Table of contents 1. Facts about DCF 77 2. The Time Code Back

	Facts about DCF 77

Station: DCF 77 Frequency: 77.5 kHz Transmitting power: 50 kW Location: Mainflingen / Germany Receiving area: 1500 km Geographical coordinates: 50° 01' N, 09° 00' E Time of transmission: permanent Modulation: 75%

	The Time-Code

Time code information according the information from the "Physikalisch Technische Bundesanstalt (PTB)"

The information is present as a continuous bit stream with a data rate of 1 bit per second by using pulse width modulation. The power of the carrier is reduced to 25% of it's nominal power at the begin of each second and then restored to it's full level. The only exception is the 59th second of every minute. The missing reduction signalises the next minute marker. Thus, the leading edge of every negative going pulse is on time. Regaining full power after 0.1 seconds represents a binary "0", after 0.2 seconds a binary "1". There are three parity bits available. Parity bit P1 combines the 7 bits of the minute information to an even number of "1". Parity bit P2 combines the 6 bits of the hour information to an even number of "1". Parity bit P3 combines the 22 bits of the date information to an even number of "1". The bits located at position 17 and 18 (Z1 and Z2) are used as an indication flag to inform about "Middle European Standard Time (MEZ)" and "Middle European Summer Time (MESZ)". If bit 17 is binary "0" (0.1 seconds) and bit 18 is a binary "1" (0.2 seconds), the time information is indicated as MEZ. If bit 17 is binary "1" and bit 18 is binary "0", MESZ is distributed.
Before each change from MEZ to MESZ or vice versa, bit 16 (A1) will provide an "attention marker" 1 hour before the change by representing a binary "1".
The bit 19 (A2) announces a leap second by representing a binary "1" for the duration of 1 hour before. The binary coded decimal (BCD code) format is used to combine binary digits in order to represent decimal numbers (for location of the information, as well as content, see drawing).
This gives the possibility to decode all necessary information of time, day of the year and year (and some additional information) out of the signal.

Please verify this information before commercial use !
http://www.ptb.de/de/org/4/43/433/_index.htm