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7.2. DESCRIPTION OF DCF AND TDF TIME CODES
The DCF77 time signal is a long-range radio wave signal transmitted by the PTB
(Physikalisch-Technische Bundesanstalt) in Germany. The power of the DCF77 is about
30kW, which allows it to broadcast throughout Europe. The carrier has a very stable
frequency of 77.5kHz, amplitude modulated, and BCD (Binary Coded Decimal) coded.
The carrier is modulated with 24V pulses (1 per second). The duration of a pulse reflects the
level of the received bit:
►
100 ms represents one bit at 0;
►
200 ms represents one bit at 1.
The time signal is emitted by a one-minute frame divided into 60 pulses (the 59
th
corresponds
to a zero pulse to give the start of the frame). The frame contains the values of minutes,
hours, days, months, years and other parameters such as the leap second.
