U.S. DEPARTMENT OF COMMERCE NATIONAL BUREAU OF STANDARDS
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 measurement 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 Institute 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 — Mechanics — Heat — Optical Physics — Nuclear

Sciences - — 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 consists of a Center for Building Technology and the following divisions and offices: Engineering and Product Standards — Weights and Measures — Invention and Innovation — Product Evaluation Technology — Electronic Technology — Technical Analysis — Measurement Engineering — Structures, Materials, and Life Safety * — Building

Environment * — Technical Evaluation and Application * — Fire Technology.

THE INSTITUTE FOR COMPUTER SCIENCES AND TECHNOLOGY conducts research

and provides technical services designed to aid Government agencies in improving cost effec- tiveness 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 Institute consists of the following

divisions: Computer Services — Systems and Software — Computer Systems Engineering — Information 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. The Office consists of the following

organizational units:

Office of Standard Reference Data — Office of Information Activities — Office of Technical

Publications — Library — Office of International Relations.

1 Headquarters and Laboratories at Gaithersburg.

Washington, D.C. 20234.

" Part of the Center for Radiation Research.

> Located at Boulder, Colorado 80302.

* Part of the Center for Building Technology.

Maryland, unless otherwise noted; mailing address
NBS

FREQUENCY AND TIME

BROADCAST SERVICES

RADIO STATIONS WWV, WWVH, WWVB, and WWVL

Peter P. Viezbicke, Editor

Time and Frequency Division

Institute for Basic Standards

National Bureau of Standards

Boulder, Colorado 80302

U.S. DEPARTMENT OF COMMERCE, Frederick B. Dent, Secretary

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts, Direcfor

Issued March 1974
National Bureau of Standards Special Publication 236

(Supersedes NBS Special Publication 236, 1973 and previous editions)

Nat. Bur. Stand. (U.S.), Spec. Publ. 236, 19 pages (Mar. 1974)

CODEN: XNBSAV

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

(Order by SD Catalog No. C13.11:236). Price 60cents.
Contents

Page

Services provided by NBS standard frequency and time 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 2

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) Coding of UTl Corrections 5

1.6. Official Announcements 7

(a) Propagation Forecasts 7

(b) Geophysical Alerts 7

(c) Weather Information 7

1.7. WWV/WWVH Time Code 8

1.8. Station Identification 9

1.9. Radiated Power, Antennas and Modulation 9

(a) Radiated Power 9

(b) Transmitting Antennas 9

(c) Modulation 9

2. WWVB Broadcast Services 9

(a) Program 9

(b) Accuracy and Stability 10

(c) Station Identification 10

(d) Radiated Power, Antenna and Coverage 10

2.1. WWVB Time Code 10

(a) Code and Carrier 10

(b) Marker Generation 10

(c) Marker Order and Groups 11

(d) Information Sets 11

(e) Digital Information 11

3. WWVL Experimental Broadcasts 12

4. How NBS Controls the Transmitted Frequencies 12

5. References 12

III

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 (NBS) 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 shows the schedules in effect on January 1, 1974. 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 notice of changes occurring between

levisions 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 fre- quencies: time signals; very low frequency.

Introduction

In March 1923 NBS started transmitting standard

radio frequencies on a regularly announced schedule

from radio station WWV. The WWV transmitter, or- iginally located at NBS. Washington, D.C., has moved

several times. Between 1931 and 1967 the station was moved successively lo College Park. Beltsville, then

to Creenbelt. Maryland, and finally to Fort Collins,

Colorado, where it went on the air at 0000 hours

Lniversal 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; and improvement in radiation patterns obtained by location in a less congested area. Original broadcast frequencies were accurate to within a few parts in a thousand. Their transmitted ac- curacy today is on the order of a part in 10^-—ap- proaching the accuracy of the NBS frequency standard

itself. To supplement the coverage of WWV, broadcasts

from WWVH, Hawaii, were instituted in 1918. These

play an increasingly important role in various types

of operations, both military and civilian, in the Pacific and Far East. 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 located at Fort Collins, Colorado, since July, 1963.

