A UNITED STATES DEPARTMENT OF COMMERCE

PUBLICATION

NBS SPECIAL PUBLICATION 236

1973 EDITION

NBS FREQUENCY AND TIME

BROADCAST SERVICES

RADIO STATIONS

WWV, WWVH, WWVB, WWVL

ANNIV

WWVH &

ATOMIC CLOCK

WWV
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 — Mechanics — Heat — 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 lead- ing to improved methods of measurement, standards, and data on the projjerties 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 pro- mote 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 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—Building Standards and Code Services*—Housing Technology^—Federal Building Technology^—Structures, Materials and Life Safety*—Building Environment*—Technical Evaluation and

Application*—Fire Technology.

THE INSTITUTE 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 Gaithersbiirg, Maryland, unless otherwise noted; mailing address Washington, D.C. 202;i4. Part of the Center for Radiation Research.

3 Located at Boulder, Colorado 80302.

* Part of the Center for Building Technolog.v.
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, Director

Issued May 1973
National Bureau of Standards Special Publication 236

(Supersedes NBS Special Publication 236, 1972 and previous editions)

Nat. Bur. Stand. (U.S.), Spec. Publ. 236, 19 pages (May 1973)

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 $0.45 domestic postpaid or $0.35 G.P.O. Bookstore.
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 6

1.6. Official Announcements 6

(a) Propagation Forecasts 6

(b) Geophysical Alerts 6

(c) Weather Information 7

(d) ATM Skylab Messages 7

1.7. WWV/WWVH Time Code 8

1.8. Station Identification 8

1.9. Radiated Power, Antennas and Modulation 8

(a) Radiated Power 8

(b) Transmitting Antennas 8

(c) Modulation 8

2. WWVB Broadcast Services 9

(a) Program 9

(b) Accvu-acy and Stability 9

(c) Station Identification 9

(d) Radiated Power, Antenna and Coverage 9

2.1. WWVB Time Code 10

(a) Code and Carrier 10

(b) Marker Generation 10

(c) Marker Order and Groups 10

(d) Information Sets 10

(e) Digital Information 11

3. WWVL Experimental Broadcasts 11

(a) Program Format 11

(b) Accuracy and Stability 11

(c) Station Identification 11

(d) Radiated Power, Antenna 11

4. How NBS Controls the Transmitted Frequencies 11

5. References 13

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, 1973. 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 revisions will be sent to users of NBS broadcast services who request

such notice on the basis of need.i

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

;

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,

originally located at NBS, Washington, D.C., has

moved several times. Between 1931 and 1967 the

station was moved successively to College Park,

to Beltsville, 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; 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

accuracy today is on the order of a part in 10'^ —

approaching the accuracy of the NBS frequency

standard itself. To supplement the coverage of WWV, broadcasts

from WWVH, Hawaii, were instituted in 1948.

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 (VLF) experimental

programs only on an intermittent basis contingent

'inquiries concerning the Time and Frequency Services Bulletin or the NBS broadcast

service policies may be addressed to Frequency-Time Broadcast Services Section, Time

and Frequency Division, NBS, Boulder, CO 80302.

upon need and fimds. WWVB, transmitting 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 acexu-ate 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 50 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 operations, as well as providing convenient time services to thousands of

listeners.

Visiting hoiu-s 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.

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) 484-2372

Charles Trembath, Engineer-in-Charge

NBS Radio Station WWVH

P.O. Box 417

Kekaha, Kauai, HI 96752

Telephone (808) 335-4217

I
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 I'Heure (BIH), Paris, France, in accord with

international agreements. Transmissions are based

upon the international time scale, Universal Coordinated 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 (3031 499-7111, Boulder,

Colorado. TTie telephone user will hear the live

broadcasts as transmitted from the station. Considering the instabilities and variable delays of

propagation by telephone, the listener should not

expect accxu-acy of the telephone time signals to be

better than 30 milliseconds. This service is automatically limited to 3 minutes per call.

