NBS SPECIAL PUBLICATION 236

1972 EDITION

NBS FREQUENCY AND TIME

BROADCAST SERVICES

RADIO STATIONS

WWV. WWVH. WWVB, WWVL
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards^ was established by an act of Congress March 3,

1901. The Bureau's overall goal is to strengthen and advance the Nation's science and

technology and facilitate their effective application for public benefit. To this end, the

Bureau conducts research and provides: (1) a basis for the Nation's physical measure- ment system, (2) scientific and technological services for industry and government, (3) a technical basis for equity in trade, and (4) technical services to promote public safety.

The Bureau consists of the Institute for Basic Standards, the Institute for Materials

Research, the Institute for Applied Technology, the Center for Computer Sciences and

Technology, and the Office for Information Programs.

THE INSTITUTE FOR BASIC STANDARDS provides the central basis within the

United States of a complete and consistent system of physical measurement; coordinates

that system with measurement systems of other nations; and furnishes essential services

leading to accurate and uniform physical measurements throughout the Nation's scientific community, industry, and commerce. The Institute consists of a Center for Radiation Research, an Office of Measurement Services and the following divisions:

Applied Mathematics—Electricity—Heat—Mechanics—Optical Physics—^Linac

Radiation^—Nuclear Radiation-—Applied Radiation^—Quantum Electronics'

Electromagnetics'—^Time and Frequency'—Laboratory Astrophysics'—Cryogenics'.

THE INSTITUTE FOR MATERIALS RESEARCH conducts materials research leading to improved methods of measurement, standards, and data on the properties of

well-characterized materials needed by industry, commerce, educational institutions, and

Government; provides advisory and research services to other Government agencies;

and develops, produces, and distributes standard reference materials. The Institute consists of the Office of Standard Reference Materials and the following divisions:

Analytical Chemistry—Polymers—Metallurgy—Inorganic Materials—Reactor

Radiation—Physical Chemistry.

THE INSTITUTE FOR APPLIED TECHNOLOGY provides technical services to promote the use of available technology and to facilitate technological innovation in industry and Government; cooperates with public and private organizations leading to the

development of technological standards (including mandatory safety standards), codes

and methods of test; and provides technical advice and services to Government agencies

upon request. The Institute also monitors NBS engineering standards activities and

provides liaison between NBS and national and international engineering standards

bodies. The Institute consists of the following divisions and offices: Engineering Standards Services—Weights and Measures—Invention and

Innovation—Product Evaluation Technology—Building Research—Electronic

Technology—Technical Analysis—Measurement Engineering—Office of Fire

Programs.

THE CENTER FOR COMPUTER SCIENCES AND TECHNOLOGY conducts re- search and provides technical services designed to aid Government agencies in improving cost effectiveness in the conduct of their programs through the selection, acquisition,

and effective utilization of automatic data processing equipment; and serves as the principal focus within the executive branch for the development of Federal standards for

automatic data processing equipment, techniques, and computer languages. The Center

consists of the following offices and divisions:

Information Processing Standards—Computer Information—Computer Services —Systems Development—Information Processing Technology.

THE OFFICE FOR INFORMATION PROGRAMS promotes optimum dissemination

and accessibility of scientific information generated within NBS and other agencies of

the Federal Government; promotes the development of the National Standard Reference

Data System and a system of information analysis centers dealing with the broader

aspects of the National Measurement System; provides appropriate services to ensure

that the NBS staff has optimum accessibility to the scientific information of the world,

and directs the public information activities of the Bureau. The Office consists of the

following organizational units:

Office of Standard Reference Data—Office of Technical Information and

Publications—Library—Office of International Relations.

1 Headquarters and Laboratories at Gaithersburg, Maryland, unless otherwise noted; mailing address Washington, D.C. 20234.

Part of the Center for Radiation Research.

3 Located at Boulder, Colorado 80302.
UNITED STATES DEPARTMENT OF COMMERCE

Peter G. Peterson, Secretary

NATIONAL BUREAU OF STANDARDS • Lewis M. Branscomb, Director

NBS

FREQUENCY AND TIME

BROADCAST SERVICES

RADIO STATIONS WWV, WWVH, WWVB, AND WWVL

P. P. Viezbicke, Editor

Time and Frequency Division

Institute for Basic Standards

National Bureau of Standards

Boulder, Colorado 80302

SPECIAL PUBLICATION 236, 1972 EDITION

(Supersedes NBS Special Publication 236, 1971 and previous editions)

Nat. Bur. Stand. (U.S.), Spec. Publ. 236, 14 pages (March 1972)

CODEN: XNBSAV

Issued March 1972

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402

(Order by SD Catalog No. C 13.11:236). Price 25 cents
Contents

Page

Services provided by NBS standard frequency and the stations 1

Introduction 1

1. WWV and WWVH Broadcast Services 2

1.1. Standard Radio Frequencies 2

(a) Program 2

(b) Accuracy and Stability 2

(c) Corrections 3

1.2. Standard Audio Frequencies 3

(a) Program 3

(b) Accuracy 3

1.3. Standard Musical Pitch 3

1.4. Standard Time Intervals 3

1.5. Time Signals 3

(a) Program 3

(b) Corrections 5

(c) UTI Corrections 5

1.6. OflBcial Announcements 6

(a) Propagation Forecasts 6

(b) Geophysical Alerts 6

(c) Weather Information 6

1.7. WWV WWVH Time Code 6

1.8. Station Identification 7

1.9. Radiated Power, Antennas, and Modulation 8

(a) Radiated Power 8

(b) Transmitting Antennas 8

(c) Modulation 8

2. WWVB Broadcast Services 8

(a) Program 8

(b) Accuracy and Stability 8

(c) Station Identification 8

(d) Radiated Power, Antenna, and Modulation 8

2.1. WWVB Time Code 8

(a) Code and Carrier 8

(b) Marker Generation 8

(c) Marker Order and Groups 8

(d) Information Sets 10

(e) Digital Information 10

3. WWVL Experimental Broadcasts 10

(a) Program Format 10

(b) Accuracy and Stability 10

(c) Station Identification 10

(d) Radiated Power, Antenna 10

4. How NBS Controls the Transmitted Frequencies H

5. References H

II
Services Provided by NBS Standard Frequency and Time Stations

Peter P. Viezbicke

Detailed descriptions are given of the technical services provided by the National Bureau of Standards radio stations WWV, WWVH, WWVB, and WWVL. These services are: 1. Standard

