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NIST TIME AND FREQUENCY BULLETIN 

NISTIR 6617-5

 NO. 535 MAY 2002 

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

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

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

4. BROADCAST OUTAGES OVER FIVE MINUTES AND WWVB 

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

5. NOTES ON NIST TIME SCALES AND PRIMARY STANDARDS............................................................... 5

6. BIBLIOGRAPHY.............................................................................................................................................. 5

7. SPECIAL ANNOUNCEMENTS..................................................................................................................... 7

This bulletin is published monthly. Address correspondence to: 

Eyvon M. Petty, Editor 

Time and Frequency Division 

National Institute of Standards and Technology

325 Broadway 

Boulder, CO 8O3O5-3328 

(3O3) 497-3295

Email: pettye@boulder.nist.gov

NOTE TO SUBSCRIBERS: Please include your address label (or a copy) 

with any correspondence regarding this bulletin. 

U.S. DEPARTMENT OF COMMERCE, DONALD L. EVANS, Secretary

TECHNOLOGY ADMINISTRATION, Dr. Cheryl L. Shavers, Under Secretary of Commerce for Technology

NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY, Dr. Arden L. Bement, Jr., Director
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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

_______________________________________________________________________________________________________

2. TIME-SCALE INFORMATION

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

averaged measurements from all available common-view GPS satellites (see bibliography on page 5). UTC - UTC(NIST) data are on 

page 3.

 0000 HOURS COORDINATED UNIVERSAL TIME

APR 2002 MJD UT1-UTC(NIST)

 (±5 ms)

UTC(USNO,MC) - UTC(NIST)

 (±20 ns)

4 52368 -191 ms -15 ns

11 52375 -196 ms -17 ns

18 52382 -200ms -14 ns

25 52389 -205 ms -12 ns

 The master clock pulses used by the WWV, WWVH, and WWVB 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. 

NOTE: There will be NO leap second inserted at the end of June 2002.

 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. There have been 22 leap seconds inserted in total. 

 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, and WWVB 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 19 October 2000

DUT1 = UT1 - UTC = +0.0 s beginning 0000 UTC 01 March 2001

-0.1 s beginning 0000 UTC 04 October 2001

-0.2 s beginning 0000UTC 14 February 2002
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The deviation of UTC(NIST) from UTC has been within +/–100 ns since July 6, 1994. The table below shows values of UTC 

- UTC(NIST) as supplied by the BIPM in their Circular T publication for the most recent 310-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. 26, 2002 52359 -15

Mar. 16, 2002 52349 -13

Mar. 6, 2002 52339 -9

Feb. 24, 2002 52329 -12

Feb. 14, 2002 52319 -19

Feb. 4, 2002 52309 -19

Jan. 25, 2002 52299 -20

Jan. 15, 2002 52289 -19

Jan. 5, 2002 52279 -11

Dec. 26, 2001 52269 -1

Dec. 16, 2001 52259 9

Dec. 6, 2001 52249 17

Nov. 26, 2001 52239 27

Nov. 16, 2001 52229 31

Nov. 6, 2001 52219 34

Oct. 27, 2001 52209 39

Oct. 17, 2001 52199 42

Oct. 7, 2001 52189 46

Sep. 27, 2001 52179 40

Sep. 17, 2001 52169 32

Sep. 7, 2001 52159 26

Aug. 28, 2001 52149 17

Aug. 18, 2001 52139 2

Aug. 8, 2001 52129 -11

July 29, 2001 52119 -18

July 19, 2001 52109 -20

July 9, 2001 52099 -23

June 29, 2001 52089 -26

June 19, 2001 52079 -23

June 9, 2001 52069 -21
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3. PHASE DEVIATIONS FOR WWVB AND LORAN-C

WWVB - The values shown for WWVB are the time differences between the time markers of the UTC(NIST) time scale 

and the first positive -going zero voltage crossover measured at the transmitting antenna. The unce rtainty of 

the individual measurements is ±0.5 μs. The values listed are for 1300 UTC.

LORAN-C - 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 stations monitored are Baudette, ND

(8970) and Fallon, NV (9940). The monitoring is done from the NIST laboratories in Boulder, Colorado.