Table 1. Services and coordinates of the NBS broadcast stations

a

.S

cs

0)u

hi9)

Si

CS Q

'SC

s

cr

<vu

cs

09 .2

'E3c

s

cru

o

eso

CO3

css

bp

hi (r>

B

H

cnC

o

4-* u

<u

bloU

c

o

s

s<

WWV 1923 1^ I/'

WWVH 1948

WWVB 1956 1^

WWVL 1960

The coordinates of these NBS radio stations are as follows

WWV

WWVB

WWVL

WWVH

40° 40' 49.0" N

40° 40' 28.3 " N

40° 40' 51.3" N

21° 59' 26.0" N

105° 02' 27.0" W

105° 02' 39.5" W

105° 03' 00.0" W

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 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 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 imcertainty of about 5

parts in 10'^ [Ij^.

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 groimd state of the cesium-133

atom" as was decided in October 1967 by the Xlllth

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'" . Frequency measurements in terms of the

NBS standard between December 1, 1957 and

January 1, 1960 need to take the above correction

into accoimt [2].

All carrier and modulation frequencies at WWV

and WWVH are derived from cesium-controlled

oscillators and are held stable to better than ± 2 parts

in 1 0 " at all times. 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

Incremental frequency adjustments not exceeding

1 part in 10" are made at WWV as necessary.

Frequency adjustments at WWVH do not exceed 2

parts in 10" . Corrections to the transmitted

frequency or phase are determined regularly with

respect to the NBS time standard and are published

monthly (since March 1966) in the NBS 'Time and

Frequency Services Bulletin.

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 Con-

^Figiires in brackets indicate the literature references at the end of this publication.

2
sultative Committee (CCIR), the frequency offset of

UTC was made permanently zero relative to In- ternational Atomic Time (TAI) effective 0000 hours

UTC January 1, 1972. Previously, the fractional

frequency offset was -150 parts in 10'" during 1960

and 1961; -130 parts in lO'o during 1962 and

1963; -150 parts in lO'o during 1964 and 1965;

and -300 parts in 10'» from 1966 through 1971.

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 hoiu- 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 acciwacy 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 transmitted continuously

from WWV and WWVH does contain this frequency

and may be used as a standard with the same ac- curacy as the audio and radio frequencies.

1.3. Standard Musical Pitch

The frequency 440 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

commenced 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 hoiu- at WWV. The tone is omitted during the zero hoiu- of

each UTC day. In addition to its application as a musical standard, the 440-Hz tone may be used to provide an hovu-ly 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 interruptions do not appreciably degrade

the intelligibility of voice announcements.

1.5. Time Signals

(a) Program

Because of common usage of the name Greenwich

Mean Time, the time announcements of WWV and

WWVH are referred to by this name.^ More

precisely, the actual reference time scale is the

Coordinated Universal Time Scale maintained by the

National Bureau of Standards, UTC(NBS). The

UTC(NBS) scale is affected by very small frequency

offsets relative to the NBS primary frequency

standard as mentioned in section 1.1. (b).

The 0 to 24 hour system is used starting with 0000

for midnight at the Greenwich Meridian (longitude

zero). The first two figiu-es give the hoiu-, and the last two figures give the number of minutes past the hour

when the tone retiu-ns. The time announcement refers to the end of an announcement interval, i.e., to the

time when the next 800-millisecond tone begins after

the announcement.

At WWV a voice announcement of Greenwich

Mean Time is given during the 7.5 seconds immediately preceding the minute. Just before 1035

GMT, for instance, the voice announcement (given in

English) is: "At the tone—^ten hours, thirty-five

minutes Greenwich Mean Time."

At WWVH a voice announcement of Greenwich

Mean Time occiu-s during the period 15 seconds to 7.5 seconds preceding the minute. It should be noted

that the voice announcement for WWVH precedes

^As noted in a resolution of Commission 31 of the International Astronomical Union. August 1970 : "The terms of 'GMT' and 'Z' are accepted as the general eouivalentfl of UTC in navigation and communication." Standard time zones are established at in- tervals of IS longitude east and west of the zero meridian. LxKal standard time differs from GMT by an integral number of hours.

