NlST TIME AND FREQUENCY BULLETIN 

NlSTlR 5082-9 

NO. 502 SEPTEMBER 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 

BlPM - Bureau International des Poids et Mesures 

CClR - International Radio Consultative Committee 

AUG 1999 MJD UT1- UTC(NIST) 

(+5 ms) 

cs 

GOES 

GPS 

IERS 

LORAN 

MC 

MJD 

NVLAP 

NET 

NOAA 

SI 

TA 

TAI 

USNO 

UTC 

V LF 

UTC(USN0,MC)-UTC(NIST1 

( +20 ns) 

- 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 JJS - microsecond 

- 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 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. 

5 51 395 + 507 ms 3 ns 

12 51402 +505 ms -2 ns 

19 5 1 409 + 500 ms -2 ns 

26 51416 +498 ms 2 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 

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

1989, 1990.1 995, and 1998. There have been 22 leap seconds in total. 

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. DUT1 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 +/-lo0 ns since July 6, 1994. The table below shows values of UTC - 

at ten day intervals. Five day interval data are available in Circular T. 

0000 Hours Coordinated Universal Time 

DATE MJD UTC-UTC(N1ST) ns 

Aug24, 1998 51049 i1 

Sep3, 1998 51059 6 

Sep 13, 1998 5 1069 1 

Sep 23, 1998 51079 -4 

Oct 3, 1998 51089 -7 

Oct 13, 1998 

Oct23, 1998 

Nov2, 1998 

Nov 12, 1998 

Nov 22, 1998 

5 1099 

51 109 

51 119 

51129 

51139 

-5 

-3 

-3 

-1 

0 

Dec2, 1998 51149 4 

Dec 12, 1998 51159 3 

Dec22, 1998 51169 10 

Jan 1, 1999 51179 10 

Jan 11, 1999 

Jan 21, 1999 

Jan31, 1999 

Feb 10, 1999 

51189 

51199 

5 1209 

51219 

19 

22 

25 

25 

Feb 20, 1999 5 1229 26 

Mar 2, 1999 

Mar 12, 1999 

Mar 22, 1999 

Apr 1, 1999 

Apr 11, 1999 

Apr21, 1999 

51239 

51249 

51259 

51269 

51279 

51289 

24 

21 

15 

10 

2 

-9 

May 1, 1999 51299 - 18 

May 11, 1999 51309 - 18 

May21, 1999 51319 - 18 

May 31, 1999 55329 - 16 

Jun 10, 1999 51339 - 16 

Jun20, 1999 51349 - 14 

Jun30, 1999 51359 - 12 

Jul 10, 1999 51369 -6 

Jul20, 1999 51379 -3 

Jul30, 1999 51389 0 

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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 k 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 NIST laboratories in Boulder, CO. 

LORAN-C - 

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

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

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

DATE MJD dud (8970) (9940) 

8/01 I99 51391 5.73 -386 +465 

8/02/99 51392 5.73 -287 -205 

8/03/99 51393 5.73 + 544 -188 

8/04/99 51 394 5.72 +201 +450 

APG/QQ 51 19% 5 73 .b ?AQ 75n 

8/06/99 51396 5.72 - -7 -475 

8/07/99 51397 5.71 + 267 -304 

8/08/99 51398 5.71 -127 i 420 

8/09/99 51399 5.71 -352 -170 

aln1QQ GiAnn 5 77 75R 5151 

811 1 I99 51401 5.73 + 265 -111 

811 2/99 5 1402 5.72 - 444 -60 

811 3/99 51403 5.72 -224 +311 

8/14/99 5 1 404 5.71 + 531 - 96 

5 5 71 -- 71 

811 6/99 51406 5.70 + 235 + 36 

811 7/99 51407 5.70 +114 - 27 

811 8/99 5 1408 5.70 i 60 + 140 

811 9/99 5 1409 5.70 + 359 - 308 

aQ 5lAln 5 7n - 4117 

812 1 I99 5141 1 5.69 + 244 -313 

8/22/99 51412 5.69 -433 + 62 

8/23/99 51413 5.68 -536 + 403 

8/24/99 51414 5.67 -45 - 44 

-al7*/QQ 5lAl5 5 fi7 1 fifi +lAQ 

8/26/99 51416 5.69 -63 + 375 

8/27/99 51417 5.67 +71 -174 

8/28/99 51418 5.67 + 390 +484 

8/29/99 51419 5.67 I-) (4 

8/30/99 5 1420 5.67 -129 +136 

8/31 199 51421 5.66 +184 + 337 

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5. BROADCAST OUTAGES OVER 5 MINUTES AND WWVB PHASE PERTURBATIONS 

Station 

WWVB 

WWV 

WWVH 

OUTAGES 

AUG 

1999 

811 

812 

813 

814 

815 

816 

811 6 

MJD 

- 

Began 

UTC 

2200 

0000 

1830 

0140 

1940 

1650 

2220 

1440 

2050 

1000 

2300 

PHASE PERT 

I I 

Ended 

UTC 

2400 

0220 

2315 

031 0 

2140 

1720 

2400 

1910 

21 03 

1100 

2340 

Freq. 

60 kHz 

RBATIONS V 

AUG 

1999 

WB 60 k 

MJD 

- z 

Began 

UTC 

- 

End 

UTC 

6. NOTES ON NET TIME SCALE AND PRIMARY STANDARDS 

Primary frequency standards developed and maintained by NET 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 cesiumbeam 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 change in frequency in any month is limited to i2 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, 

pp.133-I 38 (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 (1 980). 

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

Frequency Control, p.378 (1982). 

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). 

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

Glaze, D.J.; Hellwig, H.; Allan, D.W.; and Jarvis, S., "NBS-4 and NBSS: 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 

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(N1ST) with respect to our real-time scale AT1. To find the 

value of UTC(N1ST) - 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 xls, 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(N1ST) 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. 

Valid until 0000 on: 

(MJD) 

50783 

5081 4 

50845 

50873 

50904 

50934 

50965 

50995 

51025 

51057 

51 087 

51118 

51 148 

51 179 

51210 

51 238 

51 269 

51 299 

51 330 

51 360 

51 391 

5 1422 

51452 

51483 

*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. 

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 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. 

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