Rational Bureau of Standards

Library, K.W. Bidg

JUN 7 1S60 S

PB 1 51386.

\^ecknlcai ^\ot& 92e. 26

j5oulder laboratories

SURVEY OF CENTRAL RADIO

PROPAGATION LABORATORY RESEARCH IN

TROPOSPHERIC PROPAGATION 1948-1956

BY J. W. HERBSTREIT AND P. L. RICE

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

Functions and Activities

The functions of the National Bureau of Standards are set forth in the Act of Congress, March

3, 1901, as amended by Congress in Public Law 619, 1950. These include the development and

maintenance of the national standards of measurement and the provision of means and methods for

making measurements consistent with these standards; the determination of physical constants and

properties of materials; the development of methods and instruments for testing materials, devices,

and structures; advisory services to government agencies on scientific and technical problems; in- vention and development of devices to serve special needs of the Government; and the development

of standard practices, codes, and specifications. The work includes basic and applied research,

development, engineering, instrumentation, testing, evaluation, calibration services, and various

consultation and information services. Research projects are also performed for other government

agencies when the work relates to and supplements the basic program of the Bureau or when the

Bureau's unique competence is required. The scope of activities is suggested by the listing of

divisions and sections on the inside of the back cover.

Publications

The results of the Bureau's work take the form of either actual equipment and devices or published papers. These papers appear either in the Bureau's own series of publications or in the journals

of professional and scientific societies. The Bureau itself publishes three periodicals available from

the Government Printing Office: The Journal of Research, published in four separate sections,

presents complete scientific and technical papers; the Technical News Bulletin presents summary

and preliminary reports on work in progress; and Basic Radio Propagation Predictions provides

data for determining the best frequencies to use for radio communications throughout the world.

There are also five series of nonperiodical publications: Monographs, Applied Mathematics Series,

Handbooks, Miscellaneous Publications, and Technical Notes. Information on the Bureau's publications can be found in NBS Circular 460, Publications of the

National Bureau of Standards ($1.25) and its Supplement ($1.50), available from the Superintendent

of Documents, Government Printing Office, Washington 25, D.C.
NATIONAL BUREAU OF STANDARDS

technical ^iote

26

September, 1959

Survey of Central Radio Propagation Laboratory Research

in Tropospheric Propagation

1948-1956

by

J. W. Herbstreit and P. L. Rice

NBS Technical Notes are designed to supplement the Bureau's regular publications program. They provide a means for making available scientific data that are of transient or limited interest. Technical Notes may be

listed or referred to in the open literature. They are for sale by the Office of Technical Services, U. S. Department of Commerce, Washington 25, D. C.

DISTRIBUTED BY

UNITED STATES DEPARTMENT OF COMMERCE

OFFICE OF TECHNICAL SERVICES

WASHINGTON 25, D. C

Price $ JMi.OO

PREFACE

During 1954 a literature survey was conducted of research in

tropospheric propagation with which the Central Radio Propagation

Laboratory was directly concerned between 1948 and 1954. Originally

a bibliography, the survey was first expanded to include abstracts of

each paper and was then further expanded to include condensations or

reprints of some papers not otherwise available.

This technical note is a revision of this survey, first printed in

1957 as NBS Report 3520, revised, updating the bibliography to 1956

and deleting reprints which have been published.

More extensive and current bibliographies are available in annual - reports of the Boulder Laboratories of the National Bureau of Standards

and in two reports put out by the Meteorological Abstracts and Bibliographies . Material in these reports, plus more extensive material is

available as informal laboratory reports. A more current bibliography

will appear shortly in an NBS Technical Note 3

.

1. See for instance, the Fourth Annual Report of the Boulder Laboratories

for year ending June 30, 195 8.

2. Meteorological Abstracts and Bibliographies, Vol. 9, Nos. 9 and 10,

September and October, 1958.

3. K. A. Norton et al, "Radio Studies of Atmospheric Turbulence, " Vol. I and Vol. II. To be published as a National Bureau of Standards

Technical Note sometime in I960.

Preface to Revision, January 1957

This NBS report is being reissued with abstracts of

additional papers arranged chronologically to follow pagelll.

The author index and index of supplement titles will be found on

pages 3a - 3e instead of pages 113 - 117 as in the original version.

Where material included as a supplement to the original version

is now available in the literature, the supplement has been deleted

and an appropriate reference cited in its place.

SURVEY OF CENTRAL RADIO PROPAGATION LABORATORY

RESEARCH IN TROPOSPHERIC PROPAGATION

Purpose

The main objective of the National Bureau of Standards

tropospheric propagation research program described in this

report has been to accelerate propagation studies in the frequency

range from 30 to 6, 000 megacycles, of particular interest to the

Department of Defense and the Air Navigation Development Board

and to provide basic information for application to specific problems,

Abstract

This report summarizes and abstracts publications concerned with the National Bureau of Standards tropospheric propagation research program dating back to the formation of the

Central Radio Propagation Laboratory. Some technical papers

are reproduced here as supplements to this report and excerpts

from some of the longer technical reports are also included.

Introduction

The effects of climate, weather, and terrain on signal level

and fading, height gain and antenna gain, and space and frequency diversity are often uncertain to a high degree, since every different climatol

ogical and terrain situation strongly influences time and space
-2-

variations of tropospheric radio transmission loss. It has been

determined that propagation data which will have useful application

under the various conditions of climate and terrain encountered

throughout the world must be obtained from a variety of geographical

locations and over extended periods of time. Recordings for short

periods of time are also of value. The analysis of pertinent tropospheric radio propagation data in the light of theoretical considerations

promises to develop much more complete and accurate methods for

describing and predicting tropospheric propagation over irregular

terrain.

A large amount of data has been collected by the Tropospheric

Propagation Research Section through subcontracts, including nearly

a million hourly median values of field strength from all over the

United States, and a great deal of analysis has been completed by

CRPL.. In order for this report to most adequately serve its purpose,

activities will be reported under the following two section headings:

(I) Abstracts of CRPL-Sponsored Publications and Reports, and

(II) Status of Projects and Facilities.

Section (I) is divided into five subsections, and each of these

is further subdivided according to subject matter. Following the

subsections are additional reports arranged chronologically.