3
WWV BROADCAST

FORMAT

THE SECOND PULSE OMITTED.... BEGINNING OF EACH HOUR IDENTIFIED BY

0.8 SEC LONG 1500Hz TONE (WWV a WWVH)

BEGINNING OF EACH

MINUTE IDENTIFIED BY

0.8 SEC LONG lOOOHz TONE

THE 29th SECOND PULSE OMITTED. , .

.

BEGINNING OF EACH MINUTE IDENTIFIED BY 0.8 SECOND LONG 1200Hz TONE

WWVH BROADCAST

FORMAT

Figure 1 . The hourly broadcast schedules of WWVand WWVH.
FictRK 2. Sample characteristics of time pulse broadcast from NBS radio stations WWVand WWVH.

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 31, 1971 at 23h 59m 60.107600s UTC,

the UTC(NBS) scale was retarded 0.107600 second

to give it an initial difference of 10 seconds late with

respect to the TAI scale as maintained by BIH. As of

January 1, 1973, the UTC scale was 12 seconds late

with respect to TAI.

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 t 0.7 second. (Note: 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 UTC month, preferably on

31 December or 30 June. Thus, when required, a

leap second 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) diu-ing a leap year. Figure 3

illustrates how events are dated in the vicinity of a

leap second.

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

June 1972 and December 1972 as announced by

BIH.

NORMAL MINUTE

(NO LEAP SECOND ADDED)

1 Doting oi Event Shown:

30 June, 23^ 59'^59.5'U7C

56 58 0 2 57 59 EVENT -

30 June, 23^59'^ —p. — / July, 0^0"^

MINUTE WITH LEAP SECOND ADDED

i k

1 57 59 0 2 56 58 60

Dot\ng of Event Shown:

30 June, 23^ 59'" 60.5^ UTC

EVENT —I

30 June, 23^ 59^- <— I July, 0*^ 0"

^Effective January 1, 1972: 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.

FiGLRF, 3. Illustration of how events will be dated in the

vicinity of a leap second.

5
(c) Coding of UTl Corrections

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" 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 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 algebraic 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 diu-ing 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

correction is indicated by the weight of the control

functions that occur at the end of the code frame. The

"plus or minus" indication is encoded in the first control function. If control function #1 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 annoimcement 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 annoimcements 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 prepared by the Telecommunications Service Center, OT, Boulder, Colorado.''

The broadcast consists of the statement, "The

radio propagation quality forecast at. . . (one of the

following times: 0100, 0700, 1300, or 1900 GMT)

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 propagation forecast announcements are repeated in synoptic form cornprised of a phonetic

and a numeral. 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 diu-ing the next six hours, the

coded forecast announcement would be "November

Seven."

(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

hoiu-. 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

during the previous 24 hovus. Messages concerning

these forecasts are prepared by the Space Environment Laboratory, NOAA, Boulder, Colorado.^

^For details regarding these forecasts, write Kent D. Boggs, Telecommunications

Services Center, OT, Boulder, CO 80302.

^For details of these announcements, write Miss J. Virginia Lincoln, Deputy Secretary lUWDS, NOAA, Boulder, CO 80302.

6
(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, 1700 and 2300 UTC for

WWV and 0000, 0600, 1200, and 1800 UTC for

WWVH. These broadcasts are updated effective with

the next scheduled annoimcement 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 from WWV at 10

and 12 minutes after each hoiu- and from WWVH at 49 and 51 minutes after each hour.

Sample broadcasts that exemplify the type of

information mariners might expect to receive from

WWV, for instance, are as follows:

"North Atlantic weather. West of 35 West at 1700

GMT: Hurricane Donna, intensifying, 24 North, 60

"^For information regarding these broadcasts, contact George P. Cressman, Director, National Weather Service, Silver Spring. MD 20910.

