NATIONAL INSTITUTE OF STANDARDS &

TECHI'^OLOGY

Research Information Center

Gaithersburg, MD 20696

Time & Frequency

Bulletin

No. 386 January 1990

(NISTIR 90-3940-1)

NIST TIME & FREQUENCY BULLETIN

(Supersedes No. 385 December 1989)

NO. 386 JANUARY 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

A. 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 BULLETIN

\PL John Hopkins University Applied Physics Laboratory

BIH - International Time Bureau, France

:ciR - International Radio Consultative Committee

:rl - Communications Research Laboratories, Japan

3s - Cesium standard

3SIR0 - Commonwealth Scientific and Industrial Research Organization, Australia

30ES - Geostationary Operational Environmental Satellite

IPS - Global Positioning System

[EN - National Institute of Electronics, Italy

[NPL - National Physical Laboratory, Israel

.ORAN - Long Range Navigation

iC - Master Clock

UD - Modified Julian Date

;iST - National Institute of Standards & Technology

JPL - National Physical Laboratory, England

fRC - National Research Council, Canada

fOAA - National Oceanic and Atmospheric Administration

)P - Paris Observatory, France

>TB - Physical Technical Federal Laboratory, Germany

;i - International System of Units ns nanosecond

,v

- Space vehicle us microsecond

'A - Atomic Time ms millisecond

'AI - International Atomic Time s second

'AO - Tokyo Astronomical Observatory, Japan min - minute

UG - Technical University of Graz, Austria h hour

;SNO - United States Naval Observatory d day

rrc - Coordinated Universal Time

'LF - very low frequency

’SL Van Swinden Laboratory, Netherlands

2. TIME SCALE INFORMATION

’he values listed below are based on data from the BIH, the USNO, and the NIST. The UTC — UTC(NIST) values are 'xtrapolations since UTC is computed more than two months after the fact. The UTC(USNO,MC) - UTC(NIST) values

ire averaged measurements from NAVSTAR satellites 3,4,6, and 8 (see references on page 6).

0000 HOURS COORDINATED UNIVERSAL TIME

DECEMBER

1989 MJD

UTl - UTC (NIST)

( ± 5 ms

)

UTC - UTC(NIST)

(± 0.2 us)

UTC(USN0,MC) - UTC(NIST)

(± 0.04 us)

7 47867 -627 ms 0

1 0.94 us

14 47874 -641 ms -0.1 us 1.02 us

21 47881 -654 ms -0.1 US 1.10 us

28 47888 -665 ms 0.0 us 1.17 us

-

1 -
INTERNATIOKAL TIMING CENTER COMPARISONS VIA GPS COMMON-VIEW

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

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

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

!:ime of the measurement is interpolated to 0000 UTC for the particular MJD ending in 9. These data are

; prepared for the BIPM for the computation on TAI and of UTC. All differential delays are 0 unless otherwise

loted

.

UTC(i) -

'TC(NIST) (ns) MJD

UTC(i) SV NUMBERS 47859 47869 47879 47889

;TC(APL) - UTC(NIST) 3,6,9,11,12,13,14 // 108 114 88

JTC(CRL) - UTC(NIST) 6, 12 14 836+ 872 900 900!

JTC(CSIRO) - UTC(NIST) ++ 23729 23905 24027 24039!

!

JTC(IEN) - UTC(NIST) 11,12,13,14 168 260 395 525!

JTC(NPL) - UTC(NIST) 3, 11,12,13,14 2109 2171 2248 2286

rrC(NRC) - UTC(NIST)+++ 3,6,9,11,12,13,14 15878 15933 15964 15980

rrc(op) - UTC(NiST) 3, 11,12,13,14 69 140 242 331

rrC(PTB) - UTC(NIST) 11 -3798 -3771 -3680 -3612

rrC(TAO) - UTC(NIST) 6, 14 4641 4752 4876 49690

TC(TUG) - UTC(NIST) 3, 11,12,13,14 -3683 -3899 -4068 -4265

TC(USN0,MC) - UTC(NIST) 3,6,9,11,12,13,14 803 959 1081 1185

rrC(VSL) - UTC(NIST) 3, 11,12,13,14 -2017 -2075 -2010 -2005

'*LEASE NOTE: INPL is experiencing receiver problems. Therefore, this station is not included in this month's

Bulletin.

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

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

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

I (0).

APL is missing data for MJD 47859.

The value for MJD 47889 was extrapolated forward from MJD 47885 for these stations.

! The value for MJD 47889 was extrapolated forward from MJD 47884 for this station.

' The value for MJD 47889 was extrapolated forward from MJD 47886 for this station.

3. UTl CORSECnONS AND LEAP SECOND ADJUSTMaTTS

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

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

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

I'hanges slightly due to variations in the rotation of the earth.

'ositive 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

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

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

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

JTl — 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.

= -0.5 s beginning 0000 UTC 21 September 1989

DUTl = UTl - UTC = -0.6 s beginning 0000 UTC 16 November 1989

= +0.3 s beginning 000 UTC on 1 January 1990 (simultaneous with insertion

of the leap second.

