The Poulsen Arc: The Flame That Sang on Key Valdemar Poulsen's arc converter made a radio wave like a furnace makes heat: an arc burning in hydrogen gas, blown sideways by a magnet, singing at radio frequency. This guide covers its twenty years as the heavyweight transmitter. Quick facts Inventor Valdemar Poulsen Date 1902-03 Burns in hydrogen atmosphere Other invention wire recorder, 1898 Users Federal Tel., US Navy Arc stations had voices - operators claimed to know them by ear - and the naval networks of the First World War ran on their flame. The valve replaced them for cleanliness, not character, and the character is what the bands still miss. Free tool and guides: Morse Code Works Morse Code Works - free Morse code tools and guides. Reference chart