About Transmitter Hunting
Transmitter hunting is an activity that is primarily performed by three communities : ( 1 ) Amateur radio operators, ( 2 ) Member of government and volunteer aviation communities, and ( 3 ) Members of government and volunteer nautical communities. Some law enforcement activities also involve transmitter hunting, and other ( smaller ) communities also employ T-hunting, such as sportsmen with hunting dogs, amateur rocketry groups, etc.
The Amateur Radio Community
Amateur radio operators typically perform transmitter hunting as a social activity, usually sponsored by a club, perhaps once a month. One member of the club will "hide" with a transmitter, while the others try to find him/her. Various rules are defined to guide the hunt, and the hunts are generally limited to a few hours duration, to ensure the activity remains enjoyable.
It sounds somewhat corny and maybe even childish, but they are actually a lot of fun, bearing similarities to a collegiate "scavenger" hunt. These hunts also appeal directly to very ancient, primal hunting emotions that sometimes can reach feverish levels… all in a context that is otherwise innocent and quite harmless… They represent a chance to experience ( first hand ) a complex blend of primitive emotions coupled to sophisticated reasoning processes, all guided by radio hunting technology.
Transmitter hunting by amateurs is sometimes used in a more serious way… to track down malicious interference from other hams, or from people who have stolen amateur equipment and use it to amuse themselves by being radio "pests". Accidental interference from malfunctioning radio equipment can also pose big problems, both for amateurs and for commercial radio systems. Since most commercial radio systems are maintained by technical people who are also radio amateurs, the hunting skills they develop in amateur radio T-hunts are often directly applied in commercial situations, too.
Transmitter hunting in Europe also includes pedestrian hunts in woodland areas, with highly formalized rules and multiple transmitters. Dopplers are not really suitable for these hunts, but they deserve mention… International championships are held each year, with competing teams from many nations participating, and they are usually major events in the communities where they are held.
The Aviation Community
The aviation community employs DF hunting to locate signals from emergency beacon transmitters. These beacons ( operating at 121.5 MHz ) are installed on a wide variety of aircraft, even very small ones, and they are designed to trigger automatically in the event of a crash. Quite often, ( in fact, too often ) they will "false alarm" and generate an emergency signal when no emergency exists. In these cases, they must be located and silenced in order to keep the radio channel clear, in case a real emergency occurs with some other aircraft. This activity is sometimes performed by the FAA, sometimes by airport security personnel, and sometimes by members of a quasi-government volunteer group called the Civil Air Patrol. ( CAP )
The Nautical Community
The nautical community faces a problem similar to the aviation community… "false alarm" beacon transmitters ( at 121.5 MHz ) must be located and silenced, to keep this emergency channel clear. The nautical community also reserves VHF channel 16 ( 156.8 MHz ) for calling and distress communications, and this channel must also be kept clear. Channel 16 ( by law ) is routinely monitored by all vessels, so it is used to "call" one vessel from another. Once contact is made on channel 16, the two vessels must move to a different channel, to continue their conversation. This leaves channel 16 clear for other calls, including emergency calls.
There are 88 VHF nautical channels, so this method ensures that one specific channel is "reserved" to make contact with other vessels, instead of laboriously making calls on all 88 channels, "searching" for the specific channel that the other vessel is monitoring. Since channel 16 is heavily populated with "listening" vessels, ( waiting for possible calls ) it makes perfect sense to also use this channel for distress calls, since the probability is far greater of contacting a "nearby" vessel on channel 16, which can render assistance in a rescue, or relay the distress message to the Coast Guard.
All too often, the wear and tear on the microphone cords of nautical VHF radios causes a transmitter to "key down" accidentally, due to a badly frayed cord. Since these radios routinely are set to channel 16 when not actually in use, this "jams up" the channel, for a distance of several dozen miles, in all directions. Radio calls to the offending vessel are useless, because they cannot receive messages while transmitting, and therefore cannot hear the calls. Transmitters have a small indicator light to show they are transmitting, but this is easy to overlook, similar to a vehicle driver who has forgotten to switch off a turn indicator light.
These accidental transmissions can sometimes go on for days or even weeks, since many recreational vessels are normally left unattended in marinas, and used only occasionally. The VHF radios are usually connected directly to the vessel’s batteries, to ensure the VHF radio will be available in an emergency, should the need arise. Therefore, the transmissions will continue until the battery goes dead, which can take a VERY long time for a battery designed to start a diesel engine.
When these events occur, the transmitter must be laboriously tracked down and silenced, to restore normal operation of VHF channel 16. This is routinely done by the Coast Guard, the ( municipal ) Harbor Patrol, or quasi-government volunteers in the Coast Guard Auxiliary.
DF Technology : Now and the Future
All of these communities require DF equipment, to perform important jobs, and these jobs are getting bigger and bigger each year. The increasing use of the radio spectrum to provide wireless services, control and data links will make the need for this technology even greater in the future, as interference levels rise with the increasing radio "population".
Radios offer the promise of transmitting huge volumes of data, transactions or messages across vast distance without the expense of cable or wire installations, but they are also vulnerable to interference, either deliberate or accidental. Few people realize how powerless they are to locate a radio signal, until they actually need to do it…
There is perhaps nothing more discouraging than listening to a distress call on a radio, with absolutely no way to determine where the call is coming from…
There is perhaps nothing more irritating that listening to a fool who chooses to make life miserable for hundreds of people by jamming a popular radio channel.
There is perhaps nothing harder to explain to a superior than the fact that a wireless data link handling an important part of a company’s business has been rendered unreliable or useless by some unknown source of interference, probably caused because someone else ( in a ten mile circle ) is not properly maintaining their radio equipment.