Time & Frequency

Bulletin

No. 389 April 1990

(NISTIR 90-3940-4)

NIST TIME & FREQUENCY BULLETIN

(Supersedes No. 388 March 1990)

NO. 389 APRIL 1990

1. GENERAL BACKGROUND INFORMATION 1

2. TIME SCALE INFORMATION 1

International Timing Center comparisons via GPS common-view 2

3. UTl 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 bulleti-
1. GENERAL BACKGROUND INFORMATION

ABBREVIATIONS AND ACRONYMS USED IN THIS BULLETIN

APL John Hopkins University Applied Physics Laboratory

BIH - International Time Bureau, France

CCIR - International Radio Consultative Committee

CRL - Communications Research Laboratories, Japan

Cs - Cesium standard

CSIRO - Commonwealth Scientific and Industrial Research Organization, Australia

GOES - Geostationary Operational Environmental Satellite

GPS - Global Positioning System

lEN - 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 MS 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

2. TIMK SCALE INFORMATION

The values listed below are based on data from the BIH, the USNO, and the 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 NAVSTAR satellites 3,4,6, and 8 (see references on page 6).

0000 HOURS COORDINATED UNIVERSAL TIME

MARCH

1990 MJD

UTl - UTC(NIST)

(± 5 ms)

UTC - ITC(NIST)

(± 0.2 us)

UTC(USN0,MC) - UTC(NIST)

(± 0.04 us)

1 47951 4-208 ms 0.3 us 1.70 us

8 47958 +195 ms 0.3 us 1.70 us

15 47965 +178 ms 0.3 us 1.70 us

22 47972 +164 ms 0.3 us 1.70 MS

29 47979 +143 ms 0.3 us 1.66 MS

-1 -
INTERNATIONAL TIMING CENTER COMPARISONS VIA GPS COMMON-VIEW

The table below is a weighted average of the indicated GPS satellites used as transfer standards to measure the

time difference of Timing Center (i) - UTC(NIST) by the simultaneous common-view approach (see references, page

6). The day-to-day variations of this technique are a few nanoseconds and the accuracy is about 10 ns. The

time of the measurement is interpolated to 0000 UTC for the particular MJD ending in 9. These data are prepared for the BIP.M for the computation on TAI and of UTC. All differential delays are 0 unless otherwise

noted

.

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

LTC( i) SV NUMBERS 47949 47959 47969 47979

L’TC(APL) - UTC(NIST) 3,6,9,11,12,13,14 -193+ -272 -382 -515

UTC (CRL) - UTC (NIST) 3,6,9 12 865+ 850 845 840//

LTC (CS IRQ) - UTC (NIST) ++ 24657 24740 24806 24890//#

UTC(IEN) - UTC ( NIST )(3 11 . 12,13,14 1345 1360 1370 1366//

UTC(INPL) - UTC (NIST)! VIA OP -156991+ -158709 -160614 -162627(30

UTC(NPL) - UTC(NIST) 3, 11,12,13 2640+ 2685 2693 2728

UTC(.NRC) - UTC(NIST)+++ 3,6,9,11,12,13 973 958 905 804

UTC (OP) - UTC (NIST) 3, 11,12,13,14 827 914 1011 1097//

UTC(PTB) - UTC (NIST) 11 -3400+ -3366 -3327 -3280

UTC (TAO) - UTC (NIST) !

!

3,6,9, 12, 14 5424 5316 5167 5006

UTC (TUG) - UTC (NIST) 3, 11,12,13,14 3515+ 3314 3103 2818//

UTC(USNO,MC) - UTC (NIST) 3,6,9,11,12,13,14 1701 + 1703 1700 1662

UTC(VSL) - UTC(NIST) 3, 11,12,13,14 -2119+ -2132 -2168 -2215//

+ These values have been updated from those printed in last month's Bulletin.

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

UTC(N"RC) - UTC(NIST) has a differential delay of 41.2 ns; all other comparisons are computed using zero

( 0 )

.

lEN experiened a frequency shift of approximately -18.0 E-14 on MJD 47950.

! The value for UTC(INPL) - UTC(NIST) for MJD 47939 was incorrectly computed last month. The correct value

is -155328.

!! TAO experienced a frequency shift of approximately -26.5 E-14 on MJD 47950.

4 The values for these stations for MJD 47979 were extrapolated forward from MJD 47977.

The value for this station for MJD 47979 was extrapolated forward from MJD 47975.

The value for this station for MJD 47979 was extrapolated forward from MJD 47976.

