The physicist Karl Ferdinand Braun was an important contributor to the fieldsof television , radio, and electronics . For his work he shared the 1909 Nobel Prize for Physics with Guglielmo Marconi. Braun was born in Fulda, Germany, and later attended the Universities of Marburg and Berlin. After receivinghis doctorate in 1872, he held several academic positions at the Technical University of Karlsruhe, the University of Tübingen, and the University ofStrasbourg. He began his first important experimental work in 1874. That year, while studying mineral metal sulfide, he noted that certain crystals transmitted electricity in one direction more easily than in the other. These crystals, called rectifiers, were useful in converting alternating current (whichtravels in two directions) into direct current (which travels in one). The first use of crystal rectifier s was in crystal-set radios. These rectifiers were replaced eventually by triodes and other valve circuits, but returned later in the twentieth century--in an improved form--in solid-state circuitry. The 1890s marked a period of intense activity for Braun. It had been known forsome time that the path of electrons that coursed through a cathode-ray tubecould be altered by applying a magnetic current. Braun devised a system by which the magnetic current alternated, causing the beam to "scan" slowly; as the scanning beam hit the side of the tube, a glowing dot appeared, moving upand down. When a high-frequency alternating current was applied, the dot would scan at a faster rate, creating observable patterns. What resulted in 1897was Braun's oscilloscope , an important laboratory tool and the precursor tothe television tube. Braun also experimented with ways to improve the power and range of radio transmissions. At the time, radio antenna were connected directly to the power supply, resulting in a maximum transmitter range of aboutnine miles (15 km). Braun's idea was to remove the antenna from the power circuit and use magnetic coupling to boost the output. He patented his system in 1899, and since then magnetic coupling has been applied to radio, television, and radar. In addition to magnetic coupling Braun also invented the directional antenna. In the early twentieth century considerable controversy developed over the ownership of radio technology patents. In order to help, Braun came to the United States in 1917 to testify in a series of patent hearings. During his stay, America entered World War I. Braun, a German citizen, was taken prisoner as an enemy alien and died a year later while still imprisoned.