Other Electronics & Navigation

Radio navigation or radionavigation is the application of radio frequencies to determining a position on the Earth. Like radiolocation, it is a type of radiodetermination. more...

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RDF / ADF / NDB

The first system of radio navigation was the Radio Direction Finder, or RDF. By tuning in a radio station and then using a directional antenna to find the direction to the broadcasting antenna, radio sources replaced the stars and planets of celestial navigation with a system that could be used in all weather and times of day. By using triangulation, two such measurements can be plotted on a map where their intersection is the position. Commercial AM radio stations can be used for this task due to their long range and high power, but strings of low-power radio beacons were also set up specifically for this task. Early systems used a loop antenna that was rotated by hand to find the angle to the signal, while modern systems use a much more directional solenoid that is rotated rapidly by a motor, with electronics calculating the angle. These later systems were also called Automatic Direction Finders, or ADF.

Lorenz

In the 1930s German radio engineers developed a new system, called the "Ultrakurzwellen-Landefunkfeuer" (LFF), or simply "Leitstrahl" (guiding beam) but referred to outside Germany as Lorenz, the name of the company manufacturing the equipments. In Lorenz two signals were broadcast on the same frequencies from highly directional antennas with beams a few degrees wide. One was pointed slightly to the left of the other, with a small angle in the middle where they overlapped. The signals were chosen as dots and dashes, timed so that when the aircraft was in the small area in the middle the sound was continuous. Planes would fly into the beams by listening to the signal to identify which side of middle they were on, and then corrected until they were in the center.

Originally developed as a night and bad-weather landing system, in the late 1930s they also started developing long-range versions for night bombing. In this case a second set of signals were broadcast at right angles to the first, and indicated the point at which to drop the bombs. The system was highly accurate and a battle of the beams broke out when United Kingdom intelligence services attempted, and then succeeded, in rendering the system useless.

In the post-war era similar systems were widely deployed, notably in the United States where a system of long range "airways" was created spanning the country with stations about 200 miles (320km) apart. The signals were chosen as the A and N letters form morse code, dot-dash and dash-dot respectively. However, new developments soon rendered these systems obsolete.

Read more at Wikipedia.org