The Alexanderson Day (named after the inventor Ernst Fredrik Werner Alexanderson) is the great day of the open oor at the VLF transmitter Grimeton. On Alexanderson Day the only workable machine transmitter in the world is used to transmit short morse messages on 17.2 kHz, which should be easily receivable in whole Europe. A modern and very convenient way for their reception is a PC with a coil of its soundcard entrance using a FFT-analysis software.
