provide for constant transmission of the time code. However, it is not possible given the current design configuration for one site to act as a lower power alternate frequency backup for the other. The backups are set to automatically take over in the event that the primary transmission system 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. 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. The Mount Otakadoya transmitter survived the 2011 Tōhoku earthquake and tsunami, but is 17 km from the Fukushima I nuclear accidents, and was powered down when it was evacuated on March 12 (19:46 JST) due to the 20 km radius evacuation order. It was re-enabled April 21. JJY Time Code As with most longwave time code stations, the JJY signal is amplitude-modulated to send one bit per second, transmitting a complete time code every minute. The time