radio frequencies; 2. Standard audio frequencies; 3. Standard musical pitch; 4. Standard time

intervals; 5. Time signals; 6. UTl corrections; and 7. Official announcements. In order to provide

users with the best possible services, occasional changes in broadcasting schedules are required.

This publication shov^rs the schedules in effect on January 1, 1972. Annual revisions will be made.

Current data relating to standard frequencies and time signals are available monthly in the Time and Frequency Services Bulletin. Advance notices of changes occurring between revisions

will be sent to users of NBS broadcast services who request such notice on the basis of need.'

Key words: Broadcast of standard frequencies; high frequency; low frequency; standard

frequencies; time signals; very low frequency.

Introduction

In March 1923 the National Bureau of Standards

started transmitting standard radio frequencies on

a regularly announced schedule from radio station

WWV. The WWV transmitter, originally located

at the National Bureau of Standards, Washington,

D. C, has moved several times. From 1931 to 1966

the station was moved successively from Washington,

D. C. to Greenbelt, Maryland, and finally to Fort

Collins, Colorado, where it went on the air at 0000

hours Universal Time on December 1, 1966.

The move to Fort Collins was prompted by several

considerations: the need for wider and more uniform

coverage in the continental U.S. from a more central

location; the advantage of more precise control from

the NBS Time and Frequency Division at Boulder,

Colorado; improvement in radiation patterns obtained

by location in a less congested area; and reduction

of interference on the West Coast between time signals

from WWV and those from WWVH, Hawaii.

Original broadcasts were accurate to within a few

parts in a thousand. Their transmitted accuracy today

is on the order of a few parts in 10^^—approaching

the accuracy of the NBS frequency standard itself.

1 Inquiries concerning the Time and Frequency Services Bulletin

or the NBS broadcast service policies may be addressed to Fre- quency-Time Broadcast Services Section, Time and Frequency

, Division, NBS, Boulder, Colo. 80302.

To supplement the coverage of WWV, broadcasts

from WWVH were instituted in 1948. These play an increasingly important role in various types of

operations in the Pacific and Far East, both military

and civilian. In 1971, WWVH was moved from its former site on Maui, to its present location near Kekaha, Kauai.

WWVB began broadcasting from Boulder, Colorado in 1956, and WWVL, an experimental station,

from Sunset, Colorado in 1960. Both of these stations

have been in operation from Fort Collins, Colorado,

since July 1963. These stations, WWVB transmitting on low frequency (LF) and WWVL transmitting on

very low frequency fVLF), were designed to provide

a wide-scale distribution of the NBS standard fre- quency; WWVB also transmits time signals. They

are used to coordinate operations of the global net- works of missile and satellite stations, to assist other

government efforts which require accurate time and

frequency, to improve the uniformity of frequency

measurement on a national and international basis,

and to provide a more accurate standard of frequency, one easily available to many users for electronic re- search and development.

Thus in the 49 years since the beginning of its radio broadcasts, NBS has expanded such services so that it is making major contributions today to the nation's space and defense programs, to worldwide transportation and communications, and to a multitude of industrial operations, as well as providing convenient time service to thousands of

listeners.

1
Correspondence pertaining directly to station operations may be addressed to:

John Stanley, Engineer-Ln-Charge

NBS Radio Stations WWV/WWVB/WWVL

Route 2, Box 83-E

Fort Collins, CO 80521

Telephone (303 ) 484-2372

Charles Trembath, Engineer-in-Charge

NBS Radio Station WWVH

P. 0. Box 417

Kekaha, Kauai, HI 96752

Telephone (808) 337-5217

Visiting hours are observed at WWV, WWVB, and

WWVL every Wednesday, except holidays, from

1:00 p.m. to 4:00 p.m. Special tours may be scheduled at other times only by prior arrangement with

the Engineer-in-Charge.

1. WWV and WWVH Broadcast Services

1.1. Standard Radio Frequencies

(a) Program

WWV and WWVH broadcast nominal frequencies

and time consistent with the internationally agreed

upon time scale, Universal Coordinated Time^ (UTC).

Changes in UTC effective January 1, 1972, are dis- cussed in section 1.5(b).

WWV broadcasts on radio carrier frequencies of

2.5, 5, 10, 15, 20, and 25 MHz. WWVH broadcasts on radio carrier frequencies of 2.5, 5, 10, 15, and

20 MHz. The broadcasts on both stations are continuous, night and day.

The broadcasts of WWV may also be heard via

telephone by dialing (303) 499-7111, Boulder, Colorado. The telephone user will hear the live broadcasts

as transmitted from the station. Considering the insta-

' As noted in a resolution of Commission 31 of the International Astronomical Union, August 1970: "The terms 'GMT' and 'Z' are accepted as the general equivalents of UTC in navigation and

communication."

