A UNITED STATES DEPARTMENT OF COMMERCE

PUBLICATION

Special Publication 236

1970 EDITION

U.S.

DEPARTMENT

OF

COMMERCE

National

Bureau

of

Standards

Frequency and

Time Broadcast

Services

RADIO STATIONS WWV WWVH WWVB WWVL

UNITED STATES DEPARTMENT OF COMMERCE

Maurice H. Stans, Secretary

NATIONAL BUREAU OF STANDARDS • LEWIS M. BRANSCOMB, Director

NBS

FREQUENCY AND TIME

BROADCAST SERVICES

RADIO SIAIIOKS WWV, WWVH, WWVB, MID WWVl

P. P. Viezbicke, Editor

Frequency-Time Standards

Institute for Basic Standards

National Bureau of Standards

Boulder, Colorado 80302

SPECIAL PUBLICATION 236, 1970 EDITION

(Supersedes NBS Special Publication 236, 1969 and previous editions)

Nat. Bur. Stand. (U.S.), Spec. Publ. 236 16 pages (1970)

CODEN: XNBSA

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

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

Issued 1970
Contents

Page

Services provided by NBS standard frequency and time stations 1

Introduction 1

1. Technical Services and Related Information 2

1.1 Standard Radio Frequencies 2

(a) Program 2

(b) Accuracy and stability 2

(c) Corrections 3

(d) Offset frequencies 3

1.2. Standard Audio Frequencies 3

(a) Program 3

(b) Accuracy 3

1.3. Standard Musical Pitch 3

1.4. Standard Time Intervals 3

1.5. Time Signals 5

(a) Program 5

(b) Corrections 6

(c) UT2 Corrections 6

1.6. Propagation Forecasts 6

1.7. Geophysical Alerts 7

1.8. WWV Time Code 8

1.9. WWVB Time Code 8

(a) Code and carrier 8

(b) Marker generation 8

(c) Marker order and groups 9

(d) Information sets 9

(e) Digital information 9

1.10 Station Identification 12

1.11 Radiated Power, Antennas and Modulation 12

(a) Radiated power 12

(b) Transmitting antennas 12

(c) Modulation _ 12

2. How NBS Controls the Transmitted Frequencies 12

• • 11
Services Provided by NBS Standard Frequency and Time Stations

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. UT2 corrections; 7. Radio

propagation forecasts ; and 8. Geophysical alerts. 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 February 1, 1970. Annual revisions will be made.

Current data relating to standard frequencies and time signals are available monthly in

the Time and Frequency Services Bulletin. Advance notices of changes occurring between revisions will be sent to users of NBS broadcast services who request such notice on the basis of need.'

Key words : Broadcast of standard frequencies ; high frequency ; low frequency ; standard frequencies ; time signals ; very low frequency.

Introduction

In March 1923 the National Bureau of Standards started transmitting standard radio frequencies on a regularly announced schedule

from radio station WWV. The WWV transmitter, originally located at the National Bureau of Standards, Washington, D. C, has

moved several times, but the original towers

remain on the pioneer site. From 1931 to 1966

the station was moved successfully from Washington, D. C. to Greenbelt, Maryland and finally

to Fort Collins, Colorado, where it went on the

air at 0000 Universal Time (GMT) on December 1, 1966.

The move to Fort Collins was prompted by

several considerations: the need for wider and

more uniform coverage in the continental U.S.

from a more central location; the advantage of

more precise control from the NBS Time and

Frequency Division at Boulder, Colorado; improvement in radiation patterns obtained by

location in a less congested area; and reduction

of interference on the West Coast between time

signals from WWV and those from WWVH,

Maui, Hawaii.

Original broadcasts were accurate to within

a few parts in a thousand. Their transmitted ac- curacy today is of the order of a few parts in

'Inquiries concerning the Time and Frequency Services Bulletin or the NBS broadcast service policies may be addressed to FrequencyTime Broadcast Services Section, Time and Frequency Division,

NBS, Boulder, Colorado 80302.

10^2—approaching the accuracy of the NBS

frequency standard itself.

To supplement the coverage of WWV, broadcasts from station WWVH were instituted in

1948. These play an increasingly important

role in various types of operations in the Pacific

and Far East, both military and civilian.

WWVB began broadcasting from Boulder,

Colorado in 1956, and WWVL, an experimental

station, from Sunset, Colorado in 1960. Both

of these stations have been in operation from

Fort Collins, Colorado since July 1963. These

stations, WWVB transmitting on low frequency

(LF) and WWVL transmitting on very low frequency (VLF), make possible wide-scale distribution of the NBS frequency and time signals.

They are used to coordinate operations of the

global networks of missile and satellite stations,

to assist other government efforts which re- quire accurate time and frequency, to improve

the uniformity of frequency measurement on

a national and international basis, and to provide a more accurate standard of frequency,

one easily available to many users for electronic

research and development.

Thus in the 47 years since the beginning of

its radio broadcasts, NBS has expanded such

services so that it is making major contributions today to the nation's space and defense

programs, to world-wide transportation and

communications, and to a multitude of industrial operations, as well as providing convenient

time service to thousands of listeners.