West, moving Northwest, 20 knots, winds 75 knots;

storm, 65 North, 35 West, moving East, 10 knots,

winds 50 knots, seas 15 feet."

|d| ATM Skylab Messages

111 January 1973, WWV and WWVH began trans- mitting information messages regarding the Apollo

Telescope Movmt (ATM) observation missions which

are scheduled during the Skylab Program." These

annoimcements, designed to coordinate efforts of

participating groimd stations throughout the world,

include actual ATM observation program ac- complishments and planned programs to be executed

throughout the mission. The regular times of issue by

the Space Environment Laboratory, NOAA, are at 0222, 0622, 1022, 1422, 1822 and 2222 from WWV

and at 0225, 0625, 1025, 1425, 1825 and 2225 from

WWVH. These broadcasts are updated effective with

the next scheduled annoimcement with provisions to provide real time alert messages in the event of

tmusual solar activity. The messages are given in

voice from WWV at 22 and 24 minutes after the hour

and repeated from WWVH at 25 and 27 minutes

after the hoiu-.

"For further information regarding these messages, write Robert B. Doeker, Chief, Space Environment Services Center, NOAA, Boulder, CO 80302.

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 UT, CORRECTIONS, ETC.

4) 6 ppm POSITION IDENTIFIERS (P THROUGH P ) 5) 1 pp"s INDEX MARKERS °

*

TIME

< — ^ TIME FRAME 1 MINUTE > INDEX COUNT (1 SECOND)

0 10 20 30 40 50 0

I I I 1 [

I 1 1 I

I

I I I I

j

I 1 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 1

I

' I I I

I

I I I I

TIME IN SECONDS

-ON TIME 1 SECOND INDEX MARKER

1 SECONDW-H k P, mnjuuuuLnjmjuuu^^

^7—1 .03 SECOND

l— rJ HOLE IN CODE

FOR 0.8 SECOND

PULSE

-MINUTES- -HOURS- -DAYS- UTiCORRECTION

P^-Pj POSITION IDENTIFIERS (0.8 SECOND DURATION)

W WEIGHTED CODE DIGIT (0.5 SECOND DURATIOU)

C WEIGHTED CONTROL ELEMENT (0-5 SECOND DURATION) CONTROL FUNCTION #6

jgj

DURATION OF INDEX MARKERS UNWE I GHTED_CODE AND CONTROL ELEMENTS

Figure 4. Chart of time code transmissions from NBS radio stations WWVand WWVH.

UTl AT POINT A = 173 DAYS 21 HOURS

10 MINUTES

59.3 SECONDS

BINARY ONE DURING 'DAYLIGHT' TIME

NARY ZERO DURING 'STANDARD' TIME

0.2 SECONDS
1.7. WWV/WWVH Time Code

On July 1, 1971, WWV commenced broadcasting

the time code shown in figm-e 4. The time code is now

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 100-

Hz subcarrier is synchronous with the code pulses so that 10-millisecond resolution is readily obtained.

The code contains UTC time-of-year information

in minutes, hours, and day of year. Seconds information may be obtained by counting pulses.

The binary coded decimal (BCD) system is used.

Each minute contains seven BCD groups in this

order : two groups for minutes, two groups for horn's,

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.

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

comprises 20 cycles of 100-Hz amplitude

modulation ; a binary one pulse comprises 50 cycles

of 100-Hz amplitude modulation. Because of the 40-

millisecond hole that accompanies each seconds

marker in the WWV/WWVH format, however, the

leading 30-millisecond portion in the WWV/WWVH

time code is deleted. The leading edge of each pulse

coincides with a positive-going zero-axis crossing of

the 100-Hz modulating frequency.

Based upon a clocking rate of 60 markers per

minute, the code contains six position identification

markers per minute and a minute reference marker.

Each 6-per-minute position identification marker

consists of a 0.8-second pulse preceding a code group.

The 1-per-minute reference marker consists of a 0.8-

second pulse followed by a 1.03-second hole in the

code and eight binary zero pulses in succession. The

minute begins with the 1.03-second hole preceding

the first binary zero. UTl corrections to the nearest 0.1 second are encoded via control function pulses during the final

ten seconds of the frame. Control function #1, which

occurs as the 50th second pulse, discloses the sense of

the correction. Control fimction #1 is a binary zero when the UTl correction is negative and a binary one when the correction is positive. Control function #7,

#8, and #9, which occur as the 56th, 57th, and 58th

second pulses, identify the magnitude of the UTl

correction.