SPECIAL ANNOUNCQfQfT : A positive leap second was inserted into all UTC time scales at the end of

December 1989.

i

- 2 -
4. PHASE DEVIATICWIS FOR WWVB AND LORAN-C

WWV3 - The values shown for WWVB are the time difference between the time markers of the UTC(NIST)

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

antenna. The uncertainty of the individual measurements is ± 0.5 ms. The values listed are for 1500 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 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)

12/01/89 47861 5.67 (-) +0.09

12/02/89 47862 5.70 -0.18 -0.32

12/03/89 47863 5.73 -0.25 +0.26

12/04/89 47864 5.76 +0.07 +0.11

12/05/89 47865 5.73 +0.19 -0.06

12/06/89 47866 5.68 -0.24 -0.03

12/07/89 47867 5.64 +0.05 -0.01

12/08/89 47868 5.62 -0.22 -0.07

12/09/89 47869 5.65 (-) -0.00

12/10/89 47870 5.68 +0.63 +0.12

12/11/89 47871 5.70 -0.33 -0.20

12/12/89 47872 5.73 (-) (-)

12/13/89 47873 5.75 (-) +0.01

12/14/89 47874 5.80 (-) +0.11

12/15/89 47875 5.73 (-) -0.20

12/16/89 47876 5.71 (-) +0.02

12/17/89 47877 5.69 +0.22 +0.10

12/18/89 47878 5.67 +0.01 +0.12

12/19/89 47879 5.61 (-) -0.02

12/20/89 47880 5.61 -0.12 -0.03

12/21/89 47881 5.72 -0.38 -0.20

12/22/89 47882 5.67 -0.45 -0.12

12/23/89 47883 5.67 +0.21 -0.05

12/24/89 47884 5.66 +0.25 +0.05

12/25/89 47885 5.65 +0.40 +0.08

12/26/89 47886 5.65 +0.16 -0.04

12/27/89 47887 5.63 +0.10 -0.17

12/28/89 47888 5.63 +0.57 +0.19

12/29/89 47889 5.67 -0.37 -0.30

12/30/89 47890 5.67 -0.34 -0.06

12/31/89 47891 5.66 +0.01 -0.02
5. GOES TIME CODE INFORMATION

A. TIME CODE PERFORMANCE (1-31 December 1989)

GOES/East ; Performance within normal limits during this period. The peak-to-peak diurnal variations of

the time code (corrected for satellite position) were larger-than-normal , however, during some periods of

this month.

GOES/West

Performance within normal limits during this period.

B. SPECIAL REMINDER: Current satellite locations are 65° West longitude for GOES/East and 135° West

longitude for GOES/West.

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

satellites is June 1991 and February 1992, respectively.

D. 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 "@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

STATION

DECEMBER

1989

BEGAN

MJD (UTC)

ENDED

(UTC) FREQUENCY

DECEMBER BEGAN

1989 MJD (UTC)

ENDED

(UTC)

WWVB NONE NONE

WWV NONE NONE

WW\H NONE NONE
7. MOTES 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

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:

yUTC(NIST) 1987) - y^BS-6 1987) = (-0.6 ±2(1 sigma)) x 10'^^

for the date shown. This calibration includes a correction for the systematic offset due to room temperature blackbody radiation, which is approximately (delta ygg) = -1.7 x 10*^^. Using GPS^ the frequency of TAI for the dates shown were measured to be:

2) yr^p^i (July 1987) - y^BS-b 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 oeriod 'from October 1986 through July 1987. ^

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

and

i ^TAI “ yCs(NIST) on geoid = (+0.3 ± 0.7) x 10'^^ (July 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 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 y^ by slight frequency drift corrections of the order of 1 part in 10l3/yr. ts^Nibi;

'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 LTC(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-A and NBS-6) are used in either of two modes: as calibrators of frequency to

)rovide a reference for the SI second; or as member clocks of the NIST clock ensemble, to help keep the proper

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

GPS is the Global Positioning System, a network of navigation satellites.

- 5 -
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 Jul 88 47343 0 -1.60 ns/d 24.045 111 523 s -4.64 E-13

1 Aug 88 47374 0 -0.40 ns/d 24.045 112 802 s -4.89 E-13

1 Sep 88 47405 0 -1.00 ns/d 24.045 114 144 s -5.15 E-13

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

lt:c(nist)1 is steered in time toward UTC by occasional frequency changes of the order of a few nanosecon

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

Glaze, D.J., Hellwig, H. , Allan, D.W. , and Jarvis, S., "NBS-4 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 primar.

cesium standard operation," IEEE Trans, on Instr. and Meas . , Vol.IM-25, No. 4, pp. 453-458 (December 1

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 ANNOUNCHIENTS

AUTOMATED COMPUTEE TIME SERVICE (ACTS)

On March 9, 1988, NIST initiated operation of a telephone time service designed to provide computers with

telephone access to NIST time at accuracies approaching 1 ms. Features of the service include automated

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 so that the system is not heavily taxed in some narrow time frame (e.g., midnight). The service telephone number

is (303) 494-4774. The number may be changed at a later date. A help message can be obtained by returning a ? 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 be

measured and the on-time marker advanced to compensate for that delay. The accuracy in this mode should be

better 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 is

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 assiomption 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 the

lines are both stable and reciprocal.

In order to assist users of the service, NIST has developed documentation of the features of the service,

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 5i-in, 360-kbyte DOS

diskette with instructions for $35.00 from the NIST Office of Standard Reference Materials, B31 1 -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, 325 : Broadway, Boulder, CO 80303. i

44TH ANNUAL FREQUENCY CONTROL SYMPOSIUM

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

- 7 -
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