NlST TIME AND FREQUENCY BULLETIN 

NlSTlR 5057-5 

NO. 474 MAY 1997 

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

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

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

4. PHASE DEVIATIONS FORWWVBAND 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, Arati Prabhakar, Director 

-I- 
BlPM - CClR - cs 

GOES - 

GPS - IERS - 

LORAN - MC 

MJD - 

NVLAP - 

NIST - 

NOAA - SI 

TA 

TAI 

USNO - 

UTC - VLF 

APR 1997 

1. GENERAL BACKGROUND INFORMATION 

ABBREVIATIONS AND ACRONYMS USED IN THIS BULLETIN 

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

(25 ns) (2 20 ns) 

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 fls - 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 NIST. The UTC(USN0,MC) - UTC(NIST1 

values are averaged measurements from up to 10 GPS satellites (see bibliography on page 5). UTC-UTC(NIST1 data are 

on page 3. 

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(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 rtO.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, 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 20.9 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 UTl . 

-0.2 s beginning 0000 UTC 06 February 1997 

-0.4 s beginning 0000 UTC 08 May 1997 

DUTl = UT1 - UTC = -0.3 s beginning 0000 UTC 20 March 1997 

-2- 
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 BlPM in Circular T for the most recent 350 day period in which data are 

0000 Hours Coordinated Universal Time 

Date MJD UTC - UTC(NIST) 

ns 

Apr. 6, 96 

Apr. 16, 96 

Apr. 26, 96 

May 6, 96 

May 16, 96 

May 26, 96 

June 5, 96 

June 15, 96 

June 25, 96 

July 5, 96 

July 15, 96 

July 25, 96 

Aug. 4, 96 

Aug. 14, 96 

Aug. 24, 96 

Sep. 3, 96 

Sep. 13, 96 

Sep. 23, 96 

Oct. 3, 96 

Oct. 13, 96 

Oct. 23, 96 

Nov. 2, 96 

Nov. 12, 96 

Nov. 22, 96 

Dec. 2, 96 

Dec. 12, 96 

Dec. 22, 96 

Jan. 1, 97 

Jan. 11, 97 

Jan. 21, 97 

Jan. 31, 97 

Feb. 10, 97 

Feb. 20, 97 

Mar. 2, 97 

Mar. 12, 97 

Mar. 22, 97 

501 79 8 

501 89 1 

501 99 0 

50209 -2 

5021 9 -6 

50229 -1 0 

50239 -1 9 

50249 -23 

50259 -23 

50269 -25 

50279 -22 

50289 -24 

50299 -29 

50309 -23 

5031 9 -1 6 

50329 -7 

50339 -3 

50349 -2 

50359 0 

50369 2 

50379 6 

50389 13 

50399 23 

50409 34 

5041 9 44 

50429 49 

50439 50 

50449 44 

50459 40 

50469 36 

50479 29 

50489 27 

50499 21 

50509 20 

5051 9 12 

50529 10 

-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 50.5 ps. The values listed are for 1300 UTC. 

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 (4 is printed. 

LORAN-C - 

The master stations monitored are Dana, IN (8970) and Fallon, NV (9940). The monitoring is done from 

the NET laboratories in Boulder, CO. 

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

UTC(NIST)-WWVB(GO kHz) UTC(NIST) - LORAN PHASE (ns) 

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

DATE MJD (/ls) (8970) (9940) 

4/01 I97 50540 5.82 +262 -225 

4/02/97 50541 5.77 -103 +185 

4/03/97 50542 5.81 +21 - 169 

4/04/97 50543 5.83 +257 +335 

4/05/97 50544 5.81 +180 + 87 

4/06/97 50545 5.80 - 34 +251 

4/07/97 50546 5.76 +lo7 -189 

4/08/97 50547 5.79 - 30 +161 

4/09/97 50548 5.79 -378 + 577 

411 0197 50549 5.80 +339 - 239 

411 1197 50550 5.78 +19 +592 

411 2/97 50551 5.79 - 57 +5 

411 3/97 50552 5.80 -438 +235 

411 4/97 50553 5.83 + 47 - 36 

411 5/97 50554 5.81 +263 +81 

411 6/97 50555 5.82 -143 -150 

411 7/97 50556 5.80 + 220 - 63 

411 8/97 50557 5.81 - 86 +166 

411 9/97 50558 5.81 +124 +176 

4120197 50559 5.82 -309 +52 

4/21 197 50560 5.82 + 300 - 235 

4/22/97 50561 5.79 + 96 +81 

4/23/97 50562 5.79 -143 - 24 

4/24/97 +41 + 60 

412 5 I97 I 

4/26/97 ! 

4/27/97 ! 

4/28/97 ! 

4/29/97 ! 

4130197 ! 

- 67 + 246 

+212 +114 

+238 + 90 

- 47 + 73 

+ 308 + 30 

-338 - 55 

-4- 
5. GOES TIME CODE INFORMATION 

Station APR MJD Began Ended Freq. APR MJD Began 

1997 UTC UTC 1997 UTC 

A. TIME CODE PERFORMANCE (1-30 April 1997) 

End 

UTC 

GOESIEast: 

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

respect to UTC(NIST1. 

normal. 

GOESMlest: 

respect to UTC(NIST). 

normal. 

UTC. 

The spring eclipse season for GOESEast ended on April 13, 1997. All operations have returned to 

Currently using the GOES-9 satellite at 135O west longitude. Timing uncertainty is * 100 ,us with 

The spring eclipse season for GOESMlest ended on April 12, 1997. All operations have returned to 

A GOESMlest stationkeeping maneuver was performed on April 10, 1 997 at approximately 1330 

6. BROADCAST OUTAGES OVER 5 MINUTES AND WWVB PHASE PERTURBATIONS 

WWVB 

WWV 413 50542 0500 0620 2.5,5,10,15 

413 50542 1200 1300 20 MHz 

7. NOTES ON NIST TIME SCALES AND PRIMARY STANDARDS 

Primary frequency standards developed and maintained by NET 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 

TAINIST) 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 vvPiose 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 k 2 ns/day. The frequency of UTC(NIST1 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(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(NIST1 is generated as an offset from our real-time scale ATI. It is steered in frequency towards UTC using data 

UTC is generated at the BIPM 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 9821. 

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 1976). 

-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(NIST) and AT1 ; the parameter xIS 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 . 

Sep 96 

Oct 96 

Nov 96 

Dec 96+ 

Jan 97 

Table 7.1 

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

- 30 - 149347 -44.5 50327 50357 

- 30 - 150682 -44.0 50357 50388 

- 30 - 152046 -44.0 50388 5041 8 

- 30 - 153366 -43.8 5041 8 50434 

- 30 - 154066.8 -42.6 50434 50449 

- 30 - 154705.8 -42.5 50449 50480 

Valid until 0000 on: 

-30 I -147968 I -44.5 I 50296 I 50327 

Feb 97 

Mar 97 

Apr 97 

- 30 - 156023.3 -42.5 50480 50508 

- 30 - 15721 3.3 -42.7 50508 39 

- 30 - 158537 -42.5 50539 

May 97 

Jun 97 

505 

- 30 - 15981 2 -43.0 50569 50600 

- 30 -161450 -43.0' 50600 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 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 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 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 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. 

-7 -