Operations from WWVL were curtailed on July 1. 1972, and WWVL now broadcasts very low frequency

il-nquiries concerning the Time and Frequency Services Bulletin or the NBS broadcast service policies may be addressed to trequencyTime Broadcast Services Section, Time and Frequency Division,

NBS, Boulder, CO 80302.

(VLF) experimental programs only on an intermittent

basis contingent upon need and funds. WWVB, trans- mitting on low frequency (LF), provides widespread

distribution of the NBS frequency and time scale. The WWVB broadcasts are used to coordinate operations of continental networks of missile and satellite stations and to provide a highly accurate standard of

frequency that is readily available to many users for

electronic research and development. WWVB serves

as a national time and frequency reference for many

U.S. electric utilities and as a timing reference by

government contractor groups for a large number of

sensing stations which monitor seismological events. Thus, in the 51 years since the beginning of its radio

broadcasts, NBS has expanded these services so that

they are making major contributions today to the

nation's space and defense programs, to world-wide

transportation and communications, and to a multitude

of industrial oi)erations, as well as providing convenient

time services to thousands of listeners.

Visiting hours are observed at WWV, WWVB, and

WWVL every Wednesday, except holidays, from 1:00

to 4 :00 p.m. Special tours may be scheduled at other

times only by prior arrangement with the Engineerin-Charge.

Correspondence pertaining directly to station operations may be addressed to:

John Stanley. Engineer-in-Charge

NBS Radio Stations WWV/WWVB/WWVL

2000 East County Road 58

Fort Collins, CO 80521

Telephone (303) -181-2372

Charles Trembath, Engineer-in-Charge

NBS Radio Station WWVH

P.O. Box 417

Kekaha, Kauai, HI 96752

Telephone (808) 335-1361

1
1. WWV and WWVH Broadcast Services

1.1. Standard Radio Frequencies

(a) Program

Both WWV and WWVH transmit frequencies and

time coordinated through the Bureau International de

r Heure (BIHj, Paris, France, in accord with international agreements. Transmissions are based upon the

international time scale. Coordinated Universal Time

(UTC).

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 of both stations are continuous, day

and night.

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

telephone time signals to be better than 30 milliseconds. This service is automatically limited to 3 minutes

per call. Similar time-of-day broadcasts from WWVH can be

heard by dialing (808) 335-4363 on the Island of

Kauai.

Table 1. Services and coordinates of the NBS broad

cast stations.

">

kH

1/3

cr

v

'G3

<u3

cr

a;

4->c

C

ation adio

1

udio

usical

ime

Ii

ime S u

1—

t

1^ Q < b

WWV 1923 i>

WWVH 1918 1^ ]/* i>

WWVB 1956 t>

WWVL 1960

The coordinates of these NBS rad io 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

(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 NBS.

Relative to the primary frequency standard of NBS,

there are very small intentional offsets for coordination purposes, which may be of the order of one part

in 10^-. Up-to-date information on these small offsets can be obtained from the monthly Time and Frequency

Services Bulletin.

Atomic frequency standards have been shown to |)rovide the defined ideal cesium frequency to within

a few parts in 10'''. For example, the present NBS

frequency standard, NBS-5, and time scale system provides this frequency to an uncertainty of about 2 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 de- cided in October 1967 by the Xlllth General Confer- ence 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^". Frequency measurements in terms of the NBS standard between December 1, 1957 and January 1, 1960

need to take the above correction into account [2].

All carrier and modulation frequencies at WWV and

WWVH are derived from cesium-controlled oscillators

and are accurate to within ±1 part in 10". Deviations are normally less than 1 part in 10'- from day

to day.

Changes in the propagation medium (causing Doppler shifts, diurnal shifts, etc.) result in fluctuations in

the carrier frequencies as received which may be very

much greater than the uncertainties quoted above.

(c) Corrections

In conformity with the UTC scale, the carrier and

modulation frequencies of WWV and WWVH are no

longer offset significantly from nominal values. At the

recommendation of the International Radio Consultative Committee (CCIR), the frequency offset of UTC

was made permanently zero relative to International

Atomic Time (TAI) effective 0000 hours UTC January 1, 1972. Previously, the fractional frequency off- set was —150 parts in 10'" during 1960 and 1961;

—130 parts in 10'" during 1962 and 1963; —150

parts in 10'" during 1964 and 1965; and —300 parts

in 10'" from 1966 through 1971.

