In Amateur Radio circles, the term fox hunting refers to hunting down the location of a hidden radio transmitter. Not nearly as bloody as the pastime of the British upper crust, it can be as much fun for the fox as it is for the hunters. Basically, what is involved is a person (the fox) transmits a signal on an amateur radio frequency, following FCC guidelines, and a group of amateur radio operators try to determine the fox's location, either in a cooperative or competitive manner. Usually foxhunts are done on either the 2 meter band on VHF or 70 centimeter band on UHF, but foxhunts can be held on other frequencies as well. A foxhunt is a good way to hone skills which can be applied to more serious real world situations, such as tracking down radio interference, or finding someone who is lost or in distress.
Rules for the Fox:
The fox is allowed, and even encouraged to be crafty in order to frustrate those looking for him, but he must obey 2 sets of rules:
#1. He must abide by all FCC rules regarding amateur radio operation.
#2. He must agree on the ground rules set forth for the hunt. This usually means he must stay in one location he selects in a public place within a restricted geographic area, such as a county or township, and cannot move once he is in place. He will transmit on an agreed frequency at a certain minimum interval. Depending on the rules, the fox may or may not be allowed to use directional antennas, and his signal must be receivable at the starting point of the hunt. Often the agreed frequency will be on the input of a local repeater, which will let the rest of the ham community in the area listen in.
Strategies for the Fox
Within the rules, it is the fox's duty to make it less than easy for the hunters to track him down. It all comes down to concealment, camoflage, and craftiness. A fox carrying a handheld transceiver sitting on the bench at a little league game with dozens of people around will be a lot harder to spot than an SUV with Ham Plates and a roof bristling with antennas along a road, particularly if most of the participants know the fox and his vehicle. A crafty fox who normally drives his red Ford Bronco with a roof full of antennas to club outings might want to borrow his wife's Toyota Corolla, or ride his motorcycle instead.
Terrain can also help with concealment, hills, gullies, and urban areas can cause signals to reflect in unpredictable and confusing ways. Setting up on the opposite side of a stream or river from the direction the hunters will come can also pay rewards for the sneaky fox. I have seen crafty foxes keep hordes of hunters at bay for hours, as they stumble through the woods just yards from the fox.
Strategies for the Hunters
The job of hunting down the fox is accomplished by progressively narrowing down the area he is transmitting from. A good hunter needs to have the proper tools, and the knowledge to use them. To narrow down the location of the Fox, the hunter uses a directional antenna to get a bearing on the fox's transmitter. Small yagi and quad antennas are good choices for getting a bearing on the Fox. Once the direction is determined, a line is drawn on a map from that point on the map in the direction of the signal. The hunter then drives toward the direction of the signal, then takes another bearing, and draws a line from his new location in the direction of the signal. With 2 or more bearings taken from different location, the fox's location should start to narrow down quickly, but folks, it ain't all that easy. GPS, a good compass, and accurate, detailed maps can help, but once you get within a mile or so, signal directions often start to become indefinite, as stronger signals swamp the receiver's ability to distinguish between strong and weak signals, and terrain plays a greater role.
Working in Close
Once the hunters enter a zone close to the transmitter where signals seem to be strong in all directions, it is necessary to change tactics. Instead of using a sensitive directional antenna to acquire a bearing on a signal, it is necessary to make the radio receiver a bit hard of hearing in order to distinguish between strong and stronger signals, rather than strong and weak signals. The best way to do this is with an attentuator inserted into the line between the antenna and receiver. An attentuator is merely a dummy load which shunts most of the signal through a resistor, and passes only a small signal to the receiver. Good attentuators can be switched for different levels of attentuation, some as much as 100 decibels. Hopefully this will get the hunter close enough to pick out a familiar face from a crowd, but sometimes even this is not enough. Sometimes, it is necessary to take the antenna off completely. You can then use your body to block the signal, and in this way narrow down the area even more. By this time you should be able to study the faces of nearby people, and look for telltale signs of a cornered fox.
Once the fox is found, the hunt may continue until some more hunters arrive. Eventually, the fox's lair will be made public, and everyone will retreat to an agreed on meeting place to swap stories of the hunt. At least in our area, the reward for finding the fox first earns the winner the "honor" of being the fox the next time around.