Logo of the Physikalisch-Technische Bundesanstalt
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

Amplitude and phase trace of the DCF77 signal during one second
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.