Radio navigation allows an operator to use radio frequencies to pinpoint a specific position on a map, and is relative to radio location and radio determination.  Radio navigation functions by using measurements to and from electric beacons.  In particular, radio navigation gives the user directions through bearing, radio phases or interferometry.  Users can determine distances by ranging or measurements of travel times.  It also assists the user partly through velocity by means of radio Doppler shift in radar.  Rapid advances in technology has meant a corresponding rapid increase in the usefulness of radio navigation.  Radio navigation systems use a type of directional radio antenna to pinpoint the location of a broadcast location on the ground, while conventional navigation techniques allow the user to make a radio fix on a map.  Today radio navigation is used in a variety of applications ranging from commercial to military, however it has been made mostly obsolete by GPS navigation.  In this article we will take a look at the history of radio navigation and its applications.

Radio navigation has been in use for a long a time.  The first radio navigation systems were introduced before World War I and they were sound enough to still be useful today.  Radio direction finding (RDF) allows the user to tune into a radio station and use a directional antenna to find the direction of the broadcasting antenna.  Then another measurement is taken using another radio station.  The user can then triangulate their location by plotting the intersection between the two points and the navigator.  This form of radio navigation was heavily used by both ships and early aircraft. Commercial AM radio stations can be used for radio direction finding, but as this form of navigation became common, low-power radio beacons were set up near airports and harbors to aid in this type of navigation.  It uses loop antennas that were found on most ships and aircraft before the 1950’s.

A number of improvements were quickly made to the early radio navigation systems in the days before and during World War II.  Reverse RDF placed rotating antennas on the ground that were keyed with the Morse code identification numbers of a particular radio station.  This allowed the navigator to be certain of which radio station they were using for navigation.  An early version of this was used in Germany starting in 1907 to guide Zeppelin fleets.  Further advances reduced the size and increased the accuracy of radio navigation through the use of transistors and integrated circuits.  This led to the development of the automatic direction finder (ADF) and non-directional beacons (NDB).  Beam systems were briefly used for navigation by using signals beamed from radio stations that kept the aircraft centered in the beam but were discarded because of lack of flexibility as they didn’t allow for navigation outside the beams.

Advances in radio navigation developed quickly throughout World War II and increased after the war due to the miniaturization of technology.  The development of Lorenz radio navigation was started in Germany, taken over by the United States and then restarted in Germany in the 1930’s.  It used large antennas and powerful transmitters to pinpoint locations from two or more beams, known as Lorenz beams.  Low frequency radio range (LFR) was heavily used during World War II.  It operated on a set of four antennas that projected Lorenz beams in the four cardinal directions.  One of the beams was keyed with a Morse code single that produced steady tone when flying down the center-line.  VHF omnidirectional range (VOR) was a leap forward in the 1950’s that sent out three signals- a voice signal, a continuous signal sent in all directions and a signal that rotates at 30 RPM. Localizer and instrument landing system (ILS) operate on a fan-shaped broadcast system similar to VOR.

While advances in radio technology made it increasingly useful for commercial and military transportation, the miniaturization of electronics and the increasing sophistication of transistor technology after the 1950’s and 1960’s also made it available to the public.  Over time the traditional forms of radio navigation have been largely replaced by satellite navigation systems.  Satellite systems function in much the same way as traditional radio navigation by triangulating signals.  These systems however must take into account the shifting position of the satellites they use, requiring computerization for the calculations. Satellite technology has led to the development of global positioning systems (GPS) and the obsoletion of radio navigation. GPS is the most accurate form of navigation that has ever been developed, provided that satellites (like radio towers) are in place.  It is useful almost anywhere on Earth and requires only a few satellites and relatively inexpensive technology to work.  While satellite technology has steadily replaced most previous forms radio technology today, if we ever lost the ability to maintain and operate satellites as a civilization, radio technology is the next best thing.