1
1. Technical Services and Related Information

The standard frequency and time stations of

the National Bureau of Standards broadcast

these services:

Station

Date

in

service

Radio

frequencies

Audio

frequencies

Musical

pitch

Time

intervals

Time

signals

UT2

corrections

Propagation

forecasts

Geophysical

alerts

WWV 1923 W <> *> i>

WWVH 1948 i>

WWVB 1956 i> i>

WWVL 1960 i>

The NBS radio stations are located as follows:

WWV 40°40' 49"N 105°02' 27"W

WWVB 40°40'28.3"N 105°02'39.5"W

WWVL 40°40'51.3"N 105°03'00.0"W

WWVH 20°46' 02"N 156°27' 42"W

Correspondence pertaining directly to station

operations may be addressed to: John Stanley, Engineer-in-charge

NBS Radio Stations WWV/WWVB/WWVL

Route 2 Box 83-E

Fort Collins, Colorado 80521

Telephone (303) 484-2372.

Sadami Katahara, Engineer-in-charge

NBS Radio Station WWVH2

Box 578

Puunene, Maui, Hawaii 96784

Telephone (808) 79-4111.

Visiting hours are observed at WWV, WWVB,

and WWVL every Wednesday, except holidays,

from 1:00 pm to 4:00 pm. Special tours may

be scheduled at other times only by prior ar- rangement with the Engineer-in-charge.

1.1. Standard Radio Frequencies

(a) Program

Station WWV broadcasts on nominal radio

frequencies of 2.5, 5, 10, 15, 20, and 25 MHz.

The broadcasts are continuous, night and day,

except for an interruption of 4 min. each hour.

The silent period commences at 45 min 15 s after each hour (fig. 1). During the silent

periods, measurements of background noise

level can be made.

Station WWVH broadcasts on nominal radio

frequencies of 2.5 5, 10, and 15 MHz. The

broadcast is interrupted for approximately 4

min each hour. The silent period commences

at 15 min (plus 0 to 15 s) after each hour.

Station WWVB broadcasts on the standard

frequency of 60 kHz and station WWVL on

the nominal frequency of 20 kHz. These two

stations have scheduled maintenance periods

on alternate Tuesdays between 1300 UT and

2400 UT. Otherwise the service is continuous.

(b) Accuracy and Stability

Since December 1, 1957, the standard radio

transmissions from stations WWV and WWVH

have been held as nearly constant as possible

with respect to the atomic frequency standards

maintained and operated by the Time and Frequency Division of the National Bureau of

Standards. Carefully made atomic standards

have been shown to realize the ideal Cs resonance

frequency, /cs, to a few parts in 10^^ The

present NBS frequency standard realizes this

resonance frequency to within 5 parts in 10^^.

The number /cs=9 192 631 770 Hz, originally measured^ with an uncertainty of 2 parts

in 10", is now defined as the exact value as- signed to the atomic frequency standard to be

used for the physical measure of time. This

was officially decided by the International Committee of Weights and Measures at the XHIth

General Conference in October 1967.

On January 1, 1960, the NBS standard was

brought into agreement with /cs as quoted above

by arbitrarily increasing its assigned value by

74.5 parts in 10^". Frequencies measured in

terms of the NBS standard between December

1, 1957 and January 1, 1960, may be referred

to the above value of /cs and to the Ephemeris

second by means of this relative correction.*

The frequencies transmitted by WWV and

WWVH are held stable to better than ±2 parts

in 10" at all times. Deviations at WWV are normally much less than 1 part in 10" from

day to day. Incremental frequency adjustments

not exceeding 1 part in 10" are made at WWV

as necessary. Frequency adjustments made at

WWVH do not exceed 4 parts in 10".

Changes in the propagation medium (causing

Doppler effect, diurnal shifts, etc.) result in

fluctuations in the carrier frequencies as re- ceived which may be very much greater than

the uncertainties described above.

WWVB and WWVL frequencies are nor- mally stable to better than 2 parts in 10^^ Devi-

-WWVH is being relocated to Kauai, Hawaii, and is planned to be

operational at the new site in 1971.

'Markowitz, Hall, Essen, and Parry—Frequency of cesium in terms

of ephemeris time—Phys. Rev. Letters 1, 105 (1958).

* National standards of time and frequency in the United States, Proc. IRE 48, 105 (1960).

2
ations from day to day are less than 1 part in

10".

The effects of the propagating medium on the

received frequencies are much less at LF and

VLF. The full transmitted accuracy may be

obtained using appropriate receiving techniques.

(c) Corrections

All carrier and modulation frequencies at

WWV are derived from cesium controlled oscillators and at WWVH are derived from precision quartz oscillators. Coordinated by the

Bureau International de I'Heure (BIH) in

Paris, these frequencies are intentionally offset

from standard frequency by a small but precisely known amount to reduce departure between the time signals as broadcast and astronomical time, UT2. The offset for 1960 and

1961 was —150 parts in lO^^; in 1962 and 1963,

—130 parts in lO^O; in 1964 and 1965, -150

parts in lO^O; and in 1966 through 1970, —300

parts in lO^*'. Although UT2 is subject to unpredictable changes readily noted at this level

of precision, a particular offset from standard

frequency will remain in effect for the entire

calendar year.

