NlST TIME AND FREQUENCY BULLETIN 

NlSTlR 5071 -1 

NO. 482 JANUARY 1998 

I. GENERAL BACKGROUND INFORMATION . 

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

3. UT1 CORRECTIONS AND LEAP SECOND ADJUSTMENTS 

4. PHASE DEVIATIONS FOR WWVB AND LORAN-C . . 

5. GOES TIME CODE INFORMATION ........... 

6. BROADCAST OUTAGES OVER FIVE MINUTES AND WWVB 

PHASE PERTURBATIONS ......................... 

7. NOTES ON NlST TIME SCALES AND PRIMARY STANDARDS 

8. BIBLIOGRAPHY ............................... 

9. SPECIAL ANNOUNCEMENTS ....................... 

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. 

L 

... 2 

2 

.. .4 

I.. 5 

5 

.. 5 

...... 5 

- 

U.S. DEPARTMENT OF COMMERCEr William M. Daley, Secretary 

TECHNOLOGY ADMINISTRATION, Mary L. Good, Under Secretary for Technology 

NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY, Robert Hebner, Acting Deputy Director 

-1 - 
1. GENERAL BACKGROUND INFORMATION 

DEC 1998 

BlPM 

CClR 

cs 

GOES 

GPS 

IERS 

LORAN 

MC 

MJD 

NVLAP 

NET 

NOAA 

SI 

TA 

TAI 

USNO 

UTC 

VLF 

MJD UTI - UTC(NIST) UTC(USN0,MC) - UTC(NIST) 

(*5 ns) ( * 20 ns) 

ABBREVIATIONS AND ACRONYMS USED IN THIS BULLETIN 

- 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 

- International System of Units 

- Atomic Time 

- International Atomic Time 

- United States Naval Observatory 

- Coordinated Universal Time 

- very low frequency 

ns - nanosecond 

fls - microsecond 

ms - millisecond 

S - second 

min - minute 

2. TIME SCALE INFORMATION 

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

4 50786 +265 ms 

11 50793 +251 ms 

18 50800 +239 ms 

25 50807 +228 ms 

3 ns 

8 ns 

9 ns 

11 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 kO.9 s of the UTI 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, and 1995. 

The use of leap seconds ensures that UTI - UTC will always be held within kO.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 . 

+0.3 s beginning 0000 UTC 30 October 1997 

+0.2 s beginning 0000 UTC 18 December 1997 

+0.1 s beginning 0000 UTC 19 February 1998 

DUTl = UTI - UTC = 
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 at ten day intervals. Five day interval data are available in Circular T. 

0000 Hours Coordinated Universal Time 

DATE MJD UTC-UTC(hTST) 

ns 

Dec 12, 1996 50429 49 

Dec 22, 1996 50439 50 

Jan 1, 1997 50449 44 

ran 11, 1997 50459 40 

Jan 21, 1997 50469 36 

Jan 31, 1997 50479 29 

Feb 10, 1997 50489 27 

Feb 20, 1997 50499 21 

Mar 2, 1997 50509 20 

Mar 12, 1997 50519 12 

Mar 22, 1997 50529 10 

Apr 1, 1997 50539 5 

Apr 11, 1997 50549 6 

Apr21, 1997 50559 -3 

May 1, 1997 50569 -5 

May 11, 1997 50579 -7 

May 21, 1997 50589 -4 

May 31, 1997 50599 -6 

Jun 10, 1997 50609 -5 

Jun20, 1997 506 19 -3 

Jun 30, 1997 50629 0 

Jul 10, 1997 50639 8 

Jul20, 1997 50649 16 

Jul 30, 1997 50659 18 

Aug 9, 1997 50669 21 

Aug 19, 1997 50679 26 

Aug 29, 1997 50689 29 

Sep. 8, 1997 50699 30 

Sep. 18, 1997 50709 31 

Scp. 28, 1997 507 19 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 

-3 - 
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 k0.5 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 (-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. 

UTC(NIST)-WWV8(60 kHZ) UTC(NIST) - LORAN PHASE (nsl 

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

DATE MJD @s)u (0970) (9940) 

12/01 197 50703 5.72 i 40 -419 

12/02/97 50704 5.71 - 696 - 233 

12/03/97 50705 5.73 + 390 -156 

12/04/97 50706 5.77 - 580 - 224 

12/05/97 5 707 -4 + 43 

12/06/97 50700 5.70 + 06 -150 

12/07/97 50709 5.70 -143 -212 

12/08/97 50790 5.67 -251 i 383 

12/09/97 50791 5.69 +15 - 294 

1211 0197 50792 5.66 -194 - 226 

1211 1197 50793 5.66 -181 + 364 

1211 2/97 50794 5.69 i 290 + 424 

1211 3/97 50795 5.67 - 260 -142 

1211 4/97 50796 5.66 (-1 (4 

1211 5/97 50797 5.61 io -215 

1211 6/97 50790 5.69 -218 (4 

1211 7/97 50799 5.66 + 504 (-1 

1211 8/97 50800 5.66 - 27 - 540 

8 

1211 9/97 50001 5.67 -406 1301 

12/20/97 50002 i5 -130 

12/21/97 50003 5.67 i1 - 54 

12/22/97 50804 5.66 - 360 - 60 

12/23/97 50005 5.62 i795 i 255 

12/24/97 50006 5.63 -31 1 - 527 

121 5/97 50007 i 71 i 262 

12/26/97 50000 5.63 - 50 -176 

12/27/97 50809 5.62 i433 1199 

12/28/97 50010 5.62 -419 + 00 

12/29/97 5001 1 5.60 4-223 -421 

12130197 50012 5.65 i 69 -10 

12/31/97 50013 5.65 -131 1254 

-4- 
5. GOES TIME CODE INFORMATION 

A. TIME CODE PERFORMANCE (1-31 December 1997) 

Station 

WWVB 

GOESIEast: 

