NlST TIME AND FREQUENCY BULLETIN 

NlSTlR 5071 -8 

NO. 489 AUGUST 1998 

1. GENERAL BACKGROUND INFORMATION ............................................ 2 

2. TIME SCALE INFORMATION ..................................................... 2 

3. UT1 CORRECTIONS AND LEAP SECOND ADJUSTMENTS ................................ 2 

4. PHASE DEVIATIONS FOR WWVB AND LORAN-C ....................................... 4 

5. BROADCAST OUTAGES OVER FIVE MINUTES AND WWVB 

PHASEPERTURBATIONS ....................................................... 5 

6. NOTES ON NET TIME SCALES AND PRIMARY STANDARDS .............................. 5 

7. BIBLIOGRAPHY ............................................................... 5 

8. SPECIALANNOUNCEMENTS .................................................... 7 

This bulletin is published monthly. Address correspondence to: 

Gwen E. Bennett, Editor 

Time and Frequency Division 

National Institute of Standards and Technology 

325 Broadway 

Boulder, CO 80303-3328 

(303) 497-3295 

NOTE TO SUBSCRIBERS: Please include your address label (or a copy) 

with any correspondence regarding this bulletin. 

U.S. DEPARTMENT OF COMMERCE, William M. Daley, Secretary 

TECHNOLOGY ADMINISTRATION, Mary L. Good, Under Secretary for Technology 

NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY, Robert Hebner, Acting Deputy Director 

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1. GENERAL BACKGROUND INFORMATION 

AUG 1998 

ABBREVIATIONS AND ACRONYMS USED IN THIS BULLETIN 

BlPM - Bureau International des Poids et Mesures 

CClR - International Radio Consultative Committee 

cs - Cesium standard 

GOES - Geostationary Operational Environmental Satellite 

GPS - Global Positioning System 

IERS - International Earth Rotation Service 

LORAN - Long Range Navigation 

MC - Master Clock 

MJD - Modified Julian Date 

NVLAP - National Voluntary Laboratory Accreditation Program 

NET - National Institute of Standards & Technology 

NOAA - National Oceanic and Atmospheric Administration ns - nanosecond 

SI - International System of Units fls - microsecond 

TA - Atomic Time ms - millisecond 

TAI - International Atomic Time S - second 

USNO - United States Naval Observatory min - minute 

UTC - Coordinated Universal Time 

VLF - very low frequency 

2. TIME SCALE INFORMATION 

MJD UT1 -UTC(NIST) UTC(USN0,MC)-UTC(NIST) 

(5~5 ms) ( * 20 ns) 

The values listed below are based on data from the IERS, the USNO, and NET. The UTC(USN0,MC) - UTC(NIST) 

values are averaged measurements from up to 10 GPS satellites (see bibliography on page 5). UTC-UTC(NIST1 data are 

on page 3. 

I 

2 50996 -101 ms 

9 51003 -103 ms 

16 51010 -106 ms 

4 ns 

5 ns 

4 ns 

23 51017 -109 ms 2 ns I 30 51024 -111 ms 1 ns 

3. UT1 CORRECTIONS AND LEAP SECOND ADJUSTMENTS 

The master clock pulses used by the WWV, WWVH, WWVB, and GOES time code transmissions are referenced to the 

UTC(NIST) time scale. Occasionally, 1 s is added to the UTC time scale. This second is called a leap second. Its purpose 

is to keep the UTC time scale within kO.9 s of the UT1 astronomical time scale, which changes slightly due to variations 

in the rotation of the Earth. 

Positive leap seconds, beginning at 23 h 59 min 60 s UTC and ending at 0 h 0 min 0 s UTC, were inserted in the UTC 

timescale on 30 June 1972, 1981-1 983, 1985, 1992, 1993, 1994, and 1997, and on 31 December 1972-1 979, 1987, 

1989, 1990, and 1995. There have been 21 leap seconds in total. The next leap second will occur on 31 December 1998. 

The use of leap seconds ensures that UT1 - UTC will always be held within +0.9 s. The current value of UT1 - UTC 

is called the DUTl correction. DUTl corrections are broadcast by WWV, WWVH, WWVB, and GOES and are printed below. 

These corrections may be added to received UTC time signals in order to obtain UT1. 

