DCF77 is a long wave time signal and standard-frequency radio station. Its primary and backup transmitter are located 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.[1]

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 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 pseudo random sequence (direct-sequence spread spectrum modulation).

The transmitted data repeats each minute.

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

 Reproduced by kind permission of Physikalisch-Technische Bundesanstalt, Germany

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