Table 1. Services and coordinates of the NBS broadcast stations

i

a

o

4-1

Io

IB Q

1

'Va

ai

a

V

3

S

73s<

13

o

oU

H

O

WWV 1923 V V V V V V V

WWVH 1948 V V V V V V V

WWVB 1956 V V V V

WWVL 1960 V

The coordinates of these NBS radio stations are as follows

:

WWV 40° 40' 49.0" N 105° 02' 27.0" w

WWVB 40° 40' 28.3" N 105° 02' 39.5" w

WWVL 40° 40' 51.3" N 105° 03' 00.0" w

WWVH 21° 59' 26.0" N 159° 46' 00.0" w

bilities and variable delays of propagation by tele- phone, the listener should not expect accuracy of the

telephone time signals to be better than 30 milli- seconds. This service is automatically limited to 3

minutes per call.

(b) Accuracy and Stability

Since December 1, 1957, the standard radio trans- missions from WWV and WWVH have been held as nearly constant as possible with respect to the atomic

frequency standards maintained and operated by the

National Bureau of Standards. Atomic frequency

standards have been shown to realize the ideal cesium

resonance frequency, /cs ? to within a few parts in

10'^ The present NBS frequency standard and time

scale system realizes this resonance frequency to an

uncertainty of ± 9 parts in 10^^ [1]^

The definitions for time and frequency are based on the same physical process: "The second is the

duration of 9,192,631,770 periods of the radiation

corresponding to the transition between the two

hyperfine levels of the ground state of the cesium-133

atom" as was decided in October 1967 by the XHIth

General Conference of Weights and Measures. For

frequency, the hertz is one cycle per second.

On January 1, 1960, the NBS standard was brought

into agreement with this definition as quoted above

by increasing its assigned value by 74.5 parts in 10".

Frequencies measured in terms of the NBS standard

between December 1, 1957 and January 1, 1960 need

to take the above correction into account [2].

The frequencies transmitted by WWV and WWVH

are held stable to better than ± 2 parts in 10^^ at all times. Deviations at WWV are normally less than 1

part in 10^^ from day to day. Incremental frequency

adjustments not exceeding 1 peirt in 10^^ are made at WWV as necessary. Frequency adjustments made at WWVH do not exceed 2 parts in 10^^

Changes in the propagation medium (causing

Doppler effect, diurnal shifts, etc.) result in fluctua5 Figures in brackets indicate the literature references at the end

of this publication.

2
tions in the carrier frequencies as received which may

be very much greater than the uncertainties quoted

above.

(c) Corrections

All carrier and modulation frequencies at WWV

and WWVH are derived from cesium-controlled oscillators. These frequencies, in conformity with the

UTC scale, are broadcast with no intentional offset from the nominal frequency. Previously, the fractional

frequency offset for 1960 and 1961 was -150 parts

in 10"; in 1962 and 1963, -130 parts in lO^"; in

1964 and 1965, -150 parts in 10"; and in 1966

through 1971, -300 parts in 10".

At the recommendation of the International Radio

Consultative Committee (CCIR), the frequency offset of UTC was made permanently zero effective 0000

hours UTC January 1, 1972.

Corrections to the transmitted frequency or phase

are regularly determined with respect to the NBS time

standard and are published monthly (since March

1966) in the NBS Time and Frequency Services Bulletin.

1.2 Standard Audio Frequencies

(a) Program

The hourly broadcast format of WWV and WWVH

is presented in figure 1. Standard audio frequencies

of 440 Hz, 500 Hz, and 600 Hz are broadcast on each

radio carrier frequency by the two stations. The duration of each transmitted standard tone is approximately 45 seconds. A 600-Hz tone is broadcast during

odd minutes by WWV and during even minutes by

WWVH. A 500-Hz tone is broadcast during alternate

minutes unless voice announcements or silent periods

are scheduled. The 440-Hz tone is broadcast beginning one minute after the hour at WWVH and two minutes

after the hour at WWV. The 440-Hz tone period is omitted during the first hour of the UTC day.

No audio tones or special announcements are broadcast during a semi-silent period from either station.

The periods are from 45 minutes to 50 minutes after

the hour at WWV, and from 15 minutes to 20 minutes

after the hour at WWVH.

(b) Accuracy

The audio frequencies are derived from the carrier

and have the same basic accuracy as transmitted.

Changes in the propagation medium sometimes result

in fluctuations in the audio frequencies as received.

While the 100-Hz subcarrier (sec. 1.7) is not considered one of the standard audio frequencies, the

modified IRIG-H time code which is transmitted con- tinuously from WWV and WWVH does contain this

frequency and may be used as a standard with the same accuracy as the audio frequencies.

1.3. Standard Musical Pitch

The frequency 440 Hz, for the note A above middle

C, is the standard in the music industry in many

countries and has been in the United States since

1925. The radio broadcast of this standard was com- menced by the National Bureau of Standards in 1937.

The 440-Hz tone is broadcast for approximately 45

seconds beginning 1 minute after the hour at WWVH

and 2 minutes after the hour at WWV. The tone is omitted during the zero hour of each UTC day. In addition to its application as a musical standard, the

440-Hz tone may be used to provide an hourly marker

for chart recorders or other automated devices.

1.4. Standard Time Intervals

UTC seconds pulses at precise intervals are derived

from the same frequency standard that controls the

radio carrier frequencies; i.e., they ' commence at intervals of 5,000,000 cycles of the 5-MHz carrier.

They are given by means of double-sideband amplitude-modulation on each radio carrier frequency. Each

minute, except the first of the hour, begins with an

800-millisecond tone of 1000 Hz at WWV and 1200

Hz at WWVH. The first minute of every hour begins

with an 800-millisecond tone of 1500 Hz at both sta- tions. ' The 1 -second markers are transmitted throughout

all programs of WWV and WWVH except that the

29th and 59th markers of each minute are omitted.

As noted above, the seconds marker which begins the

minute is lengthened to 800 milliseconds. All other

markers consist of a 5-millisecond pulse of 1000 Hz at WWV and 1200 Hz at WWVH, commencing at the

beginning of the second (fig. 2).

