Rudolf Kühnhold

Rudolf Kühnhold (1903–1992) was an experimental physicist who is often given credit for initiating research that led to the Funkmessgerät (radio measuring device – radar) in Germany.

A native of Schwallungen 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 – Navy Transmissions Laboratory) 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.

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 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 tubes. 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.

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