Rudolf Kühnhold
Encyclopedia
Rudolf Kühnhold was an experimental physicist
who is often given credit for initiating research that led to the Funkmessgerät (radio measuring device – radar) in Germany.
in the Meiningen
district of Thuringia
, Kühnhold received his higher education in physics at the University of Göttingen. After graduating with a Ph.D. in physics in 1928, he took a position at the Nachrichtenmittel-Versuchsanstalt (NVA – Experimental Institute of Communication Systems) of the Kriegsmarine
(Germany Navy) in Kiel
. There he worked in acoustical research, specifically in Unterwasser-Schall (sonar
) with the objective of improving the accuracy of detection of vessels using near-surface, underwater signals. Although his efforts led to a patent, and in 1931, he was promoted to Scientific Director of the NVA, he became convinced that the desired accuracy would only be attained by using electromagnetic, rather than acoustical, techniques.
s. A reflecting target was set up at 2-km distance. The transmitter produced only 0.1 watt – too small for the 4-km total path – and the experiment failed.
For further experiments, Kühnhold turned to Paul-Gunther Erbsloh and Hans-Karl von Willisen, amateur radio operators who had started a project in a narrow-beam, VHF system for secure communications. For the effort, In January 1934, Erbsloh and von Willisen, with backing from Kühnhold, formed a new company – Gesellschaft für Electroakustische und Mechanische Apparate. From the start, this firm was always called simply GEMA.
A split-anode magnetron, producing 70 W at 50 cm (600 MHz) was purchased from the Philips
Research Laboratory in Holland. Hans E. Hollmann
and Jakob Theodor J. Schultes, both affiliated with the prestigious Heinrich Hertz Institute in Berlin, were added as consultants for developing a regenerative receiver
and Yagi antenna
s, respectively.
The transmitting and receiving antennas were set up some distance apart. In June 1934, large vessels passing through the Kiev Harbor were detected by Doppler
interference at a distance of about 2 km. The apparatus had poor reliability of detection due to frequency instability of the magnetron, a characteristic of all early split-anode devices.
At that time, the success of a number of researchers in using pulsed-transmission for measuring the height of the ionosphere was well known. Also, underwater acoustical detection used pulsed transmission. Thus, Kühnhold and the GEMA team turned their attention to developing a pulsed radio system for combined detection and range determination.
Their pulsed system used a new Philips magnetron with better frequency stability. It was modulated with 2-ms pulses at a pulse repetition frequency (PRF) of 2000 Hz. The transmitting antenna was an array of 10 pairs of dipoles with a reflecting mesh. The wide-band regenerative circuit
used Acorn triodes from RCA
, and the receiving antenna had three pairs of dipoles and incorporated lobe switching
. A blocking device shut the receiver input when the transmitter pulsed. For displaying the range, it had a Braun tube
(a CRT), improved in the late 1920s by Manfred von Ardenne
.
The equipment was placed atop a tower at a NVA test facility beside the Lubecker Bay near Pelzerhaken. This pulse-modulated system first detected returns from woods across the bay at a range of 15 km in May 1935, but had limited success detecting a ship only a short distance out on the bay. The receiver was rebuilt, becoming a superheterodyne
set, and the system then tracked vessels at up to 8-km range.
for the Kregsmarine and the Freya
for the Luftwaffe (German Air Force); these popular sets were used throughout the war.
Kühnhold remained with the NVA and also consulted for GEMA; he is often credited in Germany as being the inventor of radar. During 1936 and 1937, in a rare cooperative activity between the services, Kühnhold and the NVA worked with Hans Plendl
on Knickebein
(Bent Leg) and other radio navigation systems at the Luftwaffe’s’’ Laboratory for Aviation.
Just before the beginning of the war and for a while thereafter, some research on microwave devices was continued by Kühnhold at the NVA (in 1939 renamed Nachrichtenmittel-versuchskommando – NVK). Aside from this, little further work on microwave systems was done in Germany until after early 1943 when a British multi-cavity magnetron was found in a downed RAF bomber. A commission was formed to assess this device, but Kühnhold and Hollmann, the two scientists who likely knew more about magnetrons than anyone else in Germany, were not included.
