Six radio time-code standards, worldwide
Technical specifications for the six radio time-code signals a radio-controlled watch listens to — WWVB (USA), DCF77 (Germany), JJY40 / JJY60 (Japan), MSF (UK) and BPC (China): carrier frequency, numeral base, modulation and framing, with a live per-second decode.
Six countries, five entirely different encodings — generated live in one app.
USA NIST · AM/PWM + BPSK · 1 bps · 0 = 200 ms / 1 = 500 ms / Mark = 800 ms low · MSB first · no parity
- Authority
- USA · NIST · National Institute of Standards and Technology
- Location
- Fort Collins, Colorado
- Antenna
- Phased array: two antennas of four 122 m towers each, 857 m apart (flat; can run single-antenna at 30 kW)
- Modulation
- AM/PWM with added PM (BPSK phase modulation since 2012)
- Bit encoding
- 0 = 200 ms low · 1 = 500 ms low · Mark = 800 ms low (encodes the low duration)
- Read order
- MSB First · BCD · no parity; frame aligned via position markers
A 2012 upgrade superimposed BPSK phase modulation on top of the original AM/PWM amplitude code, greatly improving jamming resistance and weak-signal reception; this app reproduces only the legacy AM/PWM amplitude code (what virtually all radio clocks decode) and does not support the BPSK phase layer. It carries no parity, aligning frames via position markers, and is sent directly as UTC. Time-setting is unaffected by this phase layer.
- AM/PWM
- Amplitude modulation + pulse-width: the carrier amplitude varies and pulse length carries data (used by most stations here).
- Base-4
- Quaternary: each pulse carries 2 bits (used by BPC).
- BCD
- Binary-coded decimal: each decimal digit is encoded separately in binary. These stations send only the bits needed — the units digit (0–9) takes 4 bits, while the tens digit drops leading bits thanks to its small range (minutes tens 0–5: 3 bits, hours tens 0–2: 2 bits).
- bps
- Bits per second; these stations mostly run at 1 bps.
- BPSK
- Binary phase-shift keying: a second data layer added by flipping the carrier phase 180°, on top of the amplitude code — more jamming-resistant.
- DUT1
- UT1−UTC: the small (sub-second) correction between Earth-rotation time and atomic time.
- Leap second
- A 1-second insertion occasionally added to UTC; the frame announces it via warning bits (e.g. LS1/LS2).
- Marker
- Position marker: a special fixed-position pulse used to align the one-minute frame.
- MSB / LSB first
- Bit transmission order — most-significant bit first / least-significant bit first.
- OOK
- On-off keying: data sent by switching the carrier fully on/off (used by MSF).
- Parity
- Check bit: an extra bit whose parity (even/odd) detects reception errors (e.g. PA1/PA2, P1/P2/P3).
- PRN
- Pseudo-random-noise phase modulation: phase is modulated with a PRN sequence for sharper, noise-resistant lock.
- PWM
- Pulse-width modulation: the length of each pulse encodes the bit value.
Sources & further reading
The signal specifications, encoding logic and station data on this page are drawn from each country’s official timekeeping authority and public records. They are grouped below by purpose for verification and further reading.