IERS TDC NEWS No.11 TR7

Construction of New LF Station for Time and Frequency Service

Michito Imae(imae(AT)nict.go.jp)

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

HF signal has about 10^-7 or 10^-8 frequency stability at receiving point due to ionosphere while the transmission signal has 10^-12 to 10^-13 stability.
around Japan area there are several HF standard time service stations, such as BPM from China, BSF from Taiwan, HLA from Korea, and WWVH from Hawaii. Due to these foreign standard time signals, it is difficult to discriminate JJY from the others, especially in the western part of Japan.

On the other hand LF signal has following advantages over the HF signal

High stability, about 10^-11 to 10^-12, in the area of ground wave
There is no interference time service signal using Japanese LF band (40 kHz) around Japan
There is a big market, such as radio controlled clocks and watches, using LF time signals

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

(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.

(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.

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)

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