NIST TIME AND FREQUENCY BULLETIN 

NISTIR 6604-4
 

NO. 521 APRIL 2001	 

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

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

3.	 PHASE DEVIATIONS FOR WWVB AND LORAN-C 4
 

4.	 BROADCAST OUTAGES OVER FIVE MINUTES AND WWVB
 

PHASE PERTURBATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 5
 

5.	 NOTES ON NIST TIME SCALES AND PRIMARY STANDARDS. . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 5
 

6.	 BIBLIOGRAPHY 5
 

7.	 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 

Email: bennett@boulder.nist.gov 

NOTE TO SUBSCRIBERS:	 Please include your address label (or a copy) 

with any correspondence regarding this bulletin. 

U.S. DEPARTMENT OF COMMERCE, DONALD L. EVANS, Secretary 

TECHNOLOGY ADMINISTRATION, Dr. Cheryl L. Shavers, Under Secretary of Commerce for Technology 

NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY, Karen H. Brown, Acting Director 

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1. GENERAL BACKGROUND INFORMATION 

ABBREVIATIONS AND ACRONYMS USED IN THIS BULLETIN 

BIPM - Bureau International des Poids et Mesures 

CCIR - 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 

NIST - National Institute of Standards and Technology 

NOAA - National Oceanic and Atmospheric Administration ns nanosecond 

SI - International System of Units JiS - microsecond 

TA - Atomic Time ms - millisecond 

TAl - International Atomic Time s second 

USNO United States Naval Observatory min minute 

UTC - Coordinated Universal Time 

VLF - very low frequency 

2. TIME SCALE INFORMATION 

The values listed below are based on data from the IERS, the USNO, and NIST. The UTC(USNO,MC) - UTC(NIST) 

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

on page 3. 

0000 HOURS COORDINATED UNIVERSAL TIME 

MAR 2001 MJD UT1-UTC(NIST) UTC(USNO,MCI-UTC(NISTI 

(+ 5 msl (± 20 nsl 

1 51969 + 56 ms 7 ns 

8 51976 + 48 ms 5 ns 

15 51983 + 38 ms 7 ns 

22 51990 + 35 ms 10 ns 

29 51997 + 28 ms 16*ns 

*This value is extrapolated. 

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 UTl astronomical time scale, which changes slightly due to variations 

in the rotation of the Earth. 

NOTE: No positive leap second will be inserted at the end of June 2001. 

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 UTl - UTC will always be held within ± 0.9 s. The current value of UTl - UTC 

is called the DUn 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. 

+0.2s beginning 0000 UTC 13 April 2000 

DUTl un - UTC t- + 0.1 s beginning 0000 UTC 19 October 2000 

+O.Os beginning 0000 UTC 01 March 2001 

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UTC(NlST) as supplied by the BIPM in their Circular T publication for the most recent 350 day period in which data are available. 

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

DATE 

0000 Hours Coordinated Universal Time 

MID UTC-UTC(NIST) os 

Mar 16, 2000 51619 15 

Mar 26,2000 51629 15 

Apr 5,2000 51639 20 

Apr 15, 2000 51649 20 

Apr 25,2000 51659 17 

May 5, 2000 51669 17 

May 15,2000 51679 17 

May 25,2000 51689 18 

June 4,2000 51699 18 

June 14, 2000 51709 20 

June 24,2000 51719 23 

July 4,2000 51729 24 

July 14, 2000 51739 24 

July 24, 2000 51749 24 

Aug 3, 2000 51759 26 

Aug 13,2000 51769 25 

Aug 23, 2000 51779 22 

Sep 2,2000 51789 12 

Sep 12, 2000 51799 6 

Sep 22,2000 51809 0 

Oct. 2, 2000 51819 -8 

Oct. 12, 2000 51829 -13 

Oct. 22, 2000 51839 -19 

Nov. 1,2000 51849 -25 

Nov. I I, 2000 51859 -22 

Nov. 21, 2000 51869 -21 

Dec. 1,2000 51879 -16 

Dec. Il, 2000 51889 -9 

Dec. 21, 2000 51899 -5 

Dec. 31,2000 51909 -3 

Jan. 10, 2001 51919 2 

Jan. 20, 2001 51929 7 

Jan. 30, 2001 51939 Il 

Feb. 9, 2001 51949 II 

Feb. 19,2001 51959 5 

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WWVB The values shown for WWVB are the time differences 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 ±0.5 ps. 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 (-) is printed. 

