In 1874, he discovered in Leipzig while he was working there as a secondary school teacher in the Thomasschule, that a point-contact metal–semiconductor junction rectifies alternating current.

Braun's circuit afforded a much longer sustained oscillation because the energy encountered less losses swinging between coil and Leyden Jars.

Light vessels in the river Elbe and a coast station at Cuxhaven commenced a regular radio telegraph service.

Today, the term typically refers to a high-vacuum tube in which an electron beam can be deflected in both horizontal and vertical directions.

It featured a cold cathode and a moderate vacuum, which required a 100,000 V acceleration voltage to produce a visible trace of the magnetically deflected beam.

By 1899, Braun's assistant Jonathan Zenneck introduced oscillations to magnetically control the Y deflection, and later improvements included the addition of a heated cathode, a Wehnelt cylinder, and high-vacuum technology.

Braun, as a physicist, was accustomed to working under reproducible experimental conditions, which the commonly used coherer receivers at the time failed to meet.

It was only later that the electron tube replaced the crystal detector, although devices like germanium diodes continued to be used in simpler receivers for some time.

[21] In late 1898, the technology was commercialized when the chocolate manufacturer from Cologne, Ludwig Stollwerck, founded a consortium to exploit Braun's patents, contributing 560,000 marks in capital.

After the successful transmission of signals over longer distances, the consortium was transformed into the "Professor Braun’s Telegraphy Company," which eventually became Telefunken AG, set up the first world-wide network of communications[22] and was the first in the world to sell electronic televisions with cathode-ray tubes, in Germany in 1934.

[23][24] In 1900, Stollwerck facilitated contact with Professor August Raps, head of the Siemens & Halske Telegraph Construction Company, which later took over the development of the apparatus.

While Guglielmo Marconi had developed his transmitter primarily through empirical methods, Braun was able to improve it by focusing on the underlying physics.

By 1898, the resulting powerful systems made the term "long-distance telegraphy" more appropriate, as the maximum range, previously limited to 20 km, steadily increased.

Together with Georg Graf von Arco and Adolf Slaby, Braun was part of the team that developed the concept for "mobile stations for wireless telegraphy for military purposes," which in 1903 led to a practical implementation by AEG and Siemens & Halske.

The system consisted of two horse-drawn wagons: one with all the transmitting and receiving equipment, including a battery, and the other with auxiliary and reserve supplies.