- Figures in brackets indicate the literature references at the end of

this publication.

2
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 aUernate

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 con- sidered one of the standard audio frequencies, the

modified IRIG-H time code transmitted continuously

from WWV and WWVH does contain this frequency

and may be used as a standard with the same accuracy

as the audio and radio frequencies.

1.3. Standard Musical Pitch

The frequency 4 10 Hz for the note A above middle

C, is the standard of 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 15

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

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. Every 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 stations.

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 in- terruptions do not appreciably degrade the intelligibility of voice announcements.

1.5. Time Signals

(a) Program

Effective 1 January 1974, WWV and WWVH began

broadcasting voice announcements of Coordinated Universal Time (UTC) in lieu of Greenwich Mean Time

(GMT)

More precisely, the actual reference time scale is the Coordinated Universal Time Scale maintained by

the National Bureau of Standards. UTC(NBS). The

UTC(NBSl scale includes very small frequency offsets relative to the NBS primary frequency standard for

coordination purposes as mentioned in section 1.1. (b).

The 0 to 21 hour system is used starting with 0000

for midnight at the Greenwich Meridian (longitude

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 announcement interval, i.e., to the time when the next 80()-millisecond tone begins

after the announcement.

Standard time zones are established at intervals of

15° longitude east and west of the zero meridian.

Local standard time differs from UTC by an integral

number of hours. For example, as shown in figure 1, Eastern Standard Time (EST) is obtained by subtracting 5 hours from UTC or the time broadcast. Conversely, UTC is obtained from EST by adding 5 hours.

At WWV a voice announcement of the time is given

during the 7.5 seconds immediately preceding the

minute. Just before 1035 UTC, for instance, the voice

announcement given is: "At the tone—ten hours, thir- ty-five minutes Coordinated Universal Time."

At WWVH a voice announcement of the time is given at 15 seconds preceding the minute. It should

be noted that the voice announcement for WWVH pre- cedes that of WWV by about 7.5 seconds. However, the

tone markers referred to in both announcements are

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

communication."

3
WWV BROADCAST FORMAT

VIA TELEPHONE: (303) 499-7111

(NOT A TOLL-FREE NUMBER)

NO AUDIO TONE

STATION 10 440 Hz 1-HOUR MARK

NBS RESERVED

STATION ID 30 MINUTES

STORM INFORMATION

PROPAGATION

FORECASTS

GEO ALERTS

U S DEPARTMENT OF COMMERCE

National Bureau of Standards

• BEGINNING OF EACH HOUR IS lOENTIFIED BY

0 8 SEC0N0 LONG, IBOO-Hz TONE • BEGINNING OF EACH MINUTE IS IDENTIFIED BY

0 8-SECOND LONu, lOOO-Hz TONE • THE 29th & 59th SECOND PULSE OF EACH MINUTE IS OMITTED

WWVH BROADCAST FORMAT VIA TELEPHONE (808) 335-4363 (NOT A TOLL-FREE NUMBER)

STATION ID MINUTES 440 Hz 1-HOUR MARK

NBS RESERVED

STORM INFORMATION

GEO ALERTS

45>

1/74

• BEGINNING OF EACH HOUR IS IDENTIFIED BY

0 8 SEC0N0 LONG, 150Q Hz TONE • BEGINNING OF EACH MINUTE IS IDENTIFIED BY

0 8 SECOND LONG, 1200-Hz TONE

STATION ID • THE 29th & 59th SECOND PULSE OF EACH MINUTE IS OMITTED

FIGURE 1. The hourly hraadrast schedules of II H V and K W VH.

4
1.0

9

5

0.5

-0.3

y / -/- \

\ vhI

1 »

1 —1

I1

I

1

1

1

r

1 _j 1

1

1

1

I

; \ /k \ /

r

1 —

r

t —1

!

