1 Time & Frequency

Bulletin

No. 391 June 1990

(NISTIR 90-3940-6)

National

Institute of

Technology

NIST TIME & FREQUENCY BULLETIN

(Supersedes No. 390 May 1990)

NO. 391 JUNE 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 : SEL IN THIS BULLETIN

ALL - John Hopkins University Applied Physics Laboratory

B i H

- International Time Bureau, France

CCIR - International Radio Consultative Committee

C RL - Communications Research Laboratories, Japan

Cs - Cesium standard

CSIRO - Commonwealth Scientific and Industrial Research Organizat ion, Australia

GOES - Geostationary Operational Environmental Satellite

GPS - Global Positioning System

IEN - National Institute of Electronics, Italy

INPL - National Physical Laboratory, Lsrael

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. TIME 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 mere 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

1990 MJD

UT1 - UTC (NIST)

( ± 5 ms

)

UTC - UTC(NIST)

( + 0.2 us ) UTC ( USNO, MC) - UTC (NIST)

(+ 0.04 us)

3 48014 +66 ms 0.4 us 1.47 us

10 48021 +53 ms 0.4 us 1.40 us

17 48028 +4 1 ms 0.4 us 1.34 us

24 48035 + 25 ms 0.4 us 1.27 us

31 48042 + 15 ms 0.4 us 1.20 us

-L-
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 dav-to-dav variations of this technique are a few nanoseconds and the accuracy is about 10 r.s. The

tine 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

noted

.

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

UTC( i ) SV NUMBERS 48009 48019 48029 48039

LTC(APL) - UTC(NIST) 3,6,9,11,12,13,14 -798 340 5 -49

UTC (CRL ) - UTC(NIST) 3,6,9 12, 14 754 665 586 481

UTC(CSIRO) - UTC(NIST) ++ 25158 253 18 25419 25470 it

UTC(IEN) - UTC (NIST) 11,12,13,14 1427 1418 1414 1396

UTC(INPL) - UTC (NIST) VIA OP - 169049+ -170918 -173216 -175286/)

UTC(NPL) - UTC(NIST) 3, 11,12,13,14 2833 2836 2879 2919

UTC (NRC) - UTC ( NIST )+++ 3,6,9,11,12,13,14 362 148 -154 - 376!

UTC (OP ) - UTC ( NIST

)

3, 11,12,13,14 1152 1151 1133 1041

UTC(PTB) - UTC(NIST) 11 -3212 -3220 -3232 -3262

UTC(TAO) - UTC (NIST) 3,6,9, 12, 14 4522 4322 4115 3856

UTC (TUG) - UTC (NIST) 3, 11,12,13,14 2103 1830 1585 1308

UTC(USNO.MC) - UTC(NIST) 3,6,9,11,12,13,14 1503 1422 1329 1228

UTC(VSL) - UTC (NIST) 3, 11,12,13,14 .mo -2246 -2242 -2300

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

-H- UTC(CSIRO) - UTC(NIST) is computed from the average of CRL, TA0, & WWVH. +++ UTC(NRC) - UTC(NIST) has a differential delay of 41.2 ns; all other comparisons are computed using zero

( 0 ). y APL experienced a frequency shift of approximately -15.0 E-14 and a time step of approximately +800 ns on MJD 48012.

! NRC experienced abnormal clock behavior and an apparent frequency shift of approximately 4.0 E - 1 3 on or around MJD 47935. Therefore, the value for MJD 48039 was computed using raw, unfiltered data. This value

will be updated next month.

The values for these stations for MJD 48039 were extrapolated forward from MJD 48038.

3. UT1 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 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 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 r he

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 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, WWVB, and GOES and are printed below. These corrections may be added to received UTC tir° signals in order to obtain UT1.

DUT1 = UT1 - UTC

= +0.2 s beginning 0000 UTC on 1 March 1990

= +0.1 s beginning 0000 UTC on 12 April 1990

= 0.0 s beginning 0000 UTC on 10 May 1990
4. PHASE DEVIATIONS FOR WWVB AND LORAN-C

VWYB - The values shown tor WWVB are the time difference between the tine markers of the ITC(NIST')

tine scale and the first pos i t i ve-go i.ng zero voltage crossover measured at the transmitting

antenna. The uncertainty of the individual measurements is ± 0.5 us. The values listed are

for 1300 L'TC

.

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 Co hours. If data were not recorded on a particular day, the symbol

l - ) 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 us

)

DATE MJD

ANTENNA PHASE

( us ) LORAN-C (DANA)

(8970 M)

LORAN-C (FALLON)

(9940 M)

05/01/90 48012 5.68 -0.08 -0.04

05/02/90 48013 5.66 +0.18 +0.08

05/03/90 480 1

4

5.66 -0.04 -0.01

05/04/90 48015 5.65 -0.21 -0.25

05/05/90 48016 5 . 66 -0. 14 +0.13

05/06/90 48017 5.66 +0.13 +0.22

05/07/90 48018 5.67 -0.09 -0.07

05/08/90 48019 5.64 -0.15 -0.13

05/09/90 48020 5.74 +0.12 -0.06

05/10/90 48021 5.76 -0.02 -0.08

05/11/90 48022 5.73 -0.14 -0.23

05/12/90 48023 5.73 (-) (-)

05/13/90 48024 5.74 (*) (-)

05/14/90 48025 5.74 -0.05 (-)

05/15/90 48026 5.74 +0.07 -0.62

05/16/90 48027 5.68 -0.00 +0.11

05/17/90 48028 5.69 +0.03 -0.08

05/18/90 48029 5.64 -0.22 -0.35

05/19/90 48030 5.67 +0.00 -0.10

05/20/90 48031 5.70 +0.18 +0.28

05/21/90 48032 5.74 -0.06 -0.10

05/22/90 48033 5.68 +0.09 -0.09

05/23/90 48034 5.72 -0.04 +0.08

05/24/90 48035 5.74 -0.12 -0.07

05/25/90 48036 5.73 -0.15 +0.04

05/26/90 48037 5.72 +0.08 -0.12

05/27/90 48038 5.71 +0.09 +0.06

05/28/90 48039 5.70 +0.23 +0.22

05/29/90 48030 5.69 +0.20 +0.12

05/30/90 48031 5.72 -0.03 -0.09

05/31/90 48032 5.75 +0.12 +0.14

- 3 -
5. GOES TIME CODE INFORMATION

r : ME CODE PEKFORMANCE ( I

- 31 May 1990)

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

GOir.S West: Performance within normal limits during this period.

