NlST TIME AND FREQUENCY BULLETIN 

NlSTlR 5071 -1 2 

NO. 493 DECEMBER 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 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 

ABBRWIATIONS AND ACRONYMS USED IN THIS BULLETIN 

NOV 1998 

BlPM 

CClR 

cs 

GOES 

G PS 

IERS 

LORAN 

MC 

M JD 

NVLAP 

NET 

NOAA 

SI 

TA 

TAI 

USNO 

UTC 

VLF 

MJD UTI - UTC( NIST) UTC( U SNO, MC) - UTC( N IST) 

(+5 ms) ( f 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 

- International System of Units jls - microsecond 

- AtomicTime 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(NIST1 values 

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

3. 

5 51 122 -211 ms 

12 51 129 -222 ms 

18 51 136 -232 ms 

26 51 143 -240 ms 

3 ns 

2 ns 

4 ns 

6 ns 

I 

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(NIST1 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 3 1 December 1972-1 979, 1987, 

1989, 1990, and 1995. There have been 2 1 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 50.9 s. The current value of UTI - 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. 

-0.2 s beginning 0000 UTC 13 August 1998 

-0.3 s beginning 0000 UTC 26 November 1998 

+0.7s beginning 0000 UTC 1 January 1999 

DUTI = UTI - UTC = 

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

0000 Hours Coordinated Universal Time 

DATE MJD UTC-UTCO\IIST) 11s 

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 508 19 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 

Mar27, 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 

May 26, 1998 50959 26 

June 5, 1998 50969 30 

June 15, 1998 50979 27 

June 25, 1998 50989 26 

July 5, 1998 50993 24 

July 15, 1998 51009 23 

July 25, 1998 51019 22 

Aug. 4, 1998 5 1029 15 

Aug. 14, 1998 51039 16 

Aug. 24, 1998 5 1049 11 

Sep. 3, 1998 51059 6 

Sep. 13, 1998 51069 1 

Sep. 23, 1998 51079 -4 

Oct. 3, 1998 51089 -7 

Oct 13, 1998 51099 -5 

Oct 23, 1998 51109 -3 

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Data are 
4. PHASE DEVIATIONS FOR WB AND LORAN-C 

WWUB - 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 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(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. 

LORAN-C - 

UTC(NIST)-WWVB (60 kHa UTC(N1ST) - LORAN PHASE (nsl 

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

DATE MJD CS) (8970) (9940) 

11/01/98 51 118 5.76 - 407 -518 

1 1/02/98 51119 5.76 - 337 +478 

1 1/03/98 51 120 5.76 -2 - 129 

1 1/04/98 51 121 5.72 - 269 + 85 

I1LDqlqn 51177 5 75 on 77 

11/06/98 51 123 5.70 - 376 + 66 

1 1 /07/98 51 124 5.70 + 534 - 407 

1 1/08/98 51125 5.70 +556 -3 

11/09/98 51 126 5.72 - 264 - 336 

1111nIQR 51177 5 RR +A74 + 749 

1 111 1/98 51128 5.66 + 600 - 82 

11q/12/98 51 129 5.66 +41 + 100 

1 1 I1 3/98 51 130 5.68 +526 - 61 

1 1 I1 4/98 51 131 5.67 +718 +31 

l1ll5IQR 57117 E; RR 4-579 7 

1 1 I1 6/98 51133 5.68 - 327 +451 

1 1 I1 7/98 51134 5.69 +154 -421 

1 1 I1 8/98 51135 5.68 +5 - 25 

1 1 I1 9/98 51 136 5.70 -136 - 172 

11 17010R 51117 5 7n AnR AR 

11/21/98 51138 5.66 +143 -319 

11/22/98 51139 5.64 + 342 -188 

11/23/98 51 140 5.62 +168 + 37 

1 1/24/98 51 141 5.65 -326 -t 250 

I9 R 51 1A7 5 Gl 7R + R9 

1 112 6/98 51 143 5.65 - 522 - 70 

11/27/98 51 144 5.70 - 108 -2 

11/28/98 51 145 5.68 +213 + 33 

11/29/98 51 146 5.64 -71 + 365 

1 1130/98 51 147 5.62 -329 - 83 

-4- 
5. BROADCAST OUTAGES OVER 5 MINUTES AND WWVB PHASE PERTURBATIONS 

I I I I I I I I I I 

6. NOTES ON NlST TIME SCALE AND PRIMARY STANDARDS 

Primaryfrequencystandards 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 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 studylng alternate methods for incorporating the rate accuracy 

of NIST-7 into ourtime-scale algorithm, but no changes are likely until a thorough evaluation of the new procedure has been completed. 

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

computation. 

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 22 ndday. The frequency of UTC(NIST) is kept as stable as possible at other times. 

UTC is generated atthe 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. 

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 -- 

UTC(NIST) is generated as an offset from our real-time scale AT1 . It is steered in frequency towards UTC using data published by - 

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 primaryfrequency standards," 

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

pp.133-138 (September 1975). 

Annual Symposium on Frequency Control, p.334 (1 980). 

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(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 xlr, 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 xb 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 . 

Jun 98 

Jut 98 

Aug 98 

Sep 98 

Oct 98 

Nov 98 

Dec 98 

Jan 99 

-31 -176642.5 -41.5 50965 50995 

-31 - 177887.5 -41.5 50995 51025 

-31 - 179174 -41 .O 51025 5 1057 

-31 - 180445 -41 .O 51057 5 1087 

-31 - 1 81 675 -41 .O 51087 51118 

-31 -182961.5 -41.5 51118 51 148 

-31 - 184206.5 -41.5 51 148 51 179 

-32 - 185493 -41.5* 51179 51210 

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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 plorted. 

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

and the NET 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 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, email at lombardi@boulder.nist.gov, 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 Deriods of a few hours. 

You can obtain current information about WWVB on the Internet at 

http://www.boulder.nist.gov/timefreq/wwvstatus .htm 

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