Control fimction #6, which occurs as the 55th

second pulse, is programmed as a binary one

throughout those weeks when Daylight Saving Time

is in effect and as a binary zero when Standard Time

is in effect. The setting of this function is changed at 0000 GMT on the last Sunday of April and October

respectively. Throughout the U.S. mainland this

schedule allows several hours for the function to be

received before the change becomes effective locally,

i.e., at 2:00 AM. Thus, control fimction #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 Standard Time and vice versa.

1.8. Station Identification

WWV and WWVH identify by voice every 30

minutes. The station identification voice an- nouncements are automatically synchronized

recordings, not live broadcasts. The regular an- nouncer for WWV is Mr. Don Elliott of Atlanta,

Georgia; the regular announcer 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.

8
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

station 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

frequency of 60 kHz with no offset. It also broadcasts

a time code consistent with the internationally

coordinated 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 '2 . 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

returning 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

installed over a radial ground screen. Some measured

field intensity contours are shown in figure 5.

MEASURED FIELD INTENSITY CONTOURS: WWVB @13kW ERP

FiGLRF. 5. Measured field intensity contours: WWVB @ 13kW ERP

9
2.1. WWVB Time Code

(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 6.

(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 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 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 negative-going pulse is on time.

(c) Marker Order and Groups

The 10-second position markers, labeled PO

through P5 in figiu-e 6, occur respectively as the 59th,

9th, 19th, 29th, 39th, and 49th second pulses of each

minute.'' The minute reference marker begins at zero

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

seconds. Uncoded markers occur periodically as the

4th, 14th, 24th, 34th, 44th, and 54th seconds pulses

and also as the 10th, 11th, 20th, 21st, 35th, 55th,

56th, 57th, and 58th seconds pulses of each minute.

Thus every minute contains twelve groups of five

markers, each group ending either with a position

marker or an uncoded marker.

(d) Information Sets

Once every minute the code presents complete

UTC(NBS) time-of-year information in minutes,

hours, and day of the year as well as the estimated

difference between UTC and UTl. Seconds information can be obtained by coimting pulses.

The first two groups in the frame specify the

minute of the hour. The third and fourth groups

comprise 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 groups 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 positive or negative relationship of the UTl

scale with respect to UTC is indicated by the eighth

group. If UTl is late with respect to UTC, a binary one (labeled SUB in figure 6) will be broadcast in the

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

If UTl is early with respect to the code time, binary ones (labeled ADD) will be broadcast in the eighth

group as the 36th and 38th second pulses of the

minute.

TIME FRAME I MINUTE

INDEX COUNT I SECOND)

1 0 20 30

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

40 50

I I I I I I I I I I I III

ON TIME

POINT A

-| ^ 0.3 SECOND SECOND ^'^'|^ ~^^\^ ^1^°-^ SECOND 0.8 SECOND -j |j- ~LJUuir¥¥¥¥inriJiiTinjir^

MINUTES HOURS DAYS RELATIONSHIP

UT| SET1 PPM FRAME REFERENCE MARKERS

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

CONTROL FUNCTIONS (15 DIGITS) USED FOR UT, CORRECTIONS

6 PPM POSITION IDENTIFIER MARKERS AND PULSES (P„ THRU Pj)

(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)

Figure 6. Chart of time code transmissioFis from NBS radio station WWVtS.

TIME AT POINT A 258 DAYS

18 HOURS

42 MINUTES

34.3 SECONDS

10
(e) Digital Information

When used to convey numerical information, the

foiu 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 indexed

2-1, or 4-2-1, accordingly. The indices 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 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 specific example is indicated in figure 6. The

occm-rence 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

"hoiu-s set" indicate the 10 + 8 = 18th hour of the

day, while the four binary ones in the "day 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, 400 + 200 + 100 = 700

milliseconds to get an estimate of UTl. For example,

the 35th UTl interval would end 700 milliseconds

(or 0.7 second) later than the end of the 35th second.

In other words, the UTl scale reading for the end of

the 35th second would be 18h 42m 34.3s, since 35.0s

- 0.7s = 34.3s.