Corrections to the transmitted frequency and

phase are regularly determined with respect to

the NBS time standard and are published

monthly (since March 1966) in the NBS Time

and Frequency Services Bulletin.

The carrier frequency of WWVL is also offset

from standard frequency by the same amount

as noted above. Station WWVB initially transmitted with the carrier frequency offset, but

since January 1, 1965 the transmissions have

been without offset. Thus, one of the NBS

transmissions makes available to users the

standards of frequency and time interval so that atomic frequency comparisons may be

made directly. The carrier frequency of station

WWVB is not subject to annual offset changes

as are the frequencies of the other three stations.

(d) Offset Frequencies

WWV, WWVH, and WWVL transmit re- minders of the fact that all transmitted frequencies are offset from nominal by a fixed

amount (for 1966, 1967, 1968, 1969, and 1970

by —300 X 10-10). International Morse Code

symbols for M300, representing minus 300, are transmitted from WWV and WWVH immediately following the "on-the-hour" voice an- nouncement. WWVL transmits experimental

programs with multiple frequencies. Transmissions presently alternate between 20.0 kHz and

19.9 or 20.9 kHz, the change being made every

10 seconds. The transmission format and the

frequencies used by WWVL are subject to

change to meet the requirements of the particular experiment (s) being conducted. All three

of the above stations are coordinated under the

UTC (Universal Time Coordinated) system by

the BIH.

Since WWVB transmits standard frequency

without offset, no reminder is needeo. Broadcasts of this station are coordinated by the BIH

under the Stepped Atomic Time (SAT) system.

Step adjustments of 200 milliseconds are an- nounced in advance for the first of a month

when necessary to maintain the difference between the broadcast time and UT2 within about

100 milliseconds.

1.2. Standard Audio Frequencies

(a) Program

Standard audio frequencies of 440 Hz and

600 Hz are broadcast on each radio carrier frequency for WWV and WWVH. The audio frequencies are transmitted alternately at 5-min

intervals starting with 600 Hz on the hour (fig.

1). The first tone period at WWV (600 Hz) is

of 3-min duration. The remaining periods are

of 2-min duration. At WWVH all tone periods are of 3-min duration. WWVB and WWVL do

not transmit standard audio frequencies.

(b) Accuracy

The accuracy of the audio frequencies, as

transmitted, is the same as that of the carrier.

The frequency offset mentioned under 1.1 (c)

applies. Changes in the propagation medium

will sometimes result in fluctuations in the

audio frequencies as received.

While 1000 Hz is not considered one of the

standard radio frequencies, the time code which

is transmitted 10 times an hour from WWV

does contain this frequency and may be used as

a. standard with the same accuracy as the audio

frequencies. The audio tones used for the Morse

Code information prior to the voice announcements are not standard frequencies.

1.3. Standard Musical Pitch

The frequency 440 Hz, for the note A above

middle C, is the standard in the music industry

in many countries and has been in the United

States since 1925. The radio broadcast of this

standard was commenced by the National Bureau of Standards in 1937. The periods of

transmission of 440 Hz from WWV and

WWVH are shown in figure 1. With this broadcast the standard pitch is maintained, and

musical instruments are manufactured and adjusted in terms of this practical standard. The

majority of musical instruments manufactured

can be tuned to this frequency.

1.4. Standard Time Intervals

Seconds pulses at precise intervals are derived from the same oscillator that controls the

radio carrier frequencies, i.e., they commence

3
HOURLY BROADCAST SCHEDULES OF WWV, WWVH, WWVB, AND WWVL

E?i?xl STATION ANNOUNCEMENT

WWV: Morse Code - Call letters; universal time; propagation

forecast; frequency offset (on the hour only)

Voice - Greenwich mean time

WWVH: Morse Code - Call letters; universal time; frequency

offset (on the hour only)

Voice - Greenwich mean time

WWVL, WWVB: - No station identification

ma 100 pps 1 000 hz modulation mm tone modulation eoo hz

WWV timing code TONE MODULATION 440 Hz

rWI GEOALERTS IDENTIFICATION PHASE SHIFT

rum UT2 TIME CORRECTION SPECIAL TIME CODE

Figure 1. The hourly broadcast schedules of WWV, WWVH, WWVB, and WWVL.

4
FREQUENCY, Hz

Figure 2. Sample characteristics of time pulses broadcast from NBS radio stations WWV and WWVH.

at intervals of 5 000 000 cycles of the 5 MHz

carrier. They are given by means of doublesideband amplitude-modulation on each radio

carrier frequency. Intervals of 1 min are marked by the omission of the pulse at the beginning

of the last second of every minute and by commencing each minute with two pulses spaced

by 0.1 second.

