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.
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.
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.