/

t

\ / \

\

/ v

it

1 \ i \

\

J 1

1

' — f

1

\

fJ /

SCO 1000 FREQUENCY, CPS

WWV AMD WWVH SECONDS PULSES

THE SPECTRA ftRE COMPOSED OF DISCRETE FREOUENa COMPONENTS

AT INTERVALS OF 1.0 CPS, THE COMPONENTS AT THE SPECTRAL MAXIMA HAVE AMPLITUDES OF 0.005 VOLT FOR A PULSE AMPLITUDE OF 1.0 VOLT . THE WWV PULSE CONSISTS OF FIVE CYCLES OF

1000 CPS. THE WWVH PULSE CONSISTS OF SIX CYCLES OF 1200 CPS.

TONE

0.010

SEC.

0.005

SEC.

0.025

SEC. TONE

WWV

1500 2000

WWVH

FIGURE 2. Sample characteristics of time pulse hroadcast from NBS radio stations WWV and WWVH.

transmitted simultaneously. thouHh they may not be

received so because of 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 31, 1971 at 23 h 59m 60.107600s UTC. the UTC

(NBS) scale was retarded 0.107600 second to give it an initial difference of exactly 10 seconds late with

respect to the International Atomic Time (TAIl scale as maintained by BIH.

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

is no longer adjusted periodically to agree with the

earth's rotation rate, UTC departs more rapidly than

before from earth rotation time (known as UTl).

gaining about 1 second per year. Corrections to UTC

are now made in step adjustments of exactly 1 second

(called a leap second) as directed by BIH. The

leap second adjustments ensure that UTC signals as broadcast will never differ from UTl by more than

about ±0.7 second. (,\ote: the corrections no longer

relate to UT2.) BIH announces the occurrence of a leap second two months in advance.

The leap second adjustments are made as necessary

at the end of the LTC month, preferably on 31 December or 30 June. Thus, when required, a leap sec- ond is 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 could be called a leap

day) during a leap year. Figure 4 illustrates how

events are dated in the vicinity of a leap second.

A positive leaj) second was inserted in the trans- missions of all NBS broadcast stations at the end of

' During the minute in which a one-second step correction occurs, that minute will contain either 59 or 61 seconds depending on whether the correction is negative or positive.

June 1972. December 1972 and December 1973, as announced by BIH. As a result, during 1974, UTC will

differ from TAI by exactly 13 seconds.

(c) Coding of UTl Corrections

To satisfy time signal users who need to date events on the UTl time scale to better than ± 0.7 seconds,

coded corrections are provided in the broadcast for- mats giving UTl-UTC values to a resolution of 0.1

seconds.

The method of coding UTl corrections uses a system

of double seconds pulses. The first through the seventh

seconds pulses, when doubled, indicate a ''plus" cor- rection, and from the ninth through the fifteenth a "minus" correction. The eighth seconds pulse is not

NORMA! MINUTE

(NO LEAP SECOND ADDED)

1

56 58 () 2 57 59 EVENT -

30 June, 23*^59'" -

Dating of Event Shown:

30 June, 23^" 59"^ 59.5^ UTC

I July, 0^ 0"i

M/NUTE WITH lEAP SECOND ADDED

t V

1 57 59 0 1 56 58 60

EVENT

30 June, 23^ 59"i -

Dating of Event Shown:

30 June, 23^ 59'^60.5^ UTC

<— I July, 0" 0'

FIGURE 3. Illustration of how events are dated in the vicinity

of a leap second.

5
I

I

O

CO O

(O OOOOOO ^ dl (M 4- (D

O O OOOOOO

FIGURE 4. Standard Time Zones of the World.

6
used. The amount of correction in units of 0.1 second

is determined by counting the number of seconds

pulses that are doubled. For example, if the first, sec- ond, 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 algebraic relationship.

UTl = Broadcast + Correction

That is, add the numerical correction to the time

broadcast if "plus" is transmitted. 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.

UTl corrections are also encoded in the time code

(sec. 1.7) transmitted continuously on a 100-Hz subcarrier from WWV and WWVH. The value of the cor- rection is indicated by the weight of the control functions that occur at the end of the code frame. The

"plus and minus" indication is encoded in the first control function. If control function ^tl is a binary

one, the correction is positive; if it is a binary zero, the

correction is negative. The correction is expressed to the nearest 0.1 second.

1.6. Official Announcements

The 45-second announcement segments available

every other minute from WWV and WWVH are of- fered 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 NBS.