Page

A. Organization and Detailed Analysis of Data

(a) Propagation Characteristics 3f

(b) Prediction Curves 18

(c) Radio Meteorology 21

(d) Cosmic Radio Noise 28

(e) General 30

B. Development of Theory and Prediction Methods

(a) Propagation Parameters 34

(b) Propagation Mechanisms; Comparison of Theory

and Experiment 37

(c) Statistical Methods of Analysis and Prediction 47

(d) Estimating VHF, UHF, and Radar Coverage or

Service Range

(e) Radio Meteorology 54

51

Use of Theory and Prediction Methods to Solve

Specific Problems

(a) Air -to-Ground Communications 55

(b) Point -to-Point Communications 57
3-

Page

D. Description of Equipment and Equipment Standards

(a) Measurement of Field Strength 59

(b) Refractive Index Measurement and Computation 60

(c) General 62

E. Subcontractors' Progress Reports

(a) Collins Radio Company 63

(b) Federal Communications Commission 68

(c) United Broadcasting Company 72

(d) The Pennsylvania State College 80

(e) The University of Illinois 84

(f) The University of Texas 91

(g) The University of Washington 105

Within each of the twenty-two smallest divisions, reports are

arranged chronologically. A publication listed under one of these

headings is not listed in a later group, and publications are numbered

consecutively from 1 to 306, including 174 progress reports prepared

by subcontractors. An author index and an index of supplement titlrs

will be found on pages 3a - 3e . Pages 112 -112t include a supplementary

list of technical reports, numbered from 307 - 360.

Section II summarizes material in the thirteen previous quarterly

progress reports which cannot be found in the technical reports and

gives a short description of current projects, facilities, and compilations of data.
3 a AUTHOR IN D E X

Following the name of each author are the numbers of the reports

in this list of which he is an author or co-author.

Albright, W. G.

Allen, E. W.

Ammerman, C. R.

Anderson, L. J. Bailey, D. K.

Barghausen, A. F.

Bar sis, A. P.

Bateman, R.

Bean, B. R.

Berkner, L. V.

Birnbaum, G.

Blum, M.

Boese, W. C.

Booker, H. G.

Bussey, H. E.

Capps, F. M.

Carroll, T. J. Chambers, G. R.

Chatterjee, S.

Chisholm, J. S.

Cottony, H. V.

Crain, C. M.

Daniel, F. T.

Decker, M. T.

Decker, R. P.

Dickson, F. H.

Dougherty, H. T.

Eastman, A. V.

Egli, J. J. Farley, W.W. 3rd

Feinstein, J. Fine, H.

Florman, E. F.

Franeau, J. Gainen, L.

43, 98, 209 throtigh 248

30, 142, 144, 145, 146

21, 92, 132, 192 through 208

47

10

316, 335

13, 16, 18, 25, 26, 28, 96, 319,

324, 333, 334, 342

1, 10

16, 26, 28, 44, 46, 49, 50, 319, 326,

344, 354, 356, .357, 358, 359

10

37, 40, 42, 45, 116, 128, 353

102, 122

30, 143, 144, 147, 148, 149, 150,

151

10

38, 42, 45, 81, 353

22, 23, 328, 342

86, 87, 88

1140

4, 313

54

39

34, 35, 335

17, 316, 325, 347, 360

7, 136, 137, 138, 139, 140, 141

20

24, 329, 331, 355

291 through 301

20

134, 135, 136, 137, 138, 139, 140,

141

80, 85, 90, 93, 105, 106, 107

30, 78, 94, 111, 150. 151

1, 320

37

113
- 3b -

(Author Index Continued)

Gerhardt, J. R. 39

Gerks, I. H. 6, 9, 134, 135, 136, 137, 138,139,

140, 141

Ghose, R. N. 98

Goerke, V. H. 341

Gossard, E. E. 47

Greene, F. M. 125, 126, 127

Harman, J.C. 22

Herbstreit, J. W 11, 16, 20, 25, 51, 52, 63, 97, 115,

118, 119, 121, 123, 131, 318, 321, 335

Hill, J. S. 8, 29, 152 through 191

Hornberg, K. 16, 25, 28, 319, 315

Hubbard, R. W 343, 345, 350, 335

Hufford, G. A. 84, 95

Janes, H. B. 14, 17, 324, 351, 36©

Jehn, K. H. '5, 274

Johler, J. R. 52, 54

Johnson, W. E. 130, 133, 335

Jones, R. N. 22, 23

Jordon, E. C. 43

Kirby, R. S. 2, 12, 22, 23, 24, 32, 115, 311, 328,

329, 333, 346, 317, 355

LaGrone, A. H. 5, 83, 89

Larson, R. R. 42

Lawrence, R. S. 341

Maloney, L. J. 316

Mansfield, W. V 34, 108, 121, 332

McCrossen, G. 109

McGavin, R. 334

McQuate, P. L 24, 329, 355

Meaney, F. M. 46, 354

Metcalf, D. F. 249 through 290, 314

Miller, W. 82

Montgomery, G. F 9, 10

Moore, H. S. 12

Norton, K. A. 11, 16, 32, 55, 74, 75, 76, 77, 79,

97, 101, 102, 108, 110, 111, 113, 114,

115, 120, 124, 307, 308, 310, 312,

322, 323, 324, 327, 335

Omberg, A. C. 110

Phillips, E. N. 137, 138, 139, 140, 141
(Author Index Continued)

- 3c

Purcell, E. M.

Queer, E. R.

Randall, D. L.

Reber, G.

Rice, P. L.

Riddle, R. L.

Salisbury, W. W.

Schafer, G. E.

Schulkin, M.

Schultz, E. L.

Shallon, S. C.

Short, P. J. Simpson, V. R.

Smith, C. E.

Smith, E. K. , Jr.

Solow, M.

Staras, H.

Staley, R. C.

Straiton, A. W.

Sulzer, P. G.

Swarm, H. M.

Taff, J. M.

Tait, A.

Thompson, M. C.

Tolbert, C. W.

Toman, K.

Tritabaugh, K.

Vetter, M. J. Vogler, L. E.

Wait, J. R.

Waldo, G. V.

