NlST TIME AND FREQUENCY BULLETIN 

NlSTlR 50574 

NO. 473 APRIL 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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .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 ............................................................. 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 

-1 - 
BlPM - CClR - 

cs 

GOES - GPS - IERS - 

LORAN - 

MC 

MJD - NVLAP - NlST - 

NOAA - SI 

TA 

TAI 

USNO - UTC - VLF 

0000 HOURS COORDINATED UNIVERSAL TIME 

MAR 1997 MJD UT1 - UTC(NIST) UTC(USN0,MC) - UTC(NIST) 

(+5 ns) (-t 20 ns) 

6 5051 3 - 226 ms -17 ns 

13 50520 -245 ms -18 ns 

20 50527 -262 ms -21 ns 

27 50534 - 279 ms - 20 ns 7 

1. GENERAL BACKGROUND INFORMATION 

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 /IS - 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 

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(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 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 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. 

-0.2 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(NIST) 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 

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(NIST) 

ns 

Mar. 7, 96 

Mar. 17, 96 

Mar. 27, 96 

Apr. 6, 96 

Apr. 16, 96 

Apr. 26, 96 

May 6, 96 

May 16, 96 

May 26, 96 

June 5, 96 

June 15, 96 

501 49 

501 59 

501 69 

501 79 

501 89 

501 99 

50209 

5021 9 

50229 

50239 

50249 

10 

11 

7 

8 

1 

0 

-2 

-6 

-1 0 

-1 9 

-23 

June 25, 96 50259 -2 3 

July 5, 96 50269 -2 5 

July 15, 96 50279 -2 2 

July 25, 96 50289 -2 4 

Aug. 4, 96 50299 -29 

Aug. 14, 96 50309 -23 

Aug. 24, 96 5031 9 -1 6 

Sep. 3, 96 50329 -7 

Sep. 13, 96 50339 -3 

Sep. 23, 96 50349 -2 

Oct. 3, 96 50359 0 

Oct. 13, 96 50369 2 

Oct. 23, 96 50379 6 

Nov. 2, 96 50389 13 

Nov. 12, 96 50399 23 

Nov. 22, 96 50409 34 

Dec. 2, 96 5041 9 44 

Dec. 12, 96 50429 49 

Dec. 22, 96 50439 50 

Jan. 1. 97 50449 44 

Jan. 11, 97 50459 40 

Jan. 21, 97 50469 36 

Jan. 31, 97 50479 29 

Feb. 10, 97 50489 27 

Feb. 20, 97 50499 21 

-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 k0.5 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 (-1 is printed. 

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

the NIST laboratories in Boulder, CO. 

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

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

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

DATE MJD old (8970) (9940) 

3/01 197 50508 5.66 +149 + 36 

3/02/97 50509 5.66 -132 + 38 

3/03/97 50510 5.64 -437 -674 

3/04/97 5051 1 5.64 - 37 - 166 

310519 7 5051 2 5.64 +216 + 346 

3/06/97 50513 5.61 +206 - 604 

3/07/97 50514 5.65 - 88 -13 

3/08/97 50515 5.67 - 62 +3 

3/09/97 50516 5.67 - 99 +166 

311 0197 50517 5.68 -478 - 242 

311 1 I97 50518 5.69 - 338 -135 

311 2/97 50519 5.71 - 206 +352 

311 3/97 50520 5.70 -477 -252 

311 4/97 50521 5.70 +294 +271 

311 5/97 50522 5.70 + 24 + 23 

311 6/97 50523 5.70 + 93 - 35 

311 8/97 50525 5.72 + 65 - 79 

3120197 50527 5.73 -129 - 

3/21 I97 50528 5.72 +201 +109 

3/23/97 50530 5.76 + 264 - 35 

311 7/97 50524 5.70 -100 +259 

311 9/97 50526 5.72 - 220 -16 

3/22/97 50529 5.74 +110 +168 

3/24/97 50531 5.82 -353 + 272 

312 5 I9 7 50532 5.80 -174 +iao 

3/26/97 50533 5.76 - 240 - 329 

3/27/97 50534 5.80 + 560 +338 

3/29/97 50536 5.74 + 264 - 53 

3/31 I97 50538 5.73 +88 + 58 

3/28/97 50535 5.75 +231 - 183 

3130197 50537 5.74 +136 -166 

-4- 
5. GOES TIME CODE INFORMATION 

A. TIME CODE PERFORMANCE (1-31 March 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. 

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

The spring eclipse season for GOES/East began on February 26th and will continue until April 13, 

GOESMlest: 

respect to UTC(NIST). 

1997. The peak eclipse hours are from 0832 to 0944 UTC. The GOESMlest signal may be 

intermittent or erratic during the peak eclipse hours. 

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

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

6. BROADCAST OUTAGES OVER 5 MINUTES AND WWVB PHASE PERTURBATIONS 

7. NOTES ON NlST 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 US. 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 22 nslday. 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 NlST optically pumped cesium frequency standard," IEEE 

Glaze, D.J.; Hellwig, H.; Allan, D.W.; and Jarvis, S., "NBS-4 and NBS-6: The NET 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(N1ST) 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. lnstrum. 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(N1ST) and AT1 ; the parameter x,~ isthe number of leap seconds applied to both UTC(NIST1 and UTC as specified by 

the IERS. Leap seconds are not applied to AT1. 

L 

Feb 97 - 30 - 156023.3 -42.5 50480 50508 

Mar 97 - 30 - 15721 3.3 -42.7 50508 50539 

Apr 97 - 30 - 158537 -42.5 50539 50569 

May 97 - 30 - 15981 2 -42.5" 50569 50600 

'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 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 NET. 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 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 atthe 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) 497-321 2, or write to: Michael Lombardi, NIST, Division 847, 325 Broadway, Boulder, CO 80303. 

-7-