All segments except those reserved for NBS use and the semi-silent 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 from WWV at 14 minutes after every

hour. 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 pre- pared by the Telecommunications Services Center, OT.

Boulder, Colorado.^

The broadcast consists of the statement, "The radio

For details regarding these forecasts, write J. P. Murray OT'ITS.

Boulder, CO 80302.

propagation quality forecast at . . . (one of the fol- lowing 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) ." The propogation forecast announcements are repeated

in synoptic form comprised of a phonetic and a nu- meral. The phonetic (Whiskey, Uniform, or November) identifies the radio quality at the time the forecast

is made. The numeral indicates on a scale of 1 to 9

the radio propagation quality expected during the six- hour period after the forecast is issued. The meaning

of the phonetics and numerals are:

Phonetic Meaning

Whiskey disturbed

Uniform unsettled

November normal

Numeral Meaning

One useless

Two very poor

Three poor

Four poor-to-fair

Five fair

Six fair-to-good

Seven good

Eight very good

Nine excellent

If, for example, propagation conditions are normal

and expected to be good during the next six hours,

the coded forecast announcement would be "November

^even.

(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 from WWV at 18 minutes after

each hour and from WWVH at 45 minutes after each

hour. The messages are changed daily at 0400 UTC

with ])rovisions to provide real-time data alerts of

outstanding occurring events. These are followed by

a summary of selected solar and geophysical events

during the previous 24 hours. Messages 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

' For details of these announcements, write R. B. Doeker, Chief,

Space Environment Services Center, NOAA, Boulder, CO 80302.

7
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.

1700, and 2300 UTC for WWV and 0000, 0600. 1200.

and 1800 UTC for WWVH. These broadcasts are up- dated effective with the next scheduled announcement

following the time of issue. WWV broadcasts information about storms in the

western North Atlantic and eastern North Pacific,

whereas WWVH lists storms in the eastern and central

l^arts of the North Pacific. These broadcasts are given

in voice from WWV at 8. 10, and 12 minutes after

each hour and from WWVH at 17. -19 and 51 minutes

after each hour.

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 West at 1700

UTC: Hurricane Donna, intensifying, 21 North. 60

West, moving northwest. 20 knots, winds 75 knots;

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

20910.

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

Storm. 65 North. 35 West, moving east. 10 knots,

winds 50 knots, seas 15 feet."

1.7. WWV/WWVH Time Code

On July 1, 1971. WW\ commenced broadcasting the

time code shown in figure 5. The time code is now

transmitted continuously by both WWV and WWVH

on a 100-Hz subcarricr. 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 ha\ ing unambiguous time markers accurate

to about 10 milliseconds.

The code format being broadcast is a modified

lRI(i-H time code. The code is ])roduced at a 1-pps

rate and is carried on 100-Hz modulation. The 100-Hz

subcarrier is synchronous with the code pulses so

that lO-miliisecond resolution is readilv obtained.

The code contains UTC time-of-year information in minutes, hours, and day of year. Coded time-of-dav

information refers to time at the beginning of the

frame. Seconds information mav be obtained by count- ing pulses.

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, ETC.

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 I I

I

I I I I

TIME IN SECONDS

ON TIME POINT A 1 SECOND INDEX MARKER

1 SECONDw-H h- miLJuuuuuumjuuuu^^

L

^^1 .03 SECOND

R-l HOLE IN CODE

FOR 0.8 SECOND

PULSE

— <N J •MINUTES- -HOURS- -DAYS- UTiCORRbCTION

UTC AT POINT A = 173 DAYS 21 HOURS

10 MINUTES

UTI AT POINT A = 173 DAYS 21 HOURS

10 MINUTES

0.3 SECONDS

Pj-Pj POSITION IDENTIFIERS (0.8 SECOND DURATION)

W WEIGHTED CODE DIGIT (0.5 SECOND DURATION)

C WEIGHTED CONTROL ELEMENT (0.5 SECOND DURATION) CONTROL FUNCTION #6 |b|nary ZERO^DURING ^STANDARD '^T^E

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

1/74

FIGURE 5. Chart of time code transmissions from NBS radio stations WWV and WWVH
The hinaiy coded deeimal (BCD) system is used.