The first pulse marks the beginning of the

minute. The 2-min, 3-min, and 5-min intervals are synchronized with the seconds pulses and

are marked by the beginning or ending of the

periods when the audio frequencies are not

transmitted. The pulse duration is 5 milliseconds. The pulse waveform is shown in figure

2. At WWV each pulse contains 5 cycles of 1000

Hz frequency. At WWVH the pulse consists of

6 cycles of 1200 Hz frequency. The pulse spectrum is composed of discrete frequency components at intervals of 1 Hz. The components

have maximum amplitudes at approximately

995 Hz for WWV and 1194 Hz for WWVH

pulses. The tone is interrupted 40 milliseconds

for each seconds pulse. The pulse starts 10

milliseconds after commencement of the interruption.

WWVB transmits seconds pulses continuously using a special time code described in sec- tion 1.9. WWVL does not transmit seconds

markers. However, accurate time intervals may

be obtained directly from the carrier using

appropriate techniques.

1.5. Time Signals

(a) Program

The audio frequencies are interrupted at precisely 3 min before each hour at WWV and 2

min before each hour at WWVH. They are re- sumed on the hour at WWV and WWVH, and

at 5- and 10-min intervals throughout the hour

as indicated in figure 1. Universal Time, abbreviated UT after the

given time (e.g., 1000 UT) is the time of a clock

in the Coordinated Universal Time (UTC) system. This time is referenced to the Greenwich

Meridian (longitude zero), and thus is also

known as Greenwich Mean Time (GMT).

Time (GMT) is announced every five minutes

from WWV and WWVH both in International

Morse Code and by voice. The Morse Code an- nouncements immediately precede the voice on

both stations.

The 0 to 24 hour system is used starting with

0000 at midnight at 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. For example, at

1655 GMT, the four figures 1-6-5-5 are broadcast in code. The time announcement refers to

the end of an announcement interval, i.e., to the

time when the audio frequencies are resumed.

At station WWV a voice announcement of

Greenwich Mean Time is given during the last

half of every fifth minute during the hour. At

10:35 a.m. GMT, for instance, the voice an- nouncement given in English is: "National

Bureau of Standards, WWV, Fort Collins, Colorado; next tone begins at ten hours, thirty-five

minutes Greenwich Mean Time."

At station WWVH a similar voice announcement of Greenwich Mean Time occurs during

the first half of every fifth minute during the

hour. It should be noted that the voice an- nouncement for station WWVH precedes that

of WWV by 30 seconds. However, the tones

referred to in both announcements occur simultaneously, though they may not be so received

due to propagation effects. In areas where both

5
stations are received, sometimes the keying for

WWV (which occurs prior to the WWV voice

announcement) may be mistaken for the

WWVH returning tone. It it were not for the

WWV signal interference, the tone for WWVH

would be heard 30 seconds after the WWVH

voice announcement ended and there would be

no misinterpretation.

Time-of-day information is given from

WWVB using the time code described in sec- tion 1.9. Specialized equipment is needed for

reception of this time code. WWVL does not

transmit time-of-day information.

(b) Corrections

Time signals broadcast from WWV and

WWVH are kept in close agreement with UT2

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

adjustments are made at 0000 UT on the first

day of a month. Advance notice of such adjustments is given to the public upon advice by

the BIH that an adjustment is to be made. Decision to adjust the time signals is based upon

observations by a network of international observatories and is made by an international

committee. Differences between the time signals

and UT2 are published periodically by the U.S.

Naval Observatory.

Seconds pulses broadcast from WWVB will

depart from UT2 at a different rate due to the

fact that WWVB broadcasts 60 kHz with no

offset (see 1.1(c)). Step time adjustments of

200 milliseconds will be made at 0000 UT on

the first day of a month with appropriate advance notice. The BIH advises when such adjustments are to be made in order to maintain

the seconds pulses within about 100 milliseconds of UT2.

(c) UT2 Corrections

Since a majority of time users do not require

UT2 information to better than 100 milliseconds the systems described in 1.5(b) are quite

satisfactory. An additional service is provided

in cooperation with the U.S. Naval Observatory which makes available the best values of

UT2 on a daily basis. Corrections to be applied

to the time signals as broadcast are given in

International Morse Code during the last half of

the 19th min of each hour from WWV and during the last half of the 49th min of each hour

from WWVH. Similar information is incorporated in the WWVB Time Code.

The symbols which are broadcast are as follows:

"UT2," then "AD" or "SU"

followed by a three-digit number. This number

is the correction in milliseconds. To obtain UT2,

add the correction to the time indicated by the

Time Signal pulse if "AD" is broadcast. Subtract if "SU" is broadcast. Thus a clock, keeping step with the time signals being broadcast,

will be early with respect to UT2 if "SU" is

the symbol used. These corrections will be re- vised daily, the new value appearing for the

first time during the hour after 0000 UT, and

will remain unchanged for the succeeding 24

hour period.

The corrections necessary to obtain UT2 are

derived from extrapolated data furnished

weekly by the U.S. Naval Observatory. These

indicate the variation in UT2 with respect to

broadcast time. Preliminary corrections are published monthly in the Time and Frequency

Services Bulletin with a probable error of ±5

milliseconds. Final data, with a probable error

of ±1 millisecond, are published in the Time

Service Bulletins of the U.S. Naval Observatory.

