NlST TIME AND FREQUENCY BULLETIN 

NlSTlR 5057-3 

NO. 472 MARCH 1997 

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

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

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

4. PHASEDEVIATIONS FORWVB ANDLORAN-C ..................................... 3 

5. GOES TIME CODE INFORMATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 

6. BROADCAST OUTAGES OVER FIVE MINUTES AND WWVB 

PHASE PERTURBATIONS ...................................................... 4 

7. NOTES ON NIST TIME SCALES AND PRIMARY STANDARDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 

8. BIBLIOGRAPHY ............................................................. 4 

9. SPECIAL ANNOUNCEMENTS ................................................... 6 

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, Arati Prabhakar, Director 

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1. GENERAL BACKGROUND INFORMATION 

ABBREVIATIONS AND ACRONYMS USED IN THIS BULLETIN 

FEB 1997 

BlPM - CClR - cs 

GOES - GPS - IERS - LORAN - 

MC 

MJD - NVLAP - NIST - NOAA - SI 

TA 

TAI 

USNO - UTC - 

VLF 

MJD UT1 - UTC(NIST1 UTC-UTC(NIST) UTC(USN0,MC) -UTC(NIST) 

(+5 ms) (kO.1 ps) (k 20 ns) 

Bureau International des Poids et Mesures 

Intemational 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 - 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 

I l3 

50492 -187 ms 0.0 ps -15 ns 

20 50499 -198 rns 0.0 ps -17 ns 1 27 50506 -211 ms 0.0 ps -17 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 

UTCINIST) 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 f 0.9 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 rnin 0 s UTC, were inserted in the UTC 

timescale on 30 June 1972, 31 December 1972-1 979,30 June 1981 -1 983,30 June 1985, 31 December 1987, 1989, 

1990, and 1995, 30 June 1992, 1993, and 1994. There will be a leap second inserted 30 June 1997. 

The use of leap seconds ensures that UT1 - UTC will always be held within 0.9 s. The current value of UT1 - UTC 

is called the DUTl correction. DUT1 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. 

-0.1 s beginning 0000 UTC 05 December 1996 

-0.3 s beginning 0000 UTC 20 March 1997 

DUTl = UT1 - UTC = - 0.2 s beginning 0000 UTC 06 February 1997 

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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 f 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 nanoseconds). The phase 

shift is measured by comparing the output of a Loran receiver to the UTC(NIST1 time scale for a period 

of 24 h. If data were not recorded on a particular day, the symbol (4 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(BO kHz) UTC(NIST) - LORAN PHASE (ns) 

ANTENNA PHASE 

50487 5.75 f 22 +O 

50488 5.74 -41 +128 

- 99 -328 

50492 5.79 - 15 +319 

50496 5.78 - 33 -235 

50497 5.78 - 77 -425 

50498 5.77 + 506 - 207 

50502 5.72 -3 

50505 5.72 - 68 -13 

50506 5.70 +531 +238 

2/28/97 50507 5.68 - 339 -591 

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5. GOES TIME CODE INFORMATION 

Station 

WWVB 

A. TIME CODE PERFORMANCE (1 -28 February 1997) 

GOESIEast: 

respect to UTC(NIST). 

1997. The peak eclipse hours are from 0434 to 0546 UTC. The GOES/East signal may be intermittent 

or erratic during the peak eclipse hours. 

1530 UTC. 

GOESMlest: 

respect to UTC(NIST1. 

1997. The peak eclipse hours are from 0832 to 0944 UTC. The GOESNVest 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 spring eclipse season for GOESlEast began on February 26th and will continue until April 13, 

A GOESlEast stationkeeping maneuver was performed on February 25th, 1 997 at approximately 

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

The spring eclipse season for GOESNVest began on February 25th and will continue until April 12, 

FEB MJD Began Ended Freq. 

1997 UTC UTC 

6. BROADCAST OUTAGES OVER 5 MINUTES AND WWVB PHASE PERTURBATIONS 

OUTAGES PHASE PERTURBATIONS WWVB 60 KHz 

FEB 

1997 

MJD Began End 

UTC UTC 

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 NIST-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 NET-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 k2 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.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 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 

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(NIST1 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 1. 

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

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(NIST1 with respect to our real-time scale AT1. To find 

the value of UTC(NIST1 - 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 xis 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. 

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 NET Frequency 

Measurement and Analysis Service. This service is offered on a lease basis by NET 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 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 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 NlST 

guidelines, audit requirements are easily met. 

NIST 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. 

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