The
Lorenz beam was a
blind-landing radio navigation system developed by
C. Lorenz AG in
Berlin. The first system had been installed in 1932 at Berlin-
Tempelhof Central Airport, followed by
Dübendorf in
Switzerland (1934) and others
all over the world. The Lorenz company referred to it simply as the
Ultrakurzwellen-Landefunkfeuer, "ultra-short-wave landing radio beacon", or LFF. In the
UK it was known as
Standard Beam Approach (SBA).
Prior to the start of WW2, the Germans deployed the system at many
Luftwaffe airfields in and outside Germany and equipped most of their
bombers with the radio equipment needed to use it. It was also adapted into
versions with much narrower and longer-range beams that was used to guide the bombers on missions over Britain, under the name
Knickebein and
X-Gerät.
Beam navigation works for a
single point in space, making it
useful for landing or bombing, but
not as a general purpose navigation system. This led to a rotating version of the same
system for air navigation known as Elektra. Further development produced a system that worked over
very long distances, hundreds or thousands of kilometres, known as
Sonne (or often,
Elektra-Sonnen) that
allowed aircraft and U-Boats to take fixes far into the Atlantic. The
British captured Sonne receivers and maps and started to use it for their
own navigation under the name Consol.
...
The
Lorenz system worked by feeding a special three-element antenna system with a
modulated radio signal. The signal was fed to the centre
dipole, which had a slightly longer
reflector element on either side set slightly back. A switch rapidly alternated the opened midpoint connection of each reflector in turn, sending the beam slightly to the left and then slightly to the right of the centreline of the runway. The beams widened as they spread from the antennas, so there was an area directly off the runway approach where the two signals overlapped. The switch was timed so it spent longer on the right side of the antenna than the left.
Lorenz used a single radio
transmitter at 33.33 MHz (
Anflugfunkfeuer) and three
antennas placed in a line parallel to the end of the
runway. The center antenna was always powered, while the other two were short-circuited by a mechanical rotary switch turned by a simple motor. This resulted in a "kidney" shaped broadcast pattern centered on one of the two "side" antennas depending on which antenna had been short-circuited. The contacts on the switch were set so that one antenna was shorted for the time to be considered a "Dot" by a morse operator and the other as a "Dash". The signal could be detected for some distance off the end of the runway, as much as 30 km. The Lorenz obtained a sharper beam than could be created by an aerial array by having two lobes of signal.
An aircraft approaching the airport would tune one of their radios to the Lorenz frequency. If the crew was on the left side of the centreline, they would hear a series of short tones followed by long pauses, meaning the aircraft was on the
"dot" side of the antenna. Hearing the "dots", they would know that they had to turn to the right in order to fly down the centreline. If the crew was on the right side of the centerline, they would hear a series of long tones followed by short pauses, meaning the aircraft was on the
"dash" side of the antenna. Hearing the "dashes", they would know that they had to turn to the left in order to fly down the centreline.
In the centre, the radio would
receive both signals, where the dots filled in the gaps in the dashes and produced a
continual signal, the so-called
"equisignal". Flying in the known direction of the runway and keeping the equisignal on the radio,
the Lorenz could guide an aircraft down a straight line with a relatively high degree of accuracy, so much so that the aircraft could then find the runway visually except in the worst conditions.
https://en.wikipedia.org/wiki/Lorenz_beam .
https://en.wikipedia.org/wiki/Battle_of_the_Beams .
