NIST TIME AND FREQUENCY BULLETIN 

NlSTlR 5057-1 1 

NO. 480 NOVEMBER 1997 

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

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

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

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

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

6. BROADCAST OUTAGES OVER FIVE MINUTES AND WWVB 

PHASEPERTURBATIONS ...................................................... 5 

7. NOTES ON NlST TIME SCALES AND PRIMARY STANDARDS 5 

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

. . . . . . . . . . . . . . . . . . . . . . . . . . . . 

9. 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 

-1 - 
1. GENERAL BACKGROUND INFORMATION 

BlPM 

CClR 

cs 

GOES 

GPS 

IERS 

LORAN 

MC 

MJD 

NVLAP 

NlST 

NOAA 

SI 

TA 

TAI 

USNO 

UTC 

VLF 

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 81 Technology 

- National Oceanic and Atmospheric Administration ns - nanosecond 

- International System of Units - microsecond 

- Atomic Time ms - millisecond 

- International Atomic Time S - second 

- United States Naval Observatory min - minute 

- Coordinated Universal Time h - hour 

- very low frequency d - day 

2. TIME SCALE INFORMATION 

The values listed below are based on data from the IERS, the USNO, and NET. The UTC(USN0,MC) - UTC(NIST) 

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

on page 3. 

I 0000 HOURS COORDINATED UNIVERSAL TIME 

l2 50723 +389 ms 16 ns 

9 50730 +376 ms 13 ns 

16 50737 +359 ms 8 ns 

23 50744 +345 ms 7 ns 

30 50751 +331 ms 6 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(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 k0.9 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, and 1995. 

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. 

+0.4 s beginning 0000 UTC 18 September 1997 

+0.3 s beginning 0000 UTC 30 October 1997 

+0.2 s beginning 0000 UTC 18 December 1997 

DUT1 = UTl - UTC = 

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The deviation of UTC of UTC(N1ST) from UTC has been less than+/- 100 since July 6, 1984. 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. 

' Oct 13, 1996 

Oct 23, 1996 

Nov2, 1996 

Nov 12, 1996 

Nov 22, 1996 

Dec 2, 1996 

Dec 12, 1996 

Dec22, 1996 

Jan 1, 1997 

Jan 11, 1997 

Jan21, 1997 

Jan 31, 1997 

Feb 10. 1997 

Feb 20, 1997 

Mar2, 1997 

Mar 12, 1997 

Mar 22, 1997 

Apr 1. 1997 

Apr 11, 1997 

Apr21, 1997 

May 1, 1997 

May 11, 1997 

May 21, 1997 

May 31, 1997 

Jun 10, 1997 

Jun20, 1997 

Jun 30, 1997 

Jul 10, 1997 

Jul 20, 1997 

Jul 30, 1997 

Aug 9, 1997 

Aug 19, 1997 

Aug 29, 1997 

Sep. 8, 1997 

Sep. 18, 1997 

Sev. 28. 1997 

0000 Hours Coordinated Universal Time 

50369 

50379 

50389 

50399 

50409 

504 19 

50429 

50439 

50449 

50459 

50469 

50479 

50489 

50499 

50509 

50519 

50529 

50539 

50549 

50559 

50569 

50579 

50589 

50599 

50609 

50619 

50629 

50639 

50649 

50659 

50669 

50679 

50689 

50699 

50709 

507 19 

2 

6 

13 

23 

34 

44 

49 

50 

44 

40 

36 

29 

27 

21 

20 

12 

10 

5 

6 

-3 

-5 

-7 

-4 

-6 

-5 

-3 

0 

8 

16 

18 

21 

26 

29 

30 

31 

30 

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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 rt0.5 ps. The values listed are for 1300 UTC. 

LORAN-C - The values shown for Loran-C represent the daily accumulated phase shift (in nanoseconds). 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)-WWVB(GO kHz) UTC(NIST1 - LORAN PHASE (ns) 

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

DATE MJD bs) 1a970) (9940) 