+ 0.0 s beginning 0000 UTC 26 March 1998 

-0.1 s beginning 0000 UTC 07 May 1998 

-0.2 s beginning 0000 UTC 13 August 1998 

DUTl = UT1 - UTC = 

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1. GENERAL BACKGROUND INFORMATION 

AUG 1998 

ABBREVIATIONS AND ACRONYMS USED IN THIS BULLETIN 

BlPM - Bureau International des Poids et Mesures 

CClR - International Radio Consultative Committee 

cs - Cesium standard 

GOES - Geostationary Operational Environmental Satellite 

GPS - Global Positioning System 

IERS - International Earth Rotation Service 

LORAN - Long Range Navigation 

MC - Master Clock 

MJD - Modified Julian Date 

NVLAP - National Voluntary Laboratory Accreditation Program 

NlST - National Institute of Standards & Technology 

NOAA - National Oceanic and Atmospheric Administration ns - nanosecond 

SI - International System of Units PS - microsecond 

TA - Atomic Time ms - millisecond 

TAI - International Atomic Time S - second 

USNO - United States Naval Observatory min - minute 

UTC - Coordinated Universal Time 

VLF - very low frequency 

2. TIME SCALE INFORMATION 

MJD UT1 -UTC(NIST) UTC(USN0,MC)- UTC(NIST1 

(k5 ms) ( k 20 ns) 

The values listed below are based on data from the IERS, the USNO, and NET. The UTC(USN0,MC) - UTC(NIST) 

values are averaged measurements from up to 10 GPS satellites (see bibliography on page 5). UTC-UTC(N1ST) data are 

on page 3. 

I 

2 50996 -101 ms 

9 51003 -103 ms 

16 51010 -106 ms 

4 ns 

5 ns 

4 ns 

23 51017 -109 ms 2 ns I 30 51024 -111 ms 1 ns 

3. UT1 CORRECTIONS AND LEAP SECOND ADJUSTMENTS 

The master clock pulses used by the WWV, WWVH, WWVB, and GOES time code transmissions are referenced to the 

UTC(NIST) time scale. Occasionally, 1 s is added to the UTC time scale. This second is called a leap second. Its purpose 

is to keep the UTC time scale within kO.9 s of the UT1 astronomical time scale, which changes slightly due to variations 

in the rotation of the Earth. 

Positive leap seconds, beginning at 23 h 59 min 60 s UTC and ending at 0 h 0 min 0 s UTC, were inserted in the UTC 

timescale on 30 June 1972, 1981-1 983, 1985, 1992, 1993, 1994, and 1997, and on 31 December 1972-1 979, 1987, 

1989, 1990, and 1995. There have been 21 leap seconds in total. The next leap second will occur on 31 December 1998. 

The use of leap seconds ensures that UTI - UTC will always be held within +0.9 s. The current value of UT1 - UTC 

is called the DUTl correction. DUTl corrections are broadcast by WWV, WWVH, WWVB, and GOES and are printed below. 

These corrections may be added to received UTC time signals in order to obtain UT1. 

+ 0.0 s beginning 0000 UTC 26 March 1998 

-0.1 s beginning 0000 UTC 07 May 1998 

-0.2 s beginning 0000 UTC 13 August 1998 

DUTl = UT1 - UTC = 

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The deviation of UTCWIST) from UTC has been less than +/- 100 11s since July 6, 1994. The table below shows values of UTC - 

0000 Hours Coordinated Universal Time 

DATE MJD UTC-UTCOyIST) 

ns 

Jul 10, 1997 

Jul 20, 1997 

Jul 30, 1997 

Aug 9, 1997 

Aug 19, 1997 

Aug 29, 1997 

Sep. 8, 1997 

Sep. 18, 1997 

Sep. 28, 1997 

Oct. 8, 1997 

Oct. 18, 1997 

Oct. 28, 1997 

Nov. 7, 1997 

Nov. 17, 1997 

Nov. 27, 1997 

Dec. 7, 1997 

Dec. 17, 1997 

Dec. 27, 1997 

Jan. 6, 1998 

Jan. 16. 1998 

Jan. 26, 1998 

Feb. 5, 1998 

Feb. 15, 1998 

Feb. 25, 1998 

Mar7, 1998 

Mar 17, 1998 

Mar 27, 1998 

Apr 6, 1998 

Apr 16, 1998 

Apr 26, 1998 

May 6, 1998 

May 16, 1998 

May 26, 1998 

June 5, 1998 

June 15, 1998 

50639 

50649 

50659 

50669 

50679 

50689 

50699 

50709 

50719 

50729 

50739 

50749 

50759 

50769 

50779 

50789 

50799 

50809 

50819 

50829 

50839 

50849 

50859 

50869 

50879 

50889 

50899 

50909 

509 19 

50929 

50939 

50949 

50959 

50969 

50979 

8 

16 

18 

21 

26 

29 

30 

31 

31 

29 

23 

16 

8 

3 

1 

2 

-1 

3 

2 

2 

6 

7 

11 

15 

18 

22 

25 

25 

26 

26 

26 

28 

26 

30 

27 

June 25, 1998 50989 26 

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C 

Table 7.1 is a list of the parameters that are used to define UTC(N1ST) with respect to our real-time scale AT1. To find the 

