Miscellaneous Pu ilication 23

.S. DEPARTMENT OF COMMERCE

ATIONAL BUREAU OF STANDARDS

Standard Frequencies and Time Signals

from

NBS Stations WWV and WWVH
UNITED STATES DEPARTMENT OF COMMERCE • Frederick H. Mueller, Secretary NATIONAL BUREAU OF STANDARDS • A. V. Astin, Director

Standard Frequencies and Time Signals From NBS

Stations WWV and WWVH

National Bureau of Standards Miscellaneous Publication 236

Reprinted July 1, 1961 with corrections

(First issued December 1, 1960)

Detailed descriptions are given of six technical services broadcast by National Bureau

of Standards radio stations WWV and WWVH. The services include 1, standard radio

frequencies; 2, standard audio frequencies; 3, standard time intervals; 4, standard musical

pitch; 5, time signals; and 6, radio propagation forecasts. Other domestic and foreign standard frequency and time signal broadcasts are tabulated.

1. Technical Services and Related Information

The National Bureau of Standards' radio sta- tions WWV (in operation since 1923) and WWVH

(since 1948) broadcast six widely used technical

services: 1, Standard radio frequencies; 2, stand- ard audio frequencies; 3, standard time intervals;

4, standard musical pitch; 5, time signals; 6, radio propagation forecasts. 1 The radio stations are located as follows: WWV,

Beltsville, Maryland (Box 182, Route 2, Lanham,

Maryland); WWVH, Maui, Hawaii (Box 901, Punnene, Maui). Coordinates of the stations are: WWV (lat. 38°59'33" N, long. 76°50'52" W)

;

WWVH (lat. 20°46'02" N, long. 156°27'42" W).

1.1. Standard Radio Frequencies

(a) Program Station WWV broadcasts on standard radio frequencies of 2.5, 5,10, 15, 20, and 25 Mc. The

broadcasts are continuous, night and day, except WWV is interrupted for approximately 4 min each

hour. The silent period commences at 45 min

(plus 0 to 15 sec) after each hour. (See fig. 1.) Station WWVH broadcasts on standard radio frequencies of 5, 10, and 15 Mc. The broadcast

is interrupted for 3 min commencing on the hour

(plus 0 to 15 sec) and on each quarter hour thereafter, and for periods of 34 min each day beginning

at 1900 UT (Universal Time, UT, is the same as GMT and GCT).

(b) Accuracy 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 which

constitute the United States Frequency Standard

(USFS), maintained and operated by the Radio

Standards Laboratory of the National Bureau of Standards. Carefully made atomic standards have been shown to realize the idealized Cs reso- nance frequency,

/

Cs , to a few parts in 10 10 or better; and the present USFS is believed to realize this resonance to 1.5 parts in 10 11

. The fre- quency /Cs has been measured in terms of the second 2 to be

/

Cs =9, 192, 631,770 ±20 cps. This

uncertainty of 2 parts in 109

, with which frequency can be expressed in terms of the second, has usually been avoided in practice by provisionally taking

/C8 exactly equal to the above number (or to some

other stated number before the above was available). On January 1, 1960, the USFS was brought into agreement with /C9 as quoted above by arbitrarily increasing its assigned value by 74 parts in 10 10

. Frequencies measured in terms of the USFS bei All inquiries concerning the technical radio broadcast services should be

addressed_to: Radio Standards Laboratory, National Bureau of P*~

Roulder, Colo. Mai tow it./. Hall, Essen, and Parry, Frequency of cesium in terms of epbemeris time, Phys. Rev. Letters 1, 105 (1958).

For sale by the Superintendent of Documents, U.S. Government Print

Price 10 cents

; Office, Washington 25, D.C

.

2
tween 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. 3 The frequency of the transmissions from WWV

normally are held stable to 1 part in 109

, at all times. Deviations at WWV are normally less than 2 parts in 10 10 from day to day. When

necessary, frequency adjustments not exceeding

5 parts in 10 10 are made at WWV at 1900 UT.

Frequency adjustments at WWVH do not exceed

3 parts in 109

. Changes in the propagation medium (causing Doppler effect, etc.) result at times in fluctuations

in the carrier frequencies as received which can be

very much greater than the uncertainties described above.

