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Mission of Japan Standard Time Group


Dissemination of JST

The standard time and frequency transmission (JJY*) is a radio wave to supply the standard frequency and JST throughout Japan.
The primary clock of broadcast stations and telephone is synchronized with JST by reception of this standard radio wave.
Ohtakadoya-yama LF Standard Time and Frequency Transmission Station has transmitted the standard wave (40 kHz) since June 1999.
Hagane-yama LF Standard Time and Frequency Transmission Station has transmitted the standard wave (60 kHz) since October 2001.
The LF standard time and frequency transmission signal includes a time code which contains the following information; minute, hour, annual date (counted from January 1), year (last 2 digits of the dominical year), and day of the week. This time code is used for reception devices such as radio controlled clocks with automatic time correction functions.

The time code signal is expected to contribute to a wide range of applications, such as clocks in home electronic appliances, cameras, automobile clocks, and the built-in clocks of measuring instruments and seismometers. The standard frequency supplied by the LF standard time and frequency transmission signal is also expected to serve as a precise frequency standard for a variety of applications: measuring instruments, communication devices, standards for the master standard devices of electronic manufacturers, standard oscillators of ground-based digital broadcasting, and highly precise frequency standards.
For your reference: although the LF standard time and frequency transmission signal has ordinarily been transmitted for 24 hours a day, it may temporarily be interrupted because of maintenance work on devises and antennas, or measures against lightning storms.

*JJY is the call sign of the radio station and form a registered trademark(T4355749) of the NICT

(Click the picture above to see larger picture)

 In today’s computerized society, most computers transfer every data via networks. During these processes, file update times are usually defined by the built-in clocks of the individual computers. However, these built-in clocks of PCs are not highly precise, and so, without regular periodic time synchronization, inconsistencies are bound to occur in file information. Therefore, the use of NTP (Network Time Protocol) has spread so as to synchronize the time of networked computers.
The Japan Standard Time Group(JSTG) offers “Time Information Service by Networks” to time-dissemination enterprises authorized as Time Business, and internet related corporations.
Through this service, stable time information is provided by directly connecting users’ servers with an NTP server linked up with JST. The JSTG also offers an “Internet Time Service” to general users so that they too are able to use an NTP server (ntp.nict.jp) that links up with JST.

(Click the picture above to see larger picture)

Telephone JJY

Conventionally, high-frequency (HF) standard transmissions were widely used to synchronize clocks for business applications, such as the master clocks of broadcasting stations. On August 1, 1995, a new system came into operation, supplying a high-precision time signal electronically via analog telephone lines (telephone JJY). A personal computer, modem, and commercial communications software are all that is required for users to acquire time information with precise adjustment for delays in the telephone line.
Dedicated receivers for commercial use perform time synchronization using JST with precision of less than one millisecond, equivalent to the precision of conventional commercial HF receivers, by measuring and correcting the delay in communication lines using the bi-directional telephone connection. Dedicated receivers are widely used in commercial applications, especially at broadcasting stations. For more information, please visit http://jjy.jp/.

A new system for supplying JST via NTT Hikari Denwa line networks (Hikari telephone JJY) has been constructed and started an experimental operation in May 2016. The NICT aims to shift the present telephone JJY to this new system in the future. Further information will be updated on JSTG website accordingly.

As part of our duty of providing the standard frequency, our Group performs the frequency standard calibration. The frequency deviation of the frequency standard is taken measures against the national frequency standard.

Calibration of frequency standard
1) Calibration in compliance with the Radio Law

2) Calibration in compliance with the Measurement Law
(jcss calibration)

3) Commissioned calibration
a) Calibration of frequency standard (carried in)
b) Remote calibration
(conducted by time comparison through GPS satellites)

As for calibration in compliance with the Measurement Law (2), our Group is a designated calibration organization authorized by the Minister of Economy, Trade, and Industry, and we issue calibration certificates required by our clients to operate as certified businesses.
In terms of (3), commissioned frequency calibration, our calibration system was certified to be accordance with the ISO/IEC 17025:2005 (JIS Q 17025:2005) international standard and so is capable of issuing calibration certificates for global Mutual Recognition Arrangements (MRA). (Except for the disciplined oscillators; which transmit frequency by means of synchronizing with external signals.)
As for 3), in addition to commissioned frequency calibration, measurements will also be made of short-term stability.

"Carried-in" calibration is available     "Remote" calibration is available    "N/A"
Radio Law Measurement Law Commissioned
Calibraion of frequency standard Carried-in Carried-in Remote Carried-in Remote
Measurement of short-term stability N/A N/A Carried-in

 For further information, please visit http://cal.nict.go.jp/.

Frequency Standard Calibration System Frequency Standard Calibration System

Frequency Standard Calibration System