LF Radio NTP Server: How to decode the DCF-77 Broadcast Schedule

The DCF-77 time of transmission and radio frequency Mainflingen near Frankfurt, Germany. The DCF-77 time may be used by devices to provide a precise reference time. Timing of the computer equipment, such as NTP server systems, providing a precise point of reference for computer networks may use the program as an external source of accurate time. This article describes how the DCF-77 can be decoded to provide a reference to a specific timetable for NTP servers and other computer timing applications.

Before describing the format of the transmission, it is worth remembering a little 'about the history of the issuer. German national standard time and frequency radio, called DCF-77 is in operation since 1959. The spread is currently managed by T-Systems, a division of German telecommunications company Telecom Deuce. Precise information about the course of the show is produced by a cesium atomic clock maintained by the German National Physics Laboratory. The transmitter has a power of 50W, which can be received up to 1900 km from Frankfurt. The reception can be easily obtained in most of central and north-west. The transmission is transmitted as amplitude modulation, pulse width encoded data signal. Information about the hours of streaming, repeated every minute. The data is transmitted as a series of 59 pulses, one pulse per second. Each pulse represents a bit 'of data or a binary zero or binary. One hundred milliseconds pulse represents a binary zero, while the pulse is two hundred binary millisecond. The pulses can be decoded at the end of the date of the minutes and hours.

Timing information is represented in the DCF-77 transmission encoded binary coded decimal. Data bits are encoded into the carriage as follows. Data bits 1 to 14 are reserved for future improvements. Bit 15 indicates that the transmitter in operation today - the main transmitter or backup transmitter. 16 bit is the announcement of the return of summer. 17 bits indicates if DST is currently in use. Bit 18 indicates the time standard and is the inverse of 17 bits. Bit 19 indicates an impending leap second is inserted. Bit 20 indicates the start date and time. Bits 21-27 are BCD coded minutes. Bits 29-34 are BCD coded hours. Bits 36-41 are BCD encoded day of month Bits 42-44 are BCD weekday Bits 45-49 are BCD encoded encrypted year. Bits 50-57 are BCD coded years. Finally, a number of parity bits are inserted encoded data as follows. Parity bits to 28 bits 21-27. Parity bit 35-bit covers 29-34. Parity bit covers 58 bits 36-57.

To summarize, the DCF-77 transmission time is a reliable and accurate time from NTP server systems and applications, timing of other computers. The signal can be received in the vicinity of the NTP server same time, thus reducing installation costs. Furthermore, the right line before encoding the date of synchronization of the transmission allows the simple implementation of NTP server software. In fact, the standard distribution NTP server software drivers for Linux includes a reference clock for DCF-77.