(c) Corrections All carrier and modulation frequencies at WWV

are derived from a common 2.5-Mc quartz oscillator, the stability of which is described above.

In addition, since January 1, 1960, this oscillator has been intentionally offset from the USFS by a

small but precisely known amount in order to reduce departure between the time signals broadcast and astronomical time UT2. For example,

the offset for 1960 is about 150 parts in 10 10

, and

is low with respect to the USFS, since the unit

of UT2 is about this much longer than the (Ephemeris) second. Although UT2 is subject to unpredictable changes observable at this level of

precision, it is nevertheless expected that a particular offset can be left unchanged throughout each

calendar year, thus providing as constant a frequency as possible for the year. For the above reasons, corrections to the actual

oscillator frequency are continuously determined

with respect to the USFS and are published in the Proceedings oj the IRE. These wer.e begun in May, 1958 with data extending back to December

1, 1957. 4

1.2. Standard Audio Frequencies

(a) Program Two standard audio frequencies, 440 cps and

600 cps, are broadcast on each radio carrier fre- quency. The audio frequencies are given alter- nately at 5-min intervals starting on the hour with

600 cps, as shown in figure 1. At WWV, the first tone period (600 cps) of each hour is of 3-min

duration; the remaining periods are of 2-min

duration. At WWVH, all tone periods are of 3- min duration.

(b) Accuracy The accuracy of the audio frequencies, as transmitted, is the same as for the carrier. The

> National standards of time and frequency in the United States, Proc. IRE 48, 105 (1960). T„„ „ 4 W. D. George, WWV standard frequency transmissions, Proc. IRE 46, 910 (1958) and subsequent issues.

frequency offset mentioned under 1.1(c) applies. Changes in the propagation medium (causing Doppler effect, etc.) result at times in fluctuations

in the audio frequencies as received.

1.3. Standard Time Intervals

(a) Program Seconds pulses at precise intervals are derived from the same oscillator which controls the radio

carrier frequencies, e.g., they commence at intervals

of 5,000,000 cycles of the nominal 5 Mc/s carrier. They are given by means of double-sideband amplitude-modulation on each radio carrier fre- quency. Intervals of 1 min are marked by omitting the pulse at the beginning of the last second

of every minute and by commencing each minute

with two pulses spaced by 0.1 sec; the first pulse is used to mark 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 off. The pulse duration is 0.005 sec. The pulse wave form is shown in figure 2. At WWV each pulse consists of five cycles of a 1,000-cps frequency. At WWVH

each pulse consists of six cycles of a 1,200-cps frequency. The pulse spectrum is composed of discrete frequency components at intervals of 1.0 cps. The components have maximum amplitudes

at approximately 995 cps and 1,194 cps for the WWV and WWVH pulses, respectively. The

tone is interrupted 0.040 sec for each seconds

pulse. The pulse starts 0.010 sec after commence- ment of the interruption.

(b) Accuracy The accuracy of the time intervals, as trans- mitted, is the same as for the carrier with an additional limitation of ±1 Msec. The frequency

offset mentioned under 1.1(c) applies. (See note concerning time adjustments under section 1.5(b), Time Signals.)

1.4. Standard Musical Pitch The frequency 440 cps 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

cps 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 an unvarying standard.

Practically no instruments are manufactured

which cannot be tuned to 440 cps. Listeners of music are benefited because there are fewer instru- ments not in tune.
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 resumed

on the hour at WWV and at 5- and 10-minute

intervals at both stations as shown in figure 1

.

Universal Time (referenced to the zero meridian)

is announced in International Morse Code each 5 min from WWV and WWVH. This provides a quick reference to correct time where a timepiece may be in error by a few minutes. The 0-to-24-hr 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 UT, four figures (1, 6, 5, and 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 Eastern Standard Time is given before and after each International Morse Code announcement.

For example, at 9:10 a.m., EST, the voice an- nouncement in English is: "National Bureau of Standards, WWV; when the tone returns, Eastern

Standard Time is 9:10 a.m."

(b) Corrections The time signals are kept in close agreement with UT2 by making step adjustments of precisely 50 msec when necessary. Such adjustment will be made on the first of the month following the month

in which the transmitted time departs from UT2

by more than 50 msec. Corrections to the time

signals are published periodically by the U.S. Naval Observatory.