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

UTC(NIST)-WWVB (60 kHz) UTC(NIST) - LORAN PHASE (ns)

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

DATE MJD (μs) (8970) (9940)

04/01/02 52365 5.69 -180 -34

04/02/02 52366 5.66 +72 -232

04/03/02 52367 5.65 -18 -169

04/04/02 52368 5.67 +21 +498

04/05/02 52369 5.68 -65 +241

04/06/02 52370 5.68 +11 -76

04/07/02 52371 5.69 +230 -323

04/08/02 52372 5.68 +440 +34

04/09/02 52373 5.70 -220 -304

04/10/02 52374 5.66 +243 +162

04/11/02 52375 5.67 -8 -5

04/12/02 52376 5.66 -340 +200

04/13/02 52377 5.65 +108 -419

04/14/02 52378 5.65 -259 -97

04/15/02 52379 5.65 +60 +94

04/16/02 52380 5.65 +131 +93

04/17/02 52381 5.63 -186 -22

04/18/02 52382 5.67 +4 +335

04/19/02 52383 5.64 +295 +70

04/20/02 52384 5.65 -82 -19

04/21/02 52385 5.65 +299 -189

04/22/02 52386 5.66 -113 -231

04/23/02 52387 5.64 -502 +37

04/24/02 52388 5.64 +220 -252

04/25/02 52389 5.64 +299 +158

04/26/02 52390 5.62 +161 +113

04/27/02 52391 5.62 +197 +186

04/28/02 52392 5.62 +53 +74

04/29/02 52393 5.61 +34 +122

04/30/02 52394 5.60 -50 -228
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4. BROADCAST OUTAGES OVER FIVE MINUTES AND WWVB PHASE PERTURBATIONS

OUTAGES OF 5 MINUTES OR MORE

WWVB 60 kHz

PHASE PERTURBATIONS

Station APR

2002

 MJD Began 

UTC

Ended UTC Freq. APR

2002

MJD Began

 UTC

End

UTC

WWVB 4/22/02 52386 2230 2300 60 kHz

WWV

WWVH

5. NOTES ON NIST TIME SCALES AND PRIMARY STANDARDS

Primary frequency standards developed and maintained by NIST are used to provide accuracy (rate) input to the BIPM. NIST-7, which 

had served as the U.S. primary standard since 1994, has been replaced by NIST-F1, a cesium fountain frequency standard. The 

uncertainty of the new standard is currently 1.7 parts in 1015.

 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 nearly 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 AT1. It is steered in frequency towards UTC using data published by the 

BIPM in its Circular T. Changes in the steering frequency will be made, if necessary, at 0000 UTC on the first day of the month, and 

very occasionally at mid-month. A change in frequency is limited to no more than ± 2 ns/day. The frequency of UTC(NIST) is kept as 

stable as possible at other times. 

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

6. BIBLIOGRAPHY

Allan, D.W.; Hellwig, H.; and Glaze, D.J., "An accuracy algorithm for an atomic time scale," Metrologia, Vol.11, No.3,

 pp.133-138 (September 1975). 

Allan, D.W. and Weiss, M.A., "Accurate time and frequency transfer during common view of a GPS satellite," Proc. 34th

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

Allan, D.W. and Barnes, J.A., "Optimal time and frequency using GPS signals," Proc. 36th Annual Symposium on

 Frequency Control, p.378 (1982). 

Drullinger, R.E.; Glaze, D.J.; Lowe, J.P.; and Shirley, J.H., "The NIST optically pumped cesium frequency standard," IEEE

 Trans. Instrum. Meas., IM-40, 162-164 (1991).

Glaze, D.J.; Hellwig, H.; Allan, D.W.; and Jarvis, S., "NBS-4 and NBS-6: The NIST primary frequency standards,"

 Metrologia, Vol.13, pp.17-28 (1977). 

Wineland, D.J.; Allan, D.W.; Glaze, D.J.; Hellwig, H.; and Jarvis, S., "Results on limitations in primary cesium standard

 operation," IEEE Trans. Instrum. Meas., IM-25, pp.453-458 (December 1976). 
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Table 7.1 lists 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 T0 column and less than the 

entry in the last column. The values of xls, 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 xls 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.