Weintraub, S.

Wells, P. I. West, G. E.

Wickizer, G. S.

Wiesner, J. B.

Williams, C. E.

Yarborough, H.

10

192 through 208

36, 48

53

26, 29, 34, 35, 63, 97, 103, 119,

120, 121, 122, 323, 324, 335

21, 132

10

29, 97

32, 36, 41

101

135, 136

34, 63, 108, 322

142, 143

152 through 191

19, 117

125

8, 91, 99, 100, 102, 104, 112, 118,

119, 352

279

3, 314

9

291 through 305, 306

12

1321, 340, 349, 335

3, 314

43

4

340, 349

27, 322, 323, 335

336, 337, 339, 348

8, 147, 148, 149, 150, 151

117, 129

351, 335

145, 146

20

10

5

101
-3dSUPPLEMENT INDEX

I, "Correlation in VHF Propagation Over Irregular Terrain, " by R. S. Kirby and F. M. Capps.

II. "Microwave Propagation Survey in Washington, D. C. Area, " by K. Tritabaugh and J. H. Chisholm.

III. "418 Mc Propagation Measurements Over the Cedar Rapids - Quincy Path," by M. T. Decker and H. B. Janes.

IV. "Preliminary Report on Propagation Measurements From 92 - 1046 Mc at Cheyenne Mountain, Colorado, " by G. R. Chambers,

J. W. Herbstreit, and K. A. Norton.

V. "Tropospheric Propagation Measurements Within the Radio Horizon

Over Cheyenne Mountain Paths, " by A. P. Barsis.

VI. "Propagation of Radio Waves Over Land at 1046 Mc, " by

A. P. Barsis, B. R. Bean, J. W. Herbstreit, K. O. Hornberg,

and K. A. Norton.

VII. "The Rate of Fading in Tropospheric Propagation, " by K. A.

Norton and H. B. Janes.

VIII. "Radio Transmission Loss versus Distance and Antenna Height

at 100 Mc," by P. L. Rice, and F. T. Daniel.

IX. "Radio Transmission Loss versus Angular Distance and Antenna

Height at 100 Mc, " by P. L. Rice, F. T. Daniel, W. V.

Mansfield, and P. J. Short.

X. "Some Applications of the Monthly Median Refractivity Gradient

in Tropospheric Propagation, " by B. R. Bean and F. M. Meaney.

XI. "Comparison of Calculated and Measured Fields Within the Radio

Horizon for the 92 to 1046 Mc Range, " by A. P. Barsis.

XII. "An Analysis of Within-the-Hour Fading in 100-1000 Mc

Transmissions, " by H. B. Janes.
-3eSupplement Index Continued

XIII. "Trend Analysis and Prediction in a Discrete Gaussian Stationary

Process, " by H. Staras.

XIV. "Measurements of Microwave Diffraction Over Trees, " by

J. H. Chisholm.

XV. "Dependence of the Transmission Loss in Tropospheric Radio

Wave Propagation on the Angular Distance, " by K. A. Norton.

XVI. "The Cumulative Probability Distribution of the Instantaneous

Resultant Amplitude of the Vector Sum of a Constant Component

and a Randomly Phased Rayleigh Distributed Varying Component,"

by K. A. Norton, P. J. Short, and W. V. Mansfield.

XVII. "Point -to -Point Radio Relaying via the Scattering Mode of

Tropospheric Propagation, " by K. A. Norton.

XVIII. "Propagation in the UHF - TV Band," by J. W. Herbstreit.

XIX. Wright Field Letters

XX. "Analysis of the Ground Wave and Tropospheric Wave Field

Intensity Variations at a Distance Far Beyond the Line-bfSight for an FM Broadcasting Station Operating on 99.7 Mc, " by R. S. Kir by.

XXI. "Propagation Over Rough Terrain, " by K. A. Norton.

XXII. "Obstacle Gain Measurements Over Pikes Peak at 60 to 1046 Mc,

by R. S. Kirby, H. T. Dougherty, and P. L. McQuate.
-3f

I. ABSTRACTS OF CRPL-SPONSORED PUBLICATIONS AND REPORTS.

(A few reports sponsored by other agencies are included)

A. Organization and Detailed Analysis of Data

(a) Propagation Characteristics

1. R. Bateman, E. F. Florman, and A. Tait, "A Source

of Error in Radio Phase-Measuring Systems, " Proc. IRE,

Vol. 38, No. 6, p. 612, June, 1950.

ABSTRACT

When a mobile transmitter was moved between two

points over different particular paths around reradiating

structures, the measured total phase changes differed by

2irn radians, where n is an integer. If reradiation from a

reflector is of the same order of magnitude as the radiation

from an antenna, analysis of the resultant field shows that

singularities occur, and each traverse of a closed rath

around a point of singularity gives a total phase change

of 360°.
2. R. S. Kirby, " Simultaneous Mobile Measurement of

Two VHF Broadcast Stations Over Irregular Terrain."

presented at the URSI-TRE meeting of April, 1951 in

Washington, D. C.

ABSTRACT

Two FM stations, one in Washington, D. C. and one in

Baltimore, Maryland, were recorded while driving along

a perpendicular bisector to the line joining the two stations

for a distance of fifteen miles either side of the midpoint.

This paper describes the data and how it was taken.

Comment

This paper is included here as Supplement I under the

title, " Correlation in VHF Propagation over Irregular

Terrain. " Additional measurements of transmission loss

were made at the same time as those reported here by

traveling along a circular route at a relatively constant

distance from a transmitting antenna with simultaneous

transmission on two separate frequencies. These results

as well as those described in Supplement I will be made

available in a future report, titled, " Correlation in VHF

Transmission Loss Measurements."

3. A. W. Straiton and C. W. Tolbert, " Experimental

Discrimination of the Factors in VHF Radio Wave Propagation, " University of Texas EERL Report No. 52, June 20, 1951.

ABSTRACT

This report describes the results of recent experiments

performed at the Electrical Engineering Research Laboratory

of the University of Texas for the purpose of determining

the relative contributions of various possible propagation

mechanisms affecting VHF radio field strengths at distances

well beyond the optical horizon.
-5-

Height - gain curves of median level signals for propagation over distances of 78, 140, and 175 miles are reported,

and their various features interpreted in terms of propagation by refraction, return from elevated layers, and

scattering from regions of refractive index turbulence.

