Basic radio propagation predictions for August 1960: three months in advance

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Basic Radio
Propagation
Predictions

FOR AUGUST 1960

Three Months in Advance

Issued May 1960

CPRL Series D

Number 189

The Central Radio Propagation Laboratory

The propagation of radio waves over long distances depends on their reflection from the ionosphere, the electri¬
cally conducting layers in the earth’s upper atmosphere. The characteristics of these layers are continually changing.
For regular and reliable communication, it is therefore necessary to collect and analyze ionosphere data from sta¬
tions all over the world in order that predictions of usable frequencies between any two places at any hour can be
made. During the war, the United States Joint Communications Board set up the Interservice Radio Propagation
Laboratory at the National Bureau of Standards to centralize ionospheric work and predictions for the Armed
Forces of the United States.

On May 1, 1946, this activity returned to peacetime status as the Central Radio Propagation Laboratory of the
National Bureau of Standards. Designed to act as a permanent centralizing agency for propagation predictions and
studies, analogous in the held of radio to the reports of the Weather Bureau in the field of meteorology, the Central
Radio Propagation Laboratory was established in cooperation with the many government agencies vitally concerned
with communication and radio propagation problems. These agencies are represented on an Interdepartmental Coun¬
cil on Radio Propagation and Standards which assists in furthering the work of the Laboratory; included are the
Departments of State, Army, Navy, and Air Force, United States Information Agency, United States Coast Guard,
Civil Aeronautics Administration, and Federal Communications Commission. Observers have been designated by
the Air Navigation Development Board, Interdepartment Radio Advisory Committee, United States Coast and
Geodetic Survey, and United States Weather Bureau. The Council works in cooperation with a Technical Advisory
Committee appointed by the Institute of Radio Engineers at the request of the Director, National Bureau of
Standards.

The Central Radio Propagation Laboratory receives and analyzes data from approximately 120 stations located
throughout the world, including 8 domestic and 17 overseas stations which are operated either directly or under
contract by the National Bureau of Standards. Ionospheric data and predictions are disseminated to the Armed
Forces, commercial users, scientists, and laboratories. The basic ionospheric research of the Laboratory includes
theoretical and experimental studies of maximum usable frequencies, ionospheric absorption, long-time variations of
radio propagation characteristics, the effects of the sun on radio propagation, and the relation between radio dis¬
turbance and geomagnetic variation. In the microwave field, the Laboratory is investigating the relation between
radio propagation and weather phenomena, as well as methods by which predictions can be made and radio commu¬
nications improved in this portion of the radiofrequency spectrum. Another phase of the Laboratory’s work is the
development and maintenance of standards and methods of measurement of many basic electrical quantities through¬
out the entire frequency spectrum.

Basic Radio Propagation Predictions

The CRPL Series D, Basic Radio Propagation Predictions, is issued monthly as an aid in the determination of
the best sky-wave frequencies over any path at any time of day for average conditions for the month of prediction,
3 months in advance. Charts of extraordinary-wave critical frequency for the F‘2 layer, of maximum usable frequency
for a transmission distance of 4,000 km, and of percentage of time occurrence for transmission by sporadic E in ex¬
cess of 15 Me, for a distance of 2,000 km, are included.

Beginning with the January 1958 issue (CRPL-D161) the CRPL-D series, “Basic Radio
Propagation Predictions,” is available on a purchase basis from the Superintendent of Docu¬
ments, U. S. Government Printing Office, Washington 25, D. C., on the following terms:

Single copy 15 cents

Annual subscription (12 issues) $1.50

(To foreign countries, $2.00)

The rules of the Superintendent of Documents require that remittances be made in advance
either by coupons sold in sets of 20 for $1 and good until used, or by check or money order
payable to the Superintendent of Documents. Currency, if used, is at sender’s risk. Postage
stamps, foreign money, and defaced or smooth coins are not acceptable. Remittances from for¬
eign countries should be by international money order payable to the Superintendent of Docu¬
ments or by draft on a United States bank.

Address subscriptions, remittances, and all inquiries relating thereto, to the Superintendent
of Documents, U. S. Government Printing Office, Washington 25, D. C.

The printing of this publication has been approved by the Director of the Bureau of the Budget, June 24, 1958.
271930— Type C— 60

MAY

1960

U. S. DEPARTMENT OF COMMERCE

Frederick H. Mueller, Secretary

NATIONAL BUREAU OF STANDARDS
A. V. Astin, Director

CRPL Series D
NUMBER 189

BASIC RADIO PROPAGATION PREDICTIONS

FOR AUGUST 1960

THREE MONTHS IN ADVANCE

Introduction

The CRPL-D series, “Basic Radio Propagation Predictions,” issued by the National Bureau of
Standards, contains contour charts of monthly median F2-zero-MUF and F2-4000-MUF for each of
four zones, W, I (Afro-European) , E, I (Pacific), (figs. 1 to 8) ; a worldwide contour chart of
monthly median F-2000-MUF (fig. 9) ; a contour chart of median fE s (fig. 10) ; and a chart show¬
ing percentage of time occurrence for Es-2000-MUF in excess of 15 Me (fig. 11). Local time used
for North Pole: 75° W; for South Pole: 105°E.