Each minute eontains seven BCD grou])s in this order:

two groups for minutes, two groups for hours, and

three groups for day of year. The code digit weighting

is 1-2-1-8 for each BCD grouj) multipHed hy 1, 10. or 100 as (lie ease mav he. A complete time frame is

1 minute. The liinary groups follow the 1-minute refer- ence marker.

In the standard IHIG-H format, "on-time" occurs at the leading edge of all pulses. A binary zero pulse

comprises 20 cycle.- of 1()0-Hz am|)litude modulation:

a hinarv one pulse com|)rises 50 cycles of lOO-Hz amplitude iiiodulation. Because of the 10-millisecond hole

that accompanies each seconds marker in the WWV/

WWVH format, however, the leading .'^O-millisecond

portion of each marker in the WWV/WWVH time

code is deleted. Vhc leading edge of each pulse coincides with a positi\ e-going zero-axis crossing of the

100 Hz Uiodulaling frequency.

Based upon a clocking rate of 60 markers per minute, the code contains six position identification markers |)er minute and a minute reference marker. Each

6-per-minule position identification marker consists of an 0.8-second pulse preceding a code group. The 1- per-minute relerenc marker consists of a 0.8-second

|)ulse followed hy a l.().')-second hole in the code and

eight hinarv zero |)ulses in succession. The minute

begins with the 1 ,0:-)-second hole preceding the first binary zero. UTl corrections lo the nearest 0.1 second are en- coded \ia control function ])ulses during the final ten seconds of the frame Control function which oc- curs as the 50th second pulse, discloses the sense of the

correction. Control function rf 1 is a binary zero when

the I Tl correction is negali\c and a binary one when

the corrections is positi\e. Control function ir7, i^8.

and #9. which occur as the 56th. 57th. and 58th sec- ond pulses, identifv the magnitude of the UTl correction.

Control function ir6. which occurs a> the 55th sec- ond pulse, is programmed as a binary one throughout

those weeks when Daylight Saving Time is in effect and as binary zero when Standard Time is in effect. The setting of this function is changed at 0000 UTC

on the date of change as specified by Congress.

Throughout the 1 .S. mainland this schedule allows sev- eral hours for the function to be received before the

change becomes effectixe locallv. i.e., at 2:00 AM. Thus

control function :#6 provides a feature through which

clocks or digital recorders operating on local time can

be programmed to make an automatic one-hour adjustment in changing from Daylight Saving Time to Staiulard Time and vice versa.

1.8. Station Identification

WVC V 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, Geogia; the regular announcer

for WWVH is Mrs. Jane Barbe. also of Atlanta.

1.9. Radiated Power, Antennas and Modulation

(a) Rarliated Power

Erecjuency. 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 ar- rays. They are designed and oriented to radiate a car- dioid |)attern directing maximum gain in a westerly di- rection. The 2.5 MHz antenna at WWVH and all an- tennas at WWV are half-wave vertical dipoles which

rarliate omnidirectional patterns.

(c) Modulation

At WWV and WWVH, double sideband amplitude

modulation is employed with 50 |)ercent modulation on

the steady tones, 25 |)ercent for the IRKi-H code, 100

percent for seconds pulses, and 75 percent for voice.

2. WWVB Broadcast Services

WWVB transmits continuously a standard radio fre- quency, standard time signals, time intervals, and UTl

corrections. The station is located near WWV on the same site. The coordinates of WWVB are

40° 10' 28..S" N 105° 02' .39.5" W

(a) Program

WWVB broadcasts a standard radio carrier frequencv of 60 kHz with no offset. It also broadcasts a time

code consistent with the internationally coordinated

time scale I TC(NBS).

9
(b) Accuracy and Stability 2.1. WWVB Time Code

The frequency of WWVB is normally within its prescribed value to better than 1 part in 10'\ Deviations from day to day are less than 5 parts in 10^-.

Effects of the |)ro|)agation 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 Coverage

The effective radiated power from WWVB is 13 kW.

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

field intensity contours are shown in figure 6.

(a) Code and Carrier

On July 1. 1965. WWVB began broadcasting time

information using a carrier-level-shift time code. The

code, which is binary coded decimal (BCD), is broadcast continuously and is synchronized with the 60-kHz

carrier signal. Features of the WWVB time code are shown in figure 7.

