This is what I stripped from an article on TDF (Very Intersting):The current time signal is generated by extremely accurate caesium atomic clocks and phase-modulated on the 162 kHz (1850.5707284 m wavelength) carrier signal in a way that is inaudible when listening to the signal using normal Longwave receivers.
TéléDiffusion de France (TDF) uses an amplitude modulated longwave transmitter station. Time signals are transmitted by phase-modulating the carrier by ±1 radian in 0.1 s every second except the 59th second of each minute. This modulation pattern is repeated to indicate a binary one.
The binary encoding of date and time data during seconds 15 through 18 and 20 through 59 is identical to that of DCF77; the numbers of the minute, hour, day of the month, day of the week, month and year are transmitted each minute from the 21st to the 58th second, in accordance with the French legal time scale. The time transmitted is the local time of the upcoming minute.
Also like DCF77, bit 20 is always 1, bit 18 indicates that local time is UTC+1 (CET), bit 17 indicates that local time is UTC+2 (CEST), and bit 16 indicates that a change to local time will take place at the end of the current hour. Bit 15 is reserved to indicate abnormal transmitter operation.
As extensions to the DCF77 code, bit 14 is set during public holidays (14 July, Christmas, etc.), and bit 13 is set the day before public holidays.[14]
Stripped from Wikipedia