View source for JJY

{{Short description|Japanese time signal radio station}}
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| caption = JJY's transmitters are located at the [[Otakadoyayama Transmitter]] (right dot) in [[Tamura, Fukushima|Tamura City]], [[Fukushima Prefecture]], and the [[Haganeyama Transmitter]] (left dot) in [[Saga (city)|Saga City]], [[Saga Prefecture]].
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'''JJY''' is the [[call sign]] of a [[low frequency]] [[time signal]] [[radio station]] located in [[Japan]].

The station broadcasts from two sites, one on [[Otakadoyayama Transmitter|Mount Otakadoya]], near [[Fukushima (city)|Fukushima]], and the other on [[Haganeyama Transmitter|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.

== Transmission sites ==
The [[Otakadoyayama Transmitter|Mount Otakadoya site]] ({{coord|37|22|21|N|140|50|56|E|region:JP-07_type:landmark_dim:250}}<ref name=Ohtakadoya>{{Citation |url=http://jjy.nict.go.jp/LFstation/otakado/index-e.html |title=Ohtakadoya-yama LF Standard Time and Frequency Transmission Station |publisher=[[National Institute of Information and Communications Technology]] |access-date=2014-08-10 |year=2004}}</ref>) is located at an elevation of 790 meters (2,590&nbsp;ft) in [[Tamura, Fukushima|Tamura City]], [[Fukushima Prefecture]]. It broadcasts a 50 [[Watt|kW]] signal (13&nbsp;kW [[Effective radiated power|ERP]]) on 40 [[Hertz|kHz]] from an umbrella top-loading [[antenna (radio)|antenna]] situated 250 meters (820&nbsp;ft) above the ground. In March 2011, it was powered down and evacuated due to its proximity to the [[Fukushima Daiichi nuclear disaster]].<ref>{{cite web|url=http://www.pcworld.com/article/223576/article.html|date=2011-03-29|access-date=2017-05-07|work=[[PC Magazine]]|title=Nuclear Crisis Stopped Time in Japan|first1=Martyn|last1=Williams}}</ref> It resumed broadcasting on April 21, unattended by staff. It went off air again temporarily on April 25 due to lightning, but has ever since been on air.

The [[Haganeyama Transmitter|Mount Hagane site]] ({{coord|33|27|56|N|130|10|32|E|region:JP-41_type:landmark_dim:250}}<ref name=Hagane>{{Citation |url=http://jjy.nict.go.jp/LFstation/hagane/index-e.html |title=Hagane-yama LF Standard Time and Frequency Transmission Station |publisher=[[National Institute of Information and Communications Technology]] |access-date=2014-08-10 |year=2004}}</ref>) is located at an elevation of 900 meters (2,950&nbsp;ft) in [[Saga (city)|Saga City]], [[Saga Prefecture]]. It broadcasts a 50&nbsp;kW signal (23&nbsp;kW ERP) on 60&nbsp;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&nbsp;ft) above the ground. This site does not have a redundant 40&nbsp;kHz transmitter, so cannot act as a fallback for the Mount Otakadoya site.

== Time standards ==
Both [[carrier wave|carrier]] signals contain an identical [[Pulse-width modulation|pulse-width modulated]] time code and are transmitted 24 hours a day. The transmissions are at [[low frequency]] (LF) to enhance accuracy and reduce the possibility of [[atmospheric]] interference. The calculated accuracy of JJY's signal is 1×10<sup>−11</sup>.

[[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 [[Heating, ventilation, and air conditioning|environmentally controlled]] and [[Electromagnetic shielding|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 timecode|IRIG]]. Similarly to WWVB or MSF the signal of JJY is used to synchronize consumer [[radio clock|radio-controlled clocks]] sold throughout Japan.

== Transmission systems ==
Each station has an identical setup of equipment. A dual set of [[transmitter]]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 [[balun|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.

==History and former shortwave station==
On January 30, 1940, the Communications Research Laboratory (the predecessor of NICT) began operating JJY as a [[shortwave radio|shortwave]] station, broadcasting at 4, 7, 9, and 13 [[hertz|MHz]]. Over the years, the shortwave frequencies were lowered, and by the late 1950s, JJY was transmitting its time signal on standard frequencies of 2.5, 5, 8, 10, and 15&nbsp;MHz. The 2.5 and 15&nbsp;MHz broadcasts terminated in 1996. The time signals included announcements of the time, in [[Morse code]] and by a female voice, before every tenth minute: for example, "JJY JJY 1630 [[Japan Standard Time|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&nbsp;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&nbsp;kHz on June 10, 1999, and the shortwave broadcasts ceased operation on March 31, 2001. On October 1, 2001, the 60&nbsp;kHz longwave transmission from Mount Hagane began.

