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View of the Mainflingen long-wave radio station for transmission of the DCF77 signal: transmitter building (in the back), antenna building (yellow bricks) and antenna masts.

DCF77 amplitude modulation

Examples of registrations of the DCF77 carrier envelope; above: second marks 45 to 54, corresponding to calendar month 7 (July), calendar year 03 (2003); below: second marks 54 to 03 (minute change).

The amplitude of the DCF77 carrier oscillation is modulated with second marks: at the beginning of each second - except for the last second of each minute to identify the beginning of the next minute - the amplitude is lowered for 0.1 s or 0.2 s phase-synchronously with the carrier oscillation to approx 15%. The remaining amplitude allows a continuous carrier oscillation to be obtained and is intended to facilitate use of the DCF77 carrier as a standard frequency signal. The variable duration of the second marks serves for binary coding of time and date.