Editing Radio navigation (section)

==Beam systems==
[[Radio beam|Beam]] systems broadcast narrow signals in the sky, and navigation is accomplished by keeping the aircraft centred in the beam. A number of stations are used to create an [[Airway (aviation)|airway]], with the navigator tuning in different stations along the direction of travel. These systems were common in the era when electronics were large and expensive, as they placed minimum requirements on the receivers – they were simply voice radio sets tuned to the selected frequencies. However, they did not provide navigation outside of the beams, and were thus less flexible in use. The rapid miniaturization of electronics during and after World War II made systems like VOR practical, and most beam systems rapidly disappeared.{{fact|date=July 2022}}

===Lorenz===
{{Main|Lorenz beam}}
In the post-World War I era, the Lorenz company of Germany developed a means of projecting two narrow radio signals with a slight overlap in the center. By broadcasting different audio signals in the two beams, the receiver could position themselves very accurately down the centreline by listening to the signal in their headphones. The system was accurate to less than a degree in some forms.{{fact|date=July 2022}}

Originally known as "Ultrakurzwellen-Landefunkfeuer" (LFF), or simply "Leitstrahl" (guiding beam), little money was available to develop a network of stations. The first widespread radio navigation network, using Low and Medium Frequencies, was instead led by the US (see LFF, below). Development was restarted in Germany in the 1930s as a short-range system deployed at airports as a [[Instrument approach|blind landing]] aid. Although there was some interest in deploying a medium-range system like the US LFF, deployment had not yet started when the beam system was combined with the Orfordness timing concepts to produce the highly accurate [[Sonne (navigation)|Sonne]] system. In all of these roles, the system was generically known simply as a "Lorenz beam".  Lorenz was an early predecessor to the modern [[Instrument Landing System]].{{fact|date=July 2022}}

In the immediate pre-World War II era the same concept was also developed as a blind-bombing system. This used very large antennas to provide the required accuracy at long distances (over England), and very powerful transmitters. Two such beams were used, crossing over the target to triangulate it. Bombers would enter one of the beams and use it for guidance until they heard the second one in a second radio receiver, using that signal to time the dropping of their bombs. The system was highly accurate, and the '[[Battle of the Beams]]' broke out when [[United Kingdom]] [[intelligence service]]s attempted, and then succeeded, in rendering the system useless through [[electronic warfare]].{{fact|date=July 2022}}

===Low-frequency radio range===
{{Main|Low frequency radio range}}
[[File:LFR-photo.jpg|thumb|LFR ground station]]
The low-frequency radio range (LFR, also "Four Course Radio Range" among other names) was the main navigation system used by aircraft for [[Instrument flight rules|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 approach]]es.{{fact|date=July 2022}}

The ground stations consisted of a set of four antennas that projected two overlapping directional figure-eight signal patterns at a 90-degree angle to each other. One of these patterns was "keyed" with the Morse code signal "A", dit-dah, and the second pattern "N", dah-dit.  This created two opposed "A" quadrants and two opposed "N" quadrants around the station.  The borders between these quadrants created four course legs or "beams" and if the pilot flew down these lines, the "A" and "N" signal merged into a steady "on course" tone and the pilot was "on the beam". If the pilot deviated to either side the "A" or "N" tone would become louder and the pilot knew to make a correction. The beams were typically aligned with other stations to produce a set of [[Airway (aviation)|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 approach]]es down to low minimums. At its peak deployment, there were over 400 LFR stations in the US.<ref>{{Cite web |url=https://flyingthebeams.com/ |title=Low Frequency Radio Range, Flying the Beam |access-date=2021-02-01 |archive-date=2021-01-16 |archive-url=https://web.archive.org/web/20210116050317/https://flyingthebeams.com/ |url-status=dead }}</ref>

=== Glide path and the localizer of ILS ===
The remaining widely used beam systems are '''glide path''' and the '''localizer''' of the ''[[instrument landing system]]'' (ILS). ILS uses a ''localizer'' to provide horizontal position and ''glide path'' to provide vertical positioning. ILS can provide enough accuracy and redundancy to allow automated landings.<br />
For more information see also: {{main|Instrument landing system glide path|Instrument landing system localizer}}