B. SPECIAL REMINDER: Current satellite locations are 79 J West longitude for GOES/East and L35° 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, N'OAA 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-July time period and will remain

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

maintained in the Li.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 dav 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

MAY BEGAN ENDED MAY BEGAN ENDED

STATION 1990 MJD ( UTC

)

( UTC

)

FREQUENCY 1990 MJD (UTC) (UTC)

WWVB NONE NONE

WWV 21 48032 1530.00 1645.00 5.0 MHz NONE

WWVH NONE NONE
7. NOTES ON NIST TIME SCALES AND PR I MALY STANDARDS

The frequencies of the time scales, TAIN 1ST) and l'TC(NIST), are calibrated with the NIST primarv frequence

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

scale, UTC , generated at the B I H . It is used to control all of the NIST tine and frequency services. The last

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

1 ) XUTC( N'IST )

( -July 1987) — y ^ (July 198/) = (*0.6 t 2 (l si gma ) ) x 10 ' J

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

blackbodv radiation, which is approximately (delta ygg) = -1.7 x iO

-

' 4

. Using GPS'-, the frequency of TAI for

the dates shown were measured to be:

2) h’XAI (July 1987 ) - vyigs -5 (July 1987 on geoid) = (+1.7 + 2(1 sigma)) x 10~' 3

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(N’IST) 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 1- ast calibration (July 1987) covered the period

from October 1986 through July 1987.

3) -v Cs( NIST ) “ ^NBS-6 ~ ( + 1- 4 t 2 ) x 10 13 (July 1987 )

and

9) yTAI - ycs(NIST) on geoid = (+0 - 3 1 °- 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 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 33 /vr.

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 proper

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.

i

'GPS is the Global Positioning System, a network of navigat . :r. satellites.
Table 7.1 is a list of changes in the tine scale frequencies of both TA(NTST) and U7C( N 1ST) as well as list of the time and frequency differences between TA(NIST) and L'TC( NIST J at the dates of .eat seconds,

and/or frequency or frequency drift changes.

TABLE 7 .

FREQUENCY CHANGES

DAT! ( MJD

TA( NIST

UTC (NIST) TA( NIST) - UTCLNI:ST) v ( UTC ( NIST ) ] - v(TA( NIST )

1 Dec 88 4/496 0 1 ,. 50 ns/d 24., 045 1 18 088 s -4.69 E- 13

1 j <Ei n 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 47 586 0 -

,.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 47 647 0 -1 .50 ns/d 24,.045 124 078 s -4.75 E-13

1 Jun 89 A76 78 0 -1 .00 ns /d 24,. 045 125 375 s -4.92 E-13

1 Jul 89 477 08 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 89 477 7 0 0 -1 .00 ns/d ") • _ -4 ,. 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 E-13

1 Feb 90 47923 0 1 .00 ns/d -) /

,.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

1 Apr 90 47982 0 1 .00 ns/d 24.045 140 560 s -6.36 E-13

1 Mav 90 48012 0 1 .00 ns/d 24 .045 142 241 s -6.42 E-13

UTC(NIST) 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, v[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,

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

Glaze, D.J., Hellwig, H., Allan, D.W., and Jarvis, S., "N'BS-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 prima

cesium ?r an dard operation," IEEE Trans, on Instr. and Meas . , Vol.IM-25, No. 4, pp. 453-458 (December

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

AUTOMATED COMPUTER TIME SERVICE (ACTS)

On Mar cn 9, 1088, 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 te iephone - 1 i ne delay, advanced alert for changes to and from davLight savings tine and

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

modems and most computer .systems. While the system can be used to set computer Lime-of-dav docks, 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) 494-477-4. The number may be changed at a later date. A help message can be obtained bv 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-dav docks.

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 sate i 1 i te

.

2. At 1200 Baud, if the user's system echoes all characters to NIST, the round-trip line delav 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 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 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 5s-in, 360-kbyte DOS

diskette with instructions for $35.00 from the NIST Office of Standard Reference Materials, B3 1 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, 32 Broadway, Boulder, CO 80303.
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4. PE AROAminG Organization 1,1 i 91 *' ,h#" »•« '* •*'»»<«»•« »> National Institute of Standards &

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325 Broadway

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II. Supplementary NOTES

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11. ABSTRACT fA ZOO-ve^ o' ion /•«*•* **'**«'> of »*e»t i/|r»'ficoM ImfoimoVoo. // Mcammi !*«/**•• • t/falfueet

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• caltt r ad a verltty of broidcifti (And relAted lnformAtloe) to ubatb of tho

NIST services.

W. KCT nOROS f S' f to (»•/*« 0*iH9t; 0 /p* 0 HtiC 0 t o<V«r; c#*-t*n *• o*<r pro90 f •*# loportta Itr •©'Vi Rr i •rw - c o < «

deck*; dissemination; frequency; CPS; osclllstori; time

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