NlST TIME AND FREQUENCY BULLETIN 

NlSTlR 5071-10 

NO. 491 OCTOBER 1998 

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

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

3. UT1 CORRECTIONS AND LEAP SECOND ADJUSTMENTS .................................. 2 

4. PHASE DEVIATIONS FOR WVB 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, 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 

BlPM - Bureau International des Poids et Mesures 

CClR - International Radio Consultative Committee 

cs - Cesium standard 

GOES 

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 

NlST - National Institute of Standards & Technology 

NOAA - National Oceanic and Atmospheric Administration ns - nanosecond 

SI - International System of Units jls - 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 

- Geostationary Operational Environmental Satellite 

SEP 1998 MJD 

2. TIME SCALE INFORMATION 

UT1 -UTC(NIST) UTC(USN0,MC)-UTC(NIST) 

(k5 ms) (520 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, 1981-1983, 1985, 1992, 1993, 1994, and 1997, and on 31 December 1972-1979, 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. 

+O.O 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) fmm 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. 

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

Data are 

0000 Hours Coordinated Universal Time 

DATE MJD UTC-UTC(NIST) ns 

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 509 19 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 51029 15 

Aug. 14, 1998 51039 16 

Aug. 24, 1998 51049 11 

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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 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 kHZl 

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

UTC(NIST) - LORAN PHASE (nsl 

DATE MJD CS) (8970) (9940) 

9/01/98 51057 5.72 + 424 -18 

9/02/98 51058 5.71 + 383 - 324 

9/03/98 51059 5.73 +327 -16 

9/04/98 51060 5.66 +4 + 279 

QID~lQn s;10R1 Fz RF; +n 74 

910 619 8 51062 5.65 -2 + 83 

9/07/98 5 1063 5.66 +I36 + 663 

9/08/98 5 1064 5.72 - 82 - 203 

9/09/98 51065 5.74 + 39 +148 

9L1D19n r;qnfifi Fz 71 77s; 4’17 

911 1 I98 51067 5.70 -129 - 227 

911 2/98 51068 5.69 -176 + 337 

911 3/98 5 1069 5.70 +14 -456 

9/14/98 5 1070 5.67 - 82 -8 

QUK1QQ F;qn7’1 s; 6s; 9fi 1 ?R 

911 6/98 5 1072 5.63 - 198 +170 

9/17/98 51073 5.64 - 63 + 149 

911 8/98 5 1074 5.65 -24 +11 

911 9/98 51075 5.64 i597 + 299 

ql?nlQn r;1n7fi r; fi? A95 71 

9/21 I98 51077 5.61 + 644 + 385 

9/22/98 51078 5.69 + 85 +197 

9/23/98 51079 5.74 -445 -197 

9/24/98 5 1 080 5.72 i-289 - 84 

9 136 la $2 r;Tnni s; 70 467 4-19 

9/26/98 51082 5.69 - 47 - 209 

9/27/98 51083 5.68 -96 - 108 

9/28/98 5 1084 5.63 -213 +534 

9/29/98 51085 5.74 -52 - 355 

9/30/98 51086 5.74 +269 + 247 

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5. BROADCAST OUTAGES OVER 5 MINUTES AND WWVB PHASE PERTURBATIONS 

6. NOTES ON NlST TIME SCALE AND PRIMARY STANDARDS 

Pnmaryfrequency 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 NIST-7, an optically pumped cesium-beam 

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

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 ATI. 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 +2 ns/day. 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. 

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. 133-1 38 (September 1975). 

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

Frequency Control, p.378 (1 982). 

Trans. Instrum. Meas., IM-40, 162-164 (1 991). 

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

operation," IEEE Trans. Instrum. Meas., IM-25, pp.453458 (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(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 x, 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(NIST1 and AT1 ; the 

parameter x, is the number of leap seconds applied to both UTC(NIST1 and UTC as specified by the IERS. Leap seconds are 

not applied to AT1. 

~ ~~ 

Table 7.1 

UTC(N1ST) - AT1 = & + x + y(T - To) 

Apr 98 -31 - 174080.5 -42.0 50904 50934 

May 98 -31 - 175340.5 -42.0 50934 50965 

Jun 98 -31 - 176642.5 -41.5 50965 50995 

Jul98 -31 - 177887.5 -41.5 50995 51025 

Aug 98 -31 -179174 -41 .O 51 025 51057 

Sep 98 -31 - 180445 -41 .O 51 057 51087 

Oct 98 -31 - 181 675 -41 .O 51087 51118 

Nov 98 -31 -182961.5 -41.5* 51118 51 148 

*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 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 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 call Michael Lombardi at (303) 497- 

321 2, 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 periods of a few hours. 

You can obtain current information about WWVB on the Internet at 

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

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