value of UTC(NIST) - AT1 at any time T (expressed as a Modified Julian Day, including a fraction if needed), the appropriate 

equation to use is the one for which the desired T is greater than or equal to the entry in the To column and less than the 

entry in the last column. The values of xis, x, and y for that month are then used in the equation below to find the desired 

value. The parameters x and y represent the offset in time and in frequency, respectively, between UTC(NIST1 and AT1 ; 

the parameter xlS is the number of leap seconds applied to both UTC(NIST) and UTC as specified by the IERS. Leap seconds 

are not applied to AT1. 

Table 7.1 

UTC(NIST) - AT1 = xlS + x + y.(T - To) 

*Provisional rate 

'Note rate chanae in mid-month 

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8. SPECIAL ANNOUNCEMENTS 

TRACEABLE FREQUENCY CALIBRATIONS 

(Now NVLAP Certified) 

Anyone needing traceable frequency calibrations can get them by subscribing to the NlST Frequency 

Measurement and Analysis Service. This service is offered on a lease basis by NlST to provide an easy and 

inexpensive means to obtain traceability of a laboratory main oscillator and, in addition, to calibrate other devices 

in the lab. This service has been designed for ease of operation and as a practical lab calibration tool. 

All the equipment and software needed are provided by NIST. Users must provide their own oscillator(s) 

and an ordinary telephone line so that NIST can access the system by modem. A total of four oscillators can be 

calibrated at the same time. Radio signals from either Loran-C or GPS satellite are used. Results for either are at 

about the same accuracy. 

The calibration data are displayed in color and a graph is plotted daily for each oscillator connected. Data 

are also stored on disk. The user can call up any of the data and view them onscreen or in the form of plots. Many 

months of data can be plotted. 

The system plots are easy to read and understand. The system manual is written for easy understanding 

and the NlST staff is available by telephone to assist. The modem connection allows NlST to access the data and 

to prepare a monthly traceability report which is mailed to the user. 

Frequency sources of any accuracy can be calibrated. The FMAS is particularly useful at the highest levels 

of performance. This is because each user of the system contributes information and calibration data for the others. 

If an uncertainty arises, it is possible for NlST to call by modem to another user nearby. In this way problems in 

data interpretation can be resolved. 

NVLAP certification requirements for frequency measurement are met by following the NIST-FMAS 

operating manual. This service does not eliminate the NVLAP audits but, when installed and operated per the NlST 

guidelines, audit requirements are easily met. 

NlST retains title to the equipment and supplies any needed system spares. Equipment that fails is replaced 

by overnight shipment. Training for use of the system is available if requested by the user. 

The NET Frequency Measurement and Analysis Service provides a complete solution to nearly all 

frequency measurement and calibration problems. For a free information package, please call Michael Lombardi 

at (303) 497-3212, or write to: Michael Lombardi, NIST, Division 847, 325 Broadway, Boulder, CO 80303. 

WWVB 60 kHz UPGRADE INFORMATION 

As of 19 December, WWVB has been radiating 23 kilowatts of power, up from the previous value of 

10 kilowatts. Due to mechanical problems associated with antenna tuning, the radiated power may be reduced 

on rare occasions to 10 kilowatts for periods of a few hours. 

You can obtain current information about WWVB on the Internet at 

http:Ilwww.boulder.nist.gov/timefreqlwwvstatus.htm 

GPS WEEK 1024 ROLLOVER 

GPS System Time will rollover at midnight 21-22 August 1999. The GPS Week Number field has a 

maximum value of 1023, so at the end of week 1023 the GPS week number will rollover to zero. Once the rollover 

has occurred it is the responsibility of the user (i.e., user equipment or software) to account for the previous 1024 

weeks. Some receivers may display inaccurate data information or calculate incorrect navigation solutions. Please 

contact the manufacturer of your GPS receiver to determine if you will be affected by the GPS week number 

rollover. For more information try the following web sites: 

http:lltycho.usno.navy.millgps~week.html or http:llwww.navcen.uscg.millgpsly2kl. 

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