(b) Marker Generation

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

In 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 a 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. The leading edge of every negativegoing i)ulse is on time.

10
(c) Marker Order and Groups

The 10-second position markers, labeled P,, through

P-, in figure 7, occur respectively as the 59th, 9th, 19th,

29th, 39th, and t9th second pulses of each minute.

The minute reference marker begins at zero seconds.

Uncoded markers occur periodically as the Ith, 1 1th. 24th, 34th, 44th, and 5 ith seconds pulses and also as the 10th, 11th, 20th, 21st, 35th, 55th, 56th. 57th, and

58t'h seconds pulses of each minute. Thus every minute

contains twelve groups of five rriarkers, each group

ending either with a |)osition ma.ker or an uncoded

marker.

(d) Information Sets

Once every minute the code presents complete 1 TC

(NBSl time-of-year information in minutes, hours, and

day of the year as well as the estimated difference between I TC and I Tl. Coded time-of-day information

refers to time at the beginning of the frame. Seconds

information can be obtained by counting pulses.

The first two groups in the frame specify the minute

of the hour. The third and fourth groups comprise a set which sjjecifies 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 grou|)s specifies the number of milliseconds

that must be added to or subtracted from the time as broadcast in order to obtain UTl. The twelfth group is not used.

The |)ositive or negative relationship of the L Tl

scale with respect to I TC is indicated by the eighth

group. If UTl is late with respect to UTC, a binary one (labeled SUB in fig. 7) will be broadcast in the

eighth group as the 37th second pulse of the minute.

If I Tl is early with respect to the code time, binary

ones (labeled ADD) will be broadcast in the eighth

group as the 36th and 3oth second pulses 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 8-1-2-1 in that order. Sometimes only the

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

days sets. In these cases, the markers are indexed 2-1. or 1-2-1. accordingly. The indices of the first group in

each set which contains two groups are multiplied by

10. those of the second grou|) of such a set are multi-

|)lit'd by 1. The indices 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 sjiecific example is indicated in figure 7. The oc- currence of two binary ones in the "minutes set" in- dicates that the minute contemplated is the 10 +2 =

12nd minute. Similarly, the two binary ones in the

"hours set" indicate the 10 + B = 18th hour of the

day, while the four binary ones in the "davs set" in- dicate the 200 + 40 + iO + 8 = 258th dav of the

TIME FRAME 1 MINUTE

(INDEX COUNT 1 SECOND)

10 20 30

I I I I I I I I I I I I I I I I I I 1 I I

40 • 50

I I I I I I I I I I I 'I I I Ill

ON TIME POINT A

Ps

-| [- 0.8 SECOND -|[-0. 2 SECOND ^"j^ ^Uj- —{ |^ 0 . 5 SECOND 0 . 8 SECOND -| fp

iJUinmjTFmriJiiixm^^

MINUTES- HOURS DAYS

O CO o

«r tn<c •-UT,-

RELATIONSHIP

UT, SET1 PPM FRAME REFERENCE MARKERS

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

CONTROL FUNCTIONS (15 DIGITS) USED FOR UT, CORRECTIONS

6 PPM POSITION IDENTIFIER MARKERS AND PULSES (Po THRU Ps)

(REDUCED CARRIER 0.8 SECOND DURATION PLUS 0.2 SECOND DURATION PULSE)

W - WEIGHTED CODE DIGIT (CARRIER RESTORED IN 0.5 SECOND - BINARY ONE)

U - UNWEIGHTED CODE DIGIT (CARRIER RESTORED IN 0.2 SECOND - BINARY ZERO)

UTC AT POINT A 258 DAYS

18 HOURS

42 MINUTES

UTl AT POINT A 258 DAYS

18 HOURS

41 MINUTES

59.3 SECONDS

FIGURE 7. Chart of time code transmissions from NBS radio stations ff'WVB.

11
year. Il is seen fiom the "L Tl Relation; liip" group

and the "UTl Set" that one should subtract, from any

second in this minute. AOO + 200+ 100 = 700 milli- seronds to get an estimate of LTl.

