BPM: China's time signal from Lintong on 10 MHz

What you hear

At first BPM sounds like any other time station: a short tone burst every second, a longer one at the start of the minute, a carrier underneath. Stay for a while and the difference shows. For most of each half hour the ticks mark UTC, the civil time of the world. For a few minutes in each half hour they switch to UT1, the time given by the rotation of the Earth, which runs ahead of or behind UTC by a fraction of a second; the pulses become noticeably longer and the rhythm shifts by that fraction. Then come a few minutes of bare carrier, and shortly before the half hour and the hour the station identifies itself: BPM in Morse, followed by a voice announcement in Chinese naming the station and the time. There is no English on the air and no audio note between the ticks, so the station is quieter than WWV in the silent stretches.

Who transmits and why

BPM belongs to the National Time Service Center of the Chinese Academy of Sciences at Lintong, on the outskirts of Xi'an in Shaanxi province, the institute that keeps China's standard time. The station puts that time on shortwave on 2500, 5000, 10000 and 15000 kHz: 5 and 10 MHz around the clock, 2.5 MHz in the Chinese night, 15 MHz in the Chinese day. The UT1 pulses are a service for surveyors, astronomers and navigators who need the rotation-based time rather than the atomic one. The same institute runs a long-wave sister station, BPL on 100 kHz, and the 68.5 kHz BPC signal that radio-controlled clocks in China listen to.

The 10 MHz frequency is shared by international arrangement with WWV in Colorado and WWVH in Hawaii. Each station is meant to be heard on its own side of the planet, and for the most part that is how it works, with the Pacific as the meeting ground.

When and where to listen

Across China, Japan, Korea and South-East Asia BPM on 10 MHz is strong day and night, and receivers in Japan, Taiwan and Thailand hear it like a local. From Australia and the Pacific it comes in well at night, and from a receiver in Hawaii it mixes with WWVH: two sets of ticks, slightly out of step because of the different path lengths, an English voice in one part of the minute and a Chinese one in another. From Europe BPM is a night catch: the best hours are from the small hours until a little after European sunrise, when the path across Asia is in darkness, and the chance improves with every receiver you pick further east, in Finland, Poland or Russia. At that hour the 5 MHz outlet can be stronger than 10 MHz.

AM is the right mode for the full-carrier signal. If an English voice appears on 10 MHz it is WWV or WWVH coming through the same frequency; a narrow filter will usually not separate them, but the voices never overlap, because each station announces in its own seconds of the minute.

In ShackDeck

Station catalogue → Time signals → BPM China 10 MHz. The program picks a public receiver that covers 10 MHz and is placed to hear the station, tunes it to 10000 kHz in AM and shows the waterfall, where the longer UT1 pulses are plain to see. No receiver, antenna or account of your own is needed. If what comes out is English, the receiver is on the American side of the world and you are listening to WWV; choose a receiver in East Asia instead.