Measurements of cross -polarization provide additional

information as to the relative contribution of various radio

wave propagation factors. It was found that the crosspolarization ratios varied with absolute signal level. The

characteristics of these ratios are, likewise, interpreted

in terms of the contribution being made by each of the

propagation mechanisms.

4. Kenneth Tritabaugh and James H. Chisholm, "Microwave Propagation Survey in Washington D. C. Area,"

NBS Report No. 1095, August 1, 1951.

ABSTRACT

Short-term 5,000 megacycle propagation surveys were

made over four paths in the Washington, D. C. area, ranging

from about 20 to about 37 miles in length.

Comment

This work was done according to an agreement between

the Office of the Chief Signal Officer, Department of Defense,

and CRPL, as a guide for a permanent microwave installation. As data at these frequencies are still rare, this report

is included here in its entirety as Supplement II.

5. A. H. LaGrone, K. H. Jehn, and C. £. Williams,

"Characteristics of 100 Mc Radio Propagation as a Function

of Time and Distance," University of Texas £ERL Report

No. 56, August 31, 1951.
ABSTRACT

Continuous field-strength measurements were made on

KIXL-FM, Dallas, Texas, at five stations located 50, 65,

106, 144, and 175 miles respectively along a path from Dallas

to Austin. Curves of the hourly median signal level for

each station are reported along with curves showing the

hourly median signal as a function of distance. A qualitative

analysis of the observed signal as a function of certain

meteorological variables is made.

6. Irvin H. Gerks, "Propagation at 412 Mc from a HighPowered Transmitter," Proc. IRE, Vol. 39, No. 11, p.

1374, November, 1951.

ABSTRACT

Extended measurements are reported which indicate the

existence of pronounced nocturnal superrefraction during an

appreciable percentage of the summer and of very persistent

scattering by atmospheric turbulence near the surface in all

seasons. The measurements were taken over rolling midwestern terrain at a distance of about 100 miles. Mobile

road tests were made to supplement the fixed-point measurements and to provide an approximate indication of the

relation between field strength and distance. Aerial tests

were made to show the effects of antenna height at large

distances. Graphs are provided which show the effects of

distance, terrain, antenna height, and time upon the field

strength. The practical significance of the results in the

broadcast and communication fields is indicated.

7. R. P. Decker, "Notes on the Analysis of Radio

Propagation Data," Proc. IRE, Vol. 39, No. 11, p. 1382,

November, 1951.

ABSTRACT

Statistical analysis of observations on the propagation of

410 Mc signals over distances of 86 and 134 miles is described.

The equipment for indicating the percentage of time for which

a number of preselected signal levels were exceeded is

described.
-7-

8. J. S. Hill, G. V. Waldo, and Harold Staras, "VHF

Tropospheric Recording Measurements of Plane and Circular

Polarized Waves in the Great Lakes Area, " given before the

IRE Western Convention, San Francisco, California, August

22-24, 1951; abstract published in Trans. IRE PGAP-1, February, 1952, p. 42; entire paper published as FCC Mimeo

No. 62838, April 16, 1651.

ABSTRACT

Continuous field strength recordings were made of the

horizontal and vertical components as well as the circularly

polarized field over a 125 -mile path from Columbus, Ohio,

to Hudson, Ohio. The results of these recordings are

compared with recording of the propagation of plane polarized waves over the same path, as well as over other paths,

one of them 50 per cent over water.

9. G. F. Montgomery, P. G. Sulzer, and Irvin H.

Gerks, "An UHF Moon Relay, " Correspondence, IRE,

Vol. 40, No. 3, p. 361, March, 1952; see also NBS Tech.

News Bulletin, Vol. 36, No. 3, p. 35, March, 1952.

ABSTRACT

On October 28 and November 8, 1952 a CW 418 Mc

signal was successfully relayed from Cedar Rapids, Iowa

to Sterling, Virginia, by using the moon as a reflector. A

short description of this experiment is given here.

10. R. Bateman, D. K. Bailey, L. V. Berkner, H.

G. Booker, G. F. Montgomery, E. M. Purcell, W. W.

Salisbury, and J. B. Weisner, "A New Kind of Radio

Propagation at Very High Frequencies Observable Over Long

Distances, " NBS Report No. 1172, September 28, 1951;

see also Phys. Rev., Vol. 86, No. 2, p. 141, April 15, 1952;

see also NBS Tech. News Bulletin, Vol. 36, No. 10,

October, 1952.
ABSTRACT

The discovery and some results of a preliminary investigation of a new type of weak VHF propagation by means of

the ionosphere is reported. This form of propagation appears

to be observable over ranges out to about 2,000 kilometers

from the transmitter but is likely to be masked by other

kinds of propagation at distances much less than 1,000

kilometers. The initial experiments on a frequency of 49-8

Mc/sec reveal the uninterrupted presence of observable

signal over a test path of 1,245 kilometers, irrespective of

season, time of day, or geomagnetic disturbance, though

showing dependence in intensity on these factors, and

possibly on meteor activity as well. Some preliminary

speculations suggest that the mechanism of this type of

propagation may be scattering caused by ever-present

irregularities in the E region, and an approximate transmission equation is derived in terms of parameters describing inhomogeneities in the E region. Measured signal

intensities during periods of HF radio fadeouts associated

with solar flares never show any reduction in signal. On

the contrary, there is usually an enhancement of signal

intensity accompanied by a simultaneous weakening of the

background noise. This result suggests strongly that signals

are returned from a part of the E region near or just below

the absorption region for ordinary HF radio waves,

11, G, R, Chambers, J, W. Herbstreit, and K, A,

Norton, "Preliminary Report on Propagation Measurements

from 92 to 1046 Megacycles at Cheyenne Mountain,

Colorado," NBS Report No. 1826, July 23, 1952,

ABSTRACT

A description is given of the facilities provided by the

National Bureau of Standards on Cheyenne Mountain in

Colorado and in its vicinity which are used for the measurement of the transmission loss on radio transmission circuits

operated in the frequency range from 92 to 1046 Mc, Some

preliminary results of these measurements are presented,

together with tentative theoretical explanations.
Comment

Supplement IV reproduces certain tables and figures from

this report which contain general information about the

facilities and the characteristics of the transmission paths.