3. WWVL Experimental Broadcasts

WWVL broadcasts experimental |)rograms. usually

invoh ing multiple frequencies. The station is located in the same building with WWVB and on the same site with WWV. The coordinates of WWVL are:

-10° 40' 51.3" N 105° 03' 00.0" W.

Effective Oh UTC, 1 July 1972. regularly scheduled

transmissions for WWVL were discontinued. Contingent upon need and a\ ailability of funds this station now broadcasts experimental programs on an intermittent basis only. Transmissions can be made available on a subscription basis to civil organizations as well as agencies of the Federal goverinrient. Arrangements

for use of WWVL should be made through the Fre- quencv-Time Broadcasts Services Section, 273.02. National' Bureau of Standards, Boulder. CO 80302.

4. How NBS Controls the Transmitted Frequencies

A simplified diagram of the XBS frequency control

system [5] is shown in figure 8. The entire system depends ui)on the basic frequency reference shown in

this diagram as the NBS Primary Frequency Standard.

This standard, a laboratorv cesium beam device, is used

to calibrate the oscillators, dividers and clocks which

generate the controlled frequency and the NBS time

scales. Ltilizing the linc-l() horizontal synchronizing pulses

from a local telc\ision station, the Fort Collins master

clock is compared on a daily basis \\ith the NBS atomic time scale system, which provides the I TC (NBS)

time scale [6]. All other clocks and time-code generators at the Fort Collins site are then compared with

the Fort Collins master clock. Frequency corrections

of the WWVB and WWVL quartz crystal oscillators are based on their phase relative to the ITC(NBS)

time scale. The transmissions from WWV and W W VH are controlled by three commercial cesium standards located

at each site. To ensure accurate time transmission

from each station, the time-code generators are com-

])ared with the station s master clock several times

each day.

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

signals from WW Vf» as recei\ed 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 occasionally compared with the transmitting station clocks by the use

of a very precise portable clock.

References

[1] Glaze. D. J., Hellwig, H., Jaivis, S., Jr., Wainwright, A. E., and Allan, D. W., Recent Progress on the NBS Primary

Frequency Standard. 27th Annual Frequency Synip., Ft. Monmouth, NJ, (June 12-14, 1973). pp. 347-356.

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

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

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

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

Wave Propagation (Proc. AGARD/ EWP 13th Symp.,

Ankara, Turkey. Oct. 9-12, 1967). K. Davies Ed., Chapter

15 (Technivision Services, Slough, England, 1970).

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

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

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

Control. Forth Monmouth, NJ, (May 6-8, 1969). p. 248.

[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, (Aug. 1969).

[6] Tolman, J., Ptacek, V., Soucek, A., and Stechcr, R., Microsecond Clock Comparisons by Means of TV Synchronizing

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

12
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FIGURE 8. frequency control system.

13
WWVH transmitter building, Kekaha, Kauai, Hawaii. WWVB/WWVL transmitter building and antennas.
NBS-114A (REV. 7-73)

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR RICI^ORT NO.

NBS SP-236, 1974 ed.

2, Ctov 't Accession

No.

3, Rccipicnt*s Acccs.sion No

4. TITLE AND SUBTITLE

NBS Frequency and Time Broadcast Services--Radio

Stations WWV, WWVH, WWVB, WWVL

5, Publication Date March 1974

6. Performing Organization C-ode

7. AUTHOR{S)

p. p. Viezbicke, Editor

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS, Boulder Labs.

DEPARTMENT OF COMMERCE

Boulder, CO 80302

10. Projeet/Task/Work Unit No. 2730121

11. (Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Same as 9.

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;

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 shows the schedules in effect on January 1, 1974.

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.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons

)

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

frequencies; time signals; very low frequency.

18. AVAILABILITY [X" Unlimited

1

' For Official Distribution. Do Not Release to NTIS

[5Cl Order From Sup. of Doc, U.S. Government Printing Office

Washington, D.C. 20402. SD Cat. No. C13 ]] •? "^fi

1 1 Order From National Technical Information Service (NTIS)

Springfield, Virginia 22I5I

19. SECURITY CLASS

(THIS REPORT)

UNCL ASSIFIED

21. NO. OF PAGES

19

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

22. Price

6o<^

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