Time & Frequency

Bulletin

No. 397 December 1990

(NISTIR 90-3940- 12 )

NIST TIME & FREQUENCY BULLETIN

(Supersedes No. 396 November 1990)

NO. 397 DECEMBER 1990

1. GENERAL BACKGROUND INFORMATION 1

2. TIME SCALE INFORMATION 1

International Timing Center comparisons via GPS common-view 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 PHASE PERTURBATIONS ... .4

7. NOTES ON NIST TIME SCALES AND PRIMARY STANDARDS 5

8. SPECIAL ANNOUNCEMENTS 7

This bulletin is published monthly. Address correspondence to:

Gwen E. Bennett, Editor

Time and Frequency Division

National Institute of Standards & Technology

325 Broadway

Boulder, CO 80303

(303) 497-3295

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

with any correspondence regarding this bulletin.
1. GENERAL BACKGROUND INFORMATION

ABBREVIATIONS AND ACRONYMS USED IN THIS 3ULLETIN

API _ John Hopkins University Applied Physics Laboratory

BIH - International Time Bureau, France

CCIR - Internat lonai Radio Consultative Committee

CRL - Communications Research Laboratories, Japan

Cs - Cesium standard

CS IRO - Commonwealth Scientific and Industrial Research Organization, Australia

GOES - Geostationary Operational Environmental Satellite

GPS - Global Positioning System

IEN - National Institute of Electronics, Italy

INPL - National Physical Laboratory, Israel

LORAN - Long Range Navigation

MC - Master Clock

MJD - Modified Julian Date

NIST - National Institute of Standards & Technology

NPL - National Physical Laboratory, England

NRC - National Research Council, Canada

NOAA - National Oceanic and Atmospheric Administration

OP - Paris Observatory, France

PTB - Physical Technical Federal Laboratory, Germany

SI - International System of Units ns nanosecond

SV - Space vehicle us microsecond

TA - Atomic Time ms millisecond

TAI - International Atomic Time s second

TAO - Tokyo Astronomical Observatory, Japan min - minute

TUG - Technical University of Graz, Austria h hour

USNO - United States Naval Observatory d day

UTC - Coordinated Universal Time

VLF - very low frequency

VSL " Van Swinden Laboratory, Netherlands

v;e -F

I

111

I

:!•

2. TIME SCALE INFORMATION

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

extrapolations since UTC is computed more than two months after the fact. The UTC(USNO,MC) - UTC(NIST) val are averaged measurements from NAVSTAR satellites 3,4,6, and 8 (see references on page 6).

0000 HOURS COORDINATED UNIVERSAL TIME

NOVEMBER

1990 MJD

UT1 - UTC (NIST)

(± 5 ms)

UTC - UTC (NIST)

(± 0.2 us)

UTC ( USNO, MC) - UTC (NIST)

(± 0.04 us)

1 48196 -250 ms -0.4 us -0.03 us

8 48203 -265 ms -0.4 us -0.03 us

15 48210 -283 ms -0.4 us -0.04 us

22 48217 -296 ms -0.4 us -0.05 us

29 48224 -313 ms -0.4 us -0.05 us

-

1 -
INTERNATIONAL TIMING CENTER COMPARISONS VIA GPS COMMON-VIEW

~'Vj

-J

!

table below is a weighted average of the indicated GPS satellites used

e difference of Timing Center (i) - UTC(NIST) by the simultaneous common

The dav-to-day variations of this technique are a few nanoseconds and

ie of the measurement is interpolated to 0000 UTC for the particular MJD

;Dared for the BIPM for the computation on TAI and of UTC. All different

.ed

.

