BPC (time signal)
BPC is the callsign of a low-frequency time signal broadcast from the Shangqiu Time-Code Radio Station. Operating since April 1, 2002,[1] the station was jointly established by the National Time Service Center (NTSC) of the Chinese Academy of Sciences and Xi'an Gaohua Technology Co., Ltd.
However, on February 16, 2021, the major cooperation agreement between the National Time Service Center (NTSC) and Xi'an Gaohua Technology Co., Ltd. expired, and the two parties did not renew the partnership. Since then, the NTSC has independently maintained the signal transmission.[2]
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[3] at 34°27′23″N 115°50′13″E / 34.4565°N 115.8369°E.[1]
BPC broadcasts at 90 kW for 20 hours per day, with a 4-hour break from 05:00–08:00 China Standard Time (21:00–00:00 UTC) daily.[1] BPC transmits an amplitude-modulated time code during the first 400 ms of each second, and an unmodulated carrier during the last 600 ms. An additional phase-modulated spread-spectrum time code was proposed,[4] but there is no evidence that it has been implemented.
The aging infrastructure periodically undergoes extended maintenance; for example, in June 2026, the NTSC announced a 45-day scheduled maintenance on the main antenna system, temporarily reducing daily broadcast hours.[5]
Time code
[edit]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.[6]
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: The bits sent in the same second as the parity bits are not parity-checked.
References
[edit]- 1 2 3 "时间服务". Archived from the original on 2004-04-02. Retrieved 2013-03-16.
- ↑ 中国科学院国家授时中心. "中国科学院国家授时中心关于河南商丘低频时码发播台运行管理的公告----中国科学院国家授时中心". www.ntsc.ac.cn. Archived from the original on 2021-10-23. Retrieved 2021-10-15.
- ↑ "Low-frequency radio time signals". Cl.cam.ac.uk. Retrieved 2011-10-20.
- ↑ Feng, Ping; Wu, Guichen; Bai, Yan; Ding, Xiaofeng (August 2010), "Additional spread spectrum modulation timing method in BPC" (PDF), in Tan, Jiubin; Wen, Xianfang (eds.), Sixth International Symposium on Precision Engineering Measurements and Instrumentation, Proceedings of SPIE, vol. 7544, pp. 75441X–75441X–6, Bibcode:2010SPIE.7544E..1XF, doi:10.1117/12.885845, S2CID 110865336, archived from the original on 2018-09-21 The paper describes a proposed addition to the time signal, although the tenses are muddled, with portions in the present tense implying that the phase-modulated signal is operational. Sampled data captured January 2026 (see screen shot above) shows no phase jumps that would indicate phase-shift keying is present.[original research]
- ↑ "中国科学院国家授时中心关于临时调整商丘低频时码授时台发播时间的公告----中国科学院国家授时中心". ntsc.cas.cn. Retrieved 2026-07-27.
- ↑ Nikitin, Vladimir (27 Dec 2014). 68.5 time signal – via YouTube. The audio quality is good enough that the AM modulation can easily be seen in an audio editor. The sample is 65 seconds long, from 23:33:06 to 23:34:11 displayed time, so includes two complete and two partial time frames. In the last 11 seconds of the video, starting at 23:34:00 on a Saturday, the encoded time of day is — 00 00 01 11 10 00 10 01 11 00, which decodes to 07:34:00 on a Sunday. This makes sense if the displayed time is UTC, as CST is UTC+8.
- ↑ Description (in Chinese) Includes sample of time code captured around 2019-12-01 15:52. The time code diagram starts with the seconds field numbered "0" and ends with the marker numbered "19" but note in the text below that it corresponds to second 1, 21 or 41. The screenshot of a waterfall plot with the BPC signal shows that there is no signal reduction at 19:37:40.
External links
[edit]- 低频时码授时, from the National Time Service Center, Chinese Academy of Sciences
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