NlST TIME AND FREQUENCY BULLETIN 

NlSTlR 5071-9 

NO. 490 SEPTEMBER 1998 

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

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

3. UTI 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 NlST 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 

ABBREVIATIONS AND ACRONYMS USED IN THIS BULLETIN 

AUG 1998 MJD 

BlPM 

CClR 

cs 

GOES 

GPS 

IERS 

LORAN 

MC 

MJD 

NVLAP 

NIST 

NOAA 

SI 

TA 

TAI 

USNO 

UTC 

VLF 

UTI - UTC( NIST) UTC(USN0, MC) - UTC(NIST1 

(k5 ms) (+20 ns) 

- Bureau International des Poids et Mesures 

~ International Radio Consultative Committee 

- Cesium standard 

- Geostationary Operational Environmental Satellite 

- Global Positioning System 

- International Earth Rotation Service 

- Long Range Navigation 

- Master Clock 

- Modified Julian Date 

- National Voluntary Laboratory Accreditation Program 

- National Institute of Standards & Technology 

- National Oceanic and Atmospheric Administration ns - nanosecond 

- - microsecond International System of Units PS - Atomic Time ms - millisecond 

- International Atomic Time S - second 

- United States Naval Observatory min - minute 

- Coordinated Universal Time 

- very low frequency 

2. TIME SCALE INFORMATION 

The values listed below are based on data from the IERS, the USNO, and NIST. The UTC(USN0,MC) - UTC(NIST1 

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

6 51031 -1 14 ms 2 ns 

13 51038 -119 ms 0 ns 

20 51045 -122 ms -1 ns 

27 5 1052 -126 ms 0 ns 

3. UTI CORRECTIONS AND LEAP SECOND ADJUSTMENTS 

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

UTCtNIST) 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 UTl 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 kO.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 UTC(NIST) from UTC has been less than +/- 100 IIS since July 6, 1994. The table below shows values of UTC - 

0000 Hours Coordinated Universal Time 

DATE MJD UTC-UTco 

Aug 19, 1997 50679 26 

Aug 29, 1997 50689 29 

Sep. 8, 1997 50699 30 

Sep. 18, 1997 50709 31 

Sep. 28, 1997 50719 31 

Oct. 8, 1997 50729 29 

Oct. 18, 1997 50739 23 

Oct. 28, 1997 50749 16 

Nov. 7, 1997 50759 8 

Nov. 17, 1997 50769 3 

Nov. 27, 1997 50779 1 

Dec. 7, 1997 50789 2 

Dec. 17, 1997 50799 -1 

Dec. 27, 1997 50809 3 

Jan. 6, 1998 50819 2 

Jan. 16. 1998 50829 2 

Jan. 26, 1998 50839 6 

Feb. 5, 1998 50849 7 

Feb. 15, 1998 50859 11 

Feb. 25, 1998 50869 15 

Mar 7, 1998 50879 18 

Mar 17, 1998 50889 22 

Mar 27, 1998 50899 25 

Apr 6, 1998 50909 25 

Apr 16, 1998 50919 26 

Apr 26, 1998 50929 26 

May 6, 1998 50939 26 

May 16, 1998 50949 28 

May26, 1998 50959 26 

Junes, 1998 50969 30 

June 15, 1998 50979 27 

June25, 1998 50989 26 

July 5, 1998 50993 24 

July 15, 1998 51009 23 

July 25, 1998 51019 22 

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4. PHASE DEVIATIONS FOR WWVB AND LORAN-C 

WWVB - The values shown for WWVB are the time difference between the time markers of the UTC(NIST) time 

scale and the first positive-going zero voltage crossover measured at the transmitting antenna. The 

uncertainty of the individual measurements is k0.5 jls. The values listed are for 1300 UTC. 

The values shown for Loran-C represent the daily accumulated phase shift (in ns). The phase shift is 

measured by comparing the output of a Loran receiver to the UTC(NIST) time scale for a period of 24 h. 

If data were not recorded on a particular day, the symbol (-) is printed. 

The master stations monitored are Dana, IN (8970) and Fallon, NV (9940). The monitoring is done from 

the NlST laboratories in Boulder, CO. 

LORAN-C - 

Note: The values shown for Loran-C are in nanoseconds. 

UTC(NIST1-WWVB (60 kHz1 UTC(NIST) - LORAN PHASE (nsl 

ANTENNA PHASE LORAN-C (DANA) LORAN-C (FALLON) 

DATE MJD LUS) (8970) (9940) 