The Mount Otakadoya transmitter survived the [[2011 Tōhoku earthquake and tsunami]], but is 17&nbsp;km<ref>[http://www.movable-type.co.uk/scripts/latlong-vincenty.html Vincenty formula for distance between two Latitude/Longitude points] gives 17139.695&nbsp;m between ({{coord|37|22|21|N|140|50|56|E|region:JP-07_type:landmark_dim:250|name=JJY Mount Otakadoya transmitter}}) and ({{coord|37|25|17|N|141|1|57|E|region:JP-07_type:landmark_dim:250|name=Fukushima 1 nuclear power plant}}), not including altitude changes.</ref> from the [[Fukushima I nuclear accidents]], and was powered down when it was evacuated on March 12 (19:46 JST)<ref>{{Citation |url=http://www.cio.com.au/article/381374/nuclear_crisis_stopped_time_japan/ |title=Nuclear crisis stopped time in Japan |author=Martyn Williams |date=30 March 2011 |publisher=IDG News Service |access-date=2011-03-30 |quote=Engineers have evacuated a radio station that provided the national time signal |archive-date=2018-03-03 |archive-url=https://web.archive.org/web/20180303164801/https://www.cio.com.au/article/381374/nuclear_crisis_stopped_time_japan/ |url-status=dead }}</ref> due to the 20&nbsp;km radius evacuation order. It was re-enabled April 21.<ref>{{Citation |url=http://jjy.nict.go.jp/Pub/JJY40/index_.html |title=JJY Transmitted Log |date=21 April 2011 |access-date=2011-04-23}}</ref>

==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]], 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&nbsp;dB, to 10% power, until the beginning of the next second.

[[File:JJY_signal_20160803_0645z.ogg|thumb|right|Recorded signal for 2016-08-03 15:45 [[Japan Standard Time|JST]]. Note the [[Morse code]] call sign ("JJY JJY") transmitted from 0:40 to 0:49.]]

There are three different signals that are sent each second:
* 0 bits consist of 0.8&nbsp;s of full power, followed by 0.2&nbsp;s of reduced power.
* 1 bits consist of 0.5&nbsp;s of full power, followed by 0.5&nbsp;s of reduced power.
* Marker bits consist of 0.2&nbsp;s of full power, followed by 0.8&nbsp;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]] 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 time code in full is as follows:<ref name=jjy>{{Citation |url=http://jjy.nict.go.jp/jjy/trans/index-e.html |title=The Method of Emitting Standard Time and Frequency Signal Emission |publisher=[[National Institute of Information and Communications Technology]] |access-date=2009-03-28 |year=2005}}</ref><ref name=c-max>{{Citation |url=http://www.c-max-time.com/tech/jjy.php |title=The transmitters: JJY|access-date=2009-03-28 |publisher=C-MAX Time Solutions}}</ref>