as transfer standards to measure the

-view approach (see references, page"

the accuracy is about 10 ns. The

ending in 9. These data are

ial delays are 0 unless otherwise

UTC(i) - UTC ( NIST ) (ns) MJD

:U) PRN NUMBERS 48189 48199 48209 48219

1 2, 3, 6, 9, 12,13,14, 16,17, 20 101 79 68 52

> - 3,6,9 12 -1274 -1402 -1554 -1694

- :ro ++ 24219 22843 21454 20084

r

i 1— ) 12,13 20 -798 -985 -1152 -1314

k >L VIA OP 2642 3511 4392 5390

1 j 3, 12,13 375 322 318 231

• :+++ 2, 3, 6, 9, 12,13,14, 16,17, 20 -973 -984 -1000 -956

2,3, 12,13,14, 16, 20 -10 -110 -193 -264

p j 12, 16, 20 -4069 -4098 -4122 -4155

r ) 3,6,9, 12, 14, 17, 20 68 -189 -462 -748

r 3 2,3, 12,13,14, 16, 20 -3272 -3608 -3903 -4233

j 40 2, 6,9, 12,13,14, 16,17, 20 -208 -302 -403 -505

1 a 2,3, 12,13,14, 16, 20 -4146 -4171 -4313 -4378

I UTC(CSIRO) - UTC(NIST) is computed from the average via CRL, TAO, & WWVH.

+ t UTC(NRC) - UTC(NIST) has a differential delay of 41.2 ns; all other comparisons are computed using zero

( 0 ).

i:

aft 3. UT1 CORRECTIONS AND LEAP SECOND ADJUSTMENTS

ie master clock pulses used by the WWV, WWVH, WWVB, and GOES time code transmissions are referenced to the

.C(NIST) time scale. Occasionally, 1 second is added to the UTC time scale. This second is called a leap

scond. Its purpose is to keep the UTC time scale within ± 0.9 s of the UT1 astronomical time scale, which

anges slightly due to variations in the rotation of the earth.

sitive 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

C timescale on 30 June 1972, 31 December 1972-1979, 30 June 1981-1983, 30 June 1985, 31 December 1987 and

89. When future leap seconds are scheduled, advance notice will be provided in this bulletin.

1

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

! 1 — UTC is called the DUT1 correction. DUT1 corrections are broadcast by WWV, WWVH, WWVB, and GOES and are

; inted below. These corrections may be added to received UTC time signals in order to obtain UT1.

= -0.2 s beginning 0000 UTC on 20 September 1990

DUT1 = UT1 - UTC = -0.3 s beginning 0000 UTC on 1 November 1990

= +0.6 s beginning 0000 UTC on 1 January 1991

'ECIAL ANNOUNCEMENT: The International Earth Rotation Service has announced that a leap second will re iserted into the UTC time scale at the end of December 31, 1990.
4. PHASE DEVIATIONS FOR WWVB AND LORAN-C

WWv'B - The values shown for WWY3 are the tine difference between the tine narkers of the UTC(NIST)

tine scale and the first positive-going zero voltage crossover measured at the transmitting

antenna. The uncertainty of tne individual measurements is t 0.5 us. The values iisted are

for 1300 UTC

LORAN-C - The values shown for Loran-C represent the daily accumulated phase shift (in microseconds).

The phase shift is measured by comparing the output of a Loran receiver to the UTC (NIST) time

scale for a period of 24 hours. If data were not recorded on a particular dav , the symbol

( - ) is printed

The stations monitored are Dana, Indiana (3970 M) and Fallon, Nevada (9940 M). The

monitoring is done from the NIST laboratories in Boulder, Colorado.

UTC ( NIST ) - WWVB( 60 kHz)

UTC (NIST) - LORAN PHASE (in us

DATE MJD

ANTENNA PHASE

(us

LORAN-C (DANA)

( 8970 M)

LORAN-C (FALLON)

(9940 M)

11/01/90 48196 5.68 -0.07 (-)

11/02/90 48197 5.70 (-) (-)

11/03/90 48198 5.70 (-) +0.08

11/04/90 48199 5.69 -0.20 (-)

11/05/90 48200 5.68 +0.02 (-)

