DCF77 experimental transmitter

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Construction of a simple transmitter operating at 77.5 KHz is necessary for setting time on DCF77 clocks that fail to receive the signal from the German transmitter correctly. The DCF77 radio station, located in Germany, broadcasts on long wave (LW) and started functioning as a standard frequency station on January 1, 1959. Since June 1973, date and time information has been incorporated into its transmission. The DCF77 signal transmits time information using amplitude change coding, digitally coded by reducing the carrier's amplitude up to 15% of its nominal level for 0.1 or 0.2 seconds at the beginning of each second. A reduction of 0.1 seconds indicates a binary 0, and a reduction of 0.2 seconds signifies a binary 1. A DCF77 clock can receive only a 77.5 KHz carrier with variable amplitude at the rate of every second along with proper time coding. Placing a small transmitter operating at 77.5 KHz near a DCF77 clock allows for a frequency drift of +/- 300 Hz, excluding in-phase modulation, and increases the amplitude modulation depth to 100%. This makes it possible to transmit DCF77 information using ASK (Amplitude Shift Keying) modulation.