The seconds pulse spectrum is composed of Fourier

frequency components as shown in figure 2. Each

pulse is preceded by 10 milliseconds of silence and

followed by 25 milliseconds of silence. These 40-millisecond interruptions do not appreciably degrade the

intelligibility of voice announcements.

1.5. Time Signals

(a) Program

Because of the common usage of the name Greenwich Mean Time, the time announcements on WWV

and WWVH are referred to by this name (see footnote 2). More precisely, the actual reference time

scale is the Coordinated Universal Time Scale as maintained by the National Bureau of Standards,

UTC (NBS).

The 0 to 24 hour system is used starting with 0000

for midnight at longtitude zero. The first two figures

give the hour, and the last two figures give the number

of minutes past the hour when the tone returns. The

time announcement refers to the end of an announce- ment interval, i.e., to the time when the 0.8 second

long audio tone begins.

3
WWV BROADCAST

FORMAT

THE 59"> SECOND PULSE OMITTED.... BEGINNING OF EACH HOUR IDENTIFIED BY

O.a SEC LONG 1500Hz TONE (WWV a WWVH) BEGINNING OF EACH

MINUTE IDENTIFIED BY O S SEC LONG lOOOHz TONE

THE 29«h SECOND PULSE OMITTED.... BEGINNING OF EACH MINUTE IDENTIFIED BY O.e SECOND LONG l200Hi TONE

WWVH BROADCAST

FORMAT

FIGURE 1. The hourly broadcast schedules of WWV and WWVH.
FIGURE 2. Sample characteristics of time pulse broadcast from NBS radio stations WWV and WWVH.

At WWV a voice announcement of Greenwich Mean

Time is given during the last 7.5 seconds of every

minute. At 1035 GMT, for instance, the voice an- nouncement (given in English) is: "At the tone

ten hours, thirty-five minutes Greenwich Mean Time."

At WWVH a voice announcement of Greenwich

Mean Time occurs during the period 45 seconds to 52.5 seconds after the minute. It should be noted that

the voice announcement for WWVH precedes that of

WWV by 7.5 seconds. However, the tone markers

referred to in both announcements occur simultaneously, though they may not be so received due to propagation efFects.

(b) Corrections

Prior to January 1, 1972, time signals broadcast

from WWV and WWVH were kept in close agreement

with UT2 (astronomical time) by making step adjustments of 100 milliseconds as necessary.

On December 1, 1971 at 23h 59min 60.107600s

UTC (i.e., GMT), UTC(NBS) "was retarded 0.107-

600 second" to give the new UTC scale an initial difference of 10 seconds late with respect to Inter- national Atomic Time (IAT) as maintained by the

Bureau International de I'Heure (BIH) in Paris,

France.

Corrections to UTC will be made in step adjustments of exactly 1 second when the BIH determines

they are needed to keep the broadcast time signals

within ± 0.7s of astronomical time, UTl. (Note:

the corrections no longer relate to UT2.

(c) UTI Corrections

Since the new UTC rate (effective January 1, 1972)

is no longer adjusted periodically to agree with the

earth's rotation rate, the new UTC departs more

rapidly than before from earth rotation time (known

as UTl), gaining about 1 second per year. In order

to prevent this difference from exceeding 0.7 second,

step adjustments of exactly one second, to be called a leap second, will be made as necessary at the end of

the UTC month, preferably on 31 December or 30

June. Thus, when required, a leap second will be

inserted between the end of the 60th second of the

last minute of the last day of a month, and the

beginning of the next minute. This is analogous to adding an extra day (which might be called a leap

day) during a leap year. Figure 3 illustrates how

events will be dated in the vicinity of a leap second.

The BIH will announce the occurrence of leap sec- onds two months in advance.

NORMAl MINUTE

(NO LEAP SECOND ADDED)

1

i L

1 1

Dating of Event Shown;

56 58 0 2 30 June. 23''< 59'" 59.5' UTC

57 59 EVENT —I

30 June, 23^< 59"^ I July, 0''0'"

MINUTE WITH LEAP SECOND ADDED

57 59

56 58 60

Doling of Event Shown; 30 June, 23^ 59"'.60.5' UTC

EVENT -J

30 June, 23^ 59"^ > I July, 0''0'n

FIGURE 3. Illustration of how events will be dated in the

vicinity of a leap second.

The method of coding the UTl corrections uses

a system of double seconds pulses. The first through

the seventh seconds pulse, when marked by a double

pulse, will indicate a "plus" correction, and from

the ninth through the fifteenth a "minus" correction.

The eighth seconds pulse is not used. The amount

of correction in units of 0.1 second is determined by

5
counting the number of seconds pulses that are doubled. For example, if the first, second, and third

seconds pulses are doubled, the UTl correction is "plus" 0.3 second. Or if the ninth, tenth, eleventh,

twelfth, thirteenth, and fourteenth seconds pulses are doubled, the UTl correction is "minus" 0.6 second. To

obtain UTl, use the relationship

UTl - Broadcast = Correction.

That is, add the correction to the time broadcast if "plus" is transmitted, subtract if "minus" is trans- mitted. Thus, a clock keeping step with the time

signals broadcast will be early with respect to UTl

if a "minus" is broadcast. These corrections will be

revised as needed, the new value appearing for the

first time during the hour after 0000 UTC.

The UTl corrections are also encoded in the time

code transmitted continuously on a 100-Hz subcarrier

from WV and WWVH. The value of the correction

is indicated by the weight of the control bits that occur at the end of the code frame. The "plus" or "minus" indication is encoded in the first control

bit; i.e., if the bit is a binary one the correction is "plus," if it is a binary zero it is "minus." The cor- rection is to the nearest 0.1 second.

1.6. Official Announcements \

The 45-second announcement segments available

every other minute from WWV and WWVH are

offered on a subscription basis to other agencies of

the Federal Government to disseminate official and

public service information. The accuracy and content

of these announcements is the responsibility of the

originating agency—not necessarily the National Bureau of Standards.