1 .6. Radio Propagation Forecasts A forecast of radio propagation conditions is broadcast in International Morse Code on each of the standard radio carrier frequencies; from WWV

at approximately 19.5 and 49.5 min past each hour, and from WWVH at approximately 9.4 and 39.4 min past each hour, as shown in figure 1. Propagation notices were first broadcast from WWV in 1946; the present type of announcement has been

broadcast from WWV since July, 1952, and from WWVH since January, 1954. The forecast announcement tells users the condition of the ionosphere at the regular time the

forecast is made and how good or bad communication conditions are expected to be in the suc- ceeding six or more hours. The NBS forecasts

are based on information obtained from a world- wide network of geophysical and solar observatories, including radio soundings of the upper

atmosphere, short wave reception data, and similar information. Trained forecasters digest the infor- mation and formulate the predictions.

From WWV the forecasts refer only to North

Atlantic radio paths, such as Washington to London or New York to Berlin. The times of

issue are 0500, 1200 (1100 in summer), 1700, 2300 UT. These are the short-term forecasts prepared

by NBS-CRPL North Atlantic Radio Warning

Service, Box 178, Ft. Belvoir, Va. From WWVH the forecasts are for North

Pacific radio paths, such as Seattle to Tokyo, or Anchorage to San Francisco. As of March 1, 1959, the times of issue are 0600 and 1800 UT, and

the forecasts are first broadcast at 0639 and 1839 UT, respectively. These are the short-term fore- casts prepared by NBS-CRPL North Pacific Radio Warning Service, Box 1119, Anchorage,

Alaska. The forecast is broadcast as a letter and a digit. The letter portion of the announcement identifies the radio quality at the time the forecast is made. The letters denoting quality are "N," "U," and "W," signifying that radio propagation conditions

are normal, unsettled, or disturbed. The digit portion is the forecast of the radio propagation

quality on a typical North Atlantic (from WWV)

or a typical North Pacific (from WWVH) trans- mission path during the 6 or more hours after the

forecast is made. Quality is graded in steps ranging from 1 (useless) to 9 (excellent) as follows: Disturbed

grades (W)

1 —useless 2—very poor

3—poor

4—poor-to-fair

Unsettled grade (U)

5—fair

Normal

grades (N)

6—fair-to-good

7—good

8—very good

9—excellent

If, for example, propagation conditions at the time

the forecast is made are normal but are expected

to be only "poor-to-fair" within the next 6 or more hours, the announcement would be broadcast as N4 in International Morse code.

1.7. Geophysical Alerts A symbol indicating the geophysical "state of warning" as declared under the international pro- gram of the International Council of Scientific Unions, is broadcast in very slow International Morse Code on each of the standard radio carrier frequencies; from WWV at approximately 4.5 and

34.5 min past each hour, and from WWVH at approximately 14.4 and 44.4 min past each hour,

as shown in figure 1. Such notices were first broadcast during the International Geophysical Year 1957-58 and are continuing under the

similarly organized program, International World Day Service (1WDS). The "state of warning" symbol indicates to experimenters in radio, geophysical, and solar sciences the content of the IWDS Warning

Message issued at 1600 UT by the World Warning
Agency on days when outstanding geophysical

events have occurred in the preceding 24 hr. The information in each such message is first broadcast from WWV at 1604.5 UT and from WWVH at 1714.4 UT.

If the IWDS Warning Message declares an

alert, the symbol AGI AAAA is broadcast for 24 hr. This means that a significant magnetic

storm has started, with .K-index reaching 5 or higher at a midlatitude station. It can also mean

that an outstanding auroral display has been

reported (or inferred, because the i_T-index has reached at least 7) or that an outstanding increase

in cosmic ra_y flux has been observed. The IWDS

Warning Message itself, distributed through other channels including the meteorological communication networks coordinated by the World Meteorological Organization, specifies whether the

alert is Magnetic Storm, Aurora, or Cosmic Ray;

the "state of warning" symbol broadcast from WWV and WWVH does not make these distinc- tions at the present time. A Special World Interval in progress is indicated by the symbol AGI and three extra long dashes. This means that an alert, as above, has been

declared and, further, that the geophysical

activity is of sufficient interest to warrant special attention and intensified observations bv experimenters throughout the world. A Special World

Interval will usually last two or three days. The

Interval is considered to extend until 2359 UT on

the final day even though the symbol "Special World Interval in progress" is not broadcast after 1600 UT (WWV) or 1700 UT (WWVH).

