Meinberg DCF77, Operating Instructions Manual

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5
General information about DCF77
The radio clocks made by Meinberg receive the signal from the long wave transmit-
ter DCF77. This long wave transmitter installed in Mainflingen near Frankfurt/
Germany transmits the reference time of the Federal Republic of Germany. This time
reference is either the Central European Time (Mitteleuropäische Zeit, MEZ) or the
Central European Summer Time (Mitteleuropäische Sommerzeit, MESZ). The trans-
mitter 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.
At the beginning of every second the amplitude of the high precision 77.5 kHz
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.
Our radio clocks decode the highly accurate information on date and time within a
wide range around Germany. So some of our clocks are installed in Bilbao/Spain as
well as in the city of Umeå in northern Sweden - fully satisfying the requirements of
the users. The radio clocks automatically switch to summertime and back. The
reception of the time information is free of charge and does not need to be registered.
Generally it is important to position the antenna in an optimal way. It should be
mounted at least 30 centimeters away from the clock unit and from solid steel. The
antenna should be aligned at a right angle to the direction of the transmitter (Frank-
furt).
Figure: decoding scheme