11/06/90 48201 5.67 -0.00 +0.56

11/07/90 48202 5.67 -0.01 -0.00

11/08/90 48203 5.66 -0.15 -0.28

11/09/90 48204 5.68 +0.29 +0.28

11/10/90 48205 5.66 -0.04 -0.03

11/11/90 48206 5.65 +0.15 +0.31

11/12/90 48207 5.64 -0.28 +0.02

11/13/90 48208 5.63 +0.17 +0.22

11/14/90 48209 5.77 -0.10 -0.10

11/15/90 48210 5.65 -0.14 -0.03

11/16/90 48211 5.62 +0.36 +0.13

11/17/90 48212 5.65 +0.01 +0.11

11/18/90 48213 5.68 -0.22 -0.00

11/19/90 48214 5.72 -0.03 +0.07

11/20/90 48215 5.72 -0.20 +0.01

11/21/90 48216 5.70 -0.57 -0.61

11/22/90 48217 5.69 -0.64 (-)

11/23/90 48218 5.67 +0.22 (-)

11/24/90 48219 5.66 (-) +0.01

11/25/90 48220 5.64 -0.26 +0 . 46

11/26/90 48221 5.61 +0.25 +0.04

11/27/90 48222 5.76 (-) +0.04

11/28/90 48223 5.78 +0.24 +0.01

11/29/90 48224 5.66 -0.51 +0.05

11/30/90 48225 5.66 (-) -0.09

- 3 -
5. GOES TIME CODE INFORMATION

TIME CODE PERFORMANCE ( 1 - 30 November 1990)

GOES/East: Performance within normal limits during this period.

GOES/West: Performance within normal limits during this period.

1) During approximately 1700-2330 UTC on 9 November the corrected time code from GOES/East exhibited

slightly larger- than-normal deviations due to a satellite stationkeeping maneuver.

SPECIAL REMINDER: Current satellite locations are about 60° West longitude for GOES/East and 135 3 west

longitude for GOES/West.

FUTURE SATELLITE LAUNCHES: NOAA's present launch schedule for replacement of the current East and west

satellites has been moved back to February 1992 at the earliest.

DES STATUS REPORTS

A brief message from the NIST giving current GOES time code status information is available from the U.S.

Naval Observatory's Automated Data Service computer system in Washington, DC. The message may be accessed

24 hours per day without charge by using a variety of terminals operating at 300, 1200, or 2400 Baud and even paritv. Two different sets of telephone access numbers are available: (1) for 300 or 1200 Baud and

the Bell 103 standard use (202) 653-1079 (commercial), 653-1079 (FTS), or 294-1079 (Autovon); (2) for 1200

or 2400 Baud with either the CCITT V.22 standard or the Bell standard use (202) 653-1783 (commercial),

653-1783 (FTS), or 294-1783 (Autovon). To receive the GOES status message, use the following procedure:

1 . Access the USNO computer database by dialing one of the appropriate telephone numbers above;

2. In response to the prompt for identification, type your name and the name of your organization,

followed by a carriage return;

3. Type "@NBSGO" followed by a carriage return to receive the status message at your terminal;

4. Disconnect by typing Control-D.

6. BROADCAST OUTAGES OVER 5 MINUTES AND WWVB PHASE PERTURBATIONS

OUTAGES PHASE PERTURBATIONS WWVB 60 kHz

'ION

NOVEMBER

1990

BEGAN

MJD (UTC)

ENDED

(UTC) FREQUENCY

NOVEMBER BEGAN

1990 MJD (UTC)

ENDED

(UTC)

B NONE NONE

r NONE NONE

Ti NONE NONE
7. NOTES ON NIST TIME SCALES AND PRIMARY STANDARDS

The frequencies of the time scales, TA(N’IST) and UTC(NIST), are calibrated with the NIST primary frequency

standards. The UTC(NIST) scale is coordinated within a microsecond of the internationally coordinated time

scale, UTC , generated at the BIH. It is used to control all of the NIST time and frequency services. The

calibration of the relative frequency offset, y, of UTC (NIST) as generated in Boulder, Colorado, gave:

)l° r

-) yUTC(NIST) 198/) — yNBs-6 ( Jul y 1987) - (-0.6 ± 2 (1 sigma)) x 10~^ 3

: or the date shown. This calibration includes a correction for the systematic offset due to room temperatu:

blackbody radiation, which is approximately (delta yBg)

the dates shown were measured to be:

= -1.7 x 10 -14 Using GPS^-, the frequency of TAI f<

-) yTAI ( Jul y 1987) — yNBS _ 6 (July 1987 on geoid) = (+1.7 ±2(1 sigma)) x 10~ 33

where account has been taken of the gravitational "red shift."

