JJY is the
call signIn broadcasting and radio communications, a call sign is a unique designation for a transmitting station. In some countries they are used as names for broadcasting stations, but in many other countries they are not...
of a
low frequencyLow frequency or low freq or LF refers to radio frequencies in the range of 30 kHz–300 kHz. In Europe, and parts of Northern Africa and of Asia, part of the LF spectrum is used for AM broadcasting as the longwave band. In the western hemisphere, its main use is for aircraft beacon,...
time signalA time signal is a visible, audible, mechanical, or electronic signal used as a reference to determine the time of day.-Audible and visible time signals:One sort of public time signal is, of course, a striking clock...
radio stationRadio broadcasting is an audio broadcasting service, broadcast through the air as radio waves from a transmitter to an antenna and a thus to a receiving device. Stations can be linked in radio networks to broadcast common programming, either in syndication or simulcast or both...
.
The station is located in
Japanis an island country in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, People's Republic of China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
and broadcasts from two sites, one on Mount Otakadoya, near
Fukushimais the capital city of Fukushima Prefecture in the Tōhoku region of Japan.It lies about 250 km north of Tokyo and 80 km south of Sendai . Although the city is located inland, the prefecture has several Pacific ports such as Onahama and Soma...
, and the other on Mount Hagane, located on
Kyushu Islandor Kyushu is the 3rd-largest island of Japan and most southwesterly of its four main islands. Its alternate ancient names include Kyūkoku , Chinzei , and Tsukushi-no-shima...
. JJY is operated by the
National Institute of Information and Communications TechnologyThe National Institute of Information and Communications Technology is Japan's national research institute for information and communications. It is located at 4-2-1 Nukui-Kitamachi, Koganei, Tokyo 184-8795 Japan....
(NICT), an
independent administrative institutionAn Independent Administrative Institution is a newly designed type of legal body for Japanese governmental organizations regulated by the Basic Law on Reforming Government Ministries of 1998...
affiliated with the
Ministry of Internal Affairs and CommunicationsThe ' is a cabinet-level ministry in the government of Japan. The English name Ministry of Public Management, Home Affairs, Posts and Telecommunications was used prior to 2004...
of the Japanese government.
The Mount Otakadoya site is located at an elevation of 790 meters (2,590 ft). It broadcasts a 50
kWThe watt is a derived unit of power in the International System of Units . It measures rate of energy conversion. One watt is equivalent to 1 joule of energy per second....
signal on 40
kHzThe hertz is a unit of frequency. It is defined as the number of complete cycles per second. It is the basic unit of frequency in the International System of Units , and is used worldwide in both general-purpose and scientific contexts...
from an umbrella top-loading antenna situated 250 meters (820 ft) above the ground.
The Mount Hagane site is located at an elevation of 900 meters (2,950 ft).
JJY is the
call signIn broadcasting and radio communications, a call sign is a unique designation for a transmitting station. In some countries they are used as names for broadcasting stations, but in many other countries they are not...
of a
low frequencyLow frequency or low freq or LF refers to radio frequencies in the range of 30 kHz–300 kHz. In Europe, and parts of Northern Africa and of Asia, part of the LF spectrum is used for AM broadcasting as the longwave band. In the western hemisphere, its main use is for aircraft beacon,...
time signalA time signal is a visible, audible, mechanical, or electronic signal used as a reference to determine the time of day.-Audible and visible time signals:One sort of public time signal is, of course, a striking clock...
radio stationRadio broadcasting is an audio broadcasting service, broadcast through the air as radio waves from a transmitter to an antenna and a thus to a receiving device. Stations can be linked in radio networks to broadcast common programming, either in syndication or simulcast or both...
.
The station is located in
Japanis an island country in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, People's Republic of China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
and broadcasts from two sites, one on Mount Otakadoya, near
Fukushimais the capital city of Fukushima Prefecture in the Tōhoku region of Japan.It lies about 250 km north of Tokyo and 80 km south of Sendai . Although the city is located inland, the prefecture has several Pacific ports such as Onahama and Soma...
, and the other on Mount Hagane, located on
Kyushu Islandor Kyushu is the 3rd-largest island of Japan and most southwesterly of its four main islands. Its alternate ancient names include Kyūkoku , Chinzei , and Tsukushi-no-shima...