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.
{|class=wikitable style="text-align:center"
! Bit
(Second)
! Weight || Meaning
|rowspan=21|
! Bit (Second) || Weight || Meaning
|rowspan=21|
! Bit (Second) || Weight || Meaning
|- bgcolor=lightgrey
|bgcolor=lightpink| :00 ||bgcolor=lightpink| M ||bgcolor=lightpink| Start of minute marker bit
| :20 || 0 ||rowspan=2| ''Unused, always 0.''
| :40 || SU2 || Currently unused, always 0.<br/>''(Future: summer time is in effect.)''
|-
|bgcolor=#ffffcc| :01 ||bgcolor=#ffffcc| 40 ||rowspan=8 bgcolor=#ffffcc| Minutes
|bgcolor=lightgrey| :21 ||bgcolor=lightgrey| 0
| :41 || 80 ||rowspan=8| Year
|-
|bgcolor=#ffffcc| :02 ||bgcolor=#ffffcc| 20
| :22 || 200 ||rowspan=12| Day of year<br/>1=January 1<br/>365=December 31<br/>366=December 31, leap year
| :42 || 40
|-
|bgcolor=#ffffcc| :03 ||bgcolor=#ffffcc| 10
| :23 || 100
| :43 || 20
|-
|bgcolor=lightgrey| :04 ||bgcolor=lightgrey| 0
|bgcolor=lightgrey| :24 ||bgcolor=lightgrey| 0
| :44 || 10
|-
|bgcolor=#ffffcc| :05 ||bgcolor=#ffffcc| 8
| :25 || 80
| :45 || 8
|-
|bgcolor=#ffffcc| :06 ||bgcolor=#ffffcc| 4
| :26 || 40
| :46 || 4
|-
|bgcolor=#ffffcc| :07 ||bgcolor=#ffffcc| 2
| :27 || 20
| :47 || 2
|-
|bgcolor=#ffffcc| :08 ||bgcolor=#ffffcc| 1
| :28 || 10
| :48 || 1
|- bgcolor=lightpink
| :09 || P1 || Marker bit
| :29 || P3
| :49 || P5 || Marker bit
|-
|bgcolor=lightgrey| :10 ||bgcolor=lightgrey| 0 ||rowspan=2 bgcolor=lightgrey| ''Unused, always 0.''
| :30 || 8
| :50 || 4 ||rowspan=3| Day of week.<br/>0=Sunday, 6=Saturday
|-
|bgcolor=lightgrey| :11 ||bgcolor=lightgrey| 0
| :31 || 4
| :51 || 2
|-
|bgcolor=#ccffff| :12 ||bgcolor=#ccffff| 20 ||rowspan=7 bgcolor=#ccffff| Hours
| :32 || 2
| :52 || 1
|-
|bgcolor=#ccffff| :13 ||bgcolor=#ccffff| 10
| :33 || 1
| :53 || LS1 || Leap second at end of current UTC month.
|-
|bgcolor=lightgrey| :14 ||bgcolor=lightgrey| 0
|bgcolor=lightgrey| :34 ||bgcolor=lightgrey| 0 ||rowspan=2 bgcolor=lightgrey| ''Unused, always 0.''
| :54 || LS2 || Leap second type: 1=added, 0=deleted.
|-
|bgcolor=#ccffff| :15 ||bgcolor=#ccffff| 8
|bgcolor=lightgrey| :35 ||bgcolor=lightgrey| 0
|bgcolor=lightgrey| :55 ||bgcolor=lightgrey| 0 ||rowspan=4 bgcolor=lightgrey| ''Unused, always 0.''
|-
|bgcolor=#ccffff| :16 ||bgcolor=#ccffff| 4
|bgcolor=#ccffff| :36 ||bgcolor=#ccffff| PA1 ||bgcolor=#ccffff| [[Even parity]] of hours bits (:12–:18).
|bgcolor=lightgrey| :56 ||bgcolor=lightgrey| 0
|-
|bgcolor=#ccffff| :17 ||bgcolor=#ccffff| 2
|bgcolor=#ffffcc| :37 ||bgcolor=#ffffcc| PA2 ||bgcolor=#ffffcc| Even parity of minutes bits (:01–:08).
|bgcolor=lightgrey| :57 ||bgcolor=lightgrey| 0
|-
|bgcolor=#ccffff| :18 ||bgcolor=#ccffff| 1
|bgcolor=lightgrey| :38 ||bgcolor=lightgrey| SU1 ||bgcolor=lightgrey| Currently unused, always 0. ''(Future:<br/>change to/from summer time within 6 days.)''
|bgcolor=lightgrey| :58 ||bgcolor=lightgrey| 0
|- bgcolor=lightpink
| :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 is 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 in [[Morse code]] twice using [[on-off keying]] 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:
{|class=wikitable style="text-align:center"
! Bit
(Second)
! Weight || Meaning
|- bgcolor=lightpink
| :39 || P4 || Marker bit
|-
| :40–:48 ||colspan=2| Call sign announcement
|- bgcolor=lightpink
| :49 || P5 || Marker bit
|-
| :50 || ST1 ||rowspan=3| Service interruption scheduled
|-
| :51 || ST2
|-
| :52 || ST3
|-
| :53 || ST4 || Service interruption daytime only
|-
| :54 || ST5 ||rowspan=2| Service interruption duration
|-
| :55 || ST6
|- bgcolor=lightgrey
| :56 || 0 ||rowspan=3| ''Unused, always 0.''
|- bgcolor=lightgrey
| :57 || 0
|- bgcolor=lightgrey
| :58 || 0
|- bgcolor=lightpink
| :59 || P0 || Marker bit.
|}

ST1 through ST3 indicate the time of the planned service interruption:
{|class=wikitable style="text-align:center"
! 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:
{|class=wikitable style="text-align:center"
! 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.

