Meinberg GEN170TGP - Manual (Page 6)

6
General Information about DCF77
The long wave transmitter DCF77 is installed in Mainflingen near Frankfurt/Germany
and transmits the reference time of the Federal Republic of Germany. This is either the
Central European Time (Mitteleuropäische Zeit, MEZ) or the Central European Summer
Time (Mitteleuropäische Sommerzeit, MESZ). The transmitter is controlled by the
atomic clock plant at the Federal Physical Technical Institute (PTB) in Braunschweig/
Germany and transmits the current time of day, date of month and day of week in coded
second pulses. Once every minute the complete time information is available. The highly
accurate 77.5 kHz carrier frequency of DCF77 is modulated in both amplitude and
phase.
At the beginning of every second the amplitude of the carrier frequency is lowered by
75% for a period of 0.1 or 0.2 sec. The length of these time marks represent a binary
coding scheme using the short time mark for logical zeroes and the long time mark for
logical ones. The information on the current date and time as well as some parity and
status bits can be decoded from the time marks of the 15th up to the 58th second every
minute. The absence of any time mark at the 59th second of a minute signals that a new
minute will begin with the next time mark.
The amplidude modulation can be easily decoded by a simple receiver circuit.
However, decoding the phase modulation achieves much more accuracy but also
requires much larger efforts including usage of correlation techniques.
Figure: Decoding Scheme
M Start of Minute (0.1 sec)
R RF Transmission via secondary antenna
A1 Announcement of a change in daylight saving
Z1, Z2 Time zone identification
Z1,Z2 = 0,1: Daylight saving disabled
Z1,Z2 = 1,0: Daylight saving enabled
A2 Announcement of a leap second
S Start of time code information (0.2 sec)
P1, P2, P3 Even parity bits