When the "state of warning" is neither alert nor Special World Interval in progress, the symbol

broadcast is AGI EEEEE.

1.8. Radiated Power, Transmitting Antennas, Modulation

Frequency, Mc

2. 5

510

1520

25

(a) Radiated Power Power, lew WWV

1

10. 1

Power, kw

WWVH

_____

22

(b) Transmitting Antennas The broadcast on 2.5 Mc from WWV and on

5 Mc from WWVH is from a vertical quarter-wave

antenna. The broadcasts on all other frequencies

are from vertical half-wave dipoles. The antennas

are omnidirectional.

FREQUENCY DEVIATION OF RADIO STATION WWV (WITH REFERENCE TO THE ATOMIC STANDARDS SINCE DEC. 1, 1957)

DEVIATIONS FROM US NAVAL OBSERVATORY UT 2 TIME 7 "Z

WWV AND WWVH SECONDS PULSES

THE SPECTRA ARE COMPOSED OF DISCRETE FREQUENCY

COMPONENTS AT INTERVALS OF I.OCpS.THE COMPONENTS AT THE SPECTRAL MAXIMA HAVE AMPLITUDES OF 0.005 VOLT

FOR A PULSE AMPLITUDE OF 1.0 VOLT. THE WWV PULSE

CONSISTS OF FIVE CYCLES OF IOOO Cps. THE WWVH PULSE CONSISTS OF SIX CYCLES OF 1200 Cps .

0 500 1000 1500 2000 FREQUENCY , cps WWVH

Figure 1. Sample characteristics of time and frequency broadcasts from NBS stations WWV and WWVH.

5
(c) Modulation The amplitude modulation, double sideband, is: Audio frequencies 440 or 600 cps —75 percent, voice and seconds pulses, peak—100 percent. At WWV, the tone frequency 440 or 600 cps,. except on 25 Mc, is normally operated as a single upper sideband with full carrier. Power output from each sideband transmitter is about one-third

the carrier power. Single sideband tone modulation on 25 Mc may be added at a later date. Other signals (announcements and seconds pulses) are double sideband, 100-percent amplitude

modulation.

1.9. Other Standard Frequency and Radio Time

Signal Services Standard frequencies and time signals broadcast

include the stations indicated in the following

table

Call sign Location Carrier frequency Modulation Carrier power

(a) HF Broadcasts, Mc xps kw ATA New Delhi, India.. . . ... 10 1, 1000 1. FFH Paris, France 2. 5, 5, 10 1, 440, 1000 0. 3 HBN Neuchatel, Switzerland . _ 2. 5, 5 1, 500 0. 5

I AM Rome, Italy . . ... . — 5 1, 440, 600, 1000 1. IBF Turin, Italy . 5 1, 440, 1000 0. 3 JJY Tokyo, Japan. ... . . 2. 5, 5, 10, 15 1, 1000 2. LOL Buenos Aires, Argentina . 2. 5, 5, 10, 15, 20, 25 1, 440, 1000 2. MSF Rugby, England 2. 5, 5, 10 1, 1000 0. 5 OMA Prague, Czechoslovakia

.

2. 5 1, 1000 1. ZLFS Lower Hutt, New Zealand. . . . . 2. 5 0. 03 ZUO Olifantsfontein, South Africa . 5 1 4. Moscow, USSR 10, 15. 1 20.

(b) VLF Broadcasts WWVL Sunset, Colorado.. . . . ... 20 Ko 0. 02

2. Stations Operating Outside the Exclusive Bands

2.1. LF and VLF

Call sign Location Carrier frequency Modulation Carrier power WWVB ' DCF77 CHU

OMA

GBR

MSF NBA

Boulder, Colorado ...

kc 60

77. 5 3330, 7335, 14670

50

1660

18

cps kw

0. 0015

12

0. 3, 3, 5 5300

10100

Federal German Republic. ....