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.

Effective Oh UTC, 1 July 1972, regularly scheduled

transmissions from WWVL were discontinued.

Contingent upon need and availability 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 government.

Arrangements for use of WWVL should be made

through the Frequency-Time Broadcast Services

Section, 273.02, National Bureau of Standards,

Boulder, CO 80302.

(a| Program Format

WWVL transmits only carrier frequencies with no

modulation. In accordance with the new UTC system

the frequency offset used prior to January 1, 1972,

was reduced to zero on that date. 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 normally 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

installed over a radial ground screen.

4. How NBS Controls the Transmitted Frequencies

A simplified diagram of the NBS frequency control

system [5] is shown in figure 7. The entire system

depends upon the basic frequency reference shown in

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

standard is used to calibrate the oscillators, dividers

and clocks which generate the controlled frequency

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

corrections of the WWVB and WWVL quartz crystal

oscillators 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 transmissions from each

station, the time-code generators are compared with

the station's master clock several times each day.

11
MATIONAL aUie€AU of <?TAK1DAI2D$

fecQUENcv AND TiM€ fAmim

PUIMARVfPCQUEMCV

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(Atomic Ccsium Bcam)

O0CA9IONAL CALIBRATION

OF ABSOLUTt fKQUENCV

1

AMI? TlM£ QTANDAEP

(€NSeMBL£ OF aoCKS)

AT (MB9)

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Wvee TV STATIONS

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\AS DETCRMIWED BV BIH

/ 9MALL PAT-C ADJUSTMCNTS \ m NATIONAL AND INTCENATIONAL ) COOEPINATION /

(12) MBS BOULPCe CESIUM CLOCkC

'UTC (NBS)

TU e£C£IV€E

f SVNC

PUL5ES

J 1

Time Iwterval QOUWT£E hT£L£PHON€ COMMUMICATIOWS-AND'

MBUOiaULUUi!

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Time Inteeval COUMTEE J

UBS fT COLLINS a£eiuM CLOCK

20

WWV SIGNALS

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303-499-711

1

POULDEB,CO

UTC (MBS) + UT, COeKaTIONQ

15 UTC (WDC)

+UT| coee€CTiowg

Figure 7. NBS frequency control system.
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

receivers. 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 often compared

with the transmitting station clocks by the use of a very precise portable clock.

5. References

[ll 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. 19701.

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

States, Proc. IRE, IRE-48, No. 105 (I960).

[3.] Allan, D.W., and Barnes, J. A., 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, 19671. K. Davies, Ed., Chapter 15

(Technivision Services, Slough, England, in press).

[4.1 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, Fort 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).

16.) Tolman, J., Ptacek, V., Soucek, A., and Stecher, R., Microsecond clock comparisons by means of TV synchronizing

pulses, IEEE Trans.—^Instr. and Meas. IlVl-16, No. 3, (Sept.

1967). pp. 247-254.

13
NBS Fort Collins facility showing WWV transmitter building.

WWVH transmitter building, Kekaha, Kauai, Hawaii. WWVB/WWVL transmitter building and antennas.
FORM N'BS.114A (1-71)

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

BIBLIOGRAPHIC DATA NBSSP-236, 1973 ed.

SHEET

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

NBS Frequency and Time Broadcast Services - -Radio

otations w w V , w w v ri, wwvid, wwvj-i

5. Publication Date May 1973

6. Performing Organization Code

7. AUTHOR(S)

P. P. Viezbicke, Editor

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS, Boulder Labs.

DEPARTMENT OF COMMERCE

Boulder, Colorado 80302

10. Project/Task/ Work Unit No.

11. Contract/Grant No.

12. Sponsoring Organization Name and Address

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, 1973.

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 (Alphabetical order, separated by semicolons)

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

frequencies; time signals; very low frequency.

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(THIS REPORT)

21. NO. OF PAGES

UNLIMITED.

UNCL ASSIFIED

19

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TO NTIS.

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(THIS PAGE)

22, Price

$1 45 Domestic postpaid, $. 35 G. P.O. UNCLASSIFIED Bookstore.

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