A good friend of mine who encouraged me to get my license once told me a story that will remain forever etched in my brain.
He'd finished a mobile QSO on the way to visit some friends. Instead of hanging his mic back up when he arrived, apparently it got caught in one of those ergonomic wooden-beaded seat covers. Unfortunately, he must have sat on it as well and the push-to-talk became stuck on the “on” position.
Two or three hours later, same said friend’s FRIEND got a knock on his door and was surprised to see a bunch of men he didn’t know gathered on his front porch. It was the local hams who had come to inform my friend of his stuck mic. This was my first introduction to the world of the “self-policing hams” and years later while I was trying to screw up the nerve to push the key down, I remembered it. I was so afraid I was going to screw up and the Ham Police were going to come arrest me.
Of course, now I know my friend’s stuck mic was an incredible nuisance to everyone trying to use the repeater he had unknowingly tied up. And the hams? They were participating in a tech version of Hide and Seek. While it has its roots in practical application such as the one I just described, thousands of hams participate in this game annually. It’s called fox hunting. Or T-hunting. (T being for transmitter.) Or bunny hunting. Or rabbit hunting. Or radio directional finding. But whatever you call it, ‘cause you know how we hams are about jargon, it’s big fun for a lot of hams in this world. As well as non-hams, for that matter. Since there is no transmission involved, no license is required to participate.
Transmitter hunting has been around for ages. There was even one at the second National ARRL Convention in 1927. Typically, hunts are held on the two meter band, but can be held on any band, including HF. Fox hunting is not all fun and games, however. Its roots are grounded in practical applications. Like finding stuck mics, repeater jammers, spurious emissions, intermodulation and other noise. Or locating neighborhood sources of power-line interference or TV cable leakage. T-hunters also help gather evidence to lead to the prosecution of malicious interference. These skillsets and more also have been used to locate lost hikers and downed planes. To name just a few.
On the day of a fox hunt, participants gather at the designated starting place at the specified time. While they mingle and ogle each other’s home built equipment, they are given the basic information -- frequency, approximate bounding box, time limits, etc.
At the same time, a T-hider heads for their predetermined hiding spot. At the start of the race, he or she turns on the transmitter that broadcasts a distinctive sound. The transmitter itself could be a car by the road, an HT hidden in the bushes or some other form of station. It can be stationary or it can hop about from place to place (called a “bunny”). There can even be more than one transmitter. In short, it’s the ham version of the Great Race and the only objective is: Find the transmitter. Scoring can be one of two ways, first to arrive or least distance traveled to find the fox.
There are all different types of hunts. For small areas, there are on-foot hunts. These are usually held in conjunction with a meeting or a picnic. There are mobile hunts, which as the name suggests, are primarily done in cars, but the final leg may involve walking or hiking to the treasure. There are running fox hunts, which are timed events involving topographic maps, a compass, arduous terrain and, apparently, a death wish. There are quarterly “All Day” hunts which are really more like “All Weekend” hunts. The only rule is the transmitter must be hidden in the continental US. And all participants must have a patient spouse. Or no spouse, which makes life so much easier!
So, how does one find a fox with no hounds nor rifle nor trusty steed? Believe it or not, one of the best tools in your hunting arsenal is your trusty HT and it’s S-meter. The general gist of it is, if it’s a weak S-meter signal, it’s far away. If it’s a strong S-meter signal, it's close. Or…. maybe not~! It could be you’ve gained altitude. Or you might be catching multi-path reflections. (Welcome to the fun!) Readings are taken by Radio Directional Finding (RDF) equipment to determine the likely direction of the originating signal and the hunt is on. Mobile RDF equipment can be permanently mounted to the top of vehicles or, if working in teams, held out the passenger window and rotated as needed.
RDF equipment basically relies on different types and formations of antennas. The go-to choice for single antennas are quad directional antennas, with yagis being the second choice. After that, we start to get into multiple antenna configurations. Multiples rely on Time Distance of Arrival (TDOA) readings. Basically, TDOA instruments detect which antenna receives the signal first. First is closest to the transmitter.
There are a couple of different options for multiple antenna set ups. One is the Dual Directional Antenna, which is two identical antennas mounted at a precise spacing. The Doppler Shift Antenna set up is four or more antennas set up in a precise geometric pattern. The same principle applies. Whichever antenna receives the signal first is closest to the signal.
Once you start to zone in on the prey, the signal may become so strong that the S-meter is off scale. At that point you need to start dampening down the receive signal, or attenuating, so a direction is easier to discern.
There are several ways of attenuating a signal with an HT receiver. One technique is called Body Fading. Stand in an open field and hold your HT close to your body. Slowly turn a 360 degree circle while listening to the signal. When you reach the point where you believe the signal is the weakest, you have found the "signal null”. This means the signal is coming from 180 degrees behind you. Turn around and go that-away, Holmes!
Other signal attenuation ideas include removing the rubber duck antenna, moving off frequency by 5-10kHz or wrapping the receiver in aluminum foil. (WARNING: Cover the battery charging terminals with packing tape first!) If hunting on the 2 meter band, you can also tune your receiver to the third harmonic on the 70cm band. Just take the original frequency and multiply by three.
You can gauge your distance by how much attenuation is necessary to keep the s-meter on scale. Taking multiple readings from different locations will help you triangulate a location estimation, however, if contest scoring is based on mileage, beware getting too far off the beaten path to take readings.
The more hunts you participate in, the better you get. For that reason, the T-Hider’s objective is to be sure that everyone has a good time.
For beginner hunts, transmitters will be easier to locate. As the hunt goes along, the transmitter hider may make brief transmissions to encourage the hunters to find them. After a certain amount of time, hints are increased incrementally to the location of the transmitter.
For more advanced hunts, T-hiders get more creative. They bounce signals off of large objects to create multi-path. Like a ventriloquist, the signal appears to come from somewhere it’s not. They lead hunters to come through the toughest terrain to the receiver, even though there are usually much simpler routes to be had. They camouflage transmitters or hide transmitters slightly above the ground. Or they use antenna tricks to switch the polarity of the signal between vertical and horizontal, which forces hunters to determine the appropriate antenna to use for the hunt. Or they use exotic antennas such as rhombics or helicals to put English on the signal.
You see why these things could be addictive? Try a beginner hunt or two to get a feel for it. I'll bet what you actually find, along with a transmitter, is a new addition! Or organize your own hunt. All you need is a plan, good weather and a few well-planned promos on the right club nets, and you could have a monster hunt on your hands! In the meantime, try hunting up more information on these sites.