|The story of detection and
ranging on metallic objects by means of reflected high-frequency radio
impulses dates back to 30 April 1904, when the German engineer Christian
Hülsmeyer registered German and foreign patents for an apparatus the
called the Telemobiloscope. The basis for his invention was not,
however, new, as far back as 1886 Heinrich Hertz, then working at the University
of Karlsruhe, had shown, in indoor demonstrations, that electromagnetic
waves are reflected by other electric inductors. Nevertheless, Hülsmeyer
was too far ahead of his invention; even Telefunken rejected an offer to
buy his patents.
During the First World War the son of the newspaper publisher August Scherl, Richard Scherl, also hit on the idea of using radio echoes for detection, without knowledge of Hülsmeyer's previous work. Together with a well-known contemporary sience fiction writer, Hans Dominik, he designed the Raypointer (Strahlenzieler) and successfully produced an experimental set working on a 10cm wavelength. He sent details of his apparatus to the Imperial German Navy in February 1916, but his suggestions rejected as 'not being importance to the war effort'. Again, the inventor was ahead of his time; technology would in fact need decades to provide the necessary operational reliability to match the far-sighted ideas of Hülsmeyer and Scherl.
In the Summer of 1926, the Americans Breit and Tuve became the first to use the principles of radar to measure the returning echo of the earth's ionosphere. Also in the 1920s an international army of enthusiastic radio amateurs discovered, and brought to general attention, the field of high-frequency electromagnetic waves, and thus opened the way for a realization of the potential of radar, the idea being taken up almost simultaneously in France, Great Britain the USA and Germany.