. JJY is operated by the
National Institute of Information and Communications TechnologyThe National Institute of Information and Communications Technology is Japan's national research institute for information and communications. It is located at 4-2-1 Nukui-Kitamachi, Koganei, Tokyo 184-8795 Japan....
(NICT), an
independent administrative institutionAn Independent Administrative Institution is a newly designed type of legal body for Japanese governmental organizations regulated by the Basic Law on Reforming Government Ministries of 1998...
affiliated with the
Ministry of Internal Affairs and CommunicationsThe ' is a cabinet-level ministry in the government of Japan. The English name Ministry of Public Management, Home Affairs, Posts and Telecommunications was used prior to 2004...
of the Japanese government.
The Mount Otakadoya site is located at an elevation of 790 meters (2,590 ft). It broadcasts a 50
kWThe watt is a derived unit of power in the International System of Units . It measures rate of energy conversion. One watt is equivalent to 1 joule of energy per second....
signal on 40
kHzThe hertz is a unit of frequency. It is defined as the number of complete cycles per second. It is the basic unit of frequency in the International System of Units , and is used worldwide in both general-purpose and scientific contexts...
from an umbrella top-loading antenna situated 250 meters (820 ft) above the ground.
The Mount Hagane site is located at an elevation of 900 meters (2,950 ft). It broadcasts a 50 kW signal on 60 kHz to avoid interfering with the Otakadoya site as their signals overlap. The antenna for the Hagane site is also an umbrella top loading antenna and is situated 200 meters (650 ft) above the ground.
Both
carrierIn telecommunications, a carrier wave, or carrier is a waveform that is modulated with an input signal for the purpose of conveying information. This carrier wave is usually of much higher frequency than the input signal....
signals contain an identical
pulse-width modulatedPulse-width modulation is a very efficient way of providing intermediate amounts of electrical power between fully on and fully off. A simple power switch with a typical power source provides full power only, when switched on...
time code and are transmitted 24 hours a day.
Low frequencyLow frequency or low freq or LF refers to radio frequencies in the range of 30 kHz–300 kHz. In Europe, and parts of Northern Africa and of Asia, part of the LF spectrum is used for AM broadcasting as the longwave band. In the western hemisphere, its main use is for aircraft beacon,...
(LF) transmissions are used to enhance accuracy and reduce the possibility of atmospheric interference. The calculated accuracy of JJY's signal is 1×10
−11.
Japan Standard TimeJapan Standard Time or JST is the standard timezone of Japan, and is 9 hours ahead of UTC. For example, when it is midnight in UTC, it is 9 am in Japan Standard Time. There is no daylight saving time, though its introduction has been debated several times...
is set by a
caesiumCaesium or cesium is the chemical element with the symbol Cs and atomic number 55. It is a soft, silvery-gold alkali metal with a melting point of , which makes it one of only five metals that are liquid at or near room temperature...
atomic clockAn atomic clock is a type of clock that uses an atomic resonance frequency standard as its timekeeping element. They are the most accurate time and frequency standards known, and are used as primary standards for international time distribution services, and to control the frequency of television...
in
Tokyo, officially , is one of the 47 prefectures of Japan and is located on the eastern side of the main island Honshū. The twenty-three special wards of Tokyo, each governed as a city, cover the area that was once the city of Tokyo in the eastern part of the prefecture, totaling over 8 million people....
. This information is sent to the transmitter stations and is used to set a caesium
atomic clockAn atomic clock is a type of clock that uses an atomic resonance frequency standard as its timekeeping element. They are the most accurate time and frequency standards known, and are used as primary standards for international time distribution services, and to control the frequency of television...
at each station. These clocks are housed in an
environmentally controlledHVAC is an acronym that stands for the closely related functions of "Heating, Ventilating, and Air Conditioning"-the technology of indoor environmental comfort...
and
electromagnetically shieldedElectromagnetic shielding is the process of limiting the penetration of electromagnetic fields into a space, by blocking them with a barrier made of conductive material. Typically it is applied to enclosures, separating electrical devices from the 'outside world', and to cables, separating wires...
room to prevent outside interference with the clocks.
