Six radio time-code standards, worldwide

The only “positive” scheme of the six: each second starts at full carrier then drops to 10% (the others switch the carrier off at the start), so its pulses rise instead of dipping. With JJY60 it forms a dual-frequency network covering different terrain and propagation ranges.

The Saga (Hagane-yama) site; with Fukushima it gives Japan-wide dual-frequency coverage. Near seconds 15 and 45 each minute it sends the “JJY” call sign in Morse, and the frame carries leap-second (LS1/LS2) warning and stop bits.

A 2012 upgrade superimposed BPSK phase modulation on top of the original AM/PWM amplitude code, greatly improving jamming resistance and weak-signal reception. It carries no parity, aligning frames via position markers, and is sent directly as UTC. The app reproduces only the legacy AM/PWM amplitude code; the unimplemented BPSK phase layer does not affect time-setting.

WWVB and MSF mark the minute with a longer special pulse, whereas DCF77 leaves second 59 unmodulated (full carrier for the whole 1000 ms), so the receiver locks the next minute from the absence of that mark. It is also one of the few that is LSB-first, with P1/P2/P3 even-parity bits, and transmits German legal time (CET/CEST). Since 1983 DCF77 has superimposed a PRN (pseudo-random-noise) phase modulation on top of the amplitude code, greatly improving lock accuracy and interference resistance under weak signals. This app generates only the classic AM/PWM amplitude code (which radio clocks decode anyway), not the PRN phase modulation, so there is no effect on time-setting.

The only one using OOK — the carrier is switched fully off, giving the deepest waveform. Its signature is the A/B dual sequence: two bit-streams share each second, A carrying time/date and B carrying DUT1 (UT1−UTC correction) plus year and parity extras. Every second opens with a 100 ms carrier-off, and second 0 stays off for 500 ms as a frame marker. This app generates the full A-sequence date/time — DST-aware, switching BST/GMT automatically — plus the per-second A/B carrier marks; only the DUT1 correction (UT1−UTC, seconds 1–16 of Bit B) is not yet implemented. DUT1 is only a sub-second correction that radio clocks don’t use, so it has no effect on time-setting.

The only one of the six that does not use binary BCD: it uses Base-4 (quaternary) PWM, packing 2 bits into each pulse, so the same data is sent with fewer pulses. Its cycle is just 20 s and repeats three full time frames per minute (the others mostly send a single 60-second frame), so low-cost receivers lock faster. It transmits Beijing time (UTC+8).