German communications engineer and alongside George Ashley Campbell, co-founder of the theory of electrical filters .
In 1903 he published a “contribution to the theory of electric oscillations”. From 1904 to 1908 he worked as a research engineer in the high voltage laboratory at the Berlin Siemens & Schuckert company.
On 1 April 1909 he was, on the recommendation of his mentor, a job as a “provisional” telegraph engineer at Imperial telegraph office trial in Berlin. He was charged here with the improvement of the then still used Bell remote speaker to make calls over longer distances. He has worked in the areas of propagation of electric currents in long cables (traveling waves) and dielectric aftereffect. His essay, “History telegraphic characters in long cables” pleased the head of the Reich Post Office, Karl Strecker , who was involved in the construction of the trans-oceanic network of telegraph cables, so much that he hired him. With the cable steamer “Stephan” he set sail, to lay cables between West Africa and Brazil.
In 1913 he was appointed professor and member of the Physical-Technical Institute. He was appointed head of the Electrical Engineering and research laboratories here in the fields of traveling waves and theory of the chain ladder, making it in 1915 to the invention of the filter chain led.
In the First World War, he worked on the improvement of the wireless stations for pilots and submarines and developed for the army to a method of secret telephony.
In December 1918 he again entered the service of the imperial post , and was director of the telegraph-office trial. He now undertook experiments to multiple telephony and led by Deutsche Post is the carrier frequency method. This process supported the reconstruction of the collapsed during the First World War-distance transport. By organizing research Wagner gained notoriety as great as his experimental research in the field of wireless technology.
After retirement he was President of the telegraph-Technical Office.
In 1924 he founded the magazine Electric communication technique.
At the Technical University of Berlin, where he taught at the same time, he became in 1925 an honorary professor appointed. In October 1926, he wrote a (now lost) Memorandum on the establishment of an Institute for the Study of electric and acoustic vibrations. In August 1927 he was appointed Foundation Professor of General theory of vibrations at the Technical University Berlin and established of the Institute for Vibration Research. As its director, he worked on the analysis of noise and noise simulation of vowels, ionosphere, etc.
Three years after the seizure of power by the Nazis interrupted his career to an abrupt halt. Since he refused to dismiss Jewish people, he was relieved of his duties in 1936.
He also was a member of the German Academy of Sciences in Berlin, Honorary Doctor of the University of Stockholm and a member of the Royal Swedish Academy of Engineering Sciences and Honorary President of the Technical University of Darmstadt.
Among the many awards bestowed to him was the Federal Cross of Merit.
On 3 September 1953, he died from a heart attack.

Link to German Wikipedia