Starting 1 January 1975, an accuracy algorithm was implemented to bring the second used in the generation oi

' TA(NIST) closer to the NIST "best estimate" of the SI second (see references, p.6). The relative frequency

associated with this "best estimate" is denoted Ycs(NIST)' The l- ast calibration (July 1987) covered the pei ' from October 1986 through July 1987.

3 ) yCs(NIST) ” yNBS-6 = (+1* 4 ± 2) x 10 13 (July 1987)

and

4) yTAI " yCs(NIST) on geoid = (+0 * 3 ± °* 7) x 10 13 (Jul y 1987)

This algorithm should provide nearly optimum accuracy and stability for TA(NIST) since it uses all past

frequency calibrations with the NIST primary standards. These calibrations are weighted proportionately to

frequency memory of the clock ensemble that generates atomic time. This algorithm, therefore, capitalizes o weighted combination of all the frequency calibrations with the primary standards in order to gain a "best

estimate" of the SI Second while simultaneously obtaining the best uniformity available from the ensemble of

working clocks in the atomic time scale system. The relative frequency of TA(NIST) is steered toward ycs ( NI

by slight frequency drift corrections of the order of 1 part in 10^ 3 /yr.

TA(NIST) and UTC(NIST) are no longer simply related by an equation. TA(NIST) is now computed each month usi

a Kalman algorithm which minimizes the mean square time dispersion. UTC(NIST) is now independently computed

using a different algorithm and is steered in frequency to keep its time within a microsecond of UTC(BIH).

Table 7.1 lists monthly values of the time difference between UTC(NIST) and TA(NIST). A linear interpolatio

between monthly values will typically be within 10 ns of the actual time difference, TA(NIST) — UTC(NIST).

The primary standards of NIST (NBS-4 and NBS-6) are used in either of two modes: as calibrators of frequency^

provide a reference for the SI second; or as member clocks of the NIST clock ensemble, to help keep the prop

time for TA(NIST) and the coordinated time for UTC(NIST). Operating in the clock mode, NBS-4 and NBS-6 are only used and weighted according to their stability performance. Accuracy enters only when they are used as frequency calibrators, in which case clock operation is necessarily interrupted.

^GPS is the Global Positioning System, a network of navigation satellites.
Jle 7.i_ i s a list of changes in the time scale frequencies of both TA(NIST) and UTC(NIST) as well as a

J r Q f the time and frequencv differences between TA(NIST) and UTC(NIST) at the dates of leap seconds,

J:/or frequency or frequency drift changes.

