| Radio Direction Finding |
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musseum of the military aviation.]] Radio Direction Finding, or '''RDF''', is the technique of locating the direction to a radio transmission. Together with Triangulation , radio direction finding can also be used to determine the location of a radio Transmission . There are many applications for radio direction finding, including Navigation , Disaster Response , war fighting, locating the source of Radio Frequency Interference , tracking Wild Animals , and Sport . HOW IT WORKS There are two common technical approaches to radio direction finding; one approach involves the use of Directional Antenna s, and the other exploits the effects of Doppler Shift . Directional antennas are designed to be more sensitive to received Signal s in some directions than in others. When turning such as antenna around in various directions, a signal being received will either increase or decrease in strength. All other things being equal, the direction in which the signal is strongest is the likely direction in which the Radio Transmitter is located. The movement of the antenna and the determination of the peak signal strength can be made by a human operator or can be done automatically by Electronics . Another technique for radio direction finding exploits properties of Doppler Shift . Fixed Antennas are deployed in a precise Geometric pattern and an electronics system switches between the antennas very rapidly. By computing the amount of Doppler Shift present on the signal from antenna to antenna, a direction to the signal source can be computed. At ground level, both of these techniques can suffer from anomalies of Radio Propagation . Common potential problems include reflections or Multi-path . In a multi-path situation, the radio signal may be arriving at the antenna or antennas from multiple directions, perhaps because the signal is reflecting off nearby buildings, hills, or metal structures such as fences. The strongest signal may, in fact, be coming from a reflection rather than the direct path, especially if the direct path includes Terrain features that might attenuate the signal. This can result in false directional readings. These effects are largely irrelevent for airborne Radio Direction Finder s. USAGE IN NAVIGATION Due to radio's ability to travel very long distances over the horizon, it makes a particularly good Navigation system for Ship s and Aircraft that might be travelling at long distances from Land . '' Radio Direction Finder '', or ''RDF'', is a term used to describe a navigational device for finding the direction to a Radio Transmitter source. RDF was once the primary form of aircraft navigation, and strings of Beacons were used to form "airways" from airport to airport. In the 1950s, these systems were generally being replaced by the VOR system, in which the angle to the beacon can be measured from the Signal itself, with no moving parts. Since the signal being broadcast in the RDF system is non-directional, these older beacons were referred to as '' Non-directional Beacon s'', or ''NDB'' in the Aviation world. Today, all such systems are being generally removed in favour of the much more accurate and user-friendly GPS system. USAGE IN DISASTER RESPONSE There are many forms of Radio Transmitters designed to transmit as a Beacon in the event of an Emergency . Emergency Locator Transmitter s, for example, are widely deployed on civil Aircraft . Modern emergency beacons transmit not just a simple Distress indication, but a unique identification signal and even location information (often based on GPS ) that can aid in finding the exact location of the transmitter. Not all older emergency beacon transmitters are so sophisticated, however, and even those that are might malfunction during emergency situations. The ability to locate the position of emergency beacon transmitters is still a skill taught, practiced, and used by Civil Defense and Military authorities. The Civil Air Patrol (land) and US Coast Guard (sea) are responsible for US distressed aircraft rescue mission. USAGE IN WILDLIFE TRACKING Location of radio-tagged animals by Triangulation is a widely applied research technique for studying the movement of Animal Species . The technique was first used in the early 1960s, when the technology used in Radio Transmitter s and Batteries made them small enough to attach to Wild Animals , and is now widely deployed for a variety of wildlife studies. Most tracking of wild animals that have been affixed with radio transmitter equipment is done by a field researcher using a handheld radio direction finding device. When the researcher wants to locate a particular animal, the location of the animal can be triangulated by determining the direction to the transmitter from several locations. USAGE IN SPORT Events hosted by groups and organizations that involve the use of radio direction finding skills to locate transmitters at unknown locations have been popular since the end of World War II . Many of these events were first promoted in order to practice the use of radio direction finding techniques for Disaster Response and Civil Defense purposes, or to practice locating the source of Radio Frequency Interference . Radio direction finding has flourished in several forms as a recreational activity on its own. The most popular form of the sport, worldwide, is known as Amateur Radio Direction Finding or by its international acronym ARDF. ARDF competitions take place in diverse wooded terrain and combine radio direction finding skills with the land Navigation skills promoted by the sport of Orienteering . Another form of the activity, known as " Transmitter Hunting ", "mobile T-hunting," or "fox hunting" takes place in a larger geographic area, such as the metropolitan area of a large city, and most participants travel in Motor Vehicles while attempting to locate one or more Radio Transmitter s with radio direction finding techniques. |
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