Each station has an identical setup of equipment. A dual set of
transmitterA transmitter is an electronic device which, usually with the aid of an antenna, propagates an electromagnetic signal such as radio, television, or other telecommunications.-Transmitter types:...
s, a primary and a backup, provide for constant transmission of the time code. The backup is set to automatically take over in the event that the primary 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 transformerA balun, , is a type of electrical transformer that can convert electrical signals that are balanced about ground to signals that are unbalanced and vice versa. They are also often used to connect lines of differing impedance.Baluns can take many forms and their presence is not always obvious...
to perform
impedance matchingImpedance matching is the electronics design practice of setting the input impedance of an electrical load equal to the fixed output impedance of the signal source to which it is ultimately connected, usually in order to maximize the power transfer and minimize reflections from the load...
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.
The time code format is very similar to that of
WWVBWWVB is a NIST time signal radio station near Fort Collins, Colorado, co-located with WWV. WWVB is the station that radio-controlled clocks throughout North America use to synchronize themselves. The signal transmitted from WWVB is a continuous 60 kHz carrier wave, derived from a set of atomic...
in the
United StatesThe United States of America is a federal constitutional republic comprising fifty states and a federal district...
, and like it the signal of JJY is used to synchronize consumer
radio-controlled clocksA radio clock is a clock that is synchronized by a time code bit stream transmitted by a radio transmitter connected to a time standard such as an atomic clock. Such a clock may be synchronized to the time sent by a single transmitter, such as many national or regional time transmitters, or may...
sold throughout Japan.
History and former shortwave station
On January 30, 1940, the Communications Research Laboratory (the predecessor of NICT), began operations of JJY as a
shortwaveShortwave radio operates in the frequency range of 3,000 kHz to 30,000 kHz . Short wavelength corresponds to high frequency given the inverse relationship between frequency and wavelength, thus, “shortwave radio” is denominated so because its wavelengths are shorter than the long wave-lengths...
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 codeMorse code is a type of character encoding that transmits telegraphic information using rhythm. Morse code uses a standardized sequence of short and long elements to represent the letters, numerals, punctuation and special characters of a given message...
and by a female voice, before every tenth minute: for example, "JJY JJY 1630
JSTJapan Standard Time or JST is the standard timezone of Japan, and is 9 hours ahead of UTC. For example, when it is midnight in UTC, it is 9 am in Japan Standard Time. There is no daylight saving time, though its introduction has been debated several times...
" (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.
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 code is most similar to that transmitted by
WWVBWWVB is a NIST time signal radio station near Fort Collins, Colorado, co-located with WWV. WWVB is the station that radio-controlled clocks throughout North America use to synchronize themselves. The signal transmitted from WWVB is a continuous 60 kHz carrier wave, derived from a set of atomic...
, but each bit is reversed: on the second, the carrier is increased to full power. Some time during the second (depending on the bit to be transmitted), the carrier is reduced by 10 dB, to 10% power, until the beginning of the next second.
There are three different signals that are sent each second:
- 0 bits consist of 0.8 s of full power, followed by 0.2 s of reduced power.
- 1 bits consist of 0.5 s of full power, followed by 0.5 s of reduced power.
- Marker bits consist of 0.2 s of full power, followed by 0.8 s of reduced power.
As with WWVB, seconds 0, 9, 19, 29, 39, 49 and 50 of each minute are marker bits. The remaining 53 encode
Japan Standard TimeJapan Standard Time or JST is the standard timezone of Japan, and is 9 hours ahead of UTC. For example, when it is midnight in UTC, it is 9 am in Japan Standard Time. There is no daylight saving time, though its introduction has been debated several times...
using
binary-coded decimalIn computing and electronic systems, binary-coded decimal is an encoding for decimal numbers in which each digit is represented by its own binary sequence. Its main virtue is that it allows easy conversion to decimal digits for printing or display, and allows faster decimal calculations...
. JST does not include
summer timeSummertime may refer to:* Summer, one of the temperate seasons* Daylight saving time , advancing the clock one hour during summer...
, but bits are reserved to handle it. Leap second warning bits are also provided, these announce leap seconds starting at the beginning of the UTC month (09:00 JST on the first day of the month), and ending with the leap second insertion (just after 08:59 JST on the first day of the following month).
