BPC (time signal)
{{Short description|Time signal radio station in China}}
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.[http://english.ntsc.cas.cn/ns/es/201003/t20100317_51581.html], 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{{cite web|url=http://www.cl.cam.ac.uk/~mgk25/time/lf-clocks/ |title=Low-frequency radio time signals |publisher=Cl.cam.ac.uk |access-date=2011-10-20}} at {{Coord|34.457|N|115.837|E|type:landmark_region:CN-61|display=it}}.{{cite web|url=http://www.time.ac.cn/serve/e_c.htm |title=::时间服务:: |access-date=2013-03-16 |url-status=dead |archive-url=https://web.archive.org/web/20120617220116/http://www.time.ac.cn/serve/e_c.htm |archive-date=2012-06-17 }}
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).{{cite web|url=http://www.gaohua-tech.com/article-2-178.aspx|title=河南商丘BPC电波塔发播时间公布|author=西安高华科技有限公司|date=2020-01-10|lang=zh|access-date=2021-07-29|archive-date=2021-07-29|archive-url=https://web.archive.org/web/20210729090547/http://www.gaohua-tech.com/article-2-178.aspx|url-status=dead}} 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.{{Citation |title=Sixth International Symposium on Precision Engineering Measurements and Instrumentation |last1=Feng |first1=Ping |last2=Wu |first2=Guichen |last3=Bai |first3=Yan |last4=Ding |first4=Xiaofeng |chapter=Additional spread spectrum modulation timing method in BPC |date=August 2010 |volume=7544 |pages=75441X–75441X–6 |editor1=Tan, Jiubin |editor2=Wen, Xianfang |doi=10.1117/12.885845 |bibcode=2010SPIE.7544E..1XF |series=Proceedings of SPIE |s2cid=110865336 |chapter-url=https://ia800704.us.archive.org/view_archive.php?archive=/24/items/wikipedia-scholarly-sources-corpus/10.1117.zip&file=10.1117%252F12.885845.pdf}} The paper appears to be describing a proposed addition to the time signal, but the tenses are confusing and sometimes implies that the addition 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.{{cite AV media |title=68.5 time signal |date=27 Dec 2014 |first=Vladimir |last=Nikitin |via=YouTube |url=https://youtube.com/watch?v=hPJmblTgnXg}} 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 UTC, as CST is UTC+8.
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:
| class="wikitable"
|+ BPC bit coding | ||
| Duration | MSbit | LSbit |
|---|---|---|
| align=right |0 ms | colspan=2 bgcolor=lightblue| Start of time code | |
| align=right | 100 ms | 0 | 0 |
| align=right | 200 ms | 0 | 1 |
| align=right | 300 ms | 1 | 0 |
| align=right | 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.
| class="wikitable"
|+ BPC time code,{{URL|https://web.archive.org/web/20221227111420/https://www.arduino.cn/thread-104748-1-1.html|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. sent every 20 seconds on the minute | ||||
| Second | MSbit LSbit | Meaning
|rowspan=14| ! Second | MSbit LSbit | Meaning |
|---|---|---|---|---|
| 00 | bgcolor=lightblue| — | bgcolor=lightblue| Start of time code No signal gap | 10 | 12 P1 | Hour (0=AM 1=PM) Even parity over 01–09 |
| rowspan=2| 01 | rowspan=2| 40 20 | rowspan=2| Second (00, 20 or 40)
|rowspan=2| 11 | bgcolor=lightgrey| 0 | bgcolor=lightgrey| Unused |
| 16 | rowspan="3" | Day of month (01–31) | |||
| 02 | bgcolor=lightgrey| 0 0 | bgcolor=lightgrey| Unused
| 12 | 8 4 | |
| 03 | 8 4 | rowspan=2| Hour (00–11) | 13 | 2 1 |
| 04 | 2 1 | 14 | 8 4 | rowspan=2| Month (01–12) |
| 05 | 32 16 | rowspan=3| Minute (00–59) | 15 | 2 1 |
| 06 | 8 4 | 16 | 32 16 | rowspan=5| Year (00–99) |
| 07 | 2 1 | 17 | 8 4 | |
| rowspan=2| 08 | bgcolor=lightgrey| 0 | bgcolor=lightgrey| Unused
|rowspan=2| 18 | rowspan=2| 2 1 | |
| 4 | rowspan=3| Day of week 1=Monday 7=Sunday | |||
| rowspan=2| 09 | rowspan=2| 2 1 | rowspan=2| 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.
References
{{Reflist}}
External links
- [https://web.archive.org/web/20120617220116/http://www.time.ac.cn/serve/e_c.htm 低频时码授时], from the National Time Service Center, Chinese Academy of Sciences
{{Time signal stations}}
{{Time signal authorities}}
Category:Time signal radio stations
Category:Radio stations established in 2002
Category:2002 establishments in China
{{radio-comm-stub}}