Valdemar Poulsen takes Duddell's singing arc and applies three critical engineering modifications to raise the oscillation frequency from the audible range to the hundreds of kHz needed for radio: a hydrogen (or hydrocarbon vapor) atmosphere around the arc, a transverse magnetic field (drawing on Elihu Thomson's 1892 principle), and modified electrodes (carbon cathode, water-cooled copper anode). The result is the first purely electronic generator of high-frequency continuous waves (CW), enabling modulation of voice and music and giving rise to modern radio broadcasting. Patented in 1903 (Danish/US patent), it was used commercially until the 1920s.