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NTSC is the time service centre of China and we have several standard time signal transmission methods operating at present. BPM short-wave and BPL long-wave time transmission stations (figure 2) are located in Pucheng county about 70 km northeast of Lintong. They are the main centers for reliable time dissemination methods presently in China.
BPL Long-Wave Time Transmission
BPL periodically broadcasts the standard time and frequency signals at 100KHz. its ground wave can cover 1000-2000km. If combined sky wave and ground wave, its sphere of action is the whole mainland and the offing. The precision of the BPL is a few millionths of a second.
BPC Time Code Transmission
The BPC low frequency time code transmission station has been established since 1998. With an operating frequency of 68.5 kHz, it can broadcast all time code information including the year, month, day and hour, minute, second, etc. It uses the BPL antenna system and works time-shared with the BPL system.
BPM Short-Wave Time Transmission
BPM broadcasts the standard time and frequency signals at 2.5, 5, 10, 15 MHz alternatively 24 hours a day, which cover the whole country with the precision of 1 ms .Signals of UTC and UT1 are modulated by 1 KHz standard frequency. The lengths of the second signals are 10 ms (UTC) and 100 ms (), and the length of minute signal is 300 ms. BPM will disseminate the standard time code after a technical reconstruction.
Telephone Time Service System
This system was established at 1998, and it can be fit for the users who require that the time precision should be from a few thousandths of a second to a few ten milliseconds.
Network Time Service
Network Time Service System (NTS) was tested successfully at 2001. The precision of NTS is 0.5us (LAN), <300ms (WAN).
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