NlST TIME AND FREQUENCY BULLETIN 

NlSTlR 5082-8 

NO. 501 AUGUST 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. 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, 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 

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 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 

JUL 1999 MJD UT1- UTC(NIST) 

(+5ms) . 

The values listed below are based on data from the IERS, the USNO, and NIST. 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. 

UTC(USN0,MC)- UTC(NIST1 

(k20 ns) 

1 5 

8 5 

15 5 

22 5 

360 +520 ms - 5 ns 

367 +518 ms - 4 ns 

374 +515 ms - 3 ns 

38 1 +512 ms -1 ns 

29 51 388 +511 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, 1990.1 995, and 1998. There have been 22 leap seconds in total. 

The use of leap seconds ensures that UT1 - UTC will always be held within k0.9 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 +/- 100 ns since July 6, 1994. The table below shows values of UTC - 

UTC(N1ST) as supplied by the BIPM in Circular T for the most recent 350 day period in which data are available. Data are given 

0000 Hours Coordinated Universal Time 

DATE MJD UTC-UTC(N1ST) ns 

July 25, 1998 51019 22 

Aug 4, 1998 51029 15 

Aug 14, 1998 51039 16 

Aug 24, 1998 51049 11 

Sep 3, 1998 51059 6 

Sep 13, 1998 51069 1 

Sep 23, 1998 5 1079 -4 

Oct 3, 1998 5 1089 -7 

Oct 13, 1998 51099 -5 

Oct23, 1998 51 109 -3 

Nov 2, 1998 51 119 -3 

Nov 12, 1998 51 129 -1 

Nov 22, 1998 51139 0 

Dec2, 1998 51149 4 

Dec 12, 1998 51 159 3 

Dec 22, 1998 51 169 10 

Jan 1, 1999 51 179 10 

Jan 11, 1999 51189 19 

Jan21, 1999 51199 22 

Jan 31, 1999 51209 25 

Feb 10, 1999 51219 25 

Feb20, 1999 5 1229 26 

Mar 2, 1999 51239 24 

Mar 12, 1999 51249 21 

Mar22, 1999 51259 15 

Apr 1, 1999 51269 10 

Apr 11, 1999 51279 2 

Apr 21, 1999 5 1289 -9 

May 1, 1999 5 1299 - 18 

May 1 1, 1999 5 1309 - 18 

May21, 1999 51319 - 18 

May 31, 1999 55329 - 16 

Jun 10, 1999 51339 - 16 

Jun 20, 1999 51349 - 14 

Jun 30, 1999 51359 - 12 

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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(N1ST) time 

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

uncertainty of the individual measurements is kO.5 p. The values listed are for 1300 UTC. 

LORAN-C - 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 (-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. 

UTCINIST)-WWVB (60 kHZ) UTCINIST) - LORAN PHASE Ins1 

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

DATE MJD IPS) (8970) (9940) 

7/01 199 51 360 5. 69 + 598 -337 

7/02/99 51361 5.66 - 346 -215 

7/03/99 51 362 5.71 + 224 + 507 

7/04/99 51363 5.68 +185 -35 

7/nr;/qq 617fiA r; 6R + inq +LKn 

7/06/99 51 365 5.69 + 325 -123 

7/07/99 51 366 5.68 + 62 +255 

7/08/99 51367 5.68 + 245 -38 

7/09/99 51368 5.70 - 46 I-) 

I99 617fiQ 6 fi9 3 A9 - 

711 1199 51370 5.68 + 28 -234 

711 2/99 51371 5.66 +465 + 334 

711 3/99 51372 5.67 -299 -515 

7/14/99 51 373 5.66 - 96 +353 

711 6/QQ 61 174 6 fifi + 79A +7 

711 6/99 51 375 5.65 - 38 +117 

711 7/99 51376 5.66 - 56 + 87 

711 8/99 51377 5.66 -107 +353 

711 9/99 51378 5.66 + 92 -312 

717ntw 61 770 6 fi6 +?fil f-\ 

7/21 I99 51380 5.65 -41 - 377 

7/22/99 51381 5.65 +391 -a7 

7/23/99 51 382 5.65 +116 -18 

7/24/99 51 383 5.65 - 340 + 91 

7/95/09 51 7RA 6 fir; 7n3 + A76 

7/26/99 51385 5.66 - 24 -215 

7/27/99 51 386 5.74 +112 -494 

7/28/99 51 387 5.73 -119 + 305 

7/29/99 51388 5.72 -499 +186 

7130199 51389 5.72 -261 + 527 

7/31/99 51390 5.72 -450 -489 

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5. BROADCAST OUTAGES OVER 5 MINUTES AND WWVB PHASE PERTURBATIONS 

Station 

WWVB 

wwv 

WWVH 

OUTAGES 

JUN 

1999 

711 5 

711 6 

712 1 

7/22 

7/23 

7/24 

7/30 

713 1 

711 0 

MJD 

51 374 

51 375 

51380 

51381 

51 382 

51 383 

51 389 

51 390 

51 369 

Began 

UTC 

1920 

0000 

1730 

2100 

0140 

2330 

0000 

1700 

1430 

0000 

1400 

2000 

1100 

Ended 

UTC 

2400 

0220 

1910 

2400 

031 0 

2400 

031 0 

2110 

2400 

0205 

1550 

2230 

1300 

HASE PERT 

Freq. 

60 kHz 

20 MHz 

'IONS \i 

JUN 

1999 

- WB 60 I 

MJD 

- - z 

Began 

UTC 

- 

End 

UTC 

6. NOTES ON NET 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 US. 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 IOl4. 

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 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.133-138 (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 (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 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 

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. 

Aug 99 

Sep 99 

Table 7.1 

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

- 32 -194155 -41 .O 51391 5 1422 

- 32 - 195426 -41 .O* 51422 51452 

'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(s1 

and an ordinary telephone line so that NET 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 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 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 NET-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 contact Michael Lombardi 

at (303) 497-321 2, E-mail at lornbardi@boulder.nist.gov, or write to: Michael Lombardi, NIST, Division 847, 325 

Broadway, Boulder, CO 80303. 

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