Karl Ferdinand Braun was born in Fulda, Germany on June 6, 1850
As a youngster Karl attended the local gymnasium, an academic grammar school that had very strict entrance requirements. He had a talent for mathematics, natural sciences and composition. Before he finished his gymnasium studies, he had had several scientific articles published in several journals.
Karl intended to teach science at the gymnasium and began a general science and mathematics curriculum at the University of Marburg. He soon transferred to the University of Berlin, where he focused on experimental physics, graduating with a Ph.D in 1872 with a paper on the oscillations of elastic rods and strings.
On completion of his studies Karl went to work for Professor Quincke at Würzburg University and, in 1874, accepted a teaching appointment at St. Thomas Gymnasium in Leipzig.
At this time, Karl was interested in the electrical conductivity of metal salts in solution (electrolytes) and this led to his study of metal sulfide crystals and other crystalline solids which conducted electricity, even when not dissolved. After much experimentation Karl was able to report, in 1874, that for many metal sulfides the electrical resistance varies with the magnitude and polarity of the applied voltage. He used the rectifying properties of the galena crystal, a semiconductor material composed of lead sulfide, to create the cat's whisker diode for this purpose. He found this phenomenon to be especially true if at least one of the electrodes was a pointed wire. In other words, Karl Ferdinand Braun had discovered the point-contact rectifier effect. He had invented the first semiconductor device. This effect had no practical application at the time but would be rediscovered over thirty years later in the form of the "cat's whisker" crystal radio detector and would be instrumental in the point-contact transistor first produced in 1948!
In 1876 Karl was appointed "Extraordinary Professor of Theoretical Physics" at the University of Marburg, and in 1880 was invited to fill a similar post at Strasbourg University. In 1883 Karl was made Professor of Physics at the Technische Hochschule in Karlsruhe and was finally invited by the University of Tübingen in 1885; one of his tasks there was to build a new Physics Institute. In 1895 Karl returned to Strasbourg as Principal of the Physics Institute, where he remained, in spite of an invitation from Leipzig University to succeed Gustav Heinrich Wiedemann as chair of physical chemistry. During these years Karl developed several electrical measurement instruments of importance to the physicists of that day.
Karls' practical experiments led him to invent what is now called Brauns' Electrometer, and a cathode-ray oscillograph, constructed in 1897. The existence of electrons (cathode rays) had been established that year and X-rays had been discovered only two years earlier. Both were of great interest to Karl. He knew that if high voltage were applied between two electrodes in a low pressure glass tube, electrons were emitted from the cathode and traveled to the anode. He also knew that certain materials would luminesce (glow) when struck by the electrons. This information was all Karl needed in 1897 to build what he called his cathode ray indicator tube (the name cathode ray tube without the word indicator included was often used in those days to refer to any evacuated tube used for studying the effects of cathode rays).
On February 15th, 1897, Karl published in the journal "Annalen der Physik und Chemie", his research results on a method to record and study the time dependance of alternating currents ("ein Verfahren zur Demonstration und zum Studium des zeitlichen Verlaufs variabler StrF6me"). He invented and developed the so-called "Braun Tube" as a fast responding recording instrument. Karl succeeded in producing a narrow stream of electrons, guided by means of alternating voltage, that could trace patterns on a fluorescent screen. This was the first cathode-ray oscilloscope.