The master stations monitored are Dana, IN (8970) and Fallon, NV (9940). The monitoring is done from 

the NIST laboratories in Boulder, Colorado. 

Note" The values shown for Loran-C are in nanoseconds 

UTCINISTl-WWVB (60 kHzl UTC(NISTl - LORAN PHASE Ins) 

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

DATE MJD (JJs) (8970) (9940) 

03/01/01 51969 5.49 -44 -129 

03/02/01 51970 5.49 -387 -375 

03/03/01 51971 5.48 -43 +223 

03/04/01 51972 5.48 +210 + 140 

03/05/01 51973 5.48 -469 -333 

03/06/01 51974 5.50 -170 -22 

03/07/01 51975 5.49 + 156 -365 

03/08/01 51976 5.49 -25 -300 

03/09/01 51977 5.49 +219 +222 

03/10/01 51978 5.50 -193 +275 

03/11/01 51979 5.50 +37 + 73u 

03/12/01 51980 5.51 -169 -730 

03/13/01 51981 5.48 -18 +309 

03/14/01 51982 5.49 -361 +133 

03/15/01 51983 5.48 -356 -339 

03/16/01 51984 5.48 +524 -72 

03/17/01 51985 5.48 -246 -120 

03/18/01 51986 5.48 -173 +222 

03/19/01 51987 5.50 -554 -154 

03/20/01 51988 5.48 +267 +299 

03/21/01 51989 5.47 -182 +80 

03/22/01 51990 5.47 +341 -159 

03/23/01 51991 5.47 -26 -76 

03/24/01 51992 5.47 +262 +208 

03/25/01 51993 5.47 -21 +338 

03/26/01 51994 5.46 -387 +26 

03/27/01 51995 5.45 -212 +498 

03/28/01 51996 5.46 +46 -111 

03/29/01 51997 5.49 -474 -140 

03/30/01 51998 5.49 +84 +482 

03/31/01 51999 5.50 -99 -533 

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OUTAGES	 OF 5 MINUTES OR MORE PHASE PERTURBATIONS 

WWVB60 kHz 

Station	 MAR MJD Began Ended Freq. MAR MJD Began End 

2001 UTC UTC 2001 UTC UTC 

WNVB 3/2 51970 1632 1748 60 kHz 

WNV 

WNVH 

5. NOTES ON NIST TIME SCALE AND PRIMARY STANDARDS 

Primary frequency standards developed and maintained by NIST are used to provide accuracy (rate) input to the BIPM. NIST-7, 

which has served as the U.S. primary standard since 1994 is being replaced by NIST-F1, a cesium fountain frequency standard. 

The uncertainty of the new standard is currently 1.7 parts in 1015• 

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 BIPM in its Circular T. Changes in the steering frequency will be made, if necessary, at 0000 UTC on the first day of the 

month, and very occasionally at mid-month. A change in frequency is limited to no more than ± 2ns/day. The frequency of 

UTC(NIST) is kept as stable as possible at other times. 

UTC is generated at the BIPM 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. 

6. BIBLIOGRAPHY 

Allan, OW.; Hellwig, H.; and Glaze, D.J., "An accuracy algorithm for an atomic time scale," Metrologia, Vo1.11, 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). 

