Meinberg FUNKUHREN DU35K, Руководство по эксплуатации

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8
DU35K as Radio Clock
It is not possible to run this variant of the DU35K as a slave clock. The DSUB
connector (IN) at the rear panel has no effect. The DSUB connector (OUT) can be
connected to further DU35Ks or similar systems to run them as slave clocks.
An external ferrit antenna is used to receive the signal from DCF77 and supplies it
to the on-board LF receiver where it is demodulated by a synchronous detector with
automatic gain control. The demodulated time marks are fed to the clock´s micropro-
cessor.
The time marks from the receiver circuit are filtered and decoded by the micropro-
cessor system. Parity and consistency checks over a period of two minutes take care
for detecting errors in the received time string. The checked and decoded time is
written to the on-board real time clock and spread by the interfaces. A software
watchdog lets the microprocessor recover from malfunction. A power-fail comparator
resets the microprocessor if the supply voltage drops below a specified threshold.
In case of supply voltage failure the on-board real time clock keeps the time
powered by a lithium battery which has a live time of at least 10 years guaranteed.
After powering up the system the time keeped in the real time clock is displayed
immediately. A dot below the colons between hours and minutes on the display
indicates the DCF77 signal. This "Modulation Dot" appears until the first synchronisa-
tion of the clock. If the antenna is installed properly and the signal from DCF77 can be
received without strong distortions, the "Modulation Dot" starts blinking exactly once
per second, corresponding to the time marks from DCF77. Because of a better control
an acoustic signal is added to the "Modulation Dot" for 2.5 minutes. After loss of
reception for more than 6 hours the colons between hours and minutes begins to blink.