Karl had an interest in and became involved with wireless telegraphy early in 1898. He had been hired by Ludwig Stollwerck (a highly successful candy maker who had been approached to finance and market an underwater communication system) to explain the technical principles behind a working system for underwater wireless telegraphy, which had been developed by three scientifically untrained men. It also was hoped that Karl would be able to suggest ways to increase the range of the telegraphy system. In the course of making himself familiar with the, then existing, state of wireless telegraphy, Karl soon became aware of the work of Lodge, Slaby, Marconi and others. Karl was interested in determining why both Marconi and Slaby were finding it difficult to increase the distances over which their transmissions could be received. The approach they had both used involved increasing the voltage (and, hence, energy) of the spark transmitter discharges. However, large increases in the spark voltage resulted in only small increases in the distances spanned. Although Marconi had transmitted as far as 50km, successful reception beyond 15km required disproportionately larger amounts of transmitted electrical energy. Karl studied the design of Marconis' transmitter, which had the spark gap connected directly between the antenna and ground. Karl remembered that, to increase the range of the underwater telegraphy system, he had changed the original circuit which had the antenna directly coupled to the spark discharge. In Karls' improved arrangement a primary coil was placed in the oscillation producing spark gap circuit. That coil and a loosely coupled secondary coil were used to transfer energy to the antenna. The effective communication range of the underwater system had increased even more when both the oscillator circuit and the antenna circuit were in resonance. The direct coupling of the antenna was limiting the range of Marconis' transmitter. Karl hastily improvised a test of his loose coupled antenna on September 20, 1898. Within a month of his initial test, Karl, normally a conservative fellow, predicted that his aerial wireless telegraphy equipment would be able to span distances of 100km! Stollwerck and his partners, who wanted to form a corporation for developing and marketing wireless telegraphy equipment for military and commercial applications, were jubilant. Karls' improvements effectively eliminated the Marconi patent monopoly on wireless telegraphy. The new company, which would be known as "Telebraun," was formed and the company filed an application for a patent on Karls' circuit. After several subsequent mergers and name changes, the company with which Karl was associated was known as Telefunken.
On September 24, 1900, using appratus designed by Karl, the first long distance wireless telegram was sent from Helgoland to Cuxhaven, a distance of 62km (about 38½ miles, nothing today but a vast distance at the time, about 15km (about 9 miles) being the most for reliable wireless communication then).
Karl reasoned that, if loose coupling between the oscillator and antenna benefitted the performance of the transmitter, it might also improve the performance of the receiver. In 1902 he carried out experiments which demonstrated that transferring energy from the receiving antenna to the detector through two loosely coupled coils resulted in both a sharper resonance effect as well as increased received signal strength. The benefits to reliable long distance communication with resonance at both the transmitter and receiver were obvious to all who were seeking to develop wireless telegraphy. Marconi had been trying to achieve the same result and everyone, especially Marconi, knew that the person who held the strongest patent on tuning would receive great financial rewards.
Marconi filed an application for what would become known as his "four-sevens" tuning patent for transmitters on April 26, 1900. Karl noticed that the Marconi patent was very similar to the first part of his own British patent on tuning which had been filed on January 26, 1899. In addition, Karl also felt that subsequent tuning patent applications filed by Marconi in 1901 were remarkably similar to the second part of his British patent. Karl reported that, when the two men later discussed the matter, Marconi admitted with commendable frankness that he had "borrowed" Karls' ideas. For some unexplained reason, Braun-Siemens (the name, at the time, of the company with which Karl was associated) did not immediately sue Marconi. When a suit was filed later, the company found that its delay had severely weakened their legal position.
Being able to tune the transmitter and receiver helped provide privacy in communications and a greater communication range. This was very important to both military and commercial users of wireless. In 1901, Karl sought to increase both the privacy and range even more with the development of directional antennas. Karl discovered that a moderate amount of directivity in receiving could be achieved if the antenna was inclined slightly to the horizon. Reception was best for waves that passed through the vertical plane containing the antenna. Achieving directivity in transmitting antennas was somewhat more complicated. Braun first tried to replicate the action of the parabolic mirror in a searchlight by using an array of vertical antenna wires mounted on poles arranged to form a cylindrical parabola. By properly adjusting the phase of the signal applied to each wire, it would be possible (in principle) to produce a direction of maximum electromagnetic wave intensity. Achieving the desired results in practice is, however, very difficult with an antenna configuration of practical size. Karls' results using this method were unsatisfactory. He then reduced the number of antenna wires and poles to three and was able to excite the wires from a common transmitter by arranging the poles in an equilateral triangular pattern. By carefully controlling the relative phases of the transmitter currents in the three wires, significant directivity of the radiated signal was achieved.
Karl shared, with Marconi, the 1909 Nobel Prize for Physics for their work with radio.
In 1915 Karl traveled to the United States to testify in a patent dispute. The subsequent involvement of the United States in World War 1, together with an incurable illness, made it impossible for Karl to return to German y. He lived at his sons' home in Brooklyn, NY until his death. After heavy suffering Professor Karl Ferdinand Braun passed away on the morning of the 20th of April, 1918. Later he was returned to Germany and buried in his home town of Fulda.