The full time code is as follows. The first 35 seconds are identical to WWVB, but after that it diverges, including some parity and day-of-week bits not in WWVB, and omitting
DUT1The time correction DUT1 is the difference between Universal Time , which is defined by Earth's rotation, and Coordinated Universal Time , which is defined by a network of precision clocks....
information.
| Bit |
Weight |
Meaning |
|
Bit |
Weight |
Meaning |
| :00 |
M |
Start of minute marker bit |
:30 |
8 |
Day of year (continued) |
| :01 |
40 |
Minutes |
:31 |
4 |
| :02 |
20 |
:32 |
2 |
| :03 |
10 |
:33 |
1 |
| :04 |
0 |
:34 |
0 |
Unused, always 0. |
| :05 |
8 |
:35 |
0 |
| :06 |
4 |
:36 |
PA1 |
Even parity of hours bits (:12–:18). |
| :07 |
2 |
:37 |
PA2 |
Even parity of minutes bits (:1–:8). |
| :08 |
1 |
:38 |
SU1 |
Currently unused, always 0. (Future:
change to/from summer time within 6 days.) |
| :09 |
P1 |
Marker bit |
:39 |
P4 |
Marker bit |
| :10 |
0 |
Unused, always 0. |
:40 |
SU2 |
Currently unused, always 0.
(Future: summer time is in effect.) |
| :11 |
0 |
:41 |
80 |
Year |
| :12 |
20 |
Hours |
:42 |
40 |
| :13 |
10 |
:43 |
20 |
| :14 |
0 |
:44 |
10 |
| :15 |
8 |
:45 |
8 |
| :16 |
4 |
:46 |
4 |
| :17 |
2 |
:47 |
2 |
| :18 |
1 |
:48 |
1 |
| :19 |
P2 |
Marker bit |
:49 |
P5 |
Marker bit |
| :20 |
0 |
Unused, always 0. |
:50 |
4 |
Day of week.
0=Sunday, 6=Saturday |
| :21 |
0 |
:51 |
2 |
| :22 |
200 |
Day of year
1=January 1
365=December 31
366=December 31, leap year |
:52 |
1 |
| :23 |
100 |
:53 |
LS1 |
Leap second at end of current UTC month. |
| :24 |
0 |
:54 |
LS2 |
Leap second type: 1 for added, 0 for deleted. |
| :25 |
80 |
:55 |
0 |
Unused, always 0. |
| :26 |
40 |
:56 |
0 |
| :27 |
20 |
:57 |
0 |
| :28 |
10 |
:58 |
0 |
| :29 |
P3 |
:59 |
P0 |
Marker bit. |
P0 is always the last second of a minute. In the event of a leap second, an additional 0 bit in inserted before it. LS1 and LS2 are normally both 0. Both bits are set to announce an inserted leap second at the end of the current UTC month.
Twice per hour (minutes 15 and 45), the last 20 seconds of the time code are different. In lieu of the year bits, the station's call sign is broadcast at 100% modulation during seconds 40 through 48. Further, bits 50 through 55 are replaced by 6 status bits ST1 through ST6 which, if non-zero, indicate a scheduled service interruption:
| Bit |
Weight |
Meaning |
| :39 |
P4 |
Marker bit |
| :40–:48 |
Call sign announcement |
| :49 |
P5 |
Marker bit |
| :50 |
ST1 |
Service interruption scheduled |
| :51 |
ST2 |
| :52 |
ST3 |
| :53 |
ST4 |
Service interruption daytime only |
| :54 |
ST5 |
Service interruption duration |
| :55 |
ST6 |
| :56 |
0 |
Unused, always 0. |
| :57 |
0 |
| :58 |
0 |
| :59 |
P0 |
Marker bit. |
ST1 through ST3 indicate the time of the planned service interruption:
| ST1 |
ST2 |
ST3 |
Meaning |
| 0 |
0 |
0 |
No service interruption planned within 7 days. |
| 0 |
0 |
1 |
Service interruption planned within 7 days. |
| 0 |
1 |
0 |
Service interruption planned within 3–6 days. |
| 0 |
1 |
1 |
Service interruption planned within 2 days. |
| 1 |
0 |
0 |
Service interruption planned within 24 hours. |
| 1 |
0 |
1 |
Service interruption planned within 12 hours. |
| 1 |
1 |
0 |
Service interruption planned within 2 hours. |
ST4, if set, promises the service interruption will be during daylight hours only. If unset, the interruption may be all day.
ST5 and ST6 indicate the duration of the interruption:
| ST5 |
ST6 |
Meaning |
| 0 |
0 |
No service interruption planned. |
| 0 |
1 |
Interruption for 7 days or more, or unknown duration. |
| 1 |
0 |
Interruption for 2–6 days. |
| 1 |
1 |
Interruption less than 2 days. |
If no interruption is planned, all ST bits are 0.
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