Much more complete information will be found in NBS

Circular 554, December, 1954, and a detailed description

of data obtained from the Cheyenne Mountain Experiment

will be found in a forthcoming final report to the Air

Navigation Development Board.

12. R. S. Kirby, J. M. Taff, and H. S. Moore,

"Measurement of the Effect of Irregular Terrain on VHF

and UHF Directive Antenna Patterns, " NBS Report No.

1719, June 3, 1952; see also Trans. IRE PGAP-3, p. 167,

August, 1952.

ABSTRACT

Measurements of antenna patterns of directive antennas

were made while driving around transmitters at relatively

constant distances of 0.4, 10, and 30 miles. The transmitting antennas for pattern measurements were located

at Fort Dix, N. J. , and operated at frequencies of 49,

141. 75, 239i and 460 megacycles. Most measurements were

made at 12 and 15 feet above ground. Additional spot

location measurements were made with a 460 megacycle

corner reflector antenna.

13. A. P. Barsis, "Tropospheric Propagation Measure

ments Within the Radio Horizon Over Cheyenne Mountain

Paths," presented at the Symposium on Tropospheric Wave

Propagation Within the Horizon at USNEL, San Diego,

California, March 30, to April 1, 1953.

ABSTRACT

The tropospheric propagation measurements being

conducted by the Cheyenne Mountain Field Station of the

Central Radio Propagation Laboratory include several

optical paths, over which continuous recordings of field
-10-

strength are made on 100, 192.8, and 1046 Mc. Measurements

at two fixed receiving sites located on a path running 105° east

of true north from the transmitter site on Cheyenne Mountain

are analyzed, and the results of 12 months of continuous

recordings are presented in the form of charts showing

diurnal and month-to-month variations of hourly median

values of received field.

An examination of the frequency of occurrence of prolonged space-wave fadeouts shows that they are substantially

more prevalent in summer than in winter, and that they

occur principally at night.

Comment

This report is reproduced here as Supplement V.

14. H. B. Janes, "An Analysis of Within-the-Hcv.r

Fading in 100-1000 Mc Transmissions," presented at the

April, 1953 meeting of URSI-IRE in Washington, D. C.

ABSTRACT

An analysis is made of the fading range of 100 to 1000

megacycle transmissions received both within and beyond

the radio horizon in measurements made during August, 1952

over the various Cheyenne Mountain Field Station paths

and over the Cedar Rapids, Iowa - Quincy, Illinois path.

Fading range is defined as the ratio in decibels of the signal

levels exceeded 10 per cent and 90 per cent of an hour. For

each of the four frequencies studied, the extent to which

median fading range and median signal level depend on the

angular distance and time of day is shown in the form of

graphs and recording samples.

Comment

This report is reproduced here as Supplement XII.
-ills. K. A. Norton and H. B. Janes, "The Rate of Fading

in Tropospheric Propagation," presented at the 11th General

Assembly of the URSI at The Hague in August 1954.

ABSTRACT

In this paper an analysis of tropospheric fading is presented,

Fading rate is defined to be the number of times per minute that

the envelope of the received field crosses its median level

with a positive slope. It is shown that this definition of fading

rate not only provides a quantity which is easily determined

from the experimental data but also provides a quantity which

is readily identifiable with the parameters of the propagation

medium. It is also shown that this definition is as useful in

the intermediate range of distances where the scattered component of the received field is comparable to the diffracted

component as it is at the larger angular distances where the

scattered component predominates.

Comment

This report is reproduced here as Supplement VII.

16. A. P. Barsis, B. R. Bean, J. W. Herbstreit, K. O.

Hornberg, and K. A. Norton, "Propagation of Radio Waves

Over Land at 1046 Mc," NBS Report No. 2494, May 1, 1953.

ABSTRACT

This report presents experimental data on 1046 Mc obtained at the Cheyenne Mountain Field Station for the period

February 1, 1952, through January 31, 1953. The report

includes an analysis of diurnal and seasonal variations in

hourly median signal levels, analysis of variations in instantaneous signal levels, and the analysis of prolonged spacewave fadeouts within the radio horizon for the period investigated. Also included are an analysis of the effects of irregular

terrain at points within the radio horizon, including estimates

of the expected effective gains of large antenna arrays
-12-

the required spacing for diversity arrays, and the effective

intelligence -bearing bandwidths of the propagation paths.

Finally, as a result of a recent investigation of propagation

over high mountain ridges, an analysis is presented of the

"obstacle gains" expected at 1000 Mc in mountainous terrain.

Comment

With figures, this report is 134 pages. Pages 1 through

8 of the text and figures 1, 2d, 2e, 3a, 3d, 4a, 4b, 5a,

6k, 9b, 10a, 10b, 11a, lib, lie, 12a, 12b, 12e, 14a, 14b,

15a, 15b, 15d, and Appendix I of NBS Report No. 2494

are included here as Supplement VI.

17. M. T. Decker and H. B. Janes, "418 Mc Propagation Measurements Over the Cedar Rapids - Quincy Path,"

NBS Report No. 2527, May 18, 1953.

ABSTRACT

The transmitting, receiving, and recording facilities

used in propagation measurements made at 418 Mc during

the period May to December, 1951, over the 133.9-mile

Cedar Rapids - Quincy path are described. The discussion

of the received signal power data includes an analysis of

variations in instantaneous signal level, as well as analysis

of diurnal and seasonal variations in hourly median signal

levels.

Comment

This report is reproduced here as Supplement III.

18. A. P. Barsis, "Comparative 100 Mc Measurements at DistancesFar Beyond the Radio Horizon, " 1954 IRE

Convention Record, Part 2, Antennas and Communications,

p. 98; see also NBS Report No. 2539, May 26, 1953.
-13-

ABS TRACT

Results of 100 Mc measurements are evaluated in terms

of distributions of hourly median values of transmission loss.

