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., 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 05:00–09:00 China Standard Time 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.

Time code

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 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.

Second	MSbit LSbit	Meaning	Second	MSbit LSbit	Meaning
00	—	Start of time code No signal gap	10	12 P1	Hour Even parity over 01–09
01	40 20	Second	11	0	Unused
01	40 20	Second	11	16	Day of month
02	0 0	Unused	12	8 4	Day of month
03	8 4	Hour	13	2 1	Day of month
04	2 1	Hour	14	8 4	Month
05	32 16	Minute	15	2 1	Month
06	8 4	Minute	16	32 16	Year
07	2 1	Minute	17	8 4	Year
08	0	Unused	18	2 1	Year
08	4	Day of week 1=Monday 7=Sunday	18	2 1	Year
09	2 1	Day of week 1=Monday 7=Sunday	19	64	Year
09	2 1	Day of week 1=Monday 7=Sunday	19	P2	Even parity over 11–18

Note: The bits sent in the same second as the parity bits are not parity-checked.