All segments except those reserved for NBS use and the semisilent periods are available. Arrangements

for use of segments at the two stations may be made

through the Frequency-Time Broadcast Services Section, 273.02, National Bureau of Standards, Boulder,

CO 80302.

(a) Propagation Forecasts A forecast of radio propagation conditions is broadcast in voice during part of every 15th minute

of each hour from WWV. The announcements are short-term forecasts and refer to propagation along

paths in the North Atlantic area, such as Washington, D. C. to London or New York to Berlin. These

forecasts are also applicable to high latitudes provided

the appropriate time correction is made for other

latitudes. The forecasts are prepared by the Office of

Telecommunications Services Center, OT, Boulder,

Colorado.*

The broadcast consists of the statement, "The radio

propagation quality forecast at . . . (one of the follow-

* For details regarding these forecasts, write John Harris, Tele- communications Service Center, OT, Boulder, CO 80302.

ing times: 0100, 0700, 1300, or 1900 UTC) is . . .

] (one of the following adjectives: excellent, very good, | good, fair-to-good, fair, poor-to-fair, poor, very poor,

or useless). Current geomagnetic activity is . . . (one

of the following characteristics: quiet, unsettled, or disturbed) ." n

(b) Geophysical Alerts

Current geophysical alerts (Geoalerts) as declared

by the World Warning Agency of the International

Ursigram and World Days Service (lUWDS) are broadcast in voice during the 19th minute of each

hour from WWV and during the 46th minute of each

hour from WWVH. The messages are changed daily

at 0400 UTC with provisions to provide real-time

data alerts of outstanding occurring events. These

are followed by a summary of selected solar and

geophysical events in the past 24 hours. Information

concerning these forecasts are prepared by the Space

Environment Laboratory, NOAA, Boulder, Colorado."

(c) Weather Information

Weather information about major storms in the

Atlantic and Pacific areas is broadcast from WWV

and WWVH respectively.^ The brief messages are designed to tell mariners of storm threats in their areas. If there are no warnings in the designated

areas, the broadcasts will so indicate. The ocean areas involved are those for which the U.S. has warning

responsibility under international agreement. The

regular times of issue by the National Weather Service are 0500, 1100, 1600, and 2300 UTC by WWV

and 0000, 0600, 1200, and 1800 UTC by WWVH.

These broadcasts are updated effective with the next

scheduled announcement following the time of issue.

WWV broadcasts information about storms in the

western North Atlantic, and WWVH lists storms in

the eastern and central part of the North Pacific.

These broadcasts are given in voice during the 11th

and 13th minute from WWV and during the 50th and

52nd minute from WWVH.

Sample broadcasts that exemplify the type of in- formation mariners might expect to receive from

WWV, for instance, are as follows:

"North Atlantic weather, west of 35 degrees West

at 1700 GMT: Hurricane Donna, intensifying, 24

Northy 60 West, moving northwest, 20 knots, winds

75 knots; storm 65 North, 35 West, moving east, 10

knots, seas 15 feet."

1.7. WWV/WWVH Time Code

On July 1, 1971, WWV commenced broadcasting

the time code shown in figure 4. The time code is now

^ For details of these announcements, write Miss J. Virginia

Lincoln, Deputy Secretary lUWDS, NOAA, Boulder, CO 80302.

" For information regarding these broadcasts, contact George P. Cressman, Director, National Weather Service, Silver Spring, MD

20910.

6
FORMAT H, SIGNAL HOOl, IS COMPOSED OF THE FOLLOWING:

1) 1 ppm FRAME REFERENCE MARKERS R = (Po AND 1.03 SECOND "HOLE")

2) BINARY CODED DECIMAL TIME-OF-YEAR CODE WORD (23 DIGITS)

3) CONTROL FUNCTIONS (9 DIGITS) USED FOR UTi CORRECTIONS

4) 6 ppm POSITION IDENTIFIERS (P THROUGH P ) 5) 1 pps INDEX MARKERS "

^

TIME

* TIME FRAME 1 MINUTE > INDEX COUNT (1 SECOND)

0 10 20 30 40 50 0

I I I I

I

I ' I I

I

I I I '

I

' I I I [

I ' I I

I

I I I '

I

I I I I

I

I I I I

I

I I I I

I

I I I I

I

I I I I

I

' I I I

TIME IN SECONDS

-ON TIME 1 SECOND INDEX MARKER

1 SECONDp p p ^ I4. p rLJnjuuuuuuii^^

L

^7—1 .03 SECOND

R-l HOLE IN CODE

FOR 0.8 SECOND

PULSE

-MINUTES- -HOURS- DAYSPj-Pj POSITION IDENTIFIERS (0.8 SECOND DURATION)

W WEIGHTED CODE DIGIT (0.5 SECOND DURATION)

C WEIGHTED CONTROL ELEMENT (0.5 SECOND DURATION)

DURATION OF INDEX MARKERS UNWEIGHTED CODE AND CONTROL ELEMENTS = 0.2 SECONDS

UTiCORRECTION

TIME AT POINT A =

173 DAYS 21 HOURS

10 MINUTES

59.300 SECONDS

FIGURE 4. Chart of time code transmissions from NBS radio stations WWV and WWVH.

transmitted continuously by both WWV and WWVH

on a 100-Hz subcarrier. This time code provides a standardized timing base for use when scientific observations are made simultaneously at widely separated locations. It may be used, for instance, where

signals telemetered from a satellite are recorded along

with the time code; subsequent analysis of the data is then aided by having unambiguous time markers

accurate to about 10 milliseconds.

The code format being broadcast is a modified

IRIG-H time code. The code is produced at a 1-pps

rate and is carried on 100-Hz modulation.

