BPM is the People's Republic of China

People's Republic of China

China , officially the People's Republic of China , is the most populous country in the world, with over 1.3 billion citizens. Located in East Asia, the country covers approximately 9.6 million square kilometres...

's national time signal

Time signal

A time signal is a visible, audible, mechanical, or electronic signal used as a reference to determine the time of day.-Audible and visible time signals:...

 service, operated by the Chinese Academy of Sciences

Chinese Academy of Sciences

The Chinese Academy of Sciences , formerly known as Academia Sinica, is the national academy for the natural sciences of the People's Republic of China. It is an institution of the State Council of China. It is headquartered in Beijing, with institutes all over the People's Republic of China...

. It is located at 35°0′N 109°31′E.

It is broadcast from the National Time Service Center in Pucheng county

Pucheng County, Shaanxi

Pucheng County is a county of Weinan, Shaanxi, China....

 about 70 km northeast of Lintong.http://english.ntsc.cas.cn/rs/fs/200909/t20090917_39104.html (Along with an intermittent long-wave time code BPL on 100 kHz).

It broadcasts at 2.5, 5.0, 10.0, and 15.0 MHz, the same frequencies as WWV and WWVH.

BPC low-frequency service

There is also a low-frequency time code broadcast at 68.5 kHz.
BPC Shangqiu Low-Frequency Time-Code Radio Station (Shangqiu

Shangqiu

Shangqiu 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 and southeast respectively. An ancient city with a rich history, Shangqiu was also the first capital of the Shang...

 City, Henan Province, coordinates:34°56′54"N 109°32′34"E)
was 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

Transmission format

BPM transmits different signals on a half-hour schedule http://www.time.ac.cn/jianjie/3.htm, modulated with 1 kHz audio tones to provide second and minute ticks:

BPM transmission schedule http://www.time.ac.cn/jianjie/1.jpg

Minute		Duration	Transmission
00	30	10	UTC: 10 ms second ticks, 300 ms minute ticks.
10	40	5	Carrier (no time code)
15	45	10	UTC: 10 ms second ticks, 300 ms minute ticks.
25	55	4	UT1: 100 ms second ticks, 300 ms minute ticks.
29	59	1	Station identification: Morse call sign for 40 seconds, then voice announcement for 20 seconds.

BPM is idiosyncratic in that it transmits UT1 time between minutes 25 through to 29 and 55 through to 59, which creates an odd click-beep effect when heard below a stronger time signal station such as WWV.http://tufi.alphalink.com.au/time/time_hf.html

BPC includes both a conventional amplitude modulated

Amplitude modulation

Amplitude modulation is a technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. AM works by varying the strength of the transmitted signal in relation to the information being sent...

time code and an additional spread-spectrum time code, about which little is known.