Construction of New LF Station for Time and Frequency Service

Michito Imae(imae(AT)

Communications Research Laboratory
4-2-1 Nukui-kita, Koganei, Tokyo 184-8795, Japan

1. Background of New LF Station

Communications Research Laboratory (CRL) has the responsibility for national frequency and time standards in Japan. Depending on this charter CRL has been engaged in research and services in this domain, such as

(1) Development of primary frequency standards,
(2) Time keeping,
(3) International precise time transfer,
(4) Dissemination of standard frequency and time signals.
(5) Related basic researches.

Concerning the dissemination of standard frequency and time, CRL employs several dissemination ways, such as standard time signal transmission using HF and LF bands, dial-up time service using telephone lines (called Telephone JJY) and Network Time Protocol stratum-1 server for computer networks.

The construction of a new LF station for time and frequency service is one of the activities for dissemination service at CRL.

2. Why LF Time Service?

CRL started transmission of JJY (HF time signal service) in 1940. But its quality or frequency stability is not enough for recent needs, because On the other hand LF signal has following advantages over the HF signal In the global view, the ground standard time service is shifting to LF band from HF band, such as DCF-77 and MSL in England, increased power of WWVB in USA.

Of course this is the age of GPS, and using GPS signals everyone can make easily obtain positioning to better than 100 m and get time signals better than 1 microsecond. But in our policy, the LF time signal can coexist with GPS for the following reasons:

(1)the frequency stability of LF signal is of the same order as GPS in the case of SA,
(2)the receiver of LF signal is more simple compared to a GPS receiver,
(3)LF signal can be received inside buildings.

3. Outline of CRL's New LF Station

Location :southern part of Fukushima prefecture (about 200 km north of Tokyo)
Antenna type:top loading umbrella type antenna mounted on a 250 m main tower
Carrier Frequency :40 kHz
Transmitter :50 kW (solid state type)
Effective radiation power : > 10 kW (more than ten times greater than present station)

Construction schedule
Fiscal year 1997 :building and bases for antenna
Fiscal year 1998 :antenna tower, transmitters, etc.

4. Applications of LF Signal

Application areas of the new LF standard signal are expected to be the following:
For time signal:
Radio controlled clocks and watches
Time control of public transportation
Time maintenance of meteorological equipment and seismometers, etc.
For frequency standard:
Keep tractability of the frequency standard to the national frequency standard for industry
Radio frequency regression

Updated on November 20, 1997. Return to CONTENTS