==References==
{{reflist}}
{{refbegin}}
* {{Citation |date=April 2003 |url=http://www.nict.go.jp/news/pdf-box/JST2-e.pdf |title=Low Frequency Standard Time and Frequency Transmission Facilities Pamphlet |format=PDF |publisher=National Institute of Information and Communications Technology |access-date=2016-09-25 |archive-url=https://web.archive.org/web/20160803224513/http://www.nict.go.jp/news/pdf-box/JST2-e.pdf |archive-date=2016-08-03 |url-status=dead }}
* {{cite web |url=http://jjy.nict.go.jp/QandA/reference/chrono_table.html |title=History of standard time and standard frequency signal |language=ja |publisher=National Institute of Information and Communications Technology |access-date=2007-11-21 }}
* {{cite web |date=November 20, 1997 |url=http://www2.nict.go.jp/w/w114/stsi/ivstdc/news_11/tr7.html |archive-url=https://web.archive.org/web/20110929171022/http://www2.nict.go.jp/w/w114/stsi/ivstdc/news_11/tr7.html |archive-date=2011-09-29 |title=Construction of New LF Station for Time and Frequency Service |publisher=Communications Research Laboratory |access-date=2016-09-25 }}
* {{Citation |year=1996 |url=http://tycho.usno.navy.mil/ptti/1996/Vol%2028_03.pdf |archive-url=https://web.archive.org/web/20130216225319/http://tycho.usno.navy.mil/ptti/1996/Vol%2028_03.pdf |archive-date=2013-02-16 |title=Time and Frequency Keeping and its Distribution System at CRL |format=PDF |volume=28 |issue=3 |access-date=2016-09-25 |work=Proceedings of the [[Precise Time and Time Interval (PTTI)]] Meeting }}
* {{Citation |year=1999 |url=http://tycho.usno.navy.mil/ptti/ptti99/PTTI_1999_241.PDF |archive-url=https://web.archive.org/web/20130217115636/http://tycho.usno.navy.mil/ptti/ptti99/PTTI_1999_241.PDF |archive-date=2013-02-17 |title=Overview of Research Activities on Time and Frequency at the Communications Research Laboratory |format=PDF |work=Proceedings of the Precise Time and Time Interval (PTTI) Meeting |volume=31 |pages=241–246 |access-date=2007-11-21 }}
* {{cite AV media |url=http://www.kimandrewelliott.com/cw/cw_20010310.html |people=Elliott, Kim Andrew |date=March 10, 2001 |title=Communications World |medium=radio transcript |publisher=[[Voice of America]] |access-date=2007-11-21 |archive-date=2006-06-28 |archive-url=https://web.archive.org/web/20060628191448/http://www.kimandrewelliott.com/Cw/cw_20010310.html |url-status=dead }}
{{refend}}

==External links==
{{GeoGroupTemplate}}
* [http://jjy.nict.go.jp/index-e.html Japan Standard Time Group]
* Coordinates of Mount Otakadoya transmitter: {{coord|37|22|21|N|140|50|56|E|region:JP-07_type:landmark_dim:250|name=JJY - Mount Otakadoya transmitter}}
* Coordinates of Mount Hagane transmitter: {{coord|33|27|56|N|130|10|32|E|region:JP-41_type:landmark_dim:250|name=JJY - Mount Hagane transmitter}}

{{Time signal stations}}
{{Time signal authorities}}
{{Time topics}}
{{Time measurement and standards}}

{{DEFAULTSORT:Jjy}}
[[Category:Radio stations established in 1940]]
[[Category:Radio stations established in 2001]]
[[Category:1940 establishments in Japan]]
[[Category:2001 establishments in Japan]]
[[Category:Time signal radio stations]]
[[Category:Radio in Japan]]
[[Category:Mass media in Fukushima Prefecture]]