Zeitzeichensender

Zeitzeichensender are radio transmitters that broadcast precise time information to receivers over large areas, enabling clocks and time-dependent systems to synchronize automatically. The time reference usually comes from national time standards such as UTC.

Most Zeitzeichensender operate on low radio frequencies, such as longwave or very low frequency bands, chosen for reliable groundwave reception. The transmitted signal carries a time code that encodes the current hour, minute, second, date, and occasionally daylight saving time and leap seconds. Receivers demodulate the code and adjust local clocks accordingly.

The system is maintained by national metrology institutes, government broadcasters, or public utilities and is designed for wide applicability, from consumer radio clocks to industrial control networks. It provides a continuous, low-cost time reference independent of satellite navigation systems.

Notable examples include DCF77, a 77.5 kHz transmitter near Frankfurt, Germany; MSF in the United Kingdom on 60 kHz; WWVB in the United States on 60 kHz; JJY in Japan on 40 or 60 kHz; and the Allouis time signal in France on 162 kHz. These services typically offer a standard time signal with minor regional variations in codes and power.

Limitations include dependence on proper atmospheric propagation, limited indoor penetration at very long wavelengths, regional coverage gaps, and occasional maintenance or regulatory changes. In many contexts, satellite-based time sources such as GPS deliver higher precision but Zeitzeichensender remain important as a complementary terrestrial reference, particularly in regions with weak satellite reception or for redundancy.