Software-Defined Radio Decoding of DCF77: Time and Frequency Dissemination with a Sound Card

We investigate time and frequency dissemination using software-defined radio processing of signals acquired from a low-frequency emitter using a sound card. We use the resulting propagation time measurements for investigating some ionosphere physics and its interaction with cosmic ray flux. Rather than using the amplitude of the transmitted signal as classically considered, we here focus on a precise time of flight measurement by demodulating the spectrum spreading phase modulation added to the DCF77 amplitude modulation. Plain Language Summary Software-defined radio aims at reducing to its minimum the hardware setup needed to process radio frequency signals and relies on software processing for demodulation: here we demonstrate the precise measurement of an atomic clock-locked emitter, propagating at very low frequency, using only a general purpose computer sound card. Thanks to the high accuracy of the time of flight accessible through an improved modulation schemes, such physical properties as ionosphere altitude and ground wave versus air wave are detected. The frequency of the atomic clock is compared with the sound card local oscillator frequency, demonstrating the temperature dependence of the latter, readily measured in this experiment.