DCF77

DCF77 is a longwave time signal and standard-frequency radio station. Its primary and backup transmitter are located at 50°0′56″N 9°00′39″E / 50.01556°N 9.01083°E / 50.01556; 9.01083 in Mainflingen, about 25 km south-east of Frankfurt am Main, Germany. It is operated by Media Broadcast GmbH (previously a subsidiary of Deutsche Telekom AG), on behalf of the Physikalisch-Technische Bundesanstalt, Germany's national physics laboratory. DCF77 has been in service as a standard-frequency station since 1959; date and time information was added in 1973. The timestamp sent is either in UTC+1 or UTC+2 depending on daylight saving time.

The 77.5 kHz carrier signal is generated from local atomic clocks that are linked with the German master clocks in Braunschweig. With a relatively high power of 50 kW, the station can be received in large parts of Europe, as far as 2000 km from Frankfurt (and further away depending on signal propagation and local interference). As an example, reception with high-grade consumer clocks is possible in Turkey (Istanbul), Portugal and Gibraltar (during night hours). Its signal carries an amplitude-modulated, pulse-width coded 1 bit/s data signal. The same data signal is also phase modulated onto the carrier using a 512-bit long pseudorandom sequence (direct-sequence spread spectrum modulation). The transmitted data repeats each minute.

• Current date and time;
• Leap second warning bit;
• Summer time bit;
• Primary/backup transmitter identification bit;
• Several parity bits.

Since 2003, 14 previously unused bits of the time code have been used for civil defence emergency signals. This is still an experimental service, aimed to one day replace the German network of civil defence sirens.

The call sign DCF77 stands for D=Deutschland (Germany), C=long wave signal, F=Frankfurt, 77=frequency: 77.5 kHz.

Radio clocks and watches have been very popular in Europe since the late 1980s and, in main-land Europe, most of them use the DCF77 signal to set their time automatically.