In 1948, the U.S. High Commissioner for Germany relaxed restrictions on ELAC and the firm formed a Nautik Division for the design and production of nautical equipment. Kühnhold joined ELAC and initiated research in commercial radar. His work there resulted in patents, included one registered in the United States in 1954. ELAC had major financial problems, resulting in selling its Nautik Division and ending Kühnhold’s professional career in the 1960s.
Experimental physics
Within the field of physics, experimental physics is the category of disciplines and sub-disciplines concerned with the observation of physical phenomena in order to gather data about the universe...
who is often given credit for initiating research that led to the Funkmessgerät (radio measuring device – radar) in Germany.
Early life
A native of SchwallungenSchwallungen
Schwallungen is a municipality in the district Schmalkalden-Meiningen, in Thuringia, Germany....
in the Meiningen
Meiningen
Meiningen is a town in Germany - located in the southern part of the state of Thuringia and is the district seat of Schmalkalden-Meiningen. It is situated on the river Werra....
district of Thuringia
Thuringia
The Free State of Thuringia is a state of Germany, located in the central part of the country.It has an area of and 2.29 million inhabitants, making it the sixth smallest by area and the fifth smallest by population of Germany's sixteen states....
, Kühnhold received his higher education in physics at the University of Göttingen. After graduating with a Ph.D. in physics in 1928, he took a position at the Nachrichtenmittel-Versuchsanstalt (NVA – Experimental Institute of Communication Systems) of the Kriegsmarine
Kriegsmarine
The Kriegsmarine was the name of the German Navy during the Nazi regime . It superseded the Kaiserliche Marine of World War I and the post-war Reichsmarine. The Kriegsmarine was one of three official branches of the Wehrmacht, the unified armed forces of Nazi Germany.The Kriegsmarine grew rapidly...
(Germany Navy) in Kiel
Kiel
Kiel is the capital and most populous city in the northern German state of Schleswig-Holstein, with a population of 238,049 .Kiel is approximately north of Hamburg. Due to its geographic location in the north of Germany, the southeast of the Jutland peninsula, and the southwestern shore of the...
. There he worked in acoustical research, specifically in Unterwasser-Schall (sonar
Sonar
Sonar is a technique that uses sound propagation to navigate, communicate with or detect other vessels...
) with the objective of improving the accuracy of detection of vessels using near-surface, underwater signals. Although his efforts led to a patent, and in 1931, he was promoted to Scientific Director of the NVA, he became convinced that the desired accuracy would only be attained by using electromagnetic, rather than acoustical, techniques.
Background
The first demonstration of radio signals for detecting ships was made in 1904 by Christian Hülsmeyer, with an apparatus called the Telemobilskop (Telemobiloscope). This device, however, could neither distinguish between multiple targets nor directly measure the distance to a target, and was thus not accepted as of practical value. Other similar sets had come forth in the intervening decades, but none were successful.Kühnhold’s approach
Kühnhold’s analytical studies indicated that a very narrow beam could solve the multiple-target problem. In 1933, he obtain transmitting and receiving sets operating at 13.5 cm (2.22 GHz), both units using Barkhausen-Kurz tubeBarkhausen-Kurz tube
The Barkhausen-Kurz tube, also called the B-K oscillator, was commonly used in early electronic systems operating in the ultra-high frequency portion of the radio spectrum.-Development:...
s. A reflecting target was set up at 2-km distance. The transmitter produced only 0.1 watt – too small for the 4-km total path – and the experiment failed.
For further experiments, Kühnhold turned to Paul-Gunther Erbsloh and Hans-Karl von Willisen, amateur radio operators who had started a project in a narrow-beam, VHF system for secure communications. For the effort, In January 1934, Erbsloh and von Willisen, with backing from Kühnhold, formed a new company – Gesellschaft für Electroakustische und Mechanische Apparate. From the start, this firm was always called simply GEMA.