The code contains UTC time-of-year information

in minutes, hours, and day of year. Seconds information may be obtained by counting pulses. The code is synchronous with the frequency and time signals.

The binary coded decimal (BCD) system is used.

Each minute contains seven BCD groups in this order:

two groups for minutes, two groups for hours, and

three groups for day of year. The code digit weighting

is 1-2-4-8 for each BCD group multiplied by 1, 10, or 100 as the case may be.

A complete time frame is 1 minute. The binary

groups follow the 1 minute reference marker. "Ontime" occurs at the positive-going leading edge of all pulses.

The code contains 60 markers per minute clocking

rate, 6 per minute position identification markers,

and a 1 per minute reference marker. The 100-Hz

subcarrier is synchronous with the code pulses so that

10-millisecond resolution is readily obtained.

The 6 per minute position identification markers

consist of 0.8 second pulses preceding each code

group. The 1 per minute reference marker consists

of one 0.8 second pulse followed by a 1.03 second

"hole" in the code followed by eight binary zero

pulses. The minute begins with the 1.03 second "hole"

at the beginning of the code.

A binary zero pulse consists of 20 cycles of 100-Hz

amplitude modulation, and the binary one pulse consists of 50 cycles of 100-Hz amplitude modulation.

The leading edges of the time code pulses coincide

with positive-going zero-axis-crossings of the 100-Hz

modulating frequency.

1.8. Station Identification

WWV and WWVH identify by voice every 30 minutes. The station identification voice announcements

are automatically synchronized recordings, not live broadcasts. The regular announcer for WWV is Mr.
Don Elliott of Atlanta, Georgia; the regular an- nouncer for WWVH is Mrs. Jane Barbe, also of

Atlanta.

1.9. Radiated Power, Antennas and

Modulation

(a) Radiated Power

Frequency, Radiated Power, kW

MHz wwv WWVH

2.5 2.5 5

5 10 10

10 10 10

15 10 10

20 2.5 2.5 25 2.5

(b) Transmitting Antennas

The broadcasts on 5, 10, 15, and 20 MHz from

WWVH are from phased vertical half-wave dipole

arrays. They are designed and oriented to radiate a cardioid pattern directing maximum gain in a westerly

direction. The 2.5-MHz antenna at WWVH and all antennas at WWV are half-wave vertical dipoles which

radiate omnidirectional patterns.

(c) Modulation

At WWV and WWVH, double sideband amplitude

modulation is employed with 50 percent modulation on

the steady tones, 25 percent for the IRIG-H code, 100

percent for seconds pulses, and 75 percent for voice.

2. WWVB Broadcast Services

WWVB transmits a standard radio frequency,

standard time signals, time intervals, and UTl corrections. The station is located near WWV on the same site. The coordinates of WWVB are: 40°40'28.3" N 105°02'39.5" W.

Alternating its scheduled maintenance periods with

those of experimental and intermittently operated sta- tion WWVL, it suspends operation for several hours

between 1300 UTC and 2400 UTC every other

Tuesday. Otherwise the service is continuous.

(a) Program

WWVB broadcasts a standard radio carrier fre- quency of 60 kHz with no offset. It also broadcasts

a time code consistent with the internationally co- ordinated time scale UTC(NBS).

(b) Accuracy and Stability

The frequency of WWVB is normally within its prescribed value to better than 2 parts in 10^^. Deviations from day to day are less than 1 part in

10^^. Effects of the propagation medium on received

signals are relatively minor at low frequencies (LF) ;

therefore, the accuracy of the transmitted signals may

be fully utilized by employing appropriate receiving

and averaging techniques [3, 4]

.

(c) Station Identification

WWVB identifies itself by advancing its carrier

phase 45° at 10 minutes after every hour and return- ing to normal phase at 15 minutes after the hour.

WWVB can also be identified by its unique time

code.

(d) Radiated Power, Antenna, and Modulation

The effective radiated power from WWVB is 13 kW.

The antenna is a 122-meter, toploaded vertical in- stalled over a radial ground screen. The station uses 10-dB carrier-level reduction in transmitting its time code.

2.1. WWVB Time Code

(a) Code and Carrier

On July 1, 1965, WWVB began broadcasting time

information using a level-shift carrier time code. The

code, which is binary coded decimal (BCD), is broadcast continuously and is synchronized with the

60-kHz carrier signal.

(b) Marker Generation

As shown in figure 5, the signal consists of 60

markers each minute, with one marker occurring

during each second. (Time progresses from left to

right.) Each marker is generated by reducing the

power of the carrier by 10 dB at the beginning of

the corresponding second and restoring it 0.2 second

later for an uncoded marker or binary zero, 0.5 second

later for a binary one, and 0.8 second later for a

10-second position marker or for a minute reference

marker. Several examples of binary ones are indicated by I in figure 5. The leading edge of every

negative-going pulse is on time.

(e) Marker Order and Groups

The 10-second position markers, labeled PO to P5

on the diagram, occur respectively in the 60th, 10th,

20th, 30th, 40th, and 50th seconds of each minute.^

The minute reference marker occurs in the 1st second

of the minute. Uncoded markers occur periodically in

the 5th 15th, 25th, 35th, 45th, and 55th seconds of

each minute, and also in the 11th, 12th, 21st, 22nd,

36th, 56th, 57th, 58th, and 59th seconds. Thus, every

minute contains twelve groups of five markers, each

group ending either with a position marker or an uncoded marker. The signal pulses lasting for 0.2

seconds after a position marker are shown blackened

in figure 4; the signal pulses lasting for 0.8 seconds

Effective January 1, 1972: During the minute in which a one- second step correction occurs, that minute will contain either 59 or 61 seconds.

