A
PPENDIX
System 6844(RC) - V03.00
155 / 157
hopf
Elektronik GmbH
Nottebohmstr. 41
• D-58511 Lüdenscheid • Tel.: +49 (0)2351 9386-86 • Fax: +49 (0)2351 9386-93 • Internet: http://www.hopf.com • E-Mail: [email protected]
12.3 DCF77 (German Long-Wave Transmitter Frankfurt 77.5kHz)
DCF77
1
is a time signal that is radiated via a terrestrial long-wave transmitter in Frankfurt,
Germany, with a carrier frequency of 77.5kHz.
The transmission of the data is amplitude modulated whereas the transmission of the time
information is bit serial.
12.3.1 DCF77 General
The DCF77 signal transmits central European time (CET) or central European summer time
(CEST). This time is calculated from UTC plus one hour (CET) or two hours (CEST).
The DCF77 signal contains complete time information: minute, hour, day-of-week and date.
The following information is transmitted:
Local time
Current time zone (daylight saving time or standard time)
Announcement bit for daylight saving time (DST) changeover
Announcement bit for the leap second
If UTC is to be calculated from the local time transmitted by DCF77 then the receiver must
know the time offset (local time to UTC). In the CET zone this is +1 hour in an easterly direc-
tion. A
hopf
system calculates the correct UTC time from the local time, via the internally set
time offset and the DST changeover points.
12.3.1.1 DCF77 Signal Structure
The complete time information is transmitted in every minute. A part of time information is
transmitted every second of every minute, with the exception of the 59
th
second. The missing
signal in this second gives notice of an impending minute change in the next second.
The amplitude of the 77.5kHz carrier frequency is reduced from 100% to 25% at the begin-
ning of every second for a duration of 100 or 200ms (amplitude modulation). The beginning
of each reduction marks the precise second change.
The duration of reductions of 100 and 200ms (binary 0 and 1) is converted into a BCD code
and in this way decodes the transmitted time telegram.
The data string is sub-divided into different groups. Three of them followed by a parity check:
P1 = parity of minutes
P2 = parity of hours
P3 = parity of current day-of-year, day-of-week, month and year
The binary 1s’ of a group are calculated and supplemented with the parity bit to form an even
number.
When valid time information is transferred from CEST, the 17
th
second mark has a duration
of 200ms. One hour before changeover from CEST to CET, or vice-versa, the 16
th
second
mark has a duration of 200ms.
1
DCF77:
D
= Deutscher (German),
C
= Long-wave transmitter,
F
= Frankfurt,
77
= frequency