Ottawa, Canada .... _ ..

1, 200, 440

1 Czechoslovakia .... . . ... . Rugbv, England. . .. _. .. . Rugbv, England ... . ....

U.S. Navv, Canal Zone

1, 1000

1

' National Bureau of Standard* station WWVB (formerly KK2XEI) broadcasts continuously and the call letters are keyed approximately on the hour and each 20 min thereafter. The frequency is normally controlled bv an atomic standard. Present plans are to increase the radiated power to about 3 kw as soon as possible. 2.2. Other Broadcasts The U.S. Naval Observatory, Department of the Navy, broadcasts time signals continuously

or at regular intervals from a number of stations including NSS (Annapolis, Md.), NPG (Mare

Island, Calif.), NPM (Pearl Harbor, Hawaii), and NBA (Balboa, C.Z.). Detailed information may be obtained from the U.S: Naval Observatory, Washington 25, D.C. A comprehensive list of United States and

foreign radio time signals is given in chapters 3 and 9 of Radio Navigational Aids, Hydrographic

Office Publication No. 117 (formerly H.O. Pub. No. 205), for sale by local and foreign authorized

sales agents of the U.S. Navy Hydrographic

Office or direct from the U.S. Navy Hydrographic

Office, Washington 25, D.C. Price of the publication, with a binder, is $5.00; contents only

(without binder), $3.50. Boulder, Colo.

6
Changes in WWV/WWVH Standard Broadcasts

ONJanuary 1. 1961, at 0000 UT, the Bureau retarded

the time signals broadcast from radio stations WWV and WWVH by 5 msec,

1 and at the same time resumed broadcasting a special timing code 2 which

gives the day, hour, minute, and second (UT) coded

in binary form. The 5-msec retardation brought the time signals of WWV/WWVH into closer agreement

with other standardized frequency broadcasting sta- tions throughout the world. The pulse timing code,

tried out on an experimental basis for several months

during 1960, has now been returned to the air on a permanent basis. The United Kingdom and the United States began

coordinating their time and frequency transmissions

early in 1960. This coordination is the result of an agreement announced by Dr. James H. Wakelin, Jr., Assistant Secretary of the Navy (Research and Develop- ment) , Dr. Allen V. Astin, Director of the U.S. National Bureau of Standards, and in the United Kingdom by the Astronomer Royal, Royal Greenwich Observatory, and

the Director of the National Physical Laboratory. Coordination was begun to help provide a more uni- form system of time and frequency transmissions throughout the world, needed in the solution of many

scientific and technical problems in such fields as radio communications, geodesy, and the tracking of artificial

satellites. Participating in the project are the Royal Greenwich

Observatory, the National Physical Laboratory, and the Post Office Engineering Department in the United King- dom, and, in the United States, the U.S. Naval Observatory, the Naval Research Laboratory, and the National Bureau of Standards. This program follows previous

cooperative efforts of these agencies to achieve uni- formity and simplification in procedures. The transmitting stations which are included in the coordination plan are GBR and MSF at Rugby, England; NBA, Canal Zone; WWV, Beltsville, Maryland;

and WWVH, Hawaii. Although the signals emitted by all these stations are kept on as uniform a basis as is feasible, occasional

corrections are necessary. The last previous time ad- justment for WWV/WWVH, a retardation of 20 msec, was made on December 16, 1959. It is expected that such adjustments in the time signals will be made as infrequently as possible and preferably at the beginning

of each calendar year when necessary. The time sig- nals are locked to the broadcast frequency.

In 1961 it is planned to maintain the frequency stable

to 1 part in 1010 and at the same offset value as before,

i.e., —150 parts in 1010 with reference to the United

States Frequency Standard.3 The timing code provides a standardized timing basis

for use when scientific observations are made simul- taneously at widely separated locations. It can be used

for example, where signals telemetered from a satellite are recorded along with these pulse-coded time signals; 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. This 36-bit, 100-pulse/sec time code, carried on

1,000-c/s modulation, is being broadcast from radio

station WWV ( 2.5, 5, 10, 15, 20, and 25 Mc/s) . Start- ing date was January 1, 1961.

