BPC is the callsign of a time signal broadcasting from the BPC Shangqiu Low-Frequency Time-Code Radio Station, cooperatively constructed by the National Time Service Center of the Chinese Academy of Sciences and Xi'an Gaohua Technology Co., Ltd.http://english.ntsc.cas.cn/ns/es/201003/t20100317_51581.html, beginning April 25, 2002.
BPC transmits a time signal on 68.5 kHz, which can be used for synchronizing radio controlled clocks. The transmission site is situated near Shangqiu, Henan Province at .
BPC broadcasts at 90 kW for 20 hours per day, with a 4-hour break from 05:00âÂÂ09:00 China Standard Time (21:00âÂÂ01:00 UTC) daily. BPC transmits an amplitude-modulated time code during the first 400 ms of each second, and unmodulated carrier during the last 600 ms. An additional phase-modulated spread-spectrum time code was proposed, but there is no evidence that it has been implemented.
BPC transmits the time every 20 seconds, using an amplitude-modulated binary code sent at 2 bits per second. Each 20-second block encodes the China Standard Time of the beginning of that block.
To encode each pair of bits, the transmitter is reduced by 10 dB (to 10% of normal power) at the beginning of each second, and restored to full power after a multiple of 0.1 seconds. The duration of the reduction encodes the bits, as follows:
If there is no signal reduction at all, that is a special marker which marks the beginning of the time code.
Note: The bits sent in the same second as the parity bits are not parity-checked.