The DCF77 is a long wave transmitter situated in Mainflingen near Frankfurt am Main (Germany, 50.02° North, 9.00° West) that transmits time signals on 77.5 kHz with a power of 50 kW and can be received in a radius of about 1500...2500 km (about the central Europe as shown in the picture below). This signal (and its carrier) is generated from a cesium-clock situated in Braunschweig (Germany) with a precision better than 1 second over 300'000 years.
The transmitted time information is the CET (Central European Time) and DST (Daylight Savings) is also added in summer.
The frequency of the signal is in the long wave band: this ensures that reflections on the ionosphere can be neglected and that the signal arrives to all receivers by using a unique path: the surface wave. The reception is possible 24 hours a day.
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