10101 I97 50722 5.73 + 47 + 79 

10102197 50723 5.73 - 533 -336 

1 Ol03l97 50724 5.73 -11 +251 

1 0104197 50725 5.74 + 45 - 206 

10105197 50726 5.75 -125 + 46 

1 0106197 50727 5.77 -251 - 242 

10107197 50728 5.74 + 302 +13a 

1 oioa197 50729 5.78 +129 - 96 

10109197 50730 5.77 - 286 - 205 

1011 0197 50731 5.78 + 262 - 443 

1 011 1 I97 50732 5.79 + ao + 94 

1 011 2/97 50733 5.80 -213 - 69 

1011 3197 50734 5.81 - 77 +116 

1011 4197 50735 5.04 - 34 - 50 

1 011 5197 50736 5.78 +222 + 46 

1011 6197 50737 5.79 - 335 - 549 

10117197 50738 5.80 +129 - 284 

1 011 8/97 50739 5.71 +377 -71 

1 011 9/97 50740 5.71 -170 + 46 

10120197 50741 5.71 +32 - 365 

10121 197 50742 5.72 + 208 i 36 

10122197 50743 5.71 +457 -182 

10124197 50745 5.68 +265 -18 

10123197 50744 5.70 -313 + 220 

lOl25l97 50746 5.71 -120 - 86 

10126197 50747 5.72 -338 -319 

10127197 50748 5.74 +122 - 348 

1012ais7 50749 5.73 - ioa +102 

10129197 50750 5.71 -133 +157 

10130197 50751 5.74 -159 +217 

1013 1 197 50752 5.75 +553 + 402 

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5. GOES TIME CODE INFORMATION 

Station OCT MJD Began Ended Freq. OCT MJD 

1997 UTC UTC 1997 

WWVB 10/24 50745 1740 1855 60 KHz 

wwv 

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

Began End 

UTC UTC 

GOESIEast: 

respect to UTC(NIST1. 

1997. The peak eclipse hours are from 041 6 to 0528 UTC. The GOES/East signal may be intermittent 

or erratic during the peak eclipse hours. 

GOESIWest: 

respect to UTC(NIST). 

1997. The peak eclipse hours are from 081 8 to 0930 UTC. The GOES/West signal may be 

intermittent or erratic during the peak eclipse hours. 

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

The Fall eclipse season for GOES/East began on August 30th and will continue until October 15, 

A GOES/East stationkeeping maneuver was performed on October 20,1997 at about 1900 UTC. 

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

The Spring eclipse season for GOES/West began on August 31 st and will continue until October 16, 

A GOES/West stationkeeping maneuver was performed on October 31, 1997 at about 1200 UTC. 

NOTE: The next anticipated WWVB service interruptions will be in December 1997. This interruption is 

needed to test the WWVB transmitters on the antenna system. The exact dates, start times, and durations 

will be posted at http://www.bldrdoc.gov/tirnefreq/vboutage.htrn when the information becomes available. 

7. NOTES ON NlST TIME SCALES 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 U.S. primary standard from 1975 through 1992, has been replaced by NET-7, an optically 

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

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. 

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 +2 ns/day. The frequency of UTC(NIST) is 

kept as stable as possible at other times. 

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. 

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 

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(NIST) 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-I 38 (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 1. 

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

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

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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 . 

Month 

Jan 96 

Feb 96 

Mar 96 

Apr 96 

XIS X Y TO Valid until 0000 on: 

(S) (ns) (nslday) (MJD) (MJD) 

- 30 - 138687 -43.5 50083 501 14 

- 30 - 140035 -43.5 501 14 501 43 

- 30 -141297 -43.5 501 43 501 74 

- 30 - 142645 -43.5 501 74 50204 

May 96 

Jun 96 

Jul 96 - 30 

- 147968 

- 149347 

- 150682 

- 152046 

- 153366 

- 154066.8 

- 154705.8 

- 156023.3 

Aug 96 - 30 

Sep 96 - 30 

Oct 96 - 30 

Nov 96 - 30 

Dec 96+ - 30 

- 30 

-44.5 50296 50327 

-44.5 50327 50357 

-44.0 50357 50388 

-44.0 50388 5041 8 

-43.8 5041 8 50434 

-42.6 50434 50449 

-42.5 50449 50480 

-42.5 50480 50508 

I 

Jun 97 

~~ 

Jan 97 I -30 

-~ 

- 30 -161145 -43.0 50600 50630 

Feb97 I -30 

Jul 97 

Aug 97 

Sep 97 

Oct 97 

Nov 97 

Dec 97 

-143950 I -43.5 I 50204 I 50235 1 

-31 - 162435 - 43 .O 50630 50661 

-31 - 163768 -43.0 50661 50692 

-31 - 1651 01 -42.5 50692 50722 

-31 - 166376 -42.0 50722 50753 

-31 - 167678 -42.0 50753 50783 

-31 - 168938 -42.0' 50783 5081 4 

-145299 I -43.5 I 50235 I 50265 1 -146604 I -44.0 I 50265 I 50296 1 

1 ~~~ 

Mar 97 I -30 I -157213.3 I -42.7 I 50508 -1 50539 

1 ~~ ~ 

Apr 97 I -30 I -158537 I -42.5 I 50539 -1 50569 

1 ~ ~~ 

May 97 I -30 I -159812 I -43.0 I 50569 -1 50600 

*Provisional rate 

'Note rate change in mid-month 

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9. 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 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 NET 

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, NIST, Division 847, 325 Broadway, Boulder, CO 80303. 

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