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JJY

The Method of Emitting Standard Time and Frequency Signal Emission


About Standard-time and frequency-signal emission

   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.

April, 2004

Contact

National Institute of Information and Communications Technology
Applied Electromagnetic Research Institute 
Space-Time Standards Laboratory Japan Standard Time Group
4-2-1,Nukui-Kitamachi
Koganei,Tokyo 184-8795
+81-42-327-6985
+81-42-327-6689(fax)

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The specification of standard-time and frequency-signal emission

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)
Latitude
Longitude
37d 22m N
140d 51m E
33d 28m N
130d 11m E
Antenna form Umbrella type 250m high Umbrella type 200m high
Antenna power 50kW
(Effective radiated power10kW)
Frequency form A1B
Operation time Always
Standard
Frequency
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
DUT1signal Nothing
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.

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Transmission method of Low frequency JJY

1. Time code system
(1) The time code in Generally (except 15 minutes and 45 minutes of per hour)
(2) The time code on call sign sending out (15 minutes and 45 minutes of per hour)

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

(d) Year (8bits:80y,40y,20y,10y,8y,4y,2y,1y)
   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
0 0 0 Sunday
0 0 1 Monday
0 1 0 Tuesday
0 1 1 Wednesday
1 0 0 Thursday
1 0 1 Friday
1 1 0 Saturday


(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
LS1 LS2
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


(g) Parity (2bits:PA1,PA2)
   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.

SU1 SU2 Meaning
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 interuption, 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)

ST1 ST2 ST3 Meaning
0 0 0 Without transmission
interruption notice
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)

Status information ST4 Meaning
1 Only daytime
0 All day, or Without transmission
interruption notice
Period information ST5 ST6 Meaning
0 0 Without transmission
interruption notice
0 1 More than 7 days or
unknown period
1 0 Within 2 to 6 days
1 1 Less than two days

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