Editing Radio navigation (section)

===Reverse RDF===
[[File:The 'Black Beacon', Orford Ness - geograph.org.uk - 935140.jpg|thumb|right|The Orfordness Beacon as it appears today.]]
The main problem with RDF is that it required a special antenna on the vehicle, which may not be easy to mount on smaller vehicles or single-crew aircraft. A smaller problem is that the accuracy of the system is based to a degree on the size of the antenna, but larger antennas would likewise make the installation more difficult.{{fact|date=July 2022}}

During the era between [[World War I]] and [[World War II]], a number of systems were introduced that placed the rotating antenna on the ground. As the antenna rotated through a fixed position, typically due north, the antenna was keyed with the [[morse code]] signal of the station's identification letters so the receiver could ensure they were listening to the right station. Then they waited for the signal to either peak or disappear as the antenna briefly pointed in their direction. By timing the delay between the morse signal and the peak/null, then dividing by the known rotational rate of the station, the bearing of the station could be calculated.{{fact|date=July 2022}}

The first such system was the German [[Telefunken Kompass Sender]], which began operations in 1907 and was used operationally by the [[Zeppelin]] fleet until 1918.<ref name=bauer2004>{{cite web|last=Bauer|first=Arthur O.|title=Some historical and technical aspects of radio navigation, in Germany, over the period 1907 to 1945|url=http://www.cdvandt.org/Navigati.pdf|access-date=25 July 2013|date=Dec 26, 2004}}</ref>  An improved version was introduced by the UK as the [[Orfordness Beacon]] in 1929 and used until the mid-1930s. A number of improved versions followed, replacing the mechanical motion of the antennas with phasing techniques that produced the same output pattern with no moving parts. One of the longest lasting examples was [[Sonne (navigation)|Sonne]], which went into operation just before [[World War II]] and was used operationally under the name Consol until 1991. The modern VOR system is based on the same principles (see below).{{fact|date=July 2022}}