Meinberg RU226 User Manual

RU226

DCF77-receiver

FUNKUHREN

General information about DCF77

The Meinberg receiver module RU226 receives the signal of the long wave transmitter 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 (MEZ) or the Central European Summer Time (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. The complete time information is available once every
minute.

At the beginning of every second the amplitude of the high precision 77.5kHz carrier frequency
is shifted to 25% for a period of 0.1 or 0.2 sec. The length of these time marks represents a binary
coding scheme using the long time mark for logical ones and the short one for logical zeroes. The
information about the current date and time as well as some parity and status bits can be decoded
from the time marks of the 15th to the 58th second every minute. The absence of any time mark at
the 59th second of a minute indicates the beginning of a new minute with the next time mark.

Switching to MESZ or MEZ can be done automatically. The reception of the time information
is free of charge and does not need to be registered.

Figure : decoding scheme

M Start of minute (0.1 sec)
R RF transmission via secondary atenna
A1 Announcement of a change in daylight saving
Z1, Z2 Time zone identification
A2 Announcement of a leap second
S Start of time code information
P1, P2, P3 Parity bits

General information R U226

The module RU226 is mounted in a plastic case and contains the ferrite antenna and the comlete
straight receiver. Two LEDs are included for visualization of the demodulated time marks and the
field intensity of the DCF-signal. The case is delivered with a stick pad for easy mounting (e.g. on
windows/furniture). As an output-signal, the demodulated time marks are available at a four-wire
cable.

R U226

DCF77-receiver

FUNKUHREN

Antenna

Generally, the exact mounting of the antenna is important. It has to be placed in longitudinal
direction to the transmitter (Frankfurt). The antenna should be installed with a minimum distance
of 30cm to all metal objects. A distance of several meters to TV- or computermonitors should be
kept. The vicinity of computers or microprocessors must be avoided. Adjustment of the antenna
can be done by watching the LEDs. But: a large field strength on its own is no guarantee for good
conditions of receiption, because interfering signals within the bandwidth of the receiver also have
an effect on the brightness of the 'field'-LED. Therefore, only undisturbed pulses per second
together with a high field intensity is a criterion for good receiption of the DCF-signal.

P ow er supply

The receive module needs a 3,5 V to 5,5V power supply. This voltage should be sourced by a
linear regulated power supply. If the use of a switched mode power supply becomes necessary the
GND access of the RU226 has to be grounded directly or via a capacitance of min. 0.1µF. This
connection avoids the signal-to-noise ratio reducing influence of the harmonics of the switched
mode power supply.

P olarity of the pulses

If the cover of the case is removed, a jumper becomes accessible. The position of this jumper
decides on the polarity of the output signal. The selection of high-active (default) or low-active
pulses is possible.

Jumper Jumper

Output signal