JJY
Encyclopedia
JJY is the call sign
of a low frequency
time signal
radio station
.
The station is located in Japan
and broadcasts from two sites, one on Mount Otakadoya, near Fukushima
, and the other on Mount Hagane
, located on Kyushu Island
. JJY is operated by the National Institute of Information and Communications Technology
(NICT), an independent administrative institution
affiliated with the Ministry of Internal Affairs and Communications
of the Japanese government.
signal (13 kW ERP
) on 40 kHz
from an umbrella top-loading antenna situated 250 meters (820 ft) above the ground. it has been powered down and evacuated due to the Fukushima I nuclear accidents. As of April 21 it is broadcasting again but is unattended by staff. It went off the air again on April 25 due to lightning.
The Mount Hagane site (33°27′54"N 130°10′32"E) is located at an elevation of 900 meters (2,950 ft). It broadcasts a 50 kW signal (23 kW ERP) 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. This site does not have a redundant 40 kHz transmitter, so cannot act as a fallback for the Mount Otakadoya site.
signals contain an identical pulse-width modulated
time code and are transmitted 24 hours a day. Low frequency
(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 Time
is set by a caesium
atomic clock
in Tokyo
. This information is sent to the transmitter stations and is used to set a caesium atomic clock
at each station. These clocks are housed in an environmentally controlled
and electromagnetically shielded
room to prevent outside interference with the clocks.
The time code format is very similar to that of WWVB
in the United States
but technically is a variant of IRIG
. Similarly to WWVB or MSF the signal of JJY is used to synchronize consumer radio-controlled clocks
sold throughout Japan.
s, a primary and a backup, provide for constant transmission of the time code. However, it is not possible given the current design configuration for one site to act as a lower power alternate frequency backup for the other. The backups are set to automatically take over in the event that the primary transmission system 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 transformer
to perform impedance matching
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.
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 code
and by a female voice, before every tenth minute: for example, "JJY JJY 1630 JST
" (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.
The Mount Otakadoya transmitter survived the 2011 Tōhoku earthquake and tsunami
, but is 17 km from the Fukushima I nuclear accidents, and was powered down when it was evacuated on March 12 (19:46 JST) due to the 20 km radius evacuation order. It was re-enabled April 21.
The time code is most similar to that transmitted by WWVB
, 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:
As with WWVB, seconds 0, 9, 19, 29, 39, 49 and 59 of each minute are marker bits. The remaining 53 encode Japan Standard Time
using binary-coded decimal
. JST does not include summer time
, 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 DUT1
information.
P0 is always the last second of a minute. In the event of a leap second, an additional 0 bit in inserted before it, and the marker bit is transmitted during second 60. 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:
ST1 through ST3 indicate the time of the planned service interruption:
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:
If no interruption is planned, all ST bits are 0.
Call sign
In broadcasting and radio communications, a call sign is a unique designation for a transmitting station. In North America they are used as names for broadcasting stations...
of a low frequency
Low frequency
Low 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 signal
Time signal
A 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:...
radio station
Radio station
Radio broadcasting is a one-way wireless transmission over radio waves intended to reach a wide audience. Stations can be linked in radio networks to broadcast a common radio format, either in broadcast syndication or simulcast or both...
.
The station is located in Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, 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 Fukushima
Fukushima, Fukushima
is the capital city of Fukushima Prefecture in the Tōhoku Region of Japan. As of May 2011 the city has an estimated population of 290,064 and an area of 746.43 km².It lies about 250 km north of Tokyo and 80 km south of Sendai.-History:...
, and the other on Mount Hagane
Haganeyama Transmitter
Haganeyama Transmitter is an LF-time signal transmitter at Fuji-cho, Saga-city, Saga-ken, Japan used for transmitting the time signal JJY on 60 kHz...
, located on Kyushu Island
Kyushu
is the third largest island of Japan and most southwesterly of its four main islands. Its alternate ancient names include , , and . The historical regional name is referred to Kyushu and its surrounding islands....
. JJY is operated by the National Institute of Information and Communications Technology
National Institute of Information and Communications Technology
The National Institute of Information and Communications Technology is Japan's national research institute for information and communications...
(NICT), an independent administrative institution
Independent Administrative Institution
An Incorporated Administrative Agency or in lay terms an Independent Administrative Corporation or 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 Communications
Ministry of Internal Affairs and Communications
The ' or Ministry of Internal Affairs and Communications 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.
