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Content 4/4

DCF77 experimental transmitter

Construction of a simple transmitter of 77.5 KHz, to be able to set time DCF77 clocks that don't correctly receive the signal from the German transmitter. DCF77 is a radio station located in Germany, that transmits in long wave (LW). It began to function as a standard frequency station on January 1, 1959, and from June 1973 the date and time information was incorporated into the transmission. The DCF77 signal uses the amplitude change coding to transmit time information, digitally coded by reducing the amplitude of the carrier 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 indicates a binary 1.


A DCF77 clock only needs to receive a 77.5 KHz carrier, with variable amplitude at the rate of every second and the appropriate time coding. If we place a small 77.5 KHz transmitter in the vicinity of a DCF77 clock, the carrier could have a frequency drift of +/- 300 Hz, not include in-phase modulation, and increase the amplitude modulation depth to the 100% It is thus possible to transmit the DCF77 information with an ASK modulation.




May 02,2019
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