The Method of Emitting Standard Time and Frequency Signal Emission
- About Standard-time and frequency-signal emission
- The specification of standard-time and frequency-signal emission
- Tranmission method of Low frequency JJY
In order to widely inform Japan Standard Time(JST) which
is based on time and frequency standard and Coordinate Universal Time(UTC),
Standard-time and frequency-signal emission JJY is determined in National
Institute of Information and Communications Technology. Time code just
as time information is transmitted by Low Frequency band JJY.
The JST(NICT) signal is always kept highly precision than national standard.
As a national standard, obtained accuracy which is gotten with cesium beam type atomic frequency-standards, hydrogen maser type and commercial cesium beam type atomic-clocks reaches in the digit of 1*10-13, furthermore, synchronization of international standard and coordinating with other countries standard are always confirmed by international time comparison using artificial satellite and so on.
Although correct signal is transmitted, the precision of the received signal declines with the influence of atmosphere and so on. Standard-time and frequency-signal emission of the low frequency seldom influenced by the atmosphere, the precision of 1*10-11 can be acquired by the frequency comparison average of 24 hour.
The specification and the sending method will be described below, Please contact the following about detailed information of Standard-time and frequency-signal emission.
National Institute of Information and Communications
Applied Electromagnetic Research Institute
Space-Time Standards Laboratory Japan Standard Time Group
|Call sign||JJY(standard-time and frequency-signal emission)|
|Transmission station||Ohtakadoyayama LF station
(Miyakoji-cho, Tamura-city, Fukushima-ken)
|Haganeyama LF station
(Fuji-cho, Saga-city, Saga-ken)
|37d 22m N
140d 51m E
|33d 28m N
130d 11m E
|Antenna form||Umbrella type 250m high||Umbrella type 200m high|
(Effective radiated power10kW)
|Carrier||40 kHz||60 kHz|
|Modulation wave||1 Hz(Second sign)|
|Variation of modulation wave||Maximum 100%, Minimum 10%
(Unincluding call sign transmission time)
|Standard time||JST:Advanced Coordinate Universal Time(UTC) for 9 hours|
|Transmitting time of the second sign||Always|
|Accuracy of frequency and time interval||+-1*10-12|
|The format of second sign||The mark of 0.2, 0.5, 0.8 second|
|Note||1999.6.10 Starting Service||2001.10.01 Starting Service|
Time coordination(Leap second coordination)
In order to keep the difference between Standard time and earth rotation(UT1) within +-0.9 seconds, step coordination of 1 second may be performed just before nine o'clock(Japan Standard Time) in the month beginning.
However, the coordination day makes January 1st and July 1st as 1st priority date and as long as there are no special condition, and it makes April 1st and October 1st as 2nd priority date.
In addition, before this coordination is performed, it publishes in official gazette and etc in advance.
2. The definition of time code
(1) Information Contained in Time Code
Hour, minute, annual date, year (the last two digits of the dominical year), day of the week, leap seconds, parity bits for hours and minutes, and notification on future transmission interruptions.
The hour, minute, annual date, year (the last two digits of the dominical year), and day of the week are represented in binary terms [BCD (Binary Coded Decimal) positive logic].
(2) Second Signal
The start of each second corresponds to the rising of the leading edge of the pulse signal. The point at which the pulse reaches 55% of its full amplitude (midpoint between 10% and 100% amplitude) is synchronous with the second signal of standard time.
(3) Pulse Width
Marker(M) and position markers(P0~P5): Pulse width 0.2s +-5ms
Binary 0: Pulse width 0.8s +-5ms
Binary 1: Pulse width 0.5s +-5ms
(4) Output Interval
A code with a period of 60 seconds (60 bits) is transmitted every second.
(5) Standard Time of Time Code
The time(the year, the total days, the hour, the minute) of the head marker of one period is encoded and transmitted.
(6) Marker (M) Position
The marker (M) corresponds to the exact minute (the zero second of each minute).