TABLE 7.1

FREQUENCY CHANGES

DATE (MJD) TA(NIST) UTC (NIST) TA(NIST) - UTC (NIST) y[ UTC (NIST)] - y[TA(

1 Jun 89 47678 0 -1.00 ns/d 24.045 125 375 s -4.92 E- 13

1 Jul 89 47708 0 -1.00 ns/d 24.045 126 670 s -5.09 E- 13

1 Aug 89 47739 0 -1.00 ns/d 24.045 128 060 s -5.35 E- 13

1 Sep 89 47770 0 -1.00 ns/d 24.045 129 538 s -5.58 E- 13

1 Oct 89 47800 0 1.00 ns/d 24.045 131 001 s -5.68 E- 13

1 Nov 89 47831 0 1.00 ns/d 24.045 132 534 s -5.85 E- 13

1 Dec 89 47861 0 1.00 ns/d 24.045 134 082 s -6.05 E-13

1 Jan 90 47892 0 1.00 ns/d 25.045 135 724 s -6.16 E- 13

1 Feb 90 47923 0 1.00 ns/d 25.045 137 382 s -6.21 E-13

1 Mar 90 47951 0 1.00 ns/d 25.045 138 888 s -6.23 E-13

1 Apr 90 47982 0 1.00 ns/d 25.045 140 560 s -6.36 E-13

1 May 90 48012 0 1.00 ns/d 25.045 142 241 s -6.42 E-13

1 June 90 48043 0 1.00 ns/d 25.045 143 942 s -6.34 E-13

1 July 90 48073 0 0.50 ns/d 25.045 145 580 s -6.46 E-13

1 Aug 90 48104 0 0.00 ns/d 25.045 147 350 s -6.62 E-13

1 Sep 90 48135 0 -1.00 ns/d 25.045 149 130 s -6.69 E-13

1 Oct 90 48165 0 -1.00 ns/d 25.045 150 875 -6.82 E-13

1 Nov 90 48196 0 -1.50 ns/d 25.045 152 729 -6.94 E-13

'C(NIST) is steered in time toward UTC by occasional frequency changes of the order of a few nanoseconds

r day; 1 ns/d is approximately 1.16E-14. Otherwise, y[UTC(NIST)] is maintained as stable as possible.

REFERENCES

.lan, D W., Hellwig , H. and Glaze, D.J., "An accuracy algorithm for an atomic time scale," Metrologia, \ol.ll

No. 3, pp. 133-138 (September 1975).

i.aze , D.J., Hellwig, H. , Allan, D.W., and Jarvis, S.,

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

Lneland, D.J., Allan, D.W., Glaze, D.J., Hellwig, H.

,

cesium standard operation," IEEE Trans, on Instr

"NBS-4 and NBS-6: The NIST primary frequency

and Jarvis, S., "Results on limitations in primary

and Meas., Vol.IM-25, No. 4, pp. 453-458 (December 1976).

llan, D.W. and Weiss,

Satellite," Proc.

M.A., "Accurate Time and Frequency Transfer During Common View of a GPS

34th Annual Symposium on Frequency Control, p.334 (1980).

llan, D.W. and Barnes, J.A. , "Optimal Time & Frequency using GPS signals," Proc. 36th Annual

Symposium on Frequency Control, p.378 (1982).

- 6-
8 . SPECIAL ANNOUNCEMENTS

AUTOMATED COMPUTER TIME SERVICE (ACTS)

On March 9, 1988, NIST initiated operation of a telephone time service designed to provide computers \ telephone access to NIST time at accuracies approaching 1 ms. Features of the service include automated j compensation for telephone* line delay, advanced alert for changes to and from daylight savings time and

advanced notice of insertion of leap seconds. The ASCII -character time code should operate with standard

modems and most computer systems. While the system can be used to set computer time~of*day clocks, simple

hardware can also be developed to set other clock systems.

The test phase for this service is now complete and NIST is committed to long-term operation of the

service. Additional lines will be added as use expands. NIST requests that calling times be spread out sc that the system is not heavily taxed in some narrow time frame (e.g., midnight). The service telephone nuir is (303) 494-4774. The number may be changed at a later date. A help message can be obtained by returning

during the first 6 s of transmission.

With appropriate user software, the NIST-ACTS service provides three modes for checking and/or setting

computer time-of-day clocks.

1. In the simplest form of the (1200 Baud) service, the user receives the time code and an on-time

marker/ character which has been advanced a fixed period to nominally account for modem and telephone- line

delays. Accuracy in this mode should be no worse than 0.1 s unless the connection is routed through a Satellite

2. At 1200 Baud, if the user's system echoes all characters to NIST, the round-trip line delay will t easured and the on-time marker advanced to compensate for that delay. The accuracy in this mode should be

setter than 10 ms. Our experience to date indicates that the asymmetry in conventional, 1200-Baud modems

limits the accuracy at this level. Repeatability is about 1 ms.