Transmitters were located at elevations of approximately

6200, 8800, and 14, 100 feet above mean sea level on the

eastern slope of the Rocky Mountains. Receiving sites were

located at distances of 230 and 400 miles from the transmitters. Various types of antennas were employed for

transmitting and receiving. The results of studies of fading

rate and fading range are reported for the 400-mile site by

comparing signals received simultaneously on two different

antennas. These results are compared to those expected

from the application of the tropospheric scattering theory,

19. E. K. Smith, "The Effect of Sporadic E on Television Reception," Trans. IRE PGAP-2, March, 1952, pp.

54-61; see also NBS Report No. 1907, September 8, 1952,'

and Radio Electronics, Vol. 24, No. 6, June, 1953.

ABSTRACT

A study of 466 reports of high and low band television

reception greater than 200 miles shows both ionospheric

and tropospheric propagation. A rather clear line may be

drawn between the two, however. The distribution of reports

with distance indicates that those with transmission paths

between 200 and 500 miles are tropospherically propagated,

whereas those between 500 and 1500 miles are propagated

by single hop reflection from the sporadic E region of the

ionosphere.

20. F. H. Dickson, J. J. Egli, J. W. Herbstreit, and

G. S. Wickizer, "Large Reductions of VHF Transmission

Loss and Fading by the Presence of a Mountain Obstacle

inBeyond Line -of-Sight Paths , " Proc. IRE, Vol. 41,

No. 8, pp. 967-969, August, 1953; see also NBS Tech.

News Bulletin, Vol. 37, No. 12, P. 177, December 1953.
-14-

ABSTRACT

A detailed investigation of the probable mode of propagation in VHF propagation over mountain obstacles has been

made. Theory indicates that tremendous gain in received

signal strength--above what is obtained over a smooth

spherical earth--may be expected. Experimental verification of the principles involved is reported. In addition,

the fading was found to be small and even essentially nonexistent on certain very long obstructed paths.

21. C. R. Ammerman and R. L. Riddle, "A Preliminary

Study of Fading of 100 Mc/s FM Signals," Trans. IRE, Vol.

AP--2, p. 30, January, 1954.

ABSTRACT

A statistical study is made of short-period fading over

a mountainous path of about 120 miles under typical midday

conditions. Signal amplitudes have an essentially Rayleigh

distribution; amplitude variations have a Gaussian distribution. Speed of fading and values of effective wind velocity

are determined statistically; the latter are compared with

measured values.

22. R. S. Kirby, J. C. Harman, F. M. Capps, and

R. N. Jones, "Effective Radio Ground Conductivity Measurements in the United States," NBS Circular 546, February 26,

1954.

ABSTRACT

Maps are presented showing the results of effective

radio ground conductivity measurements made by various

broadcasters and consulting engineers throughout the United

States. The need for such detailed maps has been indicated

by the lack of reliability inherent in the use of general -area

conductivity maps and by studies of the correlation of

effective ground conductivity measurements with surface

soil conditions. Over 7,000 radials are shown on the maps,
-15-

and provisions have been made for entering new measurements,

as the results become available, for possible future publication. Due to the complexity of ground -wave propagation over

an inhomogeneous earth, the determination of effective ground

conductivity over a given radial strictly applies only at the

frequency at which the measurements were made.

23, F. M. Capps, R. N. Jones, and R. S. Kirby, "An

Analysis of Effective Radio Ground Conductivity by Soil

Types for the United States," in preparation.

ABSTRACT

A study has been made of the correlation between soil

type and the ground conductivity effective in surface wave

propagation, using over 7,000 separate measurements of

effective ground conductivity made in various parts of the

United States. The soil types were obtained from the

"Atlas of American Agriculture," a publication of the

U. S. Department of Agriculture, which lists 243 soil

types with detailed sectional maps showing their location.

Predictions are most reliable in the case of the 42 soil

types over which the measurements of about 5 or more

broadcast stations were available.

24. R. S. Kirby, H. T. Dougherty, and P. L. McQuate,

"Obstacle Gain at 60 McCver Pikes Peak," in preparation.

ABSTRACT

Transmission loss measurements were made over

various paths of approximately 100 miles in length in the

Pikes Peak area of Colorado in order to investigate obstacle gain phenomena in a mountainous region. The transmissions of a Denver television station, KFEL-TV,

operating on Channel 2 were used in this study. Measurements

were made at five -mile intervals at seven locations between

Canon City and Pueblo, Colorado, such that three transmission paths were west of Pikes Peak, one was directly

over Pikes Peak, and three were east of Pikes Peak.
-loin addition, recordings were made for prolonged slow-timebase recording periods for a path directly over Pikes Peak

and for a path west of Pikes Peak. For the Pikes Peak

path a strong signal and reduced fading effect., relative to

that for other paths, was observed. The measurements

were compared with expected values calculated by means

of the Fresnel-Kirchoff scatter diffraction theory and its

extension provided by Schelleng, Burrows, and Ferrell.

25. A. P. Barsis, J. W. Herbstreit, and K. O. Hornberg,

"Cheyenne Mountain Tropospheric Propagation Experiments , " NBS Circular No. 554, December, 1954.

ABSTRACT

This circular describes the facilities of the National

Bureau of Standards Cheyenne Mountain Field Station in

Colorado, the type of measurements being taken, and the

type of data analyses being made, Propagation path

characteristics are summarized in detail. The circular

is expected to be a basic reference concerning the unique

National Bureau of Standards facilities available for

tropospheric measurements.

26. A. P. Barsis, B. R. Bean, and P. L. Rice,

"UHF Tropospheric Propagation," Final Report for the Air

Navigation Development Board, in preparation.

ABSTRACT

An investigation of 960 to 1600 megacycle radio wave

propagation initiated by the Air Navigation Development Board

has been directed by the Central Radio Propagation Laboratory of the National Bureau of Standards since 1950. In

view of the evidence of interference fields well beyond

radio line -of -sight, the Cheyenne Mountain Field Station was

established in Colorado Springs, Colorado, to investigate

simulated air-to-ground transmissions, not only within

radio line-of-sight, but also far beyond line -of-sight.
-17-

Two sections of this report briefly describe the Cheyenne

Mountain project and summarize the data obtained in 1952

and 1953. Another section explains prolonged space-wave

fadeouts in detail, and the last section of the report presents

theoretical curves which compare the effects of earth reflection and of space -wave fadeouts at 100 and at 1000

megacycles on the operation of a CAA DME facility.

