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[1] at 34°27′25″N 115°50′13″E / 34.457°N 115.837°E.[2]
BPC broadcasts at 90 kW for 20 hours per day, with a 4-hour break from 05:00–09:00 China Standard Time daily (21:00–1:00 UTC).[3] BPC includes both conventional amplitude modulated time code and additional spread-spectrum time code, about which little is known.[4]
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.[5]
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:
Duration | MSbit | LSbit |
---|---|---|
0 ms | Start of time code | |
100 ms | 0 | 0 |
200 ms | 0 | 1 |
300 ms | 1 | 0 |
400 ms | 1 | 1 |
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 (0=AM 1=PM) Even parity over 01–09 | |
01 | 40 20 |
Second (00, 20 or 40) | 11 | 0 | Unused | |
16 | Day of month (01–31) | |||||
02 | 0 0 |
Unused | 12 | 8 4 | ||
03 | 8 4 |
Hour (00–11) | 13 | 2 1 | ||
04 | 2 1 |
14 | 8 4 |
Month (01–12) | ||
05 | 32 16 |
Minute (00–59) | 15 | 2 1 | ||
06 | 8 4 |
16 | 32 16 |
Year (00–99) | ||
07 | 2 1 |
17 | 8 4 | |||
08 | 0 | Unused | 18 | 2 1 | ||
4 | Day of week 1=Monday 7=Sunday | |||||
09 | 2 1 |
19 | 64 | |||
P2 | Even parity over 11–18 |
Note that the bits sent in the same second as the parity bits are not parity-checked.