Fox Hunts (T-hunts)
for hidden transmitters
The BEARS hold two types of radio direction-finding events. 1) A long distance that is always held on a Sunday and always starts from the Wapping School in South Windsor, with a transmitter hidden somewhere within a 20-mile radius. For current hunt details, join the Yahoo group at CTFoxhunter@yahoogroups.com
2) Local hunts at various times during the year, either on the grounds of a social event or from a low-power fox-box hidden in the woods somewhere within the repeater's coverage area.
Every January 1 and on occasional Sunday afternoons throughout the year, one of our members acts as "the Fox" and transmits from a publically-accessible location somewhere within a 20-mile radius of the event starting point (The Wapping Elementary School, 91 Ayers Road, South Windsor, Connecticut, USA). The "Fox" transmits on 144.510 MHz simplex for one minute and pauses for five minutes, then repeats. The rest of the hunters, in cars, try to home on the signal using all kinds of different radios, antennas, doppler units, and hand held equipment. They communicate on the BEARS two-meter repeater and gather clues and bearings from other hunters (although they must use their judgment as to whether the other hunters are telling the truth or trying to throw them off. The rules change; sometimes they incentivize being the first to find the fox; sometimes being second or last is more desirable.) They have two hours to find the fox, afterwards they are talked in. The fox, meanwhile, usually has been preparing a barbecue or a hearty stew to greet the tired hunters. Additional rules: the fox must be parked on land that is publicly accessible, within sight of a road navigable by an ordinary family car. The city limits of Hartford and Springfield are excluded from the hiding places.
Details will be posted to the Yahoo group "CTFOXHUNTER"
Low Power (QRP) Hunt
These hunts begin when BEARS President Paul Gibson, N1TUP, sets a "fox-box" in a hidden location and announces the hunt is on. The transmitter is built into a weatherproof box and generally has enough battery power to last outdoors for about two weeks. During that time, anyone who wishes to try to find the box can key a certain frequency with a specific DTMF tone combination, and the transmitter's controller will respond with a Morse Code identification and a pattern of tones. Hunters may key the transmitter as many times as they need to. Those finding the fox report it by email or phone to N1TUP, while leaving it in place for others to find. This is not a timed event, it is just an exercise in operating and observational skill, since the transmitter is often camouflaged so well that even tracking the radio signal to within a few feet is not enough to spot its location.
Here are some handy links for beginners who wish to assemble a t-hunting arsenal.
The "Tape Measure Beam" is a hand-held Yagi-style directional antenna that works well with a handi-talkie type radio. Because the elements are flexible, they are easier to take into the woods without getting tangled in trees and bushes, and can be constructed inexpensively. The PVC pipe used for the beam can be easily sawed through using dental floss if you don't have a hacksaw or pipe cutting tool.
Click HERE for an article on how to build this antenna. Also see p.37 of the January 2012 issue of QST magazine for an even simpler construction technique that eliminates the need for pipe X-fittings and for stainless steel hose clamps.
An active attenuator homebrew project. When you get close to the transmitter in a T-hunt, you will find that the strong signal overwhelms your radio and seems to be coming from all directions - no matter what direction you face, your S-meter will read maximum value. You'll need a way to cut down the signal strength so you can use the S-meter on your radio to see in which direction the signal is strongest. There are "passive attenuators" available on the commercial market in both finished and kit form. These are simply boxes containing stepped-value resistors and switches to change the total value of resistance. Some hunters prefer the "active attenuator" style pictured above, which mixes the signal with a crystal-generated frequency so that you can tune your radio away from the fox box frequency and still direction-find on it. A potentiometer (that round silver thing at the top left) lets you vary the mix between the fox and the crystal frequencies, so you can adjust the signal strength to the middle of your S-meter no matter how close you get. Click HERE for directions to build the active attenuator.
Other popular aids used by our hunters:
For the 20-mile hunts, the most popular directional antennas are Yagis or Quads set on a short roof-mounted mast that can be rotated while driving. Plans for homebuilt versions and mounts are available on line or from books on direction finding.
Also popular is a doppler direction finder that uses four whip antennas mounted on a metal plate atop the car roof, connected to a high speed switching unit. By electronically switching very quickly from one antenna to the next, it is possible to sense the direction of the strongest signal almost as effectively as by rotating a directional antenna. Several kits and commercial units are available to do this.
But wait... it's not that easy
Getting a bearing using one of the above methods is only the beginning of the process, however. Radio signals do not always travel in a straight line. They refract when crossing over bodies of water, deflect near deposits of iron ore or massive metal structures, bounce off terrain and man-made objects like water towers, and rarely point in a straight line to the source. Are you running down a reflection, or the real source?
Even after one masters the art of triangulating and plotting a potential source, converting between magnetic and true compass headings, reading maps, and following a bearing -- it's still not that easy.
Our sly foxes know exactly where you are coming from, and they choose hiding places that have no entrances from that direction. So even after you figure out exactly where the signal is coming from, you may look at your GPS and still "can't get there from here!" You will often find your path blocked by a river, railroad embankment, forest with no roads, or other obstacles. It often takes comprehensive knowledge of local roads and terrain to find a way to reach the fox.
NOTE: the club has not held recent fox hunts due to the high cost of gasoline and the difficulty of mounting directional antennas on today's highly aerodynamic hybrid vehicles.
The club also highly recommends having a ride-along partner to work the radio and navigate, so the driver to concentrate on safe operation of the vehicle. This is a perfect opportunity for new hams and potential hams to ride along with an experienced hunter, so feel free to volunteer.
Once enough club members have found solutions to these problems, look for the club to resume the hunt. This part of the ham radio hobby is too much fun to give up without a fight. The New Year's Day fox hunt, for instance, will be held no matter what.
What you'll need:
- A radio
- A directional antenna
- Compass or GPS
- Variable attenuation (optional but sure helps)
- Cell phone (for the truly clueless, call after two hours)
- CAMERA!! Send photos from the hunt to AB1GL@arrl.net