27. L. E. Vogler, "Summary of Transmission Loss

Measurements of KIXL-FM at 176 Miles Over Several

Years, " in preparation.

ABSTRACT

This report summarizes the results of an interesting

program of measurements undertaken by the University of

Texas under contract with the National Bureau of Standards.

Digested mainly in the form of cumulative distributions of

hourly median field strengths for various arbitrary "time

blocks," some of the statistical characteristics of measurements extending over twenty-four hours a day and several

years are shown.

28. A. P. Barsis, B. R. Bean, and K. O. Hornberg,

"A Comparison of UHF-VHF Propagation Phenomena Over

Water and Over Land Transmission Paths Within the Radio

Horizon, " in preparation.

ABSTRACT

Measured transmission loss data in the 100 Mc and 1000

Mc range are available over two paths with high transmitting

terminals and receiving locations at low grazing angles

just within the radio horizon. One path is largely over

water along the Pacific coast, and the other is over relatively

smooth prairie land in eastern Colorado.

Results of measurements are evaluated for both paths

in terms of hourly median values of transmission loss and its diur

nal and seasonal variations. A comparison of duration and
-18-

depth of prolonged space -wave fadeouts observed over the

two paths shows that these fadeouts are more frequent, but

of shorter duration, for the overwater path. This phenomenon

may be explained by interpretation of concurrent meteorological observations over the two paths and the general climatology

of the two areas involved.

29. P. L. Rice, J. S. Hill, and G. F. Schafer,

"Long-Term Monitoring of Two FjVi Stations at 40 sites

85 and 125 Miles from Columbus, Ohio," in preparation.

ABSTRACT

Two long-term mobile recording surveys have been

conducted by the United Broadcasting Company under contract

with the National Bureau of Standards. These surveys are

unique, in that they sample in time and over a number of

locations in such a way that time and terrain variances

are separable, A report is in progress to show the results

of analysis of these data.

(b) Prediction Curves .

30. F. W. Allen, W. C. Boese, and H. Fine,

"Summary of Tropospheric Propagation Measurements and

the Development of Fmpirical VH.T Propagation Charts,"

Reference D to the Report of the F3C Ad Hoc Committee

for the evaluation of FM and TV Propagation Factors between

50 and 250 Mc, FCC Mimeo No. 36728, May 26, 1949, T. I. D.

Report No. 2.4. 6.

ABSTRACT

A detailed description is given here of the preparation of

the FCC Ad Hoc Committee VHF prediction curves which are

included in this report and in Volume I of the Report of the

FCC Ad Hoc Committee.
-19-

31. Volume I to the Report of the FCC Ad Hoc Committee

for the Evaluation of the Radio Propagation Factors Concerning the Television and Frequency Modulation Broadcasting

Services in the Frequency Range Between 50 and 250 Mc,

FCC Mimeo 36830, May 31, 1949.

ABSTRACT

Generalized tropospheric propagation curves are presented

for adoption as the best estimates of VHF field strengths to

be expected under average conditions along the Atlantic

seaboard of the United States. In the analysis leading to

the curves, the Ad Hoc Committee considered only variations

expressed as levels exceeded for various percentages of the

total period of recording. The curves are intended to

represent fields exceeded for specified percentages of

time throughout the broadcast day and throughout the year.

32. K. A. Norton, M. Schulkin, and R. S. Kirby,

"Ground-Wave Propagation Over Irregular Terrain

at Frequencies Above 50 Mc," Reference C to the Report

of the FCC Ad Hoc Committee for the Evaluation of FM and

TV Propagation Factors Between 50 and 250 Mc, June 6, 1949.

ABSTRACT

In this report terrain correction factors are presented

for use in calculating field strength in connection with the

problem of television broadcast station allocation. These

factors, which are shown as a function of the frequency and

distance (out to 70 miles) are to be applied to field strength

calculations based on smooth-earth ground-wave propagation

theory.
-20-

33. Deleted.

34. P. L. Rice, F. T. Daniel, W. V. Mansfield, and

P. J. Short, "Radio Transmission Loss versus Angular

Distance and Antenna Height at 100 Mc," presented at the

National Bureau of Standards Boulder Laboratories Dedication

Program, September 8-14, 1954.

ABSTRACT

•1 This report describes curves of radio transmission

loss and the long-term variability in time of transmission

loss as a function of angular distance and transmitting and

receiving antenna height, with one antenna fixed at thirty

feet. Observations between 92 and 108 Mc on which the

curves are based extend over a period of several years

and are distributed geographically over the area of the

United States east of the Rocky Mountains. Data from the

Pacific coast are shown for comparison with the curves.

Comment

This report is reproduced here as Supplement IX.

35. P. L. Rice and F. T. Daniel, "Radio Transmission

Loss versus Distance and Antenna Height at 100 Mc," presented

before the Spring URSI-IRE meeting in Washington, D. C. , in 1952; presently being considered by the Papers Review

Committee of the IRE Professional Group on Antennas and

Propagation for publication in April, 1955.
-21-

ABSTRACT

This report describes curves of transmission loss versus

distance and antenna height derived from an analysis of

approximately 159,000 hourly median field strength observations between 90 and 110 Mc. These observations extend

over a period of several years and are distributed geographically over the whole United States. The curves contained

in this report are believed to be more precise for engineering

use than the FCC Ad Hoc Committee curves published in

1949.

Comment

This report is included here as Supplement VIII.

(c) Radio Meteorology.

36. D. L. Randall and M. Schulkin, "A Survey of

Meteorological Instruments Used in Tropospheric Propagation

Investigations," CRPL Report 2-1, July 21, 1947.

ABSTRACT

The Central Radio Propagation Laboratory of the National

Bureau of Standards, in order to evaluate tropospheric

propagation data with regard to the effect of weather, is

obtaining detailed meteorological information. The following

is a summary of existing low-level meteorological techniques

and instruments in use or under development which measure

the meteorological elements affecting microwave propagation

in the lowest 5,000 feet of the atmosphere. Measurements

of these elements are necessary in order to compute the

refractive index and the liquid water attenuation of the

air for microwave radio propagation.

