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[1] at 34.457°N 115.837°E / 34.457; 115.837.[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]

Time code

BPC transmits the time every 20 seconds, using an amplitude-modulated binary code sent at 2 bits per second.

To encode each pair of bits, the transmitter is suppressed (turned off or greatly attenuated) at the beginning of each second, and restored to full power after a multiple of 0.1 seconds. The duration of the gap encodes the bits, as follows:

BPC bit coding
Signal reduced at the beginning of each second
DurationMSbitLSbit
  0 msEnd of time code
100 ms00
200 ms01
300 ms10
400 ms11

If there is no signal suppression for an entire second, that is a special marker which delimits the end of one time code and the beginning of the next.

BPC time code,[5] sent every 20 seconds
SecondMSbit
LSbit		Meaning SecondMSbit
LSbit		Meaning
0040
20		Second (00, 20 or 40) 100Unused
16Day of month (01–31)
010
0		Unused 118
4
028
4		Hour (00–11)122
1
032
1		138
4		Month (01–12)
0432
16		Minute (00–59)142
1
058
4		1532
16		Year (00–99)
062
1		168
4
070Unused 172
1
4Day of week
1=Monday
7=Sunday
082
1		1864
P2		Year MSbit
Even parity over 10–17
0912
P1		Hour (0=AM 1=PM)
Even parity over 01–09		 19—End of time code
No signal gap

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

References
  1. "Low-frequency radio time signals". Cl.cam.ac.uk. Retrieved 2011-10-20.
  2. "::时间服务::". Archived from the original on 2012-06-17. Retrieved 2013-03-16.
  3. 西安高华科技有限公司 (2020-01-10). "河南商丘BPC电波塔发播时间公布" (in Chinese). Archived from the original on 2021-07-29. Retrieved 2021-07-29.
  4. Feng, Ping; Wu, Guichen; Bai, Yan; Ding, Xiaofeng (August 2010), Tan, Jiubin; Wen, Xianfang (eds.), "Additional spread spectrum modulation timing method in BPC", Sixth International Symposium on Precision Engineering Measurements and Instrumentation. Proceedings of the SPIE, Proceedings of SPIE, 7544: 75441X–75441X–6, Bibcode:2010SPIE.7544E..1XF, doi:10.1117/12.885845, S2CID 110865336
  5. Description (in Chinese) Includes sample of time code captured around 2019-12-01 15:52.
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