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TDF is a time signal controlled by the LNE–SYRTE and broadcast by TéléDiffusion de France from the Allouis longwave transmitter at 162 kHz, with a power of 2 MW.〔(SYRTE website )〕 It is also known as FI or France Inter because the transmitter primarily broadcasts the France Inter AM signal. In 1980, the first atomic clock was installed to regulate the carrier frequency.〔(Les ré-orientations )〕 The current time signal is generated by an extremely accurate caesium fountain atomic clock and phase-modulated on the 162 kHz carrier in a way that is inaudible when listening to the France Inter signal using a normal AM receivers. It requires a more complex receiver than the popular DCF77 service, but the much more powerful transmitter (40 to 80 times DCF77's 50 kW) give it a much greater range of 3500 km. The signal is almost continuous but there is a regularly scheduled interruption for maintenance from 01:03 to 05:00 every Tuesday.〔 ==Signal format== TDF is actually an amplitude modulated longwave radio station, transmitting the programs of the France Inter network. 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 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 19 indicates an upcoming leap second at the end of the current hour, 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.〔(Time signals known to BIPM )〕 The relative uncertainty of the carrier frequency is 2 parts in 1012. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「TDF time signal」の詳細全文を読む スポンサード リンク
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