(7) Positions of the Position Markers (P0-P5)
The position marker P0 normally corresponds to the start of the 59th second (for non-leap seconds). However, for a positive leap second (insertion of a second), P0 corresponds to the start of the 60th second (in this case, the 59th second is represented by a binary 0). For a negative leap second (removal of a second), P0 corresponds to the start of the 58th second.
Position markers P1-P5 correspond to the start of the 9th, 19th, 29th, 39th, and 49th seconds, respectively.
(8) Representation of Information
(a) Hour(6 bits:20h,10h,8h,4h,2h,1h)
The hour in Japan Standard Time (JST) in 24-hour representation
20h,10:The value in BCD at 10 o'clock
8h,4h,2h,1h:The value in BCD at 1 o'clock
(b) Minute(7 bits:40m,20m,10m,8m,4m,2m,1m)
The JST minute
40m,20m,10m: The value in BCD of 10 minutes
8m,4m,2m,1m: The value in BCD of 1 minute
(c) Annual date(10 bits:200d,100d,80d,40d,20d,10d,8d,4d,2d,1d)
The annual date, counting January 1 as day 1. Thus, Dec. 31 is day 365 in a non-leap year and day 366 in a leap year.
200d,100d: The value in BCD of 100 days
80d,40d,20d,10d: The value in BCD of 10days
8d,4d,2d,1d: The value in BCD of 1day
The last 2 digits of the dominical year.
80y,40y,20y,10y: The value in BCD of 10years
8y,4y,2y,1y: The value in BCD of 1year
(e) Day of the week(3bits:4w,2w,1w)
The values 0-6 are allocated to Sunday-Saturday.
|4w||2w||1w||Day of the week|
(f) Leap second information(2bits:LS1,LS2)
The leap second is inserted immediately before 9:00 (Japan standard time) of the 1st day of the month that is to contain the leap second. Leap second information is continuously transmitted from 9:00 on day 2 of the previous month to 8:59 on day 1 of the relevant month.
|The information of leap second||Meaning|
|0||0||There is not leap second within 1 month.|
|1||1||There is positive leap second(Insertion) within 1 month.|
|1||0||There is negative leap second(Deletion) within 1 month|
Parity bits are signals to determine whether the hour and minute signals were correctly read. PA1 and PA2 correspond to the hour and minute, respectively, and each is represented by an even parity of 1 bit.
PA1 = (20h+10h+8h+4h+2h+1h) mod 2
PA2 = (40m+20m+10m+8m+4m+2m+1m) mod 2
(mod 2 represents the remainder after division by 2)
(h) Spare bits(2bits:SU1,SU2)
These spare bits are reserved for future additions of items to be contained within the time code (such as daylight savings time).
For the time being, these bits will have values of 0 in transmission. Example is indicated as follows.
|0||0||There is not change to summer time within 6 days|
|1||0||There is change to summer time within 6 days|
|0||1||During summer time implementation(There is not change from summer time to usual time within 6 days.)|
|1||1||The summer time will end within 6 days|
(i) Transmission interruption notification(6bits:ST1,ST2,ST3,ST4,ST5,ST6)
When interruptions of Standard time and frequency transmission are scheduled (for maintenance and inspection, for example) advance notice is given using these bits. When there are no plans for interruption, all spare bits will have values of 0. The transmission interruption notification bit is shown as follows:
* Starting notice of transmission interruption(ST1,ST2,ST3)
|0||0||1||There will be transmission
interruption within 7 days
|0||1||0||There will be transmission
interruption within 3 to 6 days
|0||1||1||There will be transmission
interruption within 2 days
|1||0||0||There will be transmission
interruption within 24 hours
|1||0||1||There is transmission
interruption within 12 hours
|1||1||0||There is transmission
interruption within 2 hours
* Notice of transmission interruption period(ST4,ST5,ST6)
|0||All day, or Without transmission
|0||1||More than 7 days or
|1||0||Within 2 to 6 days|
|1||1||Less than two days|