BPC (time signal)

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.[1], 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 34°27′25″N 115°50′13″E / 34.457°N 115.837°E / 34.457; 115.837.

BPC broadcasts at 90 kW for 20 hours per day, with a 4-hour break from 05:00–09:00 China Standard Time daily (21:00–01:00 UTC). BPC includes both a conventional amplitude-modulated time code transmitted during the first 400  of each second, and an additional phase-modulated spread-spectrum time code transmitted during the last 600 ms of each second, about which little is known.

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 that the bits sent in the same second as the parity bits are not parity-checked.

• 低频时码授时, from the National Time Service Center, Chinese Academy of Sciences