Monitoring the ionosphere altitude variation with a sound card

DCF-77 is a German very low frequency (VLF) emitter locked on the Cs clocks of PTB used for synchronizing radiofrequency-disciplined clocks found, for example, in low-cost weather stations. VLF signals propagate through the waveguide whose boundary conditions are defined on the one hand by ground, and on the other hand by the ionosphere (charged) layer altitude. In addition to the amplitude modulation of the Cs-locked DCF-77 frequency standard, a phase modulation is imprinted on the carrier for time of flight measurement, allowing for “precise” time of flight measurements.

Video avalable at: https://fosdem.org/2017/schedule/event/dcf77/