DCF77

What is DCF77?

The acronym DCF77 is the label for a coded time signal which is transmitted on the standard frequency of 77.5 kHz on long wave. It can be received within a range of 2,000 km (1,243 miles) around Frankfurt/Main, Germany.

DCF77 derives from the international frequency list where D stands for Deutschland (Germany), C for long wave, F for "near Frankfurt" and 77 for the carrier frequency.

The time transmitted is the official time of the Federal Republic of Germany and thus the Central European time or the Central European daylight saving time.

The time base currently consists of three cesium atomic clocks, operated by the National Metrology Institute of Germany (PTB).

There are many devices on the market for receiving and converting the signal.

DCF77 signal and time information

The time information is transmitted as a digital signal on the normal carrier frequency of 77.5 kHz. The digital signal is formed by a negative modulation of the signal (decreasing the amplitude of the carrier frequency down to 25 %) in a one-second cycle.

The modulation starts at the beginning of each second from second 0 to 58 of one minute. In the 59th second, no lowering takes place and the following second mark indicates the beginning of the next minute. The length of the amplitude lowering at the beginning of a second provides the binary value of the digital signal. A 100 ms lowering stands for the value "0" (FALSE); 200 ms for "1" (TRUE).

Thus, with every second, part of the time information is transmitted so that it takes at least one minute for all of the time information to be transmitted.

The time and date are encoded by 58 digits, i.e., 58 seconds.

In addition to the pure time and date information, more information is included, such as operating information (seconds 1 to 14) as well as the transmitter type used, time zone, daylight saving time and switching seconds (second marks 15 to 19).

Connection to ibaPDA

The integrated DCF77 driver decodes the time information from a digital input signal that must be generated in compliance with the DCF77 standard.

If the ibaPDA system is installed in the range of the original DCF77 signal, there are several devices on the market that convert the DCF77 radio signal into a discrete digital signal. ASCII strings containing the time information cannot be processed by ibaPDA.

In order to be able to transmit the DCF77 time to ibaPDA, the discrete pulse outlet of the DCF77 receiver should be connected to a digital input on an ibaPADU or ibaNet device.

In the configuration dialog of the I/O Manager of ibaPDA, you then just have to select this input as the DCF77 signal.

Devices which have already been used with ibaPDA:

• Meinberg COM52HS DCF77 receiver for DIN-rail mounting

• Meinberg RU226: DCF77 receiver in compact housing

Since using a simple digital input, it is possible to synchronize the ibaPDA system time with external time sources, such as clocks.

ibaPDA can thus be synchronized even in regions where the DCF77-signal is not available.