The DCF-77 time of radio is used by the NTP server and PC systems to provide more accurate synchronization of time-critical applications. This article describes how the DCF-77 time signal is decoded by NTP server and computer systems to provide a precise reference time.
The DCF-77 time of the issuer.
The DCF-77 time signal is a long time short-wave radio antenna signal Mainflingen, near Frankfurt, Germany. The radio signal is maintained by T-Systems, a division Deuche Telecom, and has been in operation since 1959. The DCF-77 signal is generated by highly accurate atomic clocks located at the German National Physics Laboratory. When decoded, is a very specific reference to the timing and clock synchronization computer.
DCF-77 Time Code
Date and time information is transmitted continuously, repeated every minute. The data is transmitted as an amplitude modulated pulse width coded data signal. Each bit of data is transmitted as one pulse per second. The data is transmitted over time and the current date, leap second indicator, indicators of time, the identification of the issuer and the parity bit.
The duration of each pulse is decoded as follows: one mark for a second period of 100 milliseconds, is decoded as a binary zero, a second mark for a period of 200 milliseconds, is decoded as binary.
Of data transmitted.
Date and time information is presented in BCD (Binary Coded Decimal) format and is encoded as follows: 0-14 bits are not used, but can provide information on future state, bit 15 indicates that the use of backup transmitter, 16 bit (A1), said that the announcement of the change of time, 17-bit (Z1), said that summer is in use (EST) 18-bit (Z2), indicates the standard time (CET), 19 bits (A2), announces a leap second; Bit 20 indicates the start time information, bits 21-27, BCD encoded minutes and 28 bit (P1), the parity bit covers 21-bit 29-bit -27 -- BDC 34 time-coded, 35-bit (P2), the parity bit covers bits 29-34 bits 36-41, BCD encoded day of the month, bits 42-44, BCD encoded day of the week, bit 45-49, coded BCD months of the year, the bits 50-57, BCD encoded years, 58-bit (P3), parity bit covers the bit 36-57.
The DCF-77 data bits 1-14 are generally used by any algorithm, decodes and May to provide information on the status of future emissions. Z1 bit 'of time zone and Z2 indicate the current state of the economy days. When the time CET airs, Z1 and Z2 is equal to zero is for the moment CSTA is a Z1 and Z2 is equal to zero. The DST-bit ad 'of this change, A1, indicates an imminent change or HEC. The leap second announcement bit indicates the imminent introduction of a second jump. The three parity bits P1 to P3-complete information prior to an even number of ones (parity).
Examples
Received DCF-77 bit stream: 00000000000000000010100000000011010110000001001001000110011 once decoded and the date: Tuesday 01/12/1998 16:00
Received DCF-77 bit stream: 00000000000000000010110000001011010110000001001001000110011 once decoded and the date: Tuesday 01/12/1998 16:01
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