8
-TIME- TIME FRAME I MINUTE

"(INDEX COUNT 1 SECOND)"

SIGNAL

J I L I II L

10 J I L J I I L

20 —reference time

Preference marker for minutes , ,0.2 second -binary "zero"

h-0.8 second "1r (TYPICAL)

SIGNAL liJmnri^rruiriJRMijmjimnjr

-10 dB 1 I I PI

1 I I P2

[ 40 20 10 8 4 2 1 1 20 10 8 4 2 1 MINUTES SET

TIME — t

HOyRS SEI

\

20

1

1 1 1 1 1 1 1 1 30

-1 1 1— 1 1 1 1 1 1 1 40

—1—1

, ,^.5 SECOND- BINARY "ONE"

~

\ \ (TYPICAL)

LiRFmrmjirmuimra P2| I I I P3 I 200100 80 40 20 10 8 4 2 1 /

1.0 SECOND

"(TYPICAL)

I P4|

CAYS S£I

TIME AT THIS POINT EQUALS 258 DAYS. 18 HOURS.

42 MINUTES, 35 SECONDS. TO OBTAIN THE

CORRESPONDING UTI SCALE READING.

SUBTRACT 41 MILLISECONDS.

ADD^^^ADD

UIL

RELATIONSHIP

-TIME40

I I I I J I L 50

J I L J I L 60

I jjO.8 SECOND POSITION IDENTIFIER

I r~ (TYPICAL)

LjrTTTWUTnrLjriTM»FRj P4| Ann .no I P5 I PO

, 400 100

800 200

I P5 I 80 40 20 10 8 4 2 1

UTI SET

DIFFERENCE OF. UTI FROM

CODED TIME IN MILLISECONDS

GROUP 12

MARKER

]^ IMPULSE

POSITION MARKER

AND. PULSE

PERIODIC UNCODED

MARKER AND PULSE

UNCODED MARKER

AND PULSE

UlI BINARY "ONE"

n

BINARY "ZERO"

FIRST REVISION - 6.21.65

NBS TIME CODE

FORMAT "WWVB"

1 ppS CODE

FIGURE 5. Chart of time code transmissions from NBS radio station WWVB.
after a periodically uncoded marker are shaded; other

signal pulses following uncoded markers are labeled

with a U.

With the exception of the uncoded and reference

markers specifically mentioned above, the remaining

markers in each of the groups are utilized to convey

additional information.

(d) Information Sets

Each minute the code presents time-of-year information in seconds, minutes, hours, and day of the

year and the actual milliseconds difference between

the time as broadcast and the best known estimate of

UTl. The first two BCD groups in the frame specify

the minute of the hour; the third and fourth BCD

groups make up a set which specifies the hour of the

day; the fifth, sixth, and seventh groups form a set which specifies the day of the year; a set, made up

of the ninth, tenth and eleventh BCD groups, specifies

the number of milliseconds to be added or subtracted

from the code time as broadcast in order to obtain

UTl. The twelfth group is not used.

The relationship of the UTl scale to the time as coded is indicated in the eighth group. If UTl is late with respect to the code time, a binary one, labeled SUB in figure 5, will be broadcast in the

eighth group during the 38th second of the minute.

If UTl is early with respect to the code time, binary

ones, labeled ADD, will be broadcast in the eighth

group during the 37th and 39th seconds of the minute.

(e) Digital Information

When used to convey numerical information, the

four coded markers used as digits in a BCD group

are indexed 8-4-2-1 in that order. Sometimes only the

last two or three of the coded markers in a group are needed, as in the first groups of the minutes, hours,

and days sets. In these cases, the markers are in- dexed 2-1, or 4-2-1, accordingly. The indexes of the

first group in each set which contains two groups are multiplied by 10, those of the second group of such

a set are multiplied by 1. The indexes of the first group

in each set which contains three groups are multiplied

by 100, those of the second group by 10, and those

of the third group by 1.

Example

A specific example is indicated in figure 5. The oc- currence of two binary ones in the "minutes set" indicates that the minute contemplated is the

40 + 2 = 42nd minute. Similarly, the two binary

ones in the "hours set" indicate the 10 + 8 = 18th

hour of the day, while the four binary ones in the

"days set" indicate the 200 + 40 + 10 + 8 =

258th day of the year. It is seen from the "UTl Relationship" group and the "UTl Set" that one should

subtract, from any second in this minute, 40 + 1 =

41 milliseconds to get the best estimate of UTl. For

example, the 35th UTl interval would end 41 milli- seconds later than the end of the 35th second; or, in other words, the UTl scale reading for the end

of the 35th second would be 18h 42min 34.959s since

35.000 - 0.041 = 34.959.

3. WWVL Experimental Broadcasts

WWVL broadcasts experimental programs, usually

involving multiple frequencies. The station is located

in the same building with WWVB and on the same

site with WWV. The coordinates of WWVL are: 40°40'51.3" N 105°03'00.0" W.

Alternating its scheduled maintenance periods with

those of WWVB, it suspends operation for several

hours between 1300 UTC and 2400 UTC every other

Tuesday. Otherwise the programs are continuous.

Effective 0000 hours UTC, 1 January 1972, all transmissions from WWVL will be on an intermittent

and experimental basis only. These broadcasts are planned to be curtailed within a few months thereafter. Users of this service are urged to explore

alternative solutions to their needs.

(a) Program Format

WWVL transmits only carrier frequencies with no

modulation. In accordance with the new UTC sys- tem the frequency offset used prior to January 1,

1972, was reduced to zero on that date. The trans- missions presently alternate between 20.0 kHz and

19.9 kHz on a 50 percent duty cycle with each fre- quency being broadcast for 10 seconds. The 20.0

kHz transmissions commence on the minute. The

format and frequencies used by WWVL are subject

to change to meet the requirements of the particular

experiment being conducted.