A split-anode magnetron, producing 70 W at 50 cm (600 MHz) was purchased from the Philips
Philips
Koninklijke Philips Electronics N.V. , more commonly known as Philips, is a multinational Dutch electronics company....
Research Laboratory in Holland. Hans E. Hollmann
Hans Hollmann
Hans Erich Hollmann was a German electronic specialist who made several breakthroughs in the development of radar....
and Jakob Theodor J. Schultes, both affiliated with the prestigious Heinrich Hertz Institute in Berlin, were added as consultants for developing a regenerative receiver
Regenerative circuit
The regenerative circuit or "autodyne" allows an electronic signal to be amplified many times by the same vacuum tube or other active component such as a field effect transistor. It consists of an amplifying vacuum tube or transistor with its output connected to its input through a feedback...
and Yagi antenna
Yagi antenna
A Yagi-Uda array, commonly known simply as a Yagi antenna, is a directional antenna consisting of a driven element and additional parasitic elements...
s, respectively.
The transmitting and receiving antennas were set up some distance apart. In June 1934, large vessels passing through the Kiev Harbor were detected by Doppler
Doppler effect
The Doppler effect , named after Austrian physicist Christian Doppler who proposed it in 1842 in Prague, is the change in frequency of a wave for an observer moving relative to the source of the wave. It is commonly heard when a vehicle sounding a siren or horn approaches, passes, and recedes from...
interference at a distance of about 2 km. The apparatus had poor reliability of detection due to frequency instability of the magnetron, a characteristic of all early split-anode devices.
Partnership with GEMA
Kühnhold worked closely with GEMA and led their attempts to improve the continuous-wave system, but also retained his position at the NVA. In October 1934, strong reflections were observed from an aircraft that happened to fly through the beam; this opened consideration of targets other than ships and brought funding from NVA.At that time, the success of a number of researchers in using pulsed-transmission for measuring the height of the ionosphere was well known. Also, underwater acoustical detection used pulsed transmission. Thus, Kühnhold and the GEMA team turned their attention to developing a pulsed radio system for combined detection and range determination.
Their pulsed system used a new Philips magnetron with better frequency stability. It was modulated with 2-ms pulses at a pulse repetition frequency (PRF) of 2000 Hz. The transmitting antenna was an array of 10 pairs of dipoles with a reflecting mesh. The wide-band regenerative circuit
Regenerative circuit
The regenerative circuit or "autodyne" allows an electronic signal to be amplified many times by the same vacuum tube or other active component such as a field effect transistor. It consists of an amplifying vacuum tube or transistor with its output connected to its input through a feedback...
used Acorn triodes from RCA
RCA
RCA Corporation, founded as the Radio Corporation of America, was an American electronics company in existence from 1919 to 1986. The RCA trademark is currently owned by the French conglomerate Technicolor SA through RCA Trademark Management S.A., a company owned by Technicolor...
, and the receiving antenna had three pairs of dipoles and incorporated lobe switching
Lobe switching
Lobe switching is a method used on early radar sets to improve tracking accuracy. It used two slightly separated antenna elements to send the beam slightly to either side of the midline of the antenna, switching between the two to find which one gave the stronger return, thereby indicating which...
. A blocking device shut the receiver input when the transmitter pulsed. For displaying the range, it had a Braun tube
Cathode ray tube
The cathode ray tube is a vacuum tube containing an electron gun and a fluorescent screen used to view images. It has a means to accelerate and deflect the electron beam onto the fluorescent screen to create the images. The image may represent electrical waveforms , pictures , radar targets and...
(a CRT), improved in the late 1920s by Manfred von Ardenne
Manfred von Ardenne
Manfred von Ardenne was a German research and applied physicist and inventor. He took out approximately 600 patents in fields including electron microscopy, medical technology, nuclear technology, plasma physics, and radio and television technology...
.
