DCF77 is a natural for this because it already includes a phase-modulated signal (as well as the 1bps amplitude-modulation). At the moment it's a 512-bit pseudo

DCF77 is a natural for this because it already includes a phase-modulated signal (as well as the 1bps amplitude-modulation). At the moment it's a 512-bit pseudo random sequence, but could obviously carry a data stream instead.