3. UTl CORRECTIONS AND LEAP SECOND ADJUSlMBirS

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 second 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 UTl 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 :ne UTC timescale on 30 June 1972, 31 December 1972-1979, 30 June 1981-1983, 30 June 1985, 31 December 1987 and

1989. When future leap seconds are scheduled, advance notice will be provided in this bulletin.

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

L’Tl — UTC is called the DUTl correction. DUTl corrections are broadcast by WWV, WWVH, WWVB, and GOES and arp

printed below. These corrections may be added to received UTC time signals in order to obtain UTl.

= +0.3 s beginning 0000 UTC on 1 January 1990 (simultaneous with insert

of the leap second.

= +0.2 s beginning 0000 UTC on 1 March 1990

= +0.1 s beginning 0000 LTC on 12 April 1990

DUTi UTl - UTC
k, 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 posit ive-goirig zero voltage crossover measured at the transmitting

antenna. The uncertainty of the individual measurements is t 0.5 ps. The values listed are

for 1500 UTC.

L0RA.N-C - The values shown for Loran-C represent the daily accumulated phase shift (in microseconds).

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

scale for a period Oi 24 hours. j- data were not recorded on a particular day, the symbol

( - ) is printed

.

The stations monitored are Dana, Indiana (8970 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 ms)

DATE MJD

ANTENNA PHASE

(ms)

LORAN-C (DANA)

(8970 M)

LORAN-C (FALLON)

(9940 M)

03/01/90 47951 5.68 -0.19 -0.06

03/02/90 47952 5.66 -0.43 -0.14

03/03/90 47953 5.63 -0.13 -0.05

03/04/90 47954 5.61 +0.01 -0.06

03/05/90 479S5 5.59 +0.35 (-)

03/06/90 47956 5.66 +0.35 -0.73

03/07/90 47957 5.64 (-) (-)

03/08/90 47958 5.64 (-) (-)

03/09/90 47959 5.59 -0.25 +0.08

03/10/90 47960 5.61 -0.26 +0.02

03/11/90 47961 5.63 +0.10 +0.20

03/12/90 47962 5.66 -0.06 +0.13

03/13/90 47963 5.63 -0.21 +0.03

03/14/90 47964 5.70 -0.08 -0.13

03/15/90 47965 5.69 -0.02 +0.05

03/16/90 47966 5.71 +0.02 -0.05

03/17/90 47967 5.68 +0.14 +0.05

03/18/90 47968 5.66 +0.27 +0.10

03/19/90 47969 5.64 +0.03 -0.10

03/20/90 47970 5.71 +0.25 +0.00

03/21/90 47971 5.62 -0.04 -0.12

03/22/90 47972 5.73 -0.05 +0.09

03/23/90 47973 5.68 -0.37 -0.41

03/24/90 47974 5.68 +0.12 +0.16

03/25/90 47975 5.67 +0.11 -0.02

03/26/90 47976 5.67 -0.02 +0.03

03/27/90 47977 5.65 -0.05 -0.13

03/28/90 47978 5.62 -0.23 +0.01

03/29/90 47979 5.68 +0.01 +0.00

03/30/90 47980 5.71 -0.22 -0.15

03/31/90 47981 5.69 -0.13 -0.06

- 3 -
5. GOES TIME CODE INFORMATION

A. TIME CODE PERFORMANCE (1-31 March 1990)

GOES/ East : Performance within normal limits most of the time during this period. The peak-to-peak

diurnal variations of the time code (corrected for satellite position) were larger-than-normal , however,

and occasional deviations of slightly greater than 100 microseconds were observed. The GOES-5 satellite

is still drifting westward and was at about 71 degrees West longitude on March 31.

GOES/West

:

Performance within normal limits during this period.

B. SPECIAL REMINDER: Current satellite locations are 71° West longitude for GOES/East and 135° West

longitude for GOES/West.

C. SPECIAL NOTE

In response to concerns from time code users about GOES/East coverage in Europe and Africa

if GOES/East operations are shifted to GOES-7, NOAA has reconsidered its previous decision.

Currently, the plan is to transfer GOES/East operations from GOES-5 to GOES-2 (an older

standby satellite) when GOES-2 drifts into its new location at about 60° West longitude.

This transfer of operations is expected to occur about May 1, 1990 and will remain in

effect indefinitely. Exact dates will be announced in the GOES status file (NBSGO)

maintained in the U.S. Naval Observatory's Automated Data Service (see below for access information) as soon as it is known.

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

satellites is July 1991 and February 1992, respectively.

