NlST TIME AND FREQUENCY BULLETIN 

NlSTlR 5057-2 

NO. 471 FEBRUARY 1997 

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

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

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

4. PHASE DEVIATIONS FOR WWVB AND LORAN-C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 

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

6. BROADCAST OUTAGES OVER FIVE MINUTES AND WWVB 

PHASEPERTURBATIONS ...................................................... 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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2 

1. GENERAL BACKGROUND INFORMATION

_______________________________________________________________________________________________________ 

ACRONYMS AND ABBREVIATIONS 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 μs - microsecond 

TA - Atomic Time ms - millisecond 

TAI - International Atomic Time s - second 

USNO - United States Naval Observatory min - minute 

UTC - Coordinated Universal Time h - hour 

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 – UTC(NIST) values are 

extrapolations since UTC is computed more than two months after the fact. The UTC(USNO,MC) - UTC(NIST) values are averaged 

measurements from all available common-view GPS satellites (see bibliography on page 5). 

 

0000 HOURS COORDINATED UNIVERSAL TIME 

FEB 1997 MJD UT1-UTC(NIST) 

 (±5 ms) 

UTC – UTC(NIST) 

(±0.1 μs) 

UTC(USNO,MC) - UTC(NIST) 

 (±20 ns) 

6 50485 -113 ms 0.0 μs -11ns 

13 50492 -126 ms 0.0 μs -15 ns 

20 50499 -141 ms 0.0 μs -17 ns 

27 50506 -143 ms 0.0 μs -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 

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 UT1 astronomical time scale, which changes slightly due to variations in the rate of 

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, 1981-1983, 1985, 1992, 1993, 1994, and 1997, and on 31 December 1972-1979, 1987, 1989, 

1990,1995, and 1998. Advance notice of leap seconds will be provided in the bulletin.

 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 

DUT1 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 

DUT1 = UT1 - UTC = -0.2 s beginning 0000 UTC 06 February 1997 

 -0.3 s beginning 0000 UTC 20 March 1997 

 
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 f 0.5 MS. 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)-WWV8(60 kHz) UTC(NIST) - LORAN PHASE (ns) 

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

DATE MJD (CIS) (8970) (9940) 

1 I0 1 197 50449 5.73 + 33 -184 

1/02/97 50450 5.73 -372 -415 

1/03/97 5045 1 5.74 +171 + 696 

1/04/97 50452 5.74 + 204 - 63 

1 105rw 50453 5.74 - 38 +241 

1/06/97 50454 5.74 + 92 - a4 

1 I07197 50455 5.73 -428 -193 

1 /oat97 50456 5.74 -266 - 66 

1/09/97 50457 5.73 +46 +233 

1 11 or97 50458 5.73 + 285 - 75 

1 I1 1/37 50459 5.73 -190 - 66 

111 2/97 50460 5.73 -892 -21 

111 3/97 50461 5.73 + 62 +31 

1 11 4/97 50462 5.73 +I40 - 22 

1 I1 5/97 50463 5.77 - 347 - 60 

1/16/97 50464 5.74 -3 + 30 

1/17/97 50465 5.77 -112 -118 

1iia197 50466 5.76 +I93 +6 

1/19/97 50467 5.76 - 177 -96 

1120197 50468 5.76 - 238 4-4 

1 12 1 I97 50469 5.76 - 267 - 303 

1/22/97 50470 5.77 +701 +19 

1/23/97 50471 5 .a0 + 66 -256 

1/24/97 50472 5.81 - 250 +172 

1/25/97 50473 5 .SO +204 4-132 

1/26/97 50474 5.79 -11 - 632 

1/27/97 50475 5.79 -113 + a07 

112a197 50476 5.79 -160 -163 

1/29/97 50477 5.77 - 74 +212 

1 /30/97 50478 5.74 -317 -267 

1 13 1 I97 50479 5.74 + a5 - 634 

I 

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5. GOES TIME CODE INFORMATION 

Station JAN MJD Began Ended Freq. JAN MJD 

WWVB 112 ' 50450 1820 1850 60 KHz 

wwv 1 127 50475 0600 0730 15 MHz 

1 I29 50477 1230 1400 15 MHz 

1997 UTC UTC 1997 

WWVH 

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

GOESIEast: 

respect to UTC(NIST1. 

January 9 due to problems with the GOES-8 satellite. 

GOESIWest: 

respect to UTC(NIST1. 

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

GOESIEast timing was out of normal tolerance for about 24 hours, beginning at about 1330 UTC on 

Currently using the GOES-9 satellite at 1 35 O west longitude. Timing uncertainty is f 100 /IS with 

GOESNest stationkeeping maneuver was performed on January 22nd at 0930 UTC. 

Began End 

UTC UTC 

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(NIST1 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 BIPM 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(NIST1 is 

kept as stable as possible at other times. 

parameters that we use to generate UTC(NIST1 in real-time are therefore based on an extrapolation of UTC from the 

most recent data available. 

Since 1981, TA(NIST1 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 

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 

pp. 133-1 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 99 1). 

Metrologia, 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(NIST1 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. 

Aug 95 -29 - 132031 

Sep 95 -29 - 133364 

Oct 95 -29 - 134654 

~ ~~ ~~~ 

Table 7.1 

UTC(N1ST) - AT1 = xi, i x + y*(T - To) 

-43.0 49930 49961 

-43.0 4996 1 49991 

-43.5 49991 50022 

1 Mar 97 I - 30 I -157213.3 I -42.5* I 50508 50539 

'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(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 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 NET-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 NIST 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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