8/01 I98 51026 5.75 +144 +158 

8/02/98 51027 5.75 +91 +417 

8/03/98 51028 5.76 -138 -195 

8/04/98 51029 5.72 -39 + 10 

8LDKlQn 5in-m r; 77 

8/06/98 51031 5.75 -143 +312 

- - 

8/07/98 51032 5.73 + 84 -274 

8/08/98 5 1033 5.70 - 45 +11 

8/09/98 51034 5.69 +213 -201 

r; 713 +lGQ 4-716 

8/11 I98 5 1036 5.70 +123 - 640 

8/12/98 51037 5.69 +389 +147 

8/13/98 51038 5.70 -225 -103 

8/14/98 5 1039 5.70 - 230 +389 

8115'Qn E, i nAn 5 fifi 4.767 

8/16/98 5 1041 5.66 +81 -485 

- 

811 7/98 5 1042 5.66 - 233 + 65 

8/18/98 5 1043 5.63 + 423 -378 

811 9/98 5 1 044 5.66 -400 + 683 

w7nlQn GlnAC, S; 71 77 - 

8/21 198 5 1046 5.71 -125 -104 

8/22/98 5 1 047 5.69 + 500 + 265 

8/23/98 5 1048 5.68 -146 - 28 

8/24/98 5 1049 5.65 -88 -31 5 

WGIQR r;qnFin 5 G3 +l?fi + sn 

8/26/98 51051 5.57 - 446 + 38 

8/27/98 51052 5.57 + 252 - 60 

8/28/98 51053 5.87 + 561 +351 

8/29/98 51 054 5.79 -331 -193 

8/30/98 51055 5.77 -270 + 20 

8/31 198 51056 5.77 -670 -14 

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5. BROADCAST OUTAGES OVER 5 MINUTES AND WWVB PHASE PERTURBATIONS 

Station 

WWVB 

WWV 

WWVH 

AUG MJD Began Ended Freq. AUG MJD Began End 

1998 UTC UTC 1998 UTC UTC 

8/22 51047 1500 1630 60 kHz 

8/26 51051 1820 1840 

8/30 51055 1500 1540 

6. NOTES ON NlST TIME SCALE AND PRIMARY STANDARDS 

Primary frequency standards developed and maintained by NlST are used to provide accuracy (rate) input to the BIPM. NBS-6, 

which served as the U.S. primary standard from 1975 through 1992, has been replaced by NISI-7, an optically pumped cesiumbeam standard. The uncertainty of the new standard is currently 1 part in loi4. 

Since 1981, TA(NIST) has been computed retrospectively each month using a Kalman algorithm. The purpose of TA(NIST) was 

to provide a flywheel that realized our best estimate of the SI second between calibrations of our primary frequency standard, but 

the algorithm we have been using is not optimum for this purpose and is particularly unsuited to our new higher-accuracy 

environment. We therefore stopped computing TA(NIST) on 31 October 1993. We are studying alternate methods for incorporating 

the rate accuracy of NIST-7 into our time-scale algorithm, but no changes are likely until a thorough evaluation of the new procedure 

has been completed. 

The AT1 scale is run in real time using data from an ensemble of cesium standards and hydrogen masers. It is a free-running 

scale whose frequency is maintained as constant as possible by choosing the optimum weight for each clock that contributes to 

the computation. 

UTC(NIST) is generated as an offset from our real-time scale Ail. It is steered in frequency towards UTC using data published 

by the BlPM in its Circular T. Changes in the steering frequency will be made only at 0000 UTC on the first day of any month, and 

the change in frequency in any month is limited to d2 nslday. The frequency of UTC(NIST) is kept as stable as possible at other 

times. 

UTC is generated at the BlPM using a post-processed time-scale algorithm and is not available in real-time. The parameters that 

we use to generate UTC(NIST) in real-time are therefore based on an extrapolation of UTC from the most recent data available. 

7. BIBLIOGRAPHY 

Allan, D.W.; Hellwig, H.; and Glaze, D.J., "An accuracy algorithm for an atomic time scale,'' Metrologia, Vol.11, No.3, 

Allan, D.W. and Weiss, M.A., "Accurate time and frequency transfer during common view of a GPS satellite," Proc. 34th 

Allan, D.W. and Barnes, J.A., "Optimal time and frequency using GPS signals," Proc. 36th Annual Symposium on 

Drullinger, R.E.; Glaze, D.J.; Lowe, J.P.; and Shirley, J.H., "The NlST optically pumped cesium frequency standard," IEEE 

Glaze, D.J.; Hellwig, H.; Allan, D.W.; and Jarvis, S., "NBS-4 and NBS-6: The NlST primary frequency standards," 

Wineland, D.J.; Allan, D.W.; Glaze, D.J.; Hellwig, H.; and Jarvis, S., "Results on limitations in primary cesium standard 

pp.133-I 38 (September 1975). 

Annual Symposium on Frequency Control, p.334 (1980). 

Frequency Control, p.378 (1982). 

Trans. Instrum. Meas., IM-40, 162-164 (1991). 

Metrologia, Vo1.13, pp.17-28 (1977). 

operation," IEEE Trans. Instrum. Meas., IM-25, pp.453-458 (December 1976). 

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Table 7.1 is a list of the parameters that are used to define UTC(NIST) 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(NIST) 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 . 

Month 

Table 7.1 

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

XI* X Y To Valid until 0000 on: 

(S) (ns) (ns/day) (MJD) (MJD) 

Jan 98 

Feb 98 

Nov 96 I - 30 I -152046 I -44.0 I 50388 I 5041 8 

I I 

-31 - 1 70255 -42.5 508 14 50845 

-31 -171573 -42.5 50845 50873 

Mar 98 

Apr 98 

~ ~ ~ 

- 31 - 172763 -42.5 50873 50904 

- 31 - 174080.5 -42.0 50904 50934 

*Provisional rate 

'Note rate change 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 NET 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 NET. Users must provide their own oscillator(s1 

and an ordinary telephone line so that NlST 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 NIST staff is available by telephone to assist. The modem connection allows NET 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 NIST 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 NET-FMAS 

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

guidelines, audit requirements are easily met. 

NET 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) 497-321 2, or write to: Michael Lornbardi, 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://www.boulder.nist.govltimefreqlwwvstatus. 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://tycho.usno.navy.millgps-week.html or http:llwww.navcen.uscg.mil/gps/y2kl. 

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