JJY
From Wikipedia, the free encyclopedia
JJY is the call sign of a low frequency 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 (NICT), an independent administrative institution affiliated with the Ministry of Internal Affairs and Communications 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 antenna 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 possibility of atmospheric interference. The calculated accuracy of JJY's signal is 1x10-11.
Japan Standard Time is set by a caesium atomic clock in Tokyo. This information is sent to the transmitter stations and is used to set a caesium atomic clock at each station. These clocks are housed in an environmentally controlled and electromagnetically 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.
Like WWVB in the United States, the signal of JJY is used to synchronize consumer radio-controlled clocks sold throughout Japan.
[edit] History and former shortwave station
On January 30, 1940, the Communications Research Laboratory (the predecessor of NICT), began operations of JJY as a shortwave station, broadcasting at 4, 7, 9, and 13 MHz. Over the years, these were dropped and by the late 1950s, JJY was transmitting its time signal on standard frequencies of 2.5, 5, 8, 10, and 15 MHz. The 2.5 and 15 MHz broadcasts terminated in 1996. The time signals included announcements of the time, in both Morse code and by a female voice, before every tenth minute: for example, "JJY JJY 1630 JST" (the voice announcement of the time being in Japanese).
Experimental station JG2AS began broadcasting on January 10, 1966, providing digitally encoded time signals in the longwave band at 40 kHz. In 1997, the CRL, determining that the longwave time signal was more accurate when received, subject to less interference, and in wider use than the shortwave time signal, decided to construct a new longwave time station and gradually eliminate the shortwave broadcasts. The first official longwave station of JJY began broadcasting from Mount Otakadoya at 40 kHz on June 10, 1999, and the shortwave broadcasts finally ceased operation on March 31, 2001. On October 1, 2001, the 60 kHz longwave transmission from Mount Hagane began.
[edit] References
- Low Frequency Standard Time and Frequency Transmission Facilities Pamphlet (PDF). National Institute of Information and Communications Technology (April 2003). Retrieved on 2006-08-22.
- "History of standard time and standard frequency signal" (Japanese). National Institute of Information and Communications Technology. Retrieved on 2007-11-21.
- "Construction of New LF Station for Time and Frequency Service". Communications Research Laboratory (November 20, 1997). Retrieved on 2007-11-21.
- "Time and Frequency Keeping and its Distribution System at CRL" (PDF). Proceedings of the Precise Time and Time Interval (PTTI) Meeting, Vol. 28 #3 (1996). Retrieved on 2007-11-21.
- "Overview of Research Activities on Time and Frequency at the Communications Research Laboratory" (PDF). Proceedings of the Precise Time and Time Interval (PTTI) Meeting, Vol. 31 p. 241 (1999). Retrieved on 2007-11-21.
- Elliott, Kim Andrew. (March 10, 2001). "Communications World" [radio transcript]. Voice of America. Retrieved on 2007-11-21.
[edit] External links
- Japan Standard Time Group
- Coordinates of Mount Otakadoya transmitter:
- Coordinates of Mount Hagane transmitter:
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