NlST TIME AND FREQUENCY BULLETIN 

NlSTlR 5071-2 

NO. 483 FEBRUARY 1998 

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 

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

7. NOTES ON NlST TIME SCALES AND PRIMARY STANDARDS ....................................... 5 

8. BIBLIOGRAPHY ............................................................................... 5 

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 

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1. GENERAL BACKGROUND INFORMATION 

JAN 1998 

BlPM 

CClR 

cs 

GOES 

GPS 

IERS 

LORAN 

MC 

MJD 

NVIAP 

NIST 

NOAA 

SI 

TA 

TAI 

USNO 

UTC 

VLF 

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

(+5 ms) (+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 ns - nanosecond 

- International System of Units PS - microsecond 

- Atomic Time ms - millisecond 

- International Atomic Time S - second 

- United States Naval Observatory min - minute 

- Coordinated Universal Time 

- very low frequency 

2. TIME SCALE INFORMATION 

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

averaged measurements from up to 10 GPS satellites (see bibliography on page 5). UTC-UTC(N1ST) data are on page 3. 

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 rnin 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. 

The use of leap seconds ensures that UTI ~ UTC will always be held within kO.9 s. The current vaiue of UTI - UTC is called the 

DUTl correction. DUTI 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 UTI. 

+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 

DUTI = UTI - UTC = 

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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(NIST) as supplied by the BIPM in Circular T for the most recent 350 day period in which data arc 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(N1ST) 

Jan 11,1997 50459 40 

Jan21,1997 50469 36 

Jan 3 1,1997 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 

May31,1997 50599 -6 

Jun 10,1997 50609 -5 

Jun 20,1997 50619 -3 

Jun 30,1997 50629 0 

Jul 10,1997 50639 8 

Jul20, 1997 50649 16 

Jul30,1997 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 

Sep. 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 

Dec. 7, 1997 50789 2 

Dec. 17, 1997 50799 -1 

Dec 27, 1997 50809 3 

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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(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 (-) 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. 

LORAN-C - 

Note: The values shown for Loran-C are in nanoseconds. 

UTC(NIST)-VWWB (60 kHZ) UTCfNlSn - LORAN PHASE (ns) 

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

DATE MJD (PS) (8970) (9940) 

1/01 197 5081 4 5.65 +I01 - 23 

1/02/97 50815 5.63 - 633 +335 

1/03/97 50816 5.63 +314 -162 

1/04/97 50817 5.62 ~ 363 +55 

_lllW97 !in81 8 5 r-i +im 117 

1 /06/97 50819 5.62 6) +319 

1107/97 50820 5.65 (6) +576 

1/08/97 50821 5.69 (-) +148 

1/09/97 50822 5.69 (3 +36 

5n~7-4 5 69 (-1 117 

111 1/97 50824 5.69 ~ 47 +161 

1/12/97 50825 5.69 - 293 - 789 

1 /I 3/97 50826 5.74 -142 +557 

1 /I 4/97 50827 5.76 +436 +91 

47 50878 5 77 'ZRI 1 in 

1 I1 6/97 50829 5.73 +46 +273 

1 /I 7/97 50830 5.70 +402 - 396 

1 /I 8/97 50831 5.70 +351 +429 

1 /I 9/97 50832 5.70 -3 +53 

50833 R 39 7n7 

1 12 1/97 50834 5.69 ~ 142 - 233 

1/22/97 50835 5.70 +385 +409 

1123/97 50836 5.70 - 14 +59 

1/24/97 50837 5.70 +I30 ~ 155 

1 /75/97 5n8w s 713 +R49 +318 

1/26/97 50839 5.70 ~ 321 +I 33 

1/27/97 50840 5.69 +341 ~ 178 

1/28/97 50841 5.74 +I57 +a1 

1/29/97 50842 5.72 +I 42 - 135 

1/30/97 50843 5.71 +615 +137 

1 131 197 50844 5.72 -210 +125 

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5. GOES TIME CODE INFORMATION 

Station JAN MJD 

1998 

WWVB 

WWV 

WWVH 

A. TIME CODE PERFORMANCE (1-31 January 1998) 

Began Ended Freq. JAN MJD Began End 

UTC UTC 1998 UTC UTC 

GOESIEast: 

UTC( NIST). 

Currently using the GOES-8 satellite at 75" west longitude. Timing uncertainty is +I 00ps with respect to 

The GOES/East broadcast was unavailable for several hours beginning at about 1400 UTC on January 26, 

1998. 

NOTES ON NET TIME SCALE AND PRIMARY STANDARDS 

which served as the U.S. primary standard from 1975 through 1992, has been replaced by NIST-7, an optically pumped cesiumbeam standard. The uncertainty of the new standard is currently 1 part in 1OI4. 

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 nslday. The frequency of UTC(NIST) is kept as stable as possible at other 

times. 

we use to generate UTC(N1ST) in real-time are therefore based on an extrapolation of UTC from the most recent data available. 

Primary frequency standards developed and maintained by NlST are used to provide accuracy (rate) input to the BIPM. NBS-6, 

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

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

8. 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 NET 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.133-138 (September 1975). 

Annual Symposium on Frequency Control, p.334 (1980). 

Frequency Control, p.378 (1 982). 

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(NIST) with respect to our real-time scale Ail. 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 &, x, and yfor 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 ATI; the parameter x,, is the number of leap seconds applied 

to both UTC(NIST) and UTC as specified by the IERS. Leap seconds are not applied to ATI. 

Feb 98 

Mar 98 

-31 -171573 -42.5 50845 50873 

50873 50904 - 31 - 172763 -42.5* 

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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 

traceabilrty 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 NET. 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 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 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. 

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) 497-3212, 

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.bouIder.nist.gov/timefreq/wwvstatus.htm 

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