1. The code is broadcast for 1-min intervals and 10

times per hour. Except at the beginning of each hour,

it immediately follows the standard audiofrequencies

of 440 c/s and 600 c/s.

2. The code contains time-of-year information (Universal Time) in seconds, minutes, hours, and day of

year. It is locked in phase with the frequency and

time signals.

3. The code is binary coded decimal (BCD) consist- ing of 9 binary groups each second in the following

order: 2 groups for seconds, 2 groups for minutes, 2 groups for hours, and 3 groups for day of year. Code

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

4. A complete time frame is 1 sec.

5. The least significant binary group and the least significant binary digit in each group occur first. The

binary groups follow the 1-sec reference marker.

6. "On time" occurs at the leading edge of all pulses.

7. The code contains 100-per-second clocking rate, 10-per-second index markers, arid 1-per-second refer- ence marker. The 1,000 c/s is locked to the code

pulses so that millisecond resolution is easily obtained.

8. The 10-per-second index markers consist of "1"

pulses preceding each code group except at the begin- ning of the second where it is a "0" pulse.

9. The 1-sec reference marker is made up of five "1"

pulses followed by a "0" pulse. The second begins at the leading edge of the "0" pulse.

10. The code is a spaced code format; that is, a binary group (BCD) follows each of the 10-per-second index markers. The last index marker is followed by

an unused 4-bit group of "0" pulses just preceding the 1-second reference marker.

11. The unused 4-bit group may be used in the future

to transmit other types of coded information, such as

the last digit of the year, station number, etc. 12. Width coding: "0" pulse, 2 msec wide (2 cycles of 1,000 c/s) "I" pulse, 6 msec wide (6 cycles of 1,000 c/s)

13. The time code is amplitude modulated on 1,000

c/s. The leading edges of the time code pulses coin- cide with a positive-going zero-axis-crossing of the 1,000 c/s.

1 National standards of time and frequency in the United

States, Proc. IRE 48, 105-106 (Jan. 1960)

2 Experimental timing code added to WWV broadcasts, NBS Tech. News Bui. 44, 114 (July 1960)

3 Atomic frequency standards, NBS Tech. News Bui. 45, 8 (Jan. 1961).

7
FIGURE 2. Chart of time code transmissions from NBS radio station WWV.

K 0 0 2

TIME CODE ON WW\

i urn i nn inn urn mil i n n inn urn i

I I I II I |M.

[ MM, . I, ,,1111 | MM ,

i *irr T-"""" ^r;o;?:v

!us

' ..... i r:;

s;;: .... ..... i rjUUmWUTTTJUUL^^

36 BINARY DIGIT, 100 PPS CODE

I " i |- i . i I, , ,,.,

| | | M . l |

. M .|.i,, i i, rTjr

CALL SIGN AND EST (VOICE

I

IWDS WARNINGS UT I CODE I ICODE) 3 EST (VOICE)

10 20 30 40 50 10 20 30 40 50 30 40 50 60

UT (CODE) IWDS WARNINGS

CALL SIGN (CODE) (CODE)"

19 5 AND 49 5 MINUTES PftST EACH HOUR

9 4 AND 39 4 MINUTES PAST EACH HOUR

5 4 3 AND 34 3 MINUTES PAST EACH HOUR

4 14 4 AND 44,4 MINUTES PAST EACH HOUR

IWDS WARNINGS WWV | 600 | *-

j 440

|

1 600 | [440 J H

600 I

1 440 I 1 600 H44ol

PROPAGATION FORECASTS - 600 440 h

I I I I I

I J

25 30 3b 40 45 50 56 60 MINUTES

RADIO PROPAGATION FORECASTS - 600 |

1 440 I \' ' "\ 1 440 I M 600

IWDS WARNINGS ED-

\\\ \\\\\\\\\\\\\\\\\\ TTT

!

I I I I I I I I I ! I I I I I I I

I I i START B» j

| j j | J | j j' j | j |

'» J

|

16 |

16 19 2° 21 22 23 24 HOURS UT

WWVH LiiimiHMlgllUL^^

U S GOVERNMENT PRINTING OFFICE : 1961 0 —606031