The equipment was placed atop a tower at a NVA test facility beside the Lubecker Bay near Pelzerhaken. This pulse-modulated system first detected returns from woods across the bay at a range of 15 km in May 1935, but had limited success detecting a ship only a short distance out on the bay. The receiver was rebuilt, becoming a superheterodyne
Superheterodyne receiver
In electronics, a superheterodyne receiver uses frequency mixing or heterodyning to convert a received signal to a fixed intermediate frequency, which can be more conveniently processed than the original radio carrier frequency...
set, and the system then tracked vessels at up to 8-km range.
Demonstration
In September 1935, Kühnhold led a demonstration of his system given to the Commander-in-Chief of the Kriegsmarine. The equipment performance was excellent, and the apparatus was given the code name Dezimeter-Telegraphie or simply DeTe. From this time onward, GEMA had total responsibility for additional development of the system. The basic DeTe eventually evolved into the SeetaktSeetakt radar
The shipborne Seetakt radar was developed in the 1930s and was used by the German Navy during World War II.In Germany during the late 1920s, Hans Hollmann began working in the field of microwaves, which were to later become the basis of almost all radar systems. In 1935 he published Physics and...
for the Kregsmarine and the Freya
Freya radar
Freya was an early warning radar deployed by Germany during World War II, named after the Norse Goddess Freyja. During the war over a thousand stations were built. A naval version operating on a slightly different wavelength was also developed as Seetakt...
for the Luftwaffe (German Air Force); these popular sets were used throughout the war.
Kühnhold remained with the NVA and also consulted for GEMA; he is often credited in Germany as being the inventor of radar. During 1936 and 1937, in a rare cooperative activity between the services, Kühnhold and the NVA worked with Hans Plendl
Johannes Plendl
Johannes "Hans" Plendl , German radar pioneer, was the scientist whose radio navigation techniques made possible the early German bombing successes in World War II.-Biography:...
on Knickebein
Battle of the beams
The Battle of the Beams was a period early in the Second World War when bombers of the German Air Force used a number of increasingly accurate systems of radio navigation for night bombing. British "scientific intelligence" at the Air Ministry fought back with a variety of increasingly effective...
(Bent Leg) and other radio navigation systems at the Luftwaffe’s’’ Laboratory for Aviation.
Just before the beginning of the war and for a while thereafter, some research on microwave devices was continued by Kühnhold at the NVA (in 1939 renamed Nachrichtenmittel-versuchskommando – NVK). Aside from this, little further work on microwave systems was done in Germany until after early 1943 when a British multi-cavity magnetron was found in a downed RAF bomber. A commission was formed to assess this device, but Kühnhold and Hollmann, the two scientists who likely knew more about magnetrons than anyone else in Germany, were not included.
Post-war career
For the remainder of the war, most of Kühnhold’s research at the NVK was in underwater acoustic techniques, working closely with the firm Electroacoustik GmbH (ELAC) in Kiev. Founded in 1926, ELAC was the primary supplier of echo-sounding (sonar) equipment for the Kregsmarine, with a staff that peaked near 5,000. When the war ended in May 1945, the NVK was closed, and ELAC was restricted to commercial audio products and reduced to a small number of employees.In 1948, the U.S. High Commissioner for Germany relaxed restrictions on ELAC and the firm formed a Nautik Division for the design and production of nautical equipment. Kühnhold joined ELAC and initiated research in commercial radar. His work there resulted in patents, included one registered in the United States in 1954. ELAC had major financial problems, resulting in selling its Nautik Division and ending Kühnhold’s professional career in the 1960s.
General references
- Kendal, Brian; “An Overview of the Development and Introduction of Ground Radar to 1945,” Journal of Navigation, vol. 56, no. 3, 2003, pp. 343–352
- Kummritz, H.; “German radar development up to 1945,” pp. 209–226, in Development to 1945, Russell Burns (editor), Peter Peregrinus Ltd, 1988; ISBN 0-86341-139-8
- Trenkle, Fritz; Die deutschen Funkmeßverfahren bis 1945, Verlag, 1986; ISBN 3-7785-1400-8
- Watson, Raymond C., Jr.; Radar Origins Worldwid, Trafford Publishing, 2009; ISBN 978-1-4269-2111-7