page_title: Radio navigation
section_title: Low frequency radio range
hierarchical_section_title: Radio navigation / Beam systems / Low frequency radio range
caption_attribution_description: Photo w:Low frequency radio range installation
context_page_description: Radio navigation or radionavigation is the application of radio frequencies to determine a position of an object on the Earth. Like radiolocation, it is a type of radiodetermination.
  The basic principles are measurements from/to electric beacons, especially
  Angular directions, e.g. by bearing, radio phases or interferometry,
  Distances, e.g. ranging by measurement of time of flight between one transmitter and multiple receivers or vice versa,
  Distance differences by measurement of times of arrival of signals from one transmitter to multiple receivers or vice versa
  Partly also velocity, e.g. by means of radio Doppler shift.
  Combinations of these measurement principles also are important—e.g., many radars measure range and azimuth of a target.
context_section_description: The low-frequency radio range (LFR, also other names) was the main navigation system used by aircraft for instrument flying in the 1930s and 1940s in the U.S. and other countries, until the advent of the VOR in the late 1940s. It was used for both en route navigation as well as instrument approaches.
  The ground stations consisted of a set of four antennas that projected Lorenz beams in four cardinal directions. One of the beams was "keyed" with the morse code signal "A", dit-dah, with the second beam "N", dah-dit. Flying down the centreline produced a steady tone. The beams were pointed to the next station to produce a set of airways, allowing an aircraft to travel from airport to airport by following a selected set of stations. Effective course accuracy was about three degrees, which near the station provided sufficient safety margins for instrument approaches down to low minimums. At its peak deployment, there were nearly 400 LFR stations in the US.
caption: LFR ground station
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