In 1895, Zenneck left zoology and turned over to the new field of radio science, He became assistant to Ferdinand Braun and lecturer at "Physikalisches Institut" in Strasbourg, Alsace.

In 1899, Zenneck started propagation studies of wireless telegraphy, first over land, but then became more interested in the larger ranges that were reached over sea.

In 1909, he joined Badische Anilin und Sodafabrik in Ludwigshafen to experiment with electrical discharges in air to produce bound nitrogen as fertilizer.

However, in 1914, the German government sent him and Karl Ferdinand Braun to the United States as technical advisor in a patent case involving Telefunken.

The US Marconi Company sued Telefunken for patent infringement, a case spurred by the British government in an attempt to shut down transatlantic wireless telegraph between the US and Germany.

Zenneck was awarded the 1928 IRE Medal of Honor for his achievements in basic research on radio technology and for fostering academic and technical offspring he received the Siemens-Ring in 1956.