1.6. Propagation Forecasts

A forecast of radio propagation conditions is

broadcast in International Morse Code during

the last half of every fifth minute of each hour

on each of the standard frequencies from

WWV. Propagation notices were first broadcast from WWV in 1946. The announcements

each five minutes were commenced on November 15, 1963. The present type of propagation

forecasts has been broadcast from WWV since

July 1952. North Pacific forecasts were broadcast from WWVH from January 1954 until

November 1964, but these are no longer available.

The WWV forecast announcements refer to

propagation along paths in the North Atlantic

Area, such as Washington, D.C. to London or New York City to Berlin. The announcements

are the short term forecasts prepared by the

ESSA Telecommunication Services Center,

ESSA Research Laboratories, Institute for

Telecommunication Sciences, Boulder, Colorado

80302. The regular times of issue of the forecasts are 0200, 0800, 1400, and 2000 UT for

the period November 1 through April 30, and

0100, 0700, 1300, and 1900 UT for the period

May 1 through October 31.

The forecast announcement tells users the

condition of the ionosphere at the regular time

of issue and the radio quality to be expected

during the next six hours. The forecasts are based on data obtained from a worldwide network of geophysical and solar observatories.

These data include radio soundings of the upper

atomosphere, short wave reception data, observations of the geomagnetic field, solar activity, and similar information. Trained forecasters evaluate the information and formulate

the forecasts using known sun-earth relationships.

WWV broadcasts the forecast as a letter and

a number. The letter portion identifies the

radio quality at the time the forecast is made.

The letters denoting quality are "N", "U", and

6
"W", signifying that radio propagation conditions are either normal, unsettled, or disturbed,

respectively. The numlDer portion of the forecast announcement from WWV is the forecast

of radio propagation quality on a typical North

Atlantic path during the six hours after the

forecast is issued. Radio quality is based on

the ITS 1 to 9 scale which is defined as follows:

Grades of Propagation:

Disturbed (W)

Unsettled (U)

Normal (N)

Intelligibility Scale

1. useless

2. very poor

3. poor

4. poor-to-fair

5. fair

6. fair-to-good

7. good

8. very good

9. excellent

If for example, propagation conditions are normal at the time the forecast is issued but are expected to become "poor-to-fair" during the

next six hours, the forecast announcement

would be broadcast as N4 in International

Morse Code.

1.7. Geophysical Alerts

Letter symbols indicating the current geophysical alert (Geoalert) as declared by the

World Warning Agency of the International

Ursigram and World Days Service (lUWDS)

are broadcast in very slow International Morse

Code from WWV and WWVH on each of the

standard radio carrier frequencies. These

broadcasts are made from WWV during the

first half of the 19th min of each hour and

from WWVH during the first half of the 49th

min of each hour. Such notices have been broadcast since the International Geophysical Year,

1957-58 and have continued by international

agreement.

On January 1, 1968 a new coding system was

instituted for broadcasting Geoalerts. This was

necessary to make possible the dissemination

of larger quantities of information resulting

from improved techniques in observation and

prediction of geophysical events. The coding

was modified again on January 1, 1970. The

symbols used indicate to experimenters and

researchers in radio, geophysical, and solar'

sciences the content of the lUWDS Geoalert

message which is issued daily at 0400 UT to

identify days on which outstanding solar or

geophysical events are expected or have oc- curred in the preceding 24-hour period.

Geoalerts for a given day are first broadcast

at 0418 UT on station WWV, Fort Collins,

Colorado, then at 0448 UT on station WWVH,

Maui, Hawaii. These broadcasts are repeated

at hourly intervals until the new alert is issued.

Each message begins with the letters GEO in

Morse Code followed by coded information. The

new coding permits three types of information

at each broadcast—each in the form of letters

repeated three times in slow International

Morse Code.

The first set concerns either alerts of possible solar or geophysical events or the observation of a stratospheric warming (STRATWARM), together with the alert of possible

solar or geophysical events when appropriate.

Letters which may occur in the first set and

their meaning are as follows:

EEE (. ) No forecast (or STRATWARM observation) statement

III (• • ) SOLALERT in effect which means one or several eruptive or active centers are present on the sun

SSS (...) XRAYALERT or PROTONALERT is in effect

TTT (- ) MAGSTORM expected

1st letter UUU (. . - ) SOLALERT and MAGALERT

VVV (...-) PROTONALERT and MAGALERT

HHH (....) STRATWARM observed

DDD (- . . ) STRATWARM observed and SOLALERT

BBB (-...) STRATWARM observed and PROTONALERT

MMM (- - ) STRATWARM observed and MAGSTORM expected

7
The second and third sets of letters pertain

to the occurrence of and approximate time of

observed solar or geophysical events. The coding for the beginning time and type of event

is shown in the table given below:

Day before that of Issue

(hours UT)

Day of

issue

In

Progress

NIL

00-06 06-12 12-18 18-24 00-04

2nd letter set: PROTON EVENTMMM

(--)

TTT

(-)

HHH

(....)

sss

(...)

III

(..)