Currently using the GOES-8 satellite at 75 O west longitude. Timing uncertainty is rl: 100 ps with 

MJD 

D EC 

1997 

1219 50791 

1211 5 50797 

1211 6 50798 

1211 7 50799 

1211 8 50800 

12/31 5081 3 

respect to UTC(N1ST). 

GOESIWest: 

respect to UTC(NIST1. 

A GOESIEast stationkeeping maneuver was performed on December 18, 1997 at about 1800 UTC. 

Currently using the GOES-9 satellite at 135O west longitude. Timing uncertainty is f 100 ps with 

A GOESNVest stationkeeping maneuver was performed on December 21, 1997 at about 1200 UTC. 

6. BROADCAST OUTAGES OVER 5 MINUTES AND WWVB PHASE PERTURBATIONS 

DEC 

1997 

Began MJD 

UTC 

2030 

2300 

1810 

221 0 

221 5 

1820 

Ended 

UTC 

2040 

0040 

1845 

0245 

01 10 

1855 

PHASE PERTURBATIONS WWVB 60 kHz 

Freq. 

All 

outages 

on 60 kHz 

Began End 

Primary frequency standards developed 

7. NOTES ON 

and 

NlST TIME 

maintained 

SCALE 

by NlST 

AND 

are 

PRIMARY 

used to 

STANDARDS 

provide accuracy (rate) input 

t 

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 cesium-beam standard. The uncertainty of the new standard is currently 1 part in 

TA(N1ST) 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(N1ST) 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. 

running scale whose frequency is maintained as constant as possible by choosing the optimum weight for each clock 

that contributes to the computation. 

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 -t2 nslday. The frequency of UTC(N1ST) is 

kept as stable as possible at other times. 

parameters that we use to generate UTC(N1ST) in real-time are therefore based on an extrapolation of UTC from the 

most recent data available. 

Allan, D.W.; Hellwig, H.; and Glaze, D.J., "An accuracy algorithm for an atomic time scale," Metrologia, Vol.1 1, 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 

Since 1981, TA(NIST) has been computed retrospectively each month using a Kalman algorithm. The purpose of 

The AT1 scale is run in real time using data from an ensemble of cesium standards and hydrogen masers. It is a freeUTC(N1ST) is generated as an offset from our real-time scale AT1. It is steered in frequency towards UTC using data 

UTC is generated at the BlPM using a post-processed time-scale algorithm and is not available in real-time. The 

8. BIBLIOGRAPHY 

pp.133-138 (September 1975). 

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

Frequency Control, p.378 (1 982). 

Trans. Instrum. Meas., IM-40, 162-1 64 (1 991). 

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

operation," IEEE Trans. Instrum. Meas., IM-25, pp.453-458 (December 1 976). 

-5- 
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(NIST1 and AT1 ; the parameter xlS 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 . 

Month 

Mar 96 

Table 7.1 

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

XIS x. Y TO Valid until 0000 on: 

(S) (ns) (ns/day) (MJD) (MJD) 

- 30 - 141 297 -43.5 501 43 501 74 

Feb 97 

~~ ~ 

Apr 96 - 30 - 142645 -43.5 501 74 50204 

May 96 - 30 - 143950 -43.5 50204 50235 

- 30 - 156023.3 -42.5 50480 50508 

50434 

- 154066.8 

Mar 97 

I Jan 97 I -30 I -154705.8 I -42.5 I 50449 I 50480 

- 30 - 15721 3.3 -42.7 50508 50539 

Apr 97 

May 97 

- 30 - 158537 -42.5 50539 50569 

- 30 - 15981 2 -43.0 50569 50600 

Aug 97 -31 - 163768 -43.0 50661 50692 

Sep 97 -31 - 1651 01 -42.5 50692 50722 

Oct 97 -31 - 166376 -42.0 50722 50753 

Nov 97 -31 - 167678 -42.0 50753 50783 

Dec 97 -31 - 168938 -42.5 50783 50814 

Jan 98 -31 - 170255 -42.5 50814 50845 

I Feb 98 I -31 I -171573 I -42.5* I 50845 I 50873 

I Jun 97 I -30 I -161145 I -43.0 I 50600 I 50630 

I Jul 97 I -31 I -162435 I -43.0 I 50630 I 50661 

*Provisional rate 

'Note rate change in mid-month 

-6- 
9. SPECIAL ANNOUNCEMENTS 

TRACEABLE FREQUENCY CALIBRATIONS 

(Now NVLAP Certified) 

Anyone needing traceable frequency calibrations can get them by subscribing to the NET 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 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 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 NET 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 NET 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, NET, Division 847, 325 Broadway, Boulder, CO 80303. 

-7-