E. GOES 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 parity. 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 "0NBSGO" 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

STATION

MARCH

1990 MJD

BEGAN

(UTC)

ENDED

(UTC) FREQUENCY

MARCH BEGAN

1990 MJD (UTC)

ENDED

(UTC )

WWVB NONE NONE

WVTv' NONE NONE

WVv'H 05 47956 0211:00 0300:00 2. 5 MHz NONE
7. NOTES ON NIST TIME SCALES AND PRIMARY STANDARDS

The frequencies of the time scales, TA(NIST) 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 last

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

>'UTC(NIST) 1987) yNBS-6 (-1^1-y 1987) = (-0.6 ±2(1 sigma)) x 10’^^

for the date shown,

blackbody radiation,

the dates shown were

This calibration includes a correction for the systematic offset due to room temperature

which is approximately (delta ygg) = -1.7 x 10"^^. Using GPS^, the frequency of TAI for

measured to be:

2) yjys^j (July 1987 ) yNBS-6 1987 on geoid) = (+1.7 ±2(1 sigma)) x 10"^^

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 of

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)' last calibration (July 1987) covered the period

from October 1986 through July 1987.

yCs(NIST) ~ yNBS-6 " ( + 1-'^ ± 2) x 10 (July 1987)

and

4) y^Aj ~ ycs(NIST) on geoid =

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 the

frequency memory of the clock ensemble that generates atomic time. This algorithm, therefore, capitalizes on a 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(NIST)

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

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

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 interpolation

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 to

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

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.
Table 7.1 is a list of changes in the time scale frequencies of both TA(NIST) and UTC(NIST) as well as a list of the time and frequency differences between TA(NIST) and UTC(NIST) at the dates of leap seconds,

and/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(NIST)]

1 Oct 88 47435 0 1.00 ns/

d

24.045 114 515 s -5.15 E-13

1 Nov 88 47466 0 1.25 ns/d 24.045 116 854 s -4.88 E-13

1 Dec 88 47496 0 1.50 ns/d 24.045 118 088 s -4.69 E-13

1 Jan 89 47527 0 1.50 ns/d 24.045 119 325 s -4.57 E-13

1 Feb 89 47558 0 1.00 ns/

d

24.045 120 538 s -4.51 E-13

1 Mar 89 47586 0 -1.25 ns/d 24.045 121 622 s -4.58 E-13

1 Apr 89 47617 0 -1.50 ns/

d

24.045 122 871 s -4.66 E-13

1 May 89 47647 0 -1.50 ns/d 24.045 124 078 s -4.75 E-13

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

24.045 135 724 s -6.16 El- 13

1 Feb 90 47923 0 1.00 ns/

d

24.045 137 382 s -6.21 E-13

1 Mar 90 47951 0 1.00 ns/d 24.045 138 888 s -6.23 E-13

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

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

REFERENCES

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

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

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

standards," Metrologia, Vol.l3, 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, on Instr. and Meas., Vol.IM-25, No. 4, pp. 453-458 (December 1976).

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 & Frequency using GPS signals," Proc. 36th Annual

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

- 6 -
8. SPECIAL ANNOUNCEMENTS

44TH ANNUAL FREQUENCY CONTROL SYMPOSIUM

The 44th Annual Frequency Control Symposiujn will be held May 23 - 25, 1990 in Baltimore, MD . This

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

timekeeping. Authors are invited to submit papers dealing with recent progress in research, development and

applications in areas represented by the following topics:

• Fundamental properties of piezoelectric crystals

• Theory and design of piezoelectric resonators

• Resonator processing techniques

• Filters

• 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

Contact: Dr. R. L. Filler, US Army Electronics Technology and Devices Laboratory, ATTN: SLCET-EQ, Fort

Monmouth, NJ 07703-5000; (201) 544-2467.

NOBEL PRIZE WINNERS to SPEAK at the 44th ANNUAL

SYMPOSIUM on FREQUENCY CONTROL

The 1989 Nobel Prize in Physics was awarded to Norman Ramsey, Hans Dehmelt, and Wolfgang Paul for

advancements in atomic clock technology. Professor Ramsey of Harvard University and Professor Dehmelt of the

University of Washington (and possibly Professor Paul from the University of Bonn) have accepted invitations to present their Nobel lectures at the 44th Annual Symposium on Frequency Control. There will be a special

reduced registration fee for the Nobel lectures. The lectures will be presented Friday morning. May 25.

Professor Ramsey's talk is titled "Experiments with Separated Oscillatory Fields and Atomic Hydrogen

Masers." Professor Dehmelt 's talk is titled "Experiments with an Isolated Subatomic Particle at Rest."
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National Institute of Standards and Technology

Time & Frequency Division

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