3. At 300 Baud the user can obtain the same type of service as described in item 2 above, but there i generally less problem with modem asymmetry at this rate and our experience indicates that the accuracy is

about 1 ms.

The accuracy statements here are based upon the assumption that the telephone connection is reciprocal

that is, that both directions of communication follow the same path with the same delay. Discussions with

telephone carriers indicate that this is the general mode of operation and our tests to date indicate that

lines are both stable and reciprocal.

In order to assist users of the service, NIST has developed documentation of the features of the servi some example software which can be used in conjunction with certain popular personal computers and simple

circuitry which can be used to extract an on-time pulse. This material is available on a 5£-in, 360-kbyte

diskette with instructions for $35.00 from the NIST Office of Standard Reference Materials, B311-Chemistry

Bldg, NIST, Gaithersburg, MD, 20899, (301) 975-6776. Specify the Automated Computer Time Service, RM8101.

Further technical questions and comments should be directed to NIST-ACTS, NIST Time and Frequency Division,

Broadway, Boulder, CO 80303.

FREQUENCY CONTROL SYMPOSIUM ANNOUNCEMENT

The 45th Annual Frequency Control Symposium will be held May 29-31, 1991 in Los Angeles, CA. This

symposium is the leading technical conference addressing all aspects of frequency control and precision

timekeeping. Authors are invited to submit papers dealing with recent progress in research, development ar applications in areas represented by the following topics:

• Fundamental properties of piezoelectric crystals

• Theory and design of piezoelectric resonators

• Resonator processing techniques

• Surface acoustic wave devices (SAW)

• Quartz crystal oscillators

• Microwave and millimeter wave oscillators

• Signal processing and frequency control circuitry

• Atomic and molecular frequency standards

• Frequency and time coordination and distribution

• Sensors and transducers

• Applications of frequency control

• Measurement and specifications

Sponsors: IEEE-UFFC and the US Army Electronics Technology and Devices Laboratory (LABCOM).

Place: Los Angeles Airport Marriott, CA

Contact: Clark W'ardrip, P. 0. Box 6147, Vandenberg AFB, CA 93437; (805) 865-3214.
NEW NIST FREQUENCY MEASUREMENT AND ANALYSIS SERVICE

NIST is now offering a new service for calibration laboratories. This

service is called the Frequency Measurement and Analysis Service (FMAS). It

allows users to calibrate up to four precision oscillators at once, and to

graphically display and record their performance. All calibrations made are

traceable to NIST, and users receive a monthly report that certifies

traceability

.

Each subscriber to the FMAS receives a completely automatic measurement

system that they install in their laboratory. This system is about the size

of a component stereo system. It includes a Loran-C radio receiver, a time

interval counter, and a computer with a color display that continually

monitors the performance of your oscillators and graphically displays and

prints out the results. The system automatically transfers the data back to

NIST by modem.

Since the system uses highly stable Loran-C signals, it has a measurement

accuracy of about 1.00 E-12 over a 24-hour period. This allows it to measure

the performance of any oscillator, quartz, rubidium, or cesium.

The measurement system archives all of the data it records. This data

can be viewed or printed out at any time. This gives each subscriber a continuous record of the performance of each of their oscillators.

Subscribers receive all parts and supplies necessary to operate the

service. Their only requirement is to supply the oscillators to be measured

and a telephone line for data access. If any part of the system fails, NIST

ships a new part to the subscriber by overnight mail.

The cost of this service is $500 per month, with an initial one-time

start up fee of $4950. For more information, contact George Kamas or Michael

Lombardi at (303) 497-3378 or (303) 497-3212.

- 8-
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AN EQUAL OPPORTUNITY EMPLOYER

U.S. Department of Commerce

National Institute of Standards and Technology

Time & Frequency Division

Boulder, Colorado 80303

OFFICIAL BUSINESS

Penalty for Private Use, $300

GWEN BENNETT

sSU*

325 BROADWAY

BOULDER, CO 80303

FIRST-CLASS MA

POSTAGE & FEES ] NIST

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