Decoding the DCF-77 Radio Time Sign
Izvor: KiWi
The DCF-77 radio time transmission is utilised by numerous NTP server and Pc personal computer systems to provide exact synchronisation of time crucial purposes. This post describes how the DCF-77 time signal is decoded by NTP server and pc programs to deliver an precise timing reference. HF signals analysis
The DCF-77 Time Transmitter.
The DCF-77 time sign is a long-wave radio time sign broadcast from Mainflingen, in the vicinity of Frankfurt, Germany. The radio signal is managed by T-Systems, a sub-division of Deuche Telecom, and it has been in operation considering that 1959. The DCF-77 sign is produced from incredibly exact atomic clocks found on the German Countrywide Physics Laboratory. When decoded, it provides a very precise timing reference for clocks and laptop timing machines.
DCF-77 Time Code.
Time and date information is transmitted consistently, recurring each and every moment. The data is transmitted as an amplitude modulated, pulse-width coded facts sign. Every info little bit is transmitted as one pulse for each next. The data transmitted consists of the current time and day, leap second indicator, daylight conserving time indicator, transmitter identifier and parity bits.
The duration of each and every transmitted pulse is decoded as follows: a next mark with a period of a hundred milliseconds is decoded as being a binary zero; a 2nd mark by using a duration of 200 milliseconds is decoded for a binary a single.
Transmitted Data.
Time and day information and facts is offered in BCD (Binary Coded Decimal) format and is also encoded as follows: bits 0-14 are unused, but may well deliver long run standing information and facts; bit fifteen suggests use of backup transmitter; little bit 16 (A1), signifies the announcement of daylight conserving improve; little bit seventeen (Z1), indicates daylight saving is in use (CEST); bit eighteen (Z2), signifies standard time (CET); bit 19 (A2), announces a leap 2nd; bit 20, implies start out of your time facts; bits 21-27, BCD encoded minutes; bit 28 (P1), parity little bit covers bits 21-27; bits 29-34, BDC encoded hrs; bit 35 (P2), parity little bit addresses bits 29-34; bits 36-41, BCD encoded working day of thirty day period; bits 42-44, BCD encoded working day of week; bits 45-49, BCD encoded month of your yr; bits 50-57, BCD encoded yr; little bit 58 (P3), parity little bit handles bits 36-57.
The DCF-77 information bits 1-14 are commonly unused by any decoding algorithm and could provide status info in long run broadcasts. Enough time zone bits Z1 and Z2 show current daylight conserving time standing. When CET time is remaining broadcast, Z1 is zero and Z2 is one, for CEST time, Z1 is a single and Z2 is zero. The daylight conserving modify announcement bit, A1, signifies an imminent adjust to or from CET. The leap second announcement bit suggests the imminent insertion of the leap next. The three parity bits P1-P3 compliment the preceding information and facts to a fair variety of ones (even parity).