Transmission sites
The Mount Otakadoya site (37°22′22"N 140°50′56"E) is located at an elevation of 790 meters (2,590 ft). It broadcasts a 50 kWWatt
The watt is a derived unit of power in the International System of Units , named after the Scottish engineer James Watt . The unit, defined as one joule per second, measures the rate of energy conversion.-Definition:...
signal (13 kW ERP
Effective radiated power
In radio telecommunications, effective radiated power or equivalent radiated power is a standardized theoretical measurement of radio frequency energy using the SI unit watts, and is determined by subtracting system losses and adding system gains...
) on 40 kHz
Hertz
The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications....
from an umbrella top-loading antenna situated 250 meters (820 ft) above the ground. it has been powered down and evacuated due to the Fukushima I nuclear accidents. As of April 21 it is broadcasting again but is unattended by staff. It went off the air again on April 25 due to lightning.
The Mount Hagane site (33°27′54"N 130°10′32"E) is located at an elevation of 900 meters (2,950 ft). It broadcasts a 50 kW signal (23 kW ERP) 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. This site does not have a redundant 40 kHz transmitter, so cannot act as a fallback for the Mount Otakadoya site.
Time standards
Both carrierCarrier wave
In 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 a much higher frequency than the input signal...
signals contain an identical pulse-width modulated
Pulse-width modulation
Pulse-width modulation , or pulse-duration modulation , is a commonly used technique for controlling power to inertial electrical devices, made practical by modern electronic power switches....
time code and are transmitted 24 hours a day. Low frequency
Low frequency
Low 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 Time
Japan Standard Time
Japan 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 09:00 in Japan Standard Time. There is no daylight saving time, though its introduction has been debated several times. Japan Standard Time is the same as...
is set by a caesium
Caesium
Caesium 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 28 °C , which makes it one of only five elemental metals that are liquid at room temperature...
atomic clock
Atomic clock
An atomic clock is a clock that uses an electronic transition frequency in the microwave, optical, or ultraviolet region of the electromagnetic spectrum of atoms as a frequency standard for its timekeeping element...
in Tokyo
Tokyo
, ; officially , is one of the 47 prefectures of Japan. Tokyo is the capital of Japan, the center of the Greater Tokyo Area, and the largest metropolitan area of Japan. It is the seat of the Japanese government and the Imperial Palace, and the home of the Japanese Imperial Family...
. This information is sent to the transmitter stations and is used to set a caesium atomic clock
Atomic clock
An atomic clock is a clock that uses an electronic transition frequency in the microwave, optical, or ultraviolet region of the electromagnetic spectrum of atoms as a frequency standard for its timekeeping element...
at each station. These clocks are housed in an environmentally controlled
HVAC
HVAC refers to technology of indoor or automotive environmental comfort. HVAC system design is a major subdiscipline of mechanical engineering, based on the principles of thermodynamics, fluid mechanics, and heat transfer...
and electromagnetically shielded
Electromagnetic shielding
Electromagnetic shielding is the process of reducing the electromagnetic field in a space by blocking the field with barriers made of conductive and/or magnetic materials. Shielding is typically applied to enclosures to isolate electrical devices from the 'outside world' and to cables to isolate...
room to prevent outside interference with the clocks.
The time code format is very similar to that of WWVB
WWVB
WWVB is a NIST time signal radio station near Fort Collins, Colorado, co-located with WWV. WWVB is the station that radio-controlled clocks in most of 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 States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
but technically is a variant of IRIG
IRIG
The Inter Range Instrumentation Group is the standards body of the Range Commanders Council . They publish a number of standards through the RCC Secretariat at White Sands Missile Range ....
. Similarly to WWVB or MSF the signal of JJY is used to synchronize consumer radio-controlled clocks
Radio clock
A radio clock or radio-controlled 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...
sold throughout Japan.
Transmission systems
Each station has an identical setup of equipment. A dual set of transmitterTransmitter
In electronics and telecommunications a transmitter or radio transmitter is an electronic device which, with the aid of an antenna, produces radio waves. The transmitter itself generates a radio frequency alternating current, which is applied to the antenna. When excited by this alternating...
s, a primary and a backup, provide for constant transmission of the time code. However, it is not possible given the current design configuration for one site to act as a lower power alternate frequency backup for the other. The backups are set to automatically take over in the event that the primary transmission system 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 transformer
Balun
A balun is a type of electrical transformer that can convert electrical signals that are balanced about ground to signals that are unbalanced , and the reverse. They are also often used to connect lines of differing impedance...
to perform impedance matching
Impedance matching
In electronics, impedance matching is the practice of designing the input impedance of an electrical load to maximize the power transfer and/or 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.