Methods for using these charts are given in Circular 465 of the National Bureau of Stand¬
ards, entitled “Instructions for the Use of Basic Radio Propagation Predictions,” and available
from the Superintendent of Documents, U. S. Government Printing Office, Washington 25, D. C.,
price 30 cents (to foreign countries, 40 cents). Procedures described in this manual should be
modified to take into account the separate contour charts for the two I zones. Zone boundaries
are the same as shown in figure 1 of Circular 465.

Requests for the manual of instructions and for the basic predictions from members of the
Army, Navy, or Air Force should be sent to the proper service address as follows. For the Army:
Office of the Chief Signal Officer, Department of the Army, Washington 25, D. C., Attention:
SIGOL-2. For the Navy: The Director, Naval Communications. For the Air Force: Director of
Communications-Electronics, Department of the Air Force, Washington 25, D. C., Attention:
AFOAC-F/C.

Following figure 11 of each issue, sets of auxiliary figures (nos. 1, 2, 11, 12 of NBS Circular 465)
or forms CRPL-AF and AH are given in rotation, two in each issue of CRPL Series D. They are
necessary or useful for the preparation of tables and graphs of MITF and FOT (OWF), as explained
in NBS Circular 465.

The charts in this issue were constructed from data through February 1960, together with
the smoothed 12-month running-average Zurich sunspot number 115, centered on August 1960.
The mean number for the year 1959 was 159.

Information concerning the theory of radio-wave propagation, measurement technics, struc¬
ture of the ionosphere, ionospheric variations, prediction methods, absorption, field intensity,
radio noise, lowest required radiated power, and lowest useful high frequency is given in Circular
462 of the National Bureau of Standards, “Ionospheric Radio Propagation.” This circular is
available from the Superintendent of Documents, price $1.25 (to foreign countries, $1.65). Add!
tional information about radio noise may be found in NBS Circular 557, “Worldwide and Radio
Noise Levels Expected in the Frequency Band 10 Kilocycles to 100 Megacycles,” also available from
the Superintendent of Documents, price 30 cents (to foreign countries, 40 cents) and in C.C.I.R.
Report No. 65, “Revision of Atmospheric Radio Noise Data,” International Telecommunication
Union, Geneva, 1957.

LOCAL TIME

NORTH

LATITUDE

SOUTH

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LOCAL TIME

NORTH

LATITUDE

SOUTH

FIG. 3. MEDIAN F2 - ZERO - MUF, IN Me, I ZONE ( AFRO - EUROPEAN ), PREDICTED FOR AUGUST I960

CM

CM

O

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00

CO

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00

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LOCAL TIME

NORTH

LATITUDE

SOUTH

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FIG. 4. MEDIAN F2 - 4000 - MUF, IN Me, I ZONE ( AFRO - EUROPEAN) , PREDICTED FOR AUGUST I960

LOCAL TIME

90®

NORTH LATITUDE south

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OOOOOOOOo ooooooooo

FIG. 5. MEDIAN F2 - ZERO - MUF, IN Me , E ZONE, PREDICTED FOR AUGUST I960

LOCAL TIME

NORTH

LATITUDE

SOUTH

FIG. 6. MEDIAN F2 - 4000 - MUF, IN Me , E ZONE, PREDICTED FOR AUGUST I960

LOCAL TIME

90

NORTH

LATITUDE

SOUTH

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OOOOOOOOo ooooooooo

LOCAL, TIMF

NORTH

LATITUDE

SOUTH

LOCAL TIME

NORTH

LATITUDE

SOUTH

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FIG. 9. E - 2000 — MU F, IN Me, PREDICTED FOR AUGUST I960

LOCAL TIME

NORTH

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(£> if)

b Q

LATITUDE

SOUTH

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FIG 10 MEDIAN fEs , IN Me, PREDICTED FOR AUGUST I960

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LOCAL TIME

o08o06

LOCAL. TIME

NOMOGRAM FOR TRANSFORMING F2-ZERO-MUF AND F2-4000-MUF TO EQUIVALENT MAXIMUM
USABLE FREQUENCIES AT INTERMEDIATE TRANSMISSION DISTANCES, CONVERSION SCAL£
FOR OBTAINING OPTIMUM TRAFFIC FREQUENCY (FOT),

E-Loyer 2000-muf

5°-q

45-

no—

25-

20

15 —

io-

9~

8-

7 —

6 —

5-

I km=0,62t37 mile = 0.5396l rout, ml
I <nile» 1.60935 Km = 0 86836noutmL
I oout. ml. = 1.85325 km = I 1516 ml.