GGG

(--.)

EEE

(.)

3rd letter set: GEOMAGNETIC

STORM

uuu

(..-)

AAA

(.-)

BBB

(-...)

DDD

(-..)

NNN

(-.)

PPP

(.--.)

EEE

(.)

For example, the following message (in International Morse Code)

GEO TTT EEE DDD

signifies: GEO = Solar geophysical message

TTT = Magstorm expected

EEE = No PROTON EVENT between 0000 UT yesterday

and 0400 UT today

DDD = GEOMAGNETIC STORM

occurred (began) between

1800-2400 UT yesterday

1.8. WWV Time Code

On January 1, 1961 WWV commenced broadcasting the time code shown in figure 3 for one

minute out of each five, ten times an hour, as shown in figure 1. 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 a thousandth of a second. Astronomical observations may also

benefit by the increased timing potential provided by the pulse-coded signals.

The code format being broadcast is generally

known as the NASA 36-bit Time Code. The

code is produced at a 100 pps rate and is carried

on 1000 Hz modulation.

The code contains time-of-year information

in Universal Time (GMT) in seconds, minutes,

hours, and day of year. The code is synchronous

with the frequency and time signals.

The binary coded decimal (BCD) system is used. Each second contains 9 BCD groups in

this order: 2 groups for seconds, 2 groups for

minutes, 2 groups for hours, and 3 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 second. The binary groups follow the 1 second reference

marker. "On time" occurs at the leading edge

of all pulses.

The code contains 100/second clocking rate,

10/second index markers, and a 1/second refer- ence marker. The 1000 Hz is synchronous with

the code pulses so that millisecond resolution

is readily obtained.

The 10/second index markers consist of "binary one" pulses preceding each code group

except at the beginning of the second where a "binary zero" pulse is used.

The 1/second reference marker consists of

five "binary one" pulses followed by a "binary

zero" pulse. The second begins at the leading

edge of the "binary zero" pulse.

The code is a spaced code format; that is, a

binary group follows each of the 10/second index markers. The last index marker is followed

by an unused 4-bit group of "binary zero"

pulses just preceding the 1/second reference

marker.

A "binary zero" pulse consists of 2 cycles of

1000 Hz amplitude modulation, and the "binary

one" pulse consists of 6 cycles of 1000 Hz amplitude modulation. The leading edges of the time

code pulses coincide with positive-going zero- axis-crossings of the 1000 Hz modulating frequency.

1.9. WWVB Time Code

(a) Code and Carrier

On July 1, 1965, Radio Station WWVB, Fort

Collins, (Colorado began broadcasting time information using a level-shift' carrier time code.

The code, which is binary coded decimal (BCD),

is broadcast continuously and is synchronized

with the 60 kHz carrier signal. The new system replaces the method whereby seconds pulses

of uniform width obtained by level-shift carrier keying were broadcast. The carrier is no

longer interrupted for keyed station identification.

(b) Marker Generation

As shown in figure 4, the signal consists of

60 markers each minute, with one marker oc- curring 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

"

8
Mt 'fi*U( ONE SECONOl

M\ -m\ iiiiiiiiiii

36 BINARY DIGIT, 100 PPS CODE (1000 Hz CARRIER)

MC rniME ONE SEOSO

- 0 Pu.St 'Z«S: (ijujxnjwuiju^^

« I UNITS fEUS , JN^TS "rftlS , UN TS Tins UliTS TtNS MUNODEOS f 50 SECONDS 25 yiNuTtS ErCACNCC TlUC li 0»i lO hOuRS. 21 W>NUTCS. *iO SECONDS

36 BINARY DIGIT. lOO PPS CODE

0 ONI SCCCN3 aErEDtNCC W*»a(ll

t O >5 iNDE M An«C Q

» .00 OPS INOE K MASnE"

i.^uS£0 fliT

Figure 3. Chart of time code transmissions from NBS radio station WWV.

and restoring it 0.2 second later for an uncoded

marker or binary "zero," 0.5 second later for a binary "one," and 0.8 second later for a 10-

second position marker or for a minute refer- ence marker. Several examples of binary

"ones" are indicated by I in figure 4.

(c) Marker and Groups

The 10-second position markers, labeled PO to

P5 on the diagram, occur respectively in the

60th, 10th, 20th, 30th, 40th, and 50th seconds

of each minute. The minute reference marker

occurs in the 1st second of the minute. Uncoded markers occur periodically in the 5th,

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

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

22nd, 36th, 56th, 57th, 58th, and 59th seconds.

Thus, every minute contains twelve groups of

five markers, each group ending either with a

position marker or an uncoded marker. The

signal pulses lasting for 0.2 seconds after a

position marker are shown blackened in figure

4; the signal pulses lasting for 0.8 seconds after a periodically uncoded marker are shaded; other

signal pulses following uncoded markers are

labeled with a U.

With the exception of the uncoded and refer- ence markers specifically mentioned above, the

remaining markers in each of the groups are

utilized to convey additional information.