History and former shortwave station
On January 30, 1940, the Communications Research Laboratory (the predecessor of NICT), began operations of JJY as a shortwaveShortwave
Shortwave radio refers to the upper MF and all of the HF portion of the radio spectrum, between 1,800–30,000 kHz. Shortwave radio received its name because the wavelengths in this band are shorter than 200 m which marked the original upper limit of the medium frequency band first used...
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 code
Morse code
Morse code is a method of transmitting textual information as a series of on-off tones, lights, or clicks that can be directly understood by a skilled listener or observer without special equipment...
and by a female voice, before every tenth minute: for example, "JJY JJY 1630 JST
Japan Standard Time
Japan 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 09:00 in Japan Standard Time. There is no daylight saving time, though its introduction has been debated several times. Japan Standard Time is the same as...
" (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.
The Mount Otakadoya transmitter survived the 2011 Tōhoku earthquake and tsunami
2011 Tōhoku earthquake and tsunami
The 2011 earthquake off the Pacific coast of Tohoku, also known as the 2011 Tohoku earthquake, or the Great East Japan Earthquake, was a magnitude 9.0 undersea megathrust earthquake off the coast of Japan that occurred at 14:46 JST on Friday, 11 March 2011, with the epicenter approximately east...
, but is 17 km from the Fukushima I nuclear accidents, and was powered down when it was evacuated on March 12 (19:46 JST) due to the 20 km radius evacuation order. It was re-enabled April 21.
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 WWVB
WWVB
WWVB is a NIST time signal radio station near Fort Collins, Colorado, co-located with WWV. WWVB is the station that radio-controlled clocks in most of 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 59 of each minute are marker bits. The remaining 53 encode Japan Standard Time
Japan Standard Time
Japan 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 09:00 in Japan Standard Time. There is no daylight saving time, though its introduction has been debated several times. Japan Standard Time is the same as...
using binary-coded decimal
Binary-coded decimal
In computing and electronic systems, binary-coded decimal is a digital encoding method for numbers using decimal notation, with each decimal digit represented by its own binary sequence. In BCD, a numeral is usually represented by four bits which, in general, represent the decimal range 0 through 9...
. JST does not include summer time
Summer time
Summertime 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 DUT1
DUT1
The 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 | Bit | Weight | Meaning |
|---|---|---|---|---|---|---|---|---|
| :00 | M | Start of minute marker bit | :20 | 0 | Unused, always 0. | :40 | SU2 | Currently unused, always 0. (Future: summer time is in effect.) |
| :01 | 40 | Minutes | :21 | 0 | :41 | 80 | Year | |
| :02 | 20 | :22 | 200 | Day of year 1=January 1 365=December 31 366=December 31, leap year |
:42 | 40 | ||
| :03 | 10 | :23 | 100 | :43 | 20 | |||
| :04 | 0 | :24 | 0 | :44 | 10 | |||
| :05 | 8 | :25 | 80 | :45 | 8 | |||
| :06 | 4 | :26 | 40 | :46 | 4 | |||
| :07 | 2 | :27 | 20 | :47 | 2 | |||
| :08 | 1 | :28 | 10 | :48 | 1 | |||
| :09 | P1 | Marker bit | :29 | P3 | :49 | P5 | Marker bit | |
| :10 | 0 | Unused, always 0. | :30 | 8 | :50 | 4 | Day of week. 0=Sunday, 6=Saturday |
|
| :11 | 0 | :31 | 4 | :51 | 2 | |||
| :12 | 20 | Hours | :32 | 2 | :52 | 1 | ||
| :13 | 10 | :33 | 1 | :53 | LS1 | Leap second at end of current UTC month. | ||
| :14 | 0 | :34 | 0 | Unused, always 0. | :54 | LS2 | Leap second type: 1=added, 0=deleted. | |
| :15 | 8 | :35 | 0 | :55 | 0 | Unused, always 0. | ||
| :16 | 4 | :36 | PA1 | Even parity of hours bits (:12–:18). | :56 | 0 | ||
| :17 | 2 | :37 | PA2 | Even parity of minutes bits (:01–:08). | :57 | 0 | ||
| :18 | 1 | :38 | SU1 | Currently unused, always 0. (Future: change to/from summer time within 6 days.) |
:58 | 0 | ||
| :19 | P2 | Marker bit | :39 | P4 | Marker bit | :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, and the marker bit is transmitted during second 60. 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.
External links
- Japan Standard Time Group
- Coordinates of Mount Otakadoya transmitter: 37°22′21"N 140°50′56"E
- Coordinates of Mount Hagane transmitter: 33°27′56"N 130°10′32"E
- Time Signal Stoppage in Japan