Friday, August 10, 2012
Here's the difference: while Ehret imagined an FM system and patented an FM system, he failed to make a working prototype. Poulsen succeeded where Ehret failed. He imagined and patented a working model. If that's not impressive enough, he also invented magnetic recording. So... why don't you know who this guy is? More here.
He was a poor student, and was particularly bad with mathematics. He family pushed him into medical school and he didn't do so well there either. He found work at the Copenhagen Telephone Company where he had time to experiment. He may or may not have read Oberlin Smiths Electrical World article on theoretical Magnetic recording. But his world was along those lines. Oberlin thought wire recording was impractical and was thinking more aline the line of a threat embedded with ferrous particles. Smith turned out to be right in the long run. But Poulsen managed to get it to work with wire, a battery, a magnet and some telephone parts. On 1st December 1898, he filed a patent in Denmark for the Telegraphone, the first magnetic recording device in history. In a variation of the wire method he also patented a 4.5 inch diameter steel disk with an embossed magnetic recording and playback was achieved by spinning the disc... like a hard drive.
In 1908 he developed an arc converter that we now call the Poulsen Arc Transmitter. It was capable of transmitting at frequencies up to 100 kHz. This was widely used in early experimental radio before the rise of the vacuum tube. It was a huge improve ment on Duddell's Singing Arc Transmitter which only could achieve 10kHz. By 1920 some Poulsen Arc transmitters were operating as high as 1000kW!
He died on 23 July 1942. He was 73 years old. Germany had fully occupied Denmark by 1940, but they allowed the Danish government to function until 1943. So Poulsen never saw Denmark liberated, but he never saw it dominated either.