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Encyclopedia > Radio direction finder

A radio direction finder, or RDF, is a device for finding the direction to a radio source. Due to radio's ability to travel very long distances "over the horizon", it makes a particularly good navigation system for ships and aircraft that might be flying at long distances from land. There are several traditions of navigation. ...


How it works

RDF's work by pointing a directional antenna in "various directions" and then listening for the direction in which the signal from a known station came through most strongly. This sort of system was widely used in the 1930s and 1940s. RDF antennas are particularly easy to spot on German World War II aircraft, as loops under the rear section of the fuselage, whereas most US aircraft enclosed the antenna in a small teardrop-shaped fairing. A yagi antenna Most simply, an antenna is an electronic component designed to send or receive radio waves. ... // Events and trends The 1930s were spent struggling for a solution to the global depression. ... // Events and trends The 1940s were dominated by World War II, the most destructive armed conflict in history. ... World War II was a truly global conflict with many facets: immense human sacrifice, fierce indoctrinations, and the use of new, extremely devastating weapons—the atom bomb being the ultimate. ... Wikiquote has a collection of quotations by or about: United States Wikinews has a related story: United States United States government CIA World Factbook Entry for United States House. ...


In more recent times the task of finding the signal has been automated in the automatic direction finder, or ADF. In this system the antenna consists of a small cylinder of wire, a solenoid that is highly directional, which is spun by a motor. The electronics listen either for the repeated "peak" in the signal, or just as commonly, the "trough" when the signal drops to zero when the antenna is at right angles to the signal. A small lamp attached to a disk is timed to spin at the same speed as the antenna, so when the peak or trough is detected the lamp flashes briefly. To the human eye it appears to be a single spot of light on top of a compass rose. In engineering, a solenoid is a mechanical device that converts energy into linear motion. ... A compass rose is a figure displaying the orientation of the cardinal directions, north, south, east and west on a map. ...


Usage in Navigation

Signals are provided in the form of radio beacons, the radio version of a lighthouse. The signal is typically a simple AM broadcast of a morse code series of letters, which the RDF can tune in to see if the beacon is "on the air". Most modern detectors can also tune in any commercial radio stations, which is particularly useful due to their high power and location near major cities. The Peggys Point lighthouse in Nova Scotia, Canada An aid for navigation and pilotage at sea, a lighthouse is a tower building or framework sending out light from a system of lamps and lenses or, in older times, from a fire. ... Amplitude modulation (AM) is a form of modulation in which the amplitude of a carrier wave is varied in direct proportion to that of a modulating signal. ... Morse code is a system of representing letters, numbers and punctuation marks by means of a code signal sent intermittently. ...


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 beacons, or NDB in the aviation world. In Norse Mythology Vor is a goddess of the Aesir. ... A Non-directional Beacon, or NDB, is a radio broadcast station in a known location, used as a navigational aid by aircraft pilots. ...


Today all such systems are being generally removed in favour of the much more accurate and user-friendly GPS system. However the low cost of ADF systems today has meant something of a comeback, whereas the expensive VOR systems will likely all be switched off before 2010. Over fifty GPS satellites such as this NAVSTAR have been launched since 1978. ... 2010 is a common year starting on Friday of the Gregorian calendar. ...


See also:

radio navigation
VOR

  Results from FactBites:
 
Radio direction finder - Wikipedia, the free encyclopedia (478 words)
RDF's work by pointing a directional antenna in "various directions" and then listening for the direction in which the signal from a known station came through most strongly.
RDF antennas are particularly easy to spot on German World War II aircraft, as loops under the rear section of the fuselage, whereas most US aircraft enclosed the antenna in a small teardrop-shaped fairing.
RDF was once the primary form of aircraft navigation, and strings of beacons were used to form "airways" from airport to airport.
Radio Direction Finder - Wikipedia (382 words)
Een Radio Direction Finder of afgekort RDF (Nederlandse term: radiorichtingzoeker) is een apparaat waarmee de richting van de bron van een radiosignaal kan worden bepaald.
RDF's werken door een richtingsgevoelige antenne in diverse richtingen te laten wijzen, en dan te bepalen uit welke richting het radiosignaal het sterkst wordt ontvangen.
RDF's kunnen op twee manieren worden gebruikt: voor plaatsbepaling van de gebruiker, of voor plaatsbepaling van een ander doel dan de gebruiker zelf.
  More results at FactBites »

 
 

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