JJY

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JJY is the call sign of a longwave time signal radio station.

The station is located in Japan and broadcasts from two sites, one on Mount Otakadoya, near Fukushima, and the other on Mount Hagane, located on Kyushu Island. JJY is operated by the National Institute of Information and Communications Technology, a branch of the Japanese government.

The Mount Otakadoya site is located at an elevation of 790 meters (2,590 ft). It broadcasts a 50 kW signal on 40 kHz from an umbrella top-loading antenna situated 250 meters (820 ft) above the ground.

The Mount Hagane site is located at an elevation of 900 meters (2,950 ft). It broadcasts a 50 kW signal on 60 kHz to avoid interfering with the Otakadoya site as their signals overlap. The antenna for the Hagane site is also an umbrella top loading anteanna and is situated 200 meters (650 ft) above the ground.

Both carrier signals contain an identical pulse-width modulated time code, and are transmitted 24 hours a day. Low frequency (LF) transmissions are used to enhance accuracy and reduce the posibility of atmospheric interference. The calculated accuracy of JJY's signal is 1x10^-11.

Japan Standard Time is set by a cesium atomic clock in Tokyo. This information is sent to the transmitter stations and is used to set a cesium atmoic clock at each station. These clocks are housed in an environmentally controlled and electromagenteically shielded room to prevent outside interference with the clocks.

Each station has an identical setup of equipment. A dual set of transmitters, a primary and a backup, provide for constant transmission of the time code. The backup is set to automatically take over in the event that the primary has a failure. The Time Signal Control Room generates the standard LF signal and time code that is broadcast. The Impedance Matching Room has a matching transformer to perform impedance matching between the transmitter and the antenna. Due to the high power of radio frequency signals that pass through the room, it is completely shielded in copper and is off-limits during broadcasts.