(b) Accuracy and Stability

The transmitted frequencies from WWVL are nor- mally within their prescribed values to better than

2 parts in 10^\ Deviations from day to day are less than 1 part in 10^^. Because of the excellent coverage

and phase stability in the very low frequency (VLF)

region, this mode of transmission permits the frequencies to be received with an accuracy approaching that

of signals at the transmitter itself.

(c) Station Identification

WWVL is identified only by its unique program

format.

(d) Radiated Power, Antenna

The effective radiated power from WWVL is 2 kW.

The antenna is a 122-meter, top-loaded vertical in- stalled over a radial ground screen.

10
4. How NBS Controls the Transmitted Frequencies

In figure 6 a simplified diagram of the NBS fre- quency control system [5] is shown. The entire sys- tem depends upon the basic frequency reference shown

in this diagram as the Atomic Cesium (Cs) Beam.

This standard is used to calibrate the oscillators, di- viders and clocks which generate the controlled fre- quency and the NBS time scales. Utilizing the line-10 horizontal synchronizing pulses

from a local television station, the Fort Collins master

clock is compared on a daily basis with the NBS

master clock [6]. All other clocks and time-code

generators at the Fort Collins site are then compared

with the Fort Collins master clock. Frequency cor- rections of the WWVB and WWVL quartz crystal os- cillators are based on their phase relative to the NBS

master clock.

The transmissions from WWV and WWVH are

controlled by three cesium standards located at each

site. To ensure accurate time transmission from each

station, the time-code generators are compared with

the station's master clock several times each day.

Control of the signals transmitted from WWVH is based not only upon the cesium standards, but upon

signals from WWVB as received by phase-lock re- ceivers. The cesium standards controlling the trans- mitted frequencies and time signals are continuously

compared with the received signals.

To ensure that systematic errors do not enter into

the system, the NBS time scale is compared with the

transmitting station clocks by the use of a very precise

portable clock.

5. References

[1] Glaze, D. J., Improvements in Atomic Beam Frequency

Standards at the National Bureau of Standards, IEEE

Trans, on Instr. and Meas. IM-19, No. 3, 156-160, (Aug.

1970).

[2] National Standards of Time and Frequency in the United

States, Proc. IRE IRE-48, No. 105, 1960.

[3] Allan, D. W., and J. A. Barnes, Some Statistical Properties

of LF and VLF Propagation, AGARD Conf. Proc. No. 33, Phase and Frequency Instabilities in Electromagnetic Wave

Propagation (Proc. AGARD/ EPC 13th Symp., Ankara,

Turkey, Oct. 9-12, 1967). K. Davies, Ed., Chapter 15 (Technivision Services, Slough, England, in press).

[4] Guetrot, A., L. S. Higbie J. Lavanceau, and D. W. Allan,

An Application of Statistical Smoothing Techniques on VLF Signals for Comparison of Time between USNO and

NBS, (Summary) Proc. 23rd Annual Symp. on Frequency

Cx)ntrol, Fort Monmouth, NJ, May 6-8, 1%9, pp. 251-262.

[5] Milton J. B., Standard Time and Frequency: Its Generation, Control, and Dissemination from the National Bureau

of Standards Time and Frequency Division, NBS Technical Note 379, August 1969.

[6] Tolman, J., V. Ptacek, A. Soucek and R. Stecher, Microsecond clock comparisons by means of TV synchronizing

pulses, IEEE Trans.—Instr. and Meas. IM-16, No. 3, (Sept. 1967), pp. 247-254.

11
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FIGURE 6. NBS frequency control system.
NMS Fort Collins facility showing WWV transmitter building.

WWVH transmitter building, Kekaha, Kauai, Hawaii. WWVB/WWVL transmitter building and antennas.

13
FORM NBS-114A (1.71)

U.S. DEPT. OF COMM. 1. PUBLICATION OR REPORT NO. 2. Gov't Accession

BIBLIOGRAPHIC DATA , NoSHEET NBS SP-236, 1972 ed.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

NBS Frequency and Time Broadcast Services - -Radio

Stations WWV, WWVH, WWVB, WWVL

5. Publication Date March 1972

6. Performing Organization Code

7. AUTHORCS) 8. Performing Organization

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS, Boulder Labs

DEPARTMENT OF COMMERCE

Boulder, Colorado 80302

10. Project/Task/Work Unit No. 2730121

11. Contract/Grant No.

12. Sponsoring Organization Name and Address 13. Type of Report & Period

Covered

Final

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.)

Detailed descriptions are given of the technical services provided by the National

Bureau of Standards radio stations WWV, WWVH, WWVB, and WWVL. These

services are: 1. Standard radio frequencies; 2, Standard audio frequencies;

3o Standard musical pitch; 4. Standard time intervals; 5. Time signals; 6. UTl

corrections; and 7. Official announcements. In order to provide users with the

best possible services, occasional changes in broadcasting schedules are

required. This publication shows the schedules in effect on January 1, 1972.

Annual revisions will be made. Current data relating to standard frequencies

and time signals are available monthly in the Time and Frequency Services

Bxilletin. Advance notices of changes occurring between revisions will be sent

to users of NBS broadcast services who request such notice on the basis of

need.

17, KEY WORDS (Alphabetical order, separated by semicolons)

Broadcast of standard frequencies; high frequency; low frequency; standard

frequencies; time signals; very low frequency.

18. AVAILABILITY STATEMENT

fx] UNLIMITED.

I I FOR OFFICIAL DISTRIBUTION. DO NOT RELEASE

TO NTIS.

19. SECURITY CLASS

(THIS REPORT)

UNCLASSIFIED

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

21. NO. OF PAGES

14

22. Price

25 cents

USCOMM-DC 66244-P71

U.S. DEPARTMENT OF COMMERCE

lUational Bureau of Standards

Washington, D.C. 20234

OFFICIAL BUSINESS

POSTAGE AND FEES PAID

U.S. DEPARTMENT OF COMMERCE

Penalty for Private Use. $300