(d) Information Sets

Each minute the code presents time-of-year

information in seconds, minutes, hours, and day

of the year and the actual milliseconds differ- ence between the time as broadcast and the best

known estimate of UT2. A set of groups, con- taining the first two BCD groups in the minute.

specifies the minute of the hour; the third and

fourth BCD groups make up a set which specifies the hour of the day; the ififth, sixth, and

seventh groups form a set which specifies the

day of the year; a set, made up of the ninth,

tenth, and eleventh BCD groups, specifies the

number of milliseconds to be added to or subtracted from the code time as broadcast in order

to obtain UT2.

The relationship of the UT2 scale to the time

as coded is indicated in the eighth group. If

UT2 is "late" with respect to the code time, a binary "one," labeled SUB (subtract) in figure

4, will be broadcast in the eighth group during the 38th second of the minute. If UT2 is

"early" with respect to the code time, binary

"ones," labeled ADD, will be broadcast in the

eighth group during the 37th and 39th seconds

of the minute.

The twelfth group is not used to convey information.

(e) Digital Information

When used to convey numerical information,

the four coded markers used as digits in a BCD

group are indexed 8-4-2-1 in that order. Sometimes only the last two or three of the coded

markers in a group are needed, as in the first

groups in 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 sec- ond group by 10, and those by the third group

by 1.

9
-TIME- TIME FRAME 1 MINUTE

"(INDEX COUNT 1 SECOND)

SIGNAL

"ON"

SIGNAL

-10 dB

J I \ I

I L

10 20

J I I I I I \

I I I L_J

-REFERENCE TIME REFERENCE MARKER FOR MINUTES , SECOND - BINARY "ZERO" —j hrO.8 SECOND ll (TYPICAL)

I I PI

I II P2I 40 20 10 8 4 2 1 20 10 8 4 2 1

PO

MINUTES SET HOURS SET

-TIME20

J I 1 \ |__l I L 30

J I L J I I L 40

, ^_0.5 SECOND- BINARY "ONE"

\

\ (TYPICAL) 1

1.0 SECOND

'(TYPICAL)

P2 I I I P3 I / I P4 I 200100 80 40 20 10 8 4 2 1 DAYS SET

TIME AT THIS POINT EQUALS 258 DAYS, 18 HOURS,

42 MINUTES, 35 SECONDS. TO OBTAIN THE

CORRESPONDING UT2 SCALE READING,

SUBTRACT 41 MILLISECONDS.

TIME —

ADD^'^^ADD

UT2

RELATIONSHIP

40

I I I J I I L 50

J I 1

I I L 60

I l_^.8 SECOND POSITION IDENTIFIER n r (TYPICAL)

ULTTTTWimajnnnnmMMRj P4 400 100

800 200

I P5 I 80 40 20 10 8 4 2 1

PO

UT2 SET

DIFFERENCE OF UT2 FROM

CODED TIME IN MILLISECONDS

GROUP 12

MARKER

P IMPULSE

POSITION MARKER PERIODIC UNCODED

AND. PULSE MARKER AND PULSE

UNCODED MARKER

AND PULSE

mI BINARY "ONE"

n

BINARY "ZERO"

FIRST REVISION - 6.21.65

NBS TIME CODE

FORMAT "WWVB"

1 pps CODE

Figure 4. Chart of time code transmissions from NBS radio station WWVB.

Example

A specific example is indicated in figure 4.

The occurrence of two binary "ones" in the

"minutes set" indicates that the minute con- templated is the 40 -f 2 = 42nd minute. Similarly, the two binary "ones" in the "hours set"

indicate the 10 + 8 = 18th hour of the day,

while the four binary "ones" in the "days set"

indicate the 200 + 40 + 10 + 8 = 258th day of

the year. It is seen from the "UT2 Relationship" group and the "UT2 set" that one should

subtract, from any second in this minute, 40 +

1 = 41 milliseconds to get the best estimate of

UT2. For example, the 35th UT2 interval

would end 41 milliseconds later than the end

of the 35th second; or, in other words, the UT2

scale reading for the end of the 35th second

would be 18"42"'34.^959 since 35.000 — 0.041 =

34.959.

1.10. Station Identification

WWV and WWVH identify by International Morse Code and voice (in English) every

five minutes. The voice announcements are automatically synchronized magnetic-drum re- cordings, not live broadcasts. The announcer

is Mr. Don Elliott of Atlanta, Georgia.

WWVL transmits no identification other

than its unique format of alternating frequency

every 10 seconds. WWVB identifies by its

unique Time Code (see section 1.9) and by advancing the carrier phase 45° at 10 min after

each hour and returning to normal phase at

15 min after each hour.

1.11. Radiated Power, Antennas and

Modulation

(a) Radiated Power

Frequency, Radiated Power, kw

MHz WWV WWVH WWVB WWVL

0.020 _ _ _ 2

0.060 _ _ 16 —

2.5 2.5 1 — —

5 10 2 — —

10 10 2 — —

15 10 2 — —

20 2.5 — — —

25 2.5 — — —

(b) Transmitting Antennas

The broadcasts on 2.5 and 5 MHz from

WWVH are from vertical quarter-wave antennas. The broadcasts on all other frequencies

from WWVH and all frequencies from WWV

are from vertical half-wave dipoles. WWV an- tennas are omnidirectional. Effective August 1,

1967 the WWVH antennas for 5, 10, and 15

MHz have directional reflectors providing additional gain in the westerly direction. The an- tennas used by WWVB and WWVL are 400-

foot vertical antennas with capacity toploading.

