In 1932, during the economic depression, the radio receiver laboratories of AEG and Siemens were incorporated into Telefunken. Erich Zepler became the Head of Design for Receivers and Direction Finders, with responsibility for commercial and military equipment. Also, some small transmitters were designed. His department developed equipment for the state-owned broadcasting organisation, and for marine communications. An example of its work for the military sector was the FuG III transceiver used by the Luftwaffe.

Erich Zepler published articles on a wide range of subjects, many of them in Telefunken-Zeitung. Selected at random, some of these subjects were antenna coupling, feedback HF amplifiers, airborne and shipborne direction-finding equipment, and radio equipment for aircraft and for the steamship “Bremen”.

When he left Telefunken at the end of 1935 he had 37 individual patents and 22 joint patents to his name. Again selected at random, there were Zepler patents on “Selection of coupling”, “Drum switch”, “Grid input negative feedback”, “Smooth feedback operation” and “Direction finding equipment with inductive tuning”. Clearly he was an exceptionally inventive engineer, who stimulated the technical work of his large department by a stream of novel ideas, and had the energy to pursue many diverse projects.