jjy
JJY is the call sign for Japan's long-wave time signal, operated by the National Institute of Information and Communications Technology (NICT). Two transmitter stations provide nationwide coverage: Otakadoya-yama in Fukushima Prefecture (40 kHz, 50 kW) and Hagane-yama in Saga Prefecture (60 kHz, 50 kW). Together they broadcast Japan Standard Time (JST) 24 hours a day.
The JJY time code is transmitted via amplitude modulation (AM) of the carrier wave. A pulse is emitted at the start of each second, and its width encodes one of three values: 0.8 seconds for bit 0, 0.5 seconds for bit 1, and 0.2 seconds for a position marker used for synchronization. A complete frame spans 60 seconds and contains the year, month, day, hour, minute, and day of the week, all encoded in BCD (Binary-Coded Decimal).
The dual-station setup covers all of Japan. Otakadoya-yama primarily serves eastern Japan while Hagane-yama covers the west, with each complementing the other. At night, ionospheric reflection extends the reception range, sometimes allowing reception in neighboring countries such as South Korea, Taiwan, and coastal China. Indoors, reinforced concrete walls attenuate the signal significantly, so placing a radio-controlled clock near a window improves reception.
Was this article helpful?
nict
NICT is Japan's national research institute responsible for generating, maintaining, and distributing Japan Standard Time (JST), operating a fleet of atomic clocks and transmitting the JJY time signal.
radio-controlled-clock
A radio-controlled clock receives longwave time signals broadcast by a national standards authority and automatically corrects its internal quartz timekeeping, maintaining accuracy equivalent to the reference signal when reception succeeds.
jst
JST (Japan Standard Time) is the standard time of Japan at UTC+9, based on the 135th meridian east. Japan does not observe daylight saving time.