(c) Modulation

At WWV and WWVH all modulation is

double sideband amplitude, with 75 percent

modulation on the steady tones and 100 percent

modulation for seconds pulses and voice.

WWVB employs 10 dB carrier-level reduction

for transmitting time information (see section

1.10).

WWVL uses no modulation. Various experimental techniques are being studied in an attempt to develop a good timing system at Very

Low Frequencies.

2. How NBS Controls the Transmitted Frequencies

In figure 5 a simplified diagram of the NBS

frequency control system-' is shown. The entire

system depends upon the basic frequency refer- ence shown in this diagram as the Cesium (Cs)

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 #8.^ All

"J. B. Milton, Standard Time and Frequency: Its Generation Control, and Dissemination from the National Bureau of Standards Time and Frequency Division, Na. Bur. Stand. (U.S.), NBS Tech. Note 379, 30 pages (August 1969).

"J. Tolman, V. Ptacek, A. Soucek, and R. Stecher, Microsecond

clock comparisons by means of TV synchronizing pulses, IEEE

Trans.—Instr. and Meas.. IM-16, No. 3, September 1967, pp.

247-254.

other clocks and time-code generators at the

site are then compared with this master clock.

Frequency corrections of the WWVB and

WWVL quartz crystal oscillators are based on

their time or phase relative to the master clock.

The transmissions from WWV are controlled

by three cesium standards located at the site.

To ensure accurate time transmission from

WWV, the time-code generators are compared

with the Fort Collins Master Clock several

times each day.

Control of the signals transmitted from

WWVH is based upon signals from WWVB

and WWVL as received by phase-lock receivers.

The oscillator controlling the transmitted frequencies and time signals is continuously compared with the received signals. Manual adjustments are then made to the controlling oscilla12
tor to compensate for the drift characteristic into the system, the NBS time scale is compared

of quartz crystal oscillators. with the transmitting station clocks by the use To assure that systematic errors do not enter of a very precise portable clock.

NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards ' was established by an act of Congress March 3, 1901 . Today,

in addition to serving as the Nation's central measurement laboratory, the Bureau is a principal

focal point in the Federal Government for assuring maximum application of the physical and

engineering sciences to the advancement of technology in industry and commerce. To this end

the Bureau conducts research and provides central national services in four broad program

areas. These are: (1) basic measurements and standards, (2) materials measurements and

standards, (3) technological measurements and standards, and (4) transfer of technology.

The Bureau comprises the Institute for Basic Standards, the Institute for Materials Research, the

Institute for Applied Technology, the Center for Radiation Research, 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 an Office of Measurement Services and the following technical

divisions:Applied Mathematics—Electricity—Metrology—Mechanics—Heat—Atomic and Molecular Physics—Radio Physics -—Radio Engineering -—Time and Frequency -—Astrophysics -—Cryogenics.

THE INSTITUTE FOR MATERIALS RESEARCH conducts materials research leading to im- proved methods of measurement standards, and data on the properties of well-characterized

materials needed by industry, commerce, educational institutions, and Government; develops,

produces, and distributes standard reference materials; relates the physical and chemical properties of materials to their behavior and their interaction with their environments; and provides

advisory and research services to other Government agencies. The Institute consists of an Office

of Standard Reference Materials and the following divisions: Analytical Chemistry—Polymers—Metallurgy—Inorganic Materials—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 in the development of technological

standards, and test methodologies; and provides advisory and research services for Federal, state, and local government agencies. The Institute consists of the following technical divisions and

offices: Engineering Standards—Weights and Measures — Invention and Innovation — Vehicle Systems Research—Product Evaluation—Building Research—Instrument Shops—Measurement Engineering—Electronic Technology—Technical Analysis.

THE CENTER FOR RADIATION RESEARCH engages in research, measurement, and application of radiation tb the solution of Bureau mission problems and the problems of other agencies and institutions. The Center consists of the following divisions: Reactor Radiation—Linac Radiation—Nuclear Radiation—Applied Radiation. THE CENTER FOR COMPUTER SCIENCES AND TECHNOLOGY conducts research and

provides technical services designed to aid Government agencies in the selection, acquisition,

and effective use of automatic data processing equipment; and serves as the principal focus

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 — Sys- tems 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 Measure- ment System, and 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—Clearinghouse for Federal Scientific and Technical Information ' —^Office of Technical Information and Publications—Library—Office of Public Information—Office of International Relations.

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

= Located at Boulder. Colorado 80302.

=' Located at 5285 Port Royal Road. Springfield, Virginia 22151. 13
NBS Fort Collins facility showing WWV transmitter building.

U.S. DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20230

OFFICIAL BUSINESS POSTAGE AND FEES PAID

U.S. DEPARTMENT OF COMMERCE