BPC is the callsign of a

time signal A time signal is a visible, audible, mechanical, or electronic signal used as a reference to determine the time of day. Church bells or voices announcing hours of prayer gave way to automatically operated chimes on public clocks; however, au ...

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 The Chinese Academy of Sciences (CAS; ) is the national academy for natural sciences and the highest consultancy for science and technology of the People's Republic of China. It is the world's largest research organization, with 106 research i ...

and Xi'an Gaohua Technology Co., Lt

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 Shangqiu ( zh, ), Postal romanization, alternately romanized as Shangkiu, is a city in eastern Henan province, Central China. It borders Kaifeng to the northwest, Zhoukou to the southwest, and the provinces of Shandong and Anhui to the northeast ...

Henan Province Henan; alternatively Honan is a province in Central China. Henan is home to many heritage sites, including Yinxu, the ruins of the final capital of the Shang dynasty () and the Shaolin Temple. Four of the historical capitals of China, Luo ...

at . BPC broadcasts at 90 kW for 20 hours per day, with a 4-hour break from 05:00–09:00

China Standard Time The time in China follows a single standard UTC offset, time offset of UTC+08:00, where Beijing is located, even though the country spans five geographical time zones. It is the largest sovereign nation in the world that officially observes only ...

daily (21:00–01:00 UTC). 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.

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

of the beginning of that block. 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: If there is no signal reduction at all, that is a special marker which marks the beginning of the time code. Note that the bits sent in the same second as the parity bits are not parity-checked.

References

External links

低频时码授时
from the National Time Service Center, Chinese Academy of Sciences Time signal radio stations Radio stations established in 2002 2002 establishments in China {{radio-comm-stub