JJY

JJY is the Japanese longwave time signal service, the national time signal broadcast for Japan. It is operated by the National Institute of Information and Communications Technology (NICT) and provides UTC-synchronized time information to radio receivers. The service is used for clock synchronization in consumer devices, laboratories, and industrial systems that require a reliable time reference.

JJY uses multiple low-frequency transmitters on longwave bands to achieve broad coverage. The system currently employs two primary transmission frequencies, around 40 kHz and 60 kHz, broadcast from different sites. The multi-frequency arrangement enhances reliability and reception across Japan under varying atmospheric conditions and terrain.

The transmitted signal carries a dedicated time code embedded in the carrier, enabling receivers to determine the current year, month, day, hour, and minute, with the seconds encoded to maintain precise timekeeping. The code is designed to be decoded by a range of receivers, from simple consumer clocks to professional timing equipment, to synchronize their local time to UTC.

Reception characteristics reflect the nature of longwave signals: they can cover large distances, especially at night, when propagation conditions are favorable. Actual reception quality depends on factors such as location, local interference, and antenna setup. JJY remains one of several global time-signal services used to maintain accurate time across devices and infrastructure.

See also: DCF77, MSF, WWVB, and other national time signal services.