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 NIST optically pumped cesium frequency standard," IEEE 

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

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

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

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) - ATl at anv time T (expressed as a Modified Julian Dav, 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 entrv in the To column and less than the
 

entry in the last column. The values of Xis' X, and V for that month are then used in the equation below to find the desired
 

value. The parameters X and V represent the offset in time and in frequencv, respectivelv, between UTC(NIST) and AT1;
 

the parameter Xis is the number of leap seconds applied to both UTC(NIST) and UTC as specified bV the IERS. Leap seconds
 

are not applied to AT1.
 

Table 7.1 

UTC(NIST) - ATl = Xis + X + v·(T - To) 

Month Xis X V To Valid until 0000 on:

(s) (ns) (ns/day) (MJD) (MJD)
 

Aug 99 -32 -194155 -41.0 51391 51422
 

Sep 99 -32 -195426 -40.5 51422 51452
 

Oct 99 -32 -196641 -40.5 51452 51483
 

Nov 99 -32 -197896.5 -40.0 51483 51513
 

Dec 99t -32 -199096.5 -40.0 51513 51533
 

Dec 99 -32 -199896.5 -41.0 51533 51544
 

Jan 00 -32 -200347.5 -40.5 51544 51575
 

Feb 00 -32 -201603 -40.5 51575 51604
 

Mar 00 -32 -202777.5 -40.5 51604 51635
 

Apr 00 -32 -204033 -40.5 51635 51665
 

Mav OO -32 -205248 -40.25 51665 51696
 

Jun 00 -32 -206495.75 -40.25 51696 51725 tt
 

Jul 00 -32 -207663 -40.0 51725 tt 51757
 

Aug 00 -32 -208943 -39.5 51757 51788
 

Sep 00 -32 -210167.5 -39.0 51788 51818
 

Oct 00 -32 -211337.5 -39.0 51818 51849
 

Nov 00 -32 -212546.5 -40.0 51849 51879
 

Dec 00 -32 -213746.5 -40.0 51879 51910
 

Jan 01 -32 -214986.5 -40.0 51910 51941
 

Feb 01 -32 -216226.5 -39.0 51941 51969
 

Mar 01 -32 -217318.5 -39.5 51969 52000
 

Apr 01 -32 -218543 -39.0 52000 52030
 

May 01 -32 -219713 -39.0· 52030 52061
 

t Rate change in mid-month
 

tt Rate change one day early
 

·Provisional rate
 

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I

: 
7. SPECIAL ANNOUNCEMENTS 

TRACEABLE FREQUENCY CALIBRATIONS 

(Now NVLAP Certified) 

Laboratories needing traceable frequency calibrations can get them by subscribing to the NIST Frequency 

Measurement and Analysis Service. This service is offered on a lease basis by NIST to provide an easy and 

inexpensive means to obtain traceability of a laboratory frequency standard and, in addition, to calibrate other 

devices in the lab. This service has been designed for ease of operation and as a practical calibration tool. 

All necessary hardware and software is provided by NIST. Users must provide their own oscillator(s) and 

an ordinary telephone line so that NIST can access the system by modem. A total of five oscillators can be 

calibrated at the same time. Radio signals from GPS satellites are used and the measurement uncertainty is 

± 2 x 10-13 per day. Any frequency from 1 Hz to 120 MHz can be measured in 1 Hz increments. 

The calibration data are displayed in color and a graph is plotted daily for each oscillator. 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. Up to 5 

months of data can be plotted on one graph. 

The system plots are easy to read and understand. The system manual is written clearly and the NIST staff 

is available by telephone to assist. The modem connection allows NIST 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 NIST 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 NIST 

guidelines, audit requirements are easily met. 

NIST retains title to the equipment and supplies. All necessary replacement parts are replaced by overnight 

shipment. Training for use of the system is available if requested by the user. 

The NIST 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) 497-3212, E-mail at !ombardi@boulder.nist.gov, or write to: Michael Lombardi, NIST, Division 847, 325 

Broadway, Boulder, CO 80303. 

IMPORTANT NOTICE! 

TheTime and Frequency Bulletin data are.now online at 

www.boulder.nist.gov/timefreq/ 

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