NlST TIME AND FREQUENCY BULLETIN 

NlSTlR 5082-7 

NO. 500 JULY 1999 

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 NlST TIME SCALES AND PRIMARY STANDARDS ............................... 5 

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

8. SPECIAL ANNOUNCEMENTS. ...................................................... 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, Gary R. Bachula, Acting Under Secretary for Technology 

NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY, Karen Brown, Deputy Director 

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1. GENERAL BACKGROUND INFORMATION 

ABBREVIATIONS AND ACRONYMS USED IN THIS BULLETIN 

- 0000 HOURS COORDINATED UNIVERSAL TIME 

JUN 1999 MJD UT 1 - UTC (NIST) UTC(USN0, MC)- UTC(NIST) 

(f5 ms) ( f 20 ns) 

BlPM 

CClR 

cs 

GOES 

G PS 

IERS 

LORAN 

MC 

MJD 

NVLAP 

NIST 

NOAA 

SI 

TA 

TAI 

USNO 

UTC 

VLF 

- 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 

- International System of Units /IS - microsecond 

- Atomic Time 

- International Atomic Time S - second 

- United States Naval Observatory min - minute 

- Coordinated Universal Time 

- very low frequency 

ms - millisecond 

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(NIST) data are on page 

3. 

3 51332 +552 ms -22 ns 

10 51 339 +548 ms -15 ns 

17 51 346 +545 ms -11 ns 

24 51353 +542 ms -8 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 +0.9 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, 1981-1983, 1985, 1992, 1993, 1994, and 1997, and on 31 December 1972-1979, 1987, 

1989, 1990,1995, and 1998. There have been 22 leap seconds in total. 

The use of leap seconds ensures that UT1 - UTC will always be held within f0.9 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. 

+0.7s beginning 0000 UTC 01 January 1999 

+0.6s beginning 0000 UTC 04 March 1999 

+ 0.5s beginning 0000 UTC 27 May 1999 

DUTl = UT1 - UTC = 

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The deviation of UTC(N1ST) from UTC has been less than +I- 100 ns since July 6, 1994. The table below shows values (if UTC 

0000 Hours Coordinated Universal Time 

DATE MJD UTC-UTC(N1ST) ns 

June25, 1998 

July 5, 1998 

July 15, 1998 

luly 25, 1998 

Aug 4, 1998 

Aug 14, 1998 

Aug 24, 1998 

Sep3, 1998 

Sep 13, 1998 

Sep23, 1998 

Oct 3, 1998 

Oct 13, 1998 

Oct 23, 1998 

Nov 2, 1998 

Nov 12, 1998 

Nov 22, 1998 

Dec 2, 1998 

Dec 12, 1998 

Drx: 22, 1998 

Jan 1, 1999 

Jan 11, 1999 

Jan 21, 1999 

Jan 3 I, 1999 

Feb 10, 1999 

Feb 20, 1999 

Mar2, 1999 

Mar 12, 1999 

Mar 22, 1999 

Apr 1, 1999 

Apr 11, 1999 

Apr 21, 1999 

May 1, 1999 

May 11, 1999 

May 21, 1999 

May 31, 1999 

50989 

50993 

5 1009 

51019 

51029 

51039 

51049 

51059 

5 1069 

5 1079 

51089 

51099 

51109 

51119 

51 129 

51 139 

51 149 

51159 

51169 

51 179 

51189 

51 199 

5 1209 

51219 

51229 

5 1239 

51249 

51259 

51269 

5 1279 

51289 

5 1299 

51309 

1319 

5329 

26 

24 

23 

22 

15 

16 

11 

6 

1 

-4 

-7 

-5 

-3 

3 

1 

0 

4 

3 

10 

10 

19 

22 

25 

25 

26 

24 

21 

15 

10 

1 

9 

18 

18 

18 

16 

Data are 

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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(NIST1 time 

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

uncertainty of the individual measurements is * 0.5 ps. 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(N1ST) time scale for a period of 24 h. 