MUF

Me

1.5-

l-J

Distance,

Kilometers

2500-4000
=- 2000

— 1500

1000
900

800
700

600

500

— 400

— 300

— 200

— 100
L- 0

Exomple shown by
doshed lines:

Olslonce * 500 Kllomattrt

2 000* km E mu» = 20 Me

Combined E-oad F,-Loyer mut « 8.4 Me

NOMOGRAM FOR TRANSFORMING E-LAYER 2000-MUF TO EQUIVALENT MAXIMUM
USABLE FREQUENCIES AND OPTIMUM TRAFFIC FREQUENCIES DUE TO COMBINED
EFFECT OF E LAYER AND Fi LAYER AT OTHER TRANSMISSION DISTANCES.

Notes on Use of Predictions

It is believed that these predictions are reasonably accurate for vertical incidence and for one-hop F2 trans¬
mission for average layer height for 4000-km distance over a great circle path. In practice, the picture is often
more complicated. The effective antenna-radiated power at low angles of departure may not be sufficient for maxi¬
mum single hop distance. Also, for a given distance various modes, or combinations of modes, of propagation are
often possible, including combinations of E- and F-layer single or multiple hops. Ionospheric forward scatter, back-
scatter, off-great-circle transmission, and sporadic E may increase the actual MUF for a given circuit over that
expected for the simplest great circle mode. Sporadic E may be particularly important during night hours in
auroral zones, and during the middle of the day in the summer in temperate zones. Ionospheric layer tilt, horizontal
ionization gradients, meteoric or auroral propagation may play an important part.

For many circuits, these may explain why the median MUF may give a better estimate of the FOT than the
usual procedure of percentage reduction of the MUF. Use of operating experience in conjunction with these pre¬
dictions will aid in maintaining the highest possible circuit efficiency.

Reports to this laboi’atory of discrepancies between predictions and experience are helpful in improving these
predictions. Communications should be addressed to Central Radio Propagation Laboratory, National Bureau of
Standards, Boulder, Colorado. Please note this is not an address for subscriptions. Subscription information is
given elsewhere in this report.

<L

<

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CRPL Reports

[A detailed list of CRPL publications is available from the Central Radio Propagation Laboratory upon request]

u •

Radio disturbance forcasts, every half hour from broadcast stations WWV and WWVH of the National Bureau
of Standards.

Telephoned and telegraphed reports of ionospheric, solar, geomagnetic, and radio propagation data.

Semiweekly :

CRPL— J.

CRPL— Jp.

North Atlantic Radio Propagation Forecast (of days most likely to be disturbed during following
month) .

North Atlantic Radio Propagation Forecast (of days most likely to be disturbed during following-
month ) .

Semimonthly :

CRPL — Ja. Semimonthly Frequency Revision Factors For CRPL Basic Propagation Prediction Reports.

Monthly :

CRPL — D Basic Radio Propagation Predictions — Three months in advance. (Dept, of the Army, TB 11 —

499 — , monthly supplements to TM 11 — 499; Dept, of the Air Force, TO 31 — 3 — 28 series). On
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CRPL — F. (Part A). Ionospheric Data.

(PartB). Solar-Geophysical Data.

Limited distribution. These publications are in general disseminated only to those
individuals or scientific organizations which collaborate in the exchange of iono¬
spheric, solar, geomagnetic, or other radio propagation data.

Catalog of Data:

A catalog of records and data on file at the U. S. IGY World Data Center A for Airglow and Ionosphere, Boulder
Laboratories, National Bureau of Standards, which includes a fee schedule to cover the cost of supplying copies,
is available upon request.

The publications listed above may be obtained without charge from the Central Radio Propagation Laboratory,
National Bureau of Standards, Boulder Laboratories, Boulder, Colorado, unless otherwise indicated. Please note
that the F series is not generally available.

Circulars of the National Bureau of Standards pertaining to Radio Sky Wave Transmission:

NBS Circular 462.
NBS Circular 465.
NBS Circular 557.

NBS Circular 582.

Ionospheric Radio Propagation. $1.25.

Instructions for the Use of Basic Radio Propagation Predictions. 30 cents.

Worldwide Radio Noise Levels Expected in the Frequency Band 10 Kilocycles to 100 Mega¬
cycles. 30 cents.

Worldwide Occurrence of Sporadic E. $3.25.

These Circulars are on sale by the Superintendent of Documents, U. S. Government
Printing Office, Washington 25, D. C. Members of the Armed Forces should address
the respective military office having cognizance of radio wave propagation.

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Washington 25, D. C. Price 15 cents (single copy). Subscription price: $1.50 a year;
50 cents additional for foreign mailing.

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