Table 7.1

UTC(NIST) - AT1 = xls + x + y*(T - T0)

Month xls

(s)

x

(ns)

y

(ns/d)

 T0

(MJD)

Valid until 0000 on:

(MJD)

May 02 -32 -231829.5 -41.5* 52395 52426*

Apr 02 -32 -233558.5 -41.0 52377 52395

Apr 02 -32 -231829.5 -40.5 52365 52377†

Mar 02 -32 -232829.5 -40.0 52359 52365

Mar 02 -32 -231829.5 -40.0 52334 52359†

Feb 02 -32 -231255.5 -41.0 52320 52334

Feb 02 -32 -230695.5 -40.0 52306 52320†

Jan 02 -32 -230169.0 -40.5 52293 52306

Jan 02 -32 -229467.0 -39.0 52275 52293†

Dec 01 -32 -228258.0 -39.0 52244 52275

Nov 01 -32 -227073.0 -39.5 52214 52244

Oct 01 -32 -225848.5 -39.5 52183 52214

Sep 01 -32 -224633.5 -40.5 52153 52183

Aug 01 -32 -223362.5 -41.0 52122 52153

Jul 01 -32 -222122.5 -40.0 52091 52122

Jun 01 -32 -220937.5 -39.5 52061 52091

Apr 01 -32 -218543.0 -39.0 52000 52030

Dec 00 -32 -213746.5 -40.0 51879 51910

Nov 00 -32 -212546.5 -40.0 51849 51879

Oct 00 -32 -211337.5 -39.0 51818 51849

Sep 00 -32 -210167.5 -39.0 51788 51818

† Rate change in mid-month

†† Rate change one day early

*Provisional value
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IMPORTANT NOTICE!

The Time and Frequency Bulletin data are now online at

http://tf.nist.gov

7. SPECIAL ANNOUNCEMENTS 

TRACEABLE FREQUENCY CALIBRATIONS

(Now NVLAP Certified)

Laboratories can get any needed traceable frequency calibrations by subscribing to the NIST Frequency

Measurement and Analysis Service. This service is offered on a lease basis by NIST to provide an easy and inexpensive 

means to obtain traceability of a laboratory frequency standard and, in addition, to calibrate other devices in the lab. This 

service has been designed for ease of operation and as a practical calibration tool.

All necessary hardware and software is provided by NIST. Users must provide their own oscillator(s) and an 

ordinary telephone line so that NIST can access the system by modem. A maximum total of five oscillators can be calibrated 

at the same time. Radio signals from GPS satellites are used and the measurement uncertainty is 

±2 x 10-13 per day. Any frequency from 1 Hz to 120 MHz (in 1 Hz increments) can be measured.

The calibration data are displayed in color, and a graph is plotted daily for each oscillator. 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. Up to 5 months of data can be 

plotted on one graph.

The system plots are easy to read and understand. The system manual is written clearly and the NIST staff are

available by telephone to assist. The modem connection allows NIST 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.

NIST retains title to the equipment and supplies. All necessary replacement parts are 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 phone Michael Lombardi at (303) 497-3212,

or E-mail him at lombardi@boulder.nist.gov, or write to Michael Lombardi, NIST, Division 847, 325 Broadway, Boulder, CO 

80305.

NOTICE TO DISCONTINUE INVOLVEMENT WITH GOES TIME CODE SERVICE

NIST has announced that it will discontinue its involvement with the time code broadcast from the GOES WEST and 

GOES EAST satellites operated by the National Oceanic and Atmosphere Administration (NOAA) on January 1, 2005. 

This decision has been jointly made by NIST and NOAA in response to the fact that nearly all users requiring time more 

accurate than 1 millisecond now use the Global Positioning System (GPS), and as a result, commercial sources for 

GOES timing receivers no longer exist.

NOAA is expected to continue to provide a GOES time code indefinitely after January 1, 2005, and existing receivers 

should be able to continue to receive and decode the time signal. However, the time code will no longer be controlled 

and checked by NIST, and the received time is expected to be less accurate when NIST discontinues its involvement. 

The GOES satellites currently broadcast continuously updated position information in addition to the time, so that GOES 

receivers can automatically correct for path delay changes caused by satellite motion. This allows the current system to 

have a time uncertainty of less than 100 microseconds. NOAA is expected to continuously broadcast a fixed position 

from the satellites, which could increase the time uncertainty to 1 millisecond or more. 

The GOES time broadcasts began in 1974 and have served many applications and thousands of users. NIST will 

continue to control and monitor the time code through January 1, 2005 to allow users who require a high accuracy 

signal sufficient time to replace their existing receivers. If you have additional questions, please contact Michael 

Lombardi, 303-497-3212, or email lombardi@boulder.nist.gov.