If data were not recorded on a particular day, the symbol (-1 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. 

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

LORAN-C - 

UTC(NIST1-WWVB ( 60 kHd UTCINIST) - LORAN PHASE (ns) 

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

DATE MJD w (8970) (9940) 

610 1/99 51330 5. 71 -241 + 105 

6/02/99 51331 5.69 +415 + 36 

6/03/99 51332 5.69 + 60 + 52 

6/04/99 5 1333 5.70 + 128 (-1 

€iln!=.‘QQ c,i??a c, 7n 175 1-1 

6/06/99 5 1335 5.71 - a8 (-) 

6/07/99 5 1336 5.71 + 386 (-1 

6/08/99 5 1337 5.69 - 382 288 

6/09/99 5 i 338 5.70 + 343 i 44 

fV1nlqQ 5 1 ??q c, fi9 16 7 

611 1/99 5 1340 5.65 i 146 237 

611 2/99 51341 5.70 - 501 302 

611 3/99 5 1342 5.70 i577 + 89 

6/14/99 5 1343 5.69 210 +3 

fi/’15/qq 6 1 7AA 5 7n +??R Ac, 

611 6/99 5 1345 5.67 - 25 +119 

611 7/99 5 1346 5.71 +421 (-1 

611 8/99 51347 5.69 +21 - 400 

611 9/99 5 1348 5.70 - 243 + a2 

DnlQQ 5l?Aq c, 7n 4. An? 71 

612 1 I99 5 1350 5.71 -315 - 152 

612 219 9 51351 5.71 + 333 + 500 

6/23/99 51352 5.70 346 163 

6/24/99 51353 5.70 +131 +260 

u25’Qq E;i?c,a c, 70 la? 95 

6/26/99 5 1355 5.69 + 158 416 

6/27/99 5 1356 5.70 + 290 208 

6/28/99 51357 5.68 - 145 + 355 

612 9 I9 9 51358 5.66 i 255 6 

6130199 51359 5.69 + 357 + 396 

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5. BROADCAST OUTAGES OVER 5 MINUTES AND WWVB PHASE PERTURBATIONS 

Station 

WWVB 

WWV 

WWVH 

OUTAGES 

I I 

JUN MJD 

1999 

6/17 51 346 

611 9 51 348 

6/26 51 355 

6/29 51 358 

PHASE PERTURBATIONS WWVB 60 kHz 

6. NOTES ON NlST TIME SCALE AND PRIMARY STANDARDS 

Prirnaryfrequencystandards 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 NIST-7, an optically pumped cesium-beam 

standard. The uncertainty of the new standard is currently 1 part in 

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 AT1 . 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 8. 

change in frequency in any month is limited to ?2 ns/day. 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, 

pp.133-138 (September 1975). 

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

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

Frequency Control, p.378 (1 982). 

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 

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

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

Metrologia, Vol. 13, pp. 17-28 (1 977). 

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

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 xb, 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 x, 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. 

May 99 

~ Jun99 

Jul 99 

1 AUg 99 

I 

Table 7.1 

UTC(NIST) - AT1 = x,, + x + y(T - T(,) 

- 32 ~ 190383 -41 .O 51299 51 330 

-32 -191654 -41 .O 51 330 51 360 

- 32 - 192884 -41 .O 51 360 51391 

- 32 - 1941 55 -41 .O* 51391 51422 

*Provisional rate 

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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 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 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 NlST Frequency Measurement and Analysis Service provides a complete solution to nearly all frequency 

measurement and calibration problems. For a free information package, please contact Michael Lombardi at (303) 

497-321 2, E-mail at lombardi@boulder.nist.gov, or write to: Michael Lombardi, NIST, Division 847, 325 Broadway, 

Boulder, CO 80303. 

IMPOR NOTICE! 

e and Frequency Bulletin is now online at 

www. boulder.nist.gov/timefreq/puhs/bulletin/index. htm 

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