, so our annual ARDF training camp at Mt. Pinos had to be cancelled.  The forest probably will not re-open before cold mountain weather sets in.  Watch this site for news of upcoming SoCal ARDF sessions, which we hope will be able to take place before many weeks go by.  For earliest notification of these events, you can join the southern California ARDF mailing list.  If you live elsewhere, there is a calendar of upcoming ARDF sessions all over the USA.  This Homing In site also has results and photos of previous southern California radio-orienteering events.

CQThe August 2020 issue of CQ Amateur Radio Magazine is now online and has been mailed to print subscribers.  In it, my Homing In column is titled "Socially-Distanced Radio Foxhunting" and is all about how hidden transmitter hunting has changed in the days of COVID-19.  It's different nowadays, but it can be done and it has been a welcome respite from days of isolation at home for many hams.  Some ham radio stores may also have the May 2020 issue, in which my column tells how hams are helping youth in public schools near the Colorado River in Arizona and California to learn about electronics, ham radio and hidden transmitter hunting.  The kids are also designing and building a line of "fox" transmitter kits for sale.  My column on radio direction finding appears in CQ Magazine at least 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.

CQ-WWFWThe nineteenth annual CQ Worldwide Foxhunting Weekend (CQ WW FW) was May 9-10, 2020.  If your club put on a transmitter hunt, I hope you will send in a report and perhaps some good photos.  The report form is here.  If you haven't celebrated FW yet, it's not too late.  Any time is a good time for a transmitter hunt!  Large gatherings in local parks for on-foot transmitter hunting may be contrary to "safer-at-home" regulations.  However, there are many ham groups around the country that are legally enjoying in-vehicle hidden transmitter hunts, following appropriate social distancing and related precautions.  For more on Foxhunting Weekend, read the announcement at this site and my article in the February 2020 issue of CQ Magazine.

THRDFS cover Boston ARDFThe twentieth USA ARDF Championships scheduled for June 9-14, 2020 near Boston, Massachusetts were canceled due to the COVID-19 situation.  These championships will be rescheduled for a future date, to be announced here.  Events were to include two days of practice sessions followed by competitions in foxoring and sprint as well as 80m and 2m classic ARDF.  Meet Director was to be Jen Harker W5JEN.  USA's ARDF Championships are open to anyone who can safely navigate the woods with map, compass and direction-finding gear.  Medal winners will be under consideration for positions on ARDF Team USA to the ARDF World Championships.  More information is here.

ARRLMembers of the new American Radio Relay League (ARRL) ARDF Committee were officially approved at the January 2020 meeting of the ARRL Board of Directors.  In addition to the ARDF Co-Coordinators (Jerry Boyd WB8WFK and Charles Scharlau NZØI), the Board announced a member-at-large and the members of three subcommittees:  Team Selection, Sanctioning and Rules.  This article tells the purposes of the three subcommittees and the names of the members.  It also has information on the newly approved rules for ARDF competitions in the USA, which you can download from this site.

Championships iconAmateur Radio Union of Serbia (SRS) was scheduled to host the Twentieth ARDF World Championships, August 30 through September 5, 2020.  The site was to be the resort of Zlatibor, Serbia, about 230 km from Belgrade.  At least 30 countries were expected to participate, including USA.  World Championshps feature formal competitions on two meters and 80 meters, plus sprints and foxoring.  Each country may have up to three persons per age/gender category on its team.  Team USA positions are filled based on performance in recent ARDF events, but there is usually room for inexperienced foxhunters in some categories.  Get the details here.  UPDATE:  The Serbian organizers have asked IARU to postpone these championships to 2021 due to COVID-19.  All 2021 regional championships would take place in 2022, and so forth.  The decision of IARU will be reported here when available.

CQ cover AppsEasy-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.

BOK 2019The Nineteenth USA and Tenth IARU Region 2 ARDF Championships took place in beautiful forests near Raleigh, North Carolina.  Training sessions were July 28 - 31, 2019, followed by full-course classic events, sprints and foxoring from August 1 - 4.  Sponsoring organization was the Backwoods Orienteering Klub.  The USA Championships are open to anyone at any skill level, with or without a ham radio license.  Qualified medal winners may be selected for positions on USA's team to the World Championships in Serbia during 2020.  Visiting competitors from outside USA were welcome.  Get more details here, including links to results.

Quick Links to Information for Beginners
What Do You Want to Do?

CQ Mag April 2009 Learn about international-rules on-foot hunting (ARDF, radio-orienteering)

Obtain RDF equipment for two-meter hunting on foot UPDATED

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

Top-Hit Transmitter Hunting Topics

USA ARDFMore 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.

FRCThe 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!

T-hunting vehicleMobile 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."

Ammo-can foxWhen 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.

Foxoring mapFor 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.

6m LoopHave you tried transmitter hunting on the six-meter band?  A group of hams in the Riverside, California area holds Saturday morning mobile hunts on 50.3 MHz FM simplex, usually twice a year.  The next hunt will be Saturday, November 14, 2020,  Bring your hunting gear and be at the hilltop home of Will Anderson AA6DD before the hunt begins at 9:30 AM.  This is intended to be an easy hunt with the hiders waiting for you to find them within a 15-mile radius.  Most hunters will be using simple loop antennas.  Download a flyer with address and other details.  More information on six-meter RDF and results of previous hunts are now in this site.

Dual-polarization QuadFor over ten 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."

DFjrThe 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.

There are over 100 additional fact-filled pages in this site, including techniques, product information and build-it-yourself projects for radio direction finding.  For the complete Table of Contents and site search, click or scroll down.

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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.

Start of a mobile T-huntRadio 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 fifty 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.

Start of an on-foot hamfest huntMobile 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.

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Joe MoellWho is KØOV? A registered professional electronic engineer and an active Amateur Radio enthusiast since age 11, Joe Moell KØOV has 50 years of experience designing radio-frequency circuits and systems for broadcast, communications, and radar, ranging from near-DC through microwave frequencies.  He has designed new devices for radio direction finding and has written about RDF and other topics for almost every ham radio publication in the USA.  In February 1998, he was appointed by the American Radio Relay League (ARRL) as the USA's first ARDF Coordinator, to promote international-style foxhunting and to organize Team USA for international ARDF competitions.  He also conducts the annual CQ Worldwide Foxhunting Weekend.

Joe collaborated with Tom Curlee WB6UZZ to write TRANSMITTER HUNTING---Radio Direction Finding Simplified, a comprehensive text on RDF, and has written over 270 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 new 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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Surfing suggestion: For a quick start into the world of RDF and mobile hidden transmitter hunting, jump to Let's Go T-Hunting.

Please note that this Web site is built and maintained independently by Joe Moell. It is not sponsored by or affiliated with CQ Publications, 73 Amateur Radio Today, Wayne Green Enterprises, TAB/McGraw-Hill, ARRL, or any other commercial or non-commercial entity. All content is protected by applicable intellectual property laws.

Entire site Copyright © 1996-2020 Joseph D. Moell. Text, photos and original graphics may not be served or reproduced elsewhere without permission.

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This page updated 19 October 2020  





Mobile T-Hunting | ARDF/Radio-O | CQWWFW | Local Events | Wildlife Tracking | Projects
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