37. G. Birnbaum, J. Franeau, "Measurement of the

Dielectric Constant and Loss of Solids and Liquids by a

Cavity Perturbation Method, " Jour. Appl. Phys. Vol. 20,

p. 817, August, 1949.
-22-

ABSTRACT

The changes /f, i'Q in the resonance frequency and Q of a cavity resonator when ?. small cylindrical sample of a

solid is inserted are measured. by a method in which the

resonance curve, together with a pair of calibrated variable

frequency markers, are displayed on a cathode ray

oscilloscope screen. Formulas due to Bethe and Schwinger

relate t.i and /Q to the complex dielectric constant of the

solid. A Block diagram of the equipment is given. Typical

results are tabulated and compared with that of Bleaney,

Loubser, and Penrose. The method described extends the

usefulness of Sproull and Lander 1 s method by its sensitive

technique for measuring small frequency differences.

38. Howard E. Bussey, "Microwave Attenuation

Statistics Estimated from Rainfall and Water Vapor Statistics," Proc. IRE, Vol. 38, No. 7, p. 781, July, 1950; see

also NBS Tech. News Bulletin, Vol. 33, No. 12, p. 144,

December, 1949.

ABSTRACT

Annual probability curves are obtained for values of

total atmospheric attenuation over a 50 km path and a 1 km

path at Washington, D. C. These results are obtained by

analyzing the available meteorological data, though these

are usually ill-suited to the purpose; theoretical coefficients

are used for converting into radio attenuation values.

Extension of the results to other portions of the country is

discussed.

39. J. R. Gerhardt, C. M. Grain, "Measurements of

the Parameters Involved in the Theory of Radio Scattering

in the Troposphere," Proc. IRE, Vol. 40, No. 1, p. 50,

January, 1952.
-23-

ABSTRACT

Booker and Gordon have recently proposed a theory of

radio scattering in the troposphere. Using atmospheric

inhomogeneities in refractive index, the scattered power was

shown to be a function of the intensity and scale of the

existing turbulent variations. Lacking experimental data on

the nature of the refractive index variations which may be

present in the atmosphere, they predicted the magnitude of

refractive index changes on the basis of limited temperature

fluctuation measurements. Measurements have been made

of refractive index and associated temperature fluctuations

by the Electrical Engineering Research Laboratory of the

University of Texas since 1948 with a somewhat detailed

study being made from 10 inches to 50 feet above the ground

since December, 1949. This paper includes a brief discussion of the recording ref Tactometer and recording

thermometer used for these studies, a meteorological

analysis of the problem, and tracings of the refractive

index and temperature fluctuations for several various

conditions of the lower atmosphere.

40. G. Birnbaum and S. Chatterjee, "The Dielectric

Constant of Water Vapor in the Microwave Region," Jour.

Appl. Phys. , Vol. 23, p. 220, February, 1952.

ABSTRACT

Using a cavity method described previously, measurements were made over the temperature range 32° - 103°C

at a frequency of 9.28 kmc and at the single temperature

of 24.5° C at 24.8 kmc. Results are discussed.

41. Morris Schulkin, "Average Radio-Ray Refraction

in the Lower Atmosphere," CRPL Report 2-2, August 11,

1947; see also Proc. IRE, Vol. 40, No. 5, p. 554, May, 1952,
-24-

ABSTRACT

Existing corrections for atmospheric refraction in radiofield intensity computations are reviewed with respect to their

application to computation of ray bending. A practical scheme

is presented for calculating atmospheric refraction of radiofrequency rays numerically from radiosonde data. Ray-bending

computations are made for a range of climatological conditions

for rays passing entirely through the atmosphere and arriving

or departing tangentially at the earth's surface. Some discussion

is included regarding the uncertainty in refractive -index computations from meteorological sounding data.

42. G. Birnbaum, H. E. Bussey, and R. R. Larson,

"The Measurement of Variations in Atmospheric Refractive

Index," NBS Report 1874, August 19, 1952.

ABSTRACT

A recording microwave ref Tactometer has been adapted

for measuring variations in the refractive index of the

atmosphere and for determining scale of refractive index

inhomogeneities . The following features are discussed:

cavity design and arrangement, response time of instrument,

and calibration.

With the aid of a small wind tunnel, the thermal errors

attendant on sampling the atmosphere with cavity resonators

have been investigated. These errors arise because of a change in temperature of the air sample on coming in contact

with the cavity, and because of thermal expansion effects

on the cavity frequency. The former effect may amount to

20 per cent; methods for reducing latter are suggested.

Other possible errors in the measurement of ri, those due

to condensation and adsorption of water vapor, are apparently

not significant.

Observations during August, 1941, were made with refractometers and meteorological equipment installed on two levels
-25-

of a 420-foot tower at the Brookhaven National Laboratory,

Long Island, New York. It has been found from a preliminary

data analysis that ri variations were caused mostly by variations

in water vapor density. The ri data at 410 feet show a wide

range of Fourier components, corresponding to wavelengths of

roughly 10 to 1,000 meters.

43. K. Toman, W. G. Albright, and E. C. Jordan,

"Meteorological Effects of VHF Propagation," Trans. IRE

PGAP, p. 20, December, 1952.

ABSTRACT

It is the purpose of this paper to describe briefly the

results of one and one -half years' recording of FM and TV

stations in Illinois by the University of Illinois. An attempt

has been made to isolate certain modes of propagation by

means of the radiosonde data, and in terms of the corresponding signal levels. It will be shown that when atmospheric

conditions are more or less uniform over the path, it is

possible to ascribe to certain signal levels specific atmospheric conditions which are described in terms of the gradient

of the dielectric constant.

44. B. R. Bean, "Geographical and Height Distribution

of the Gradient of Refractive Index," NBS Report No. 1720,

May 20, 1952; see also Proc. IRE, Vol. 41, No. 4, pp. 549,

550, April, 1953.

ABSTRACT

Charts are presented of the February and August distribution

of effective earth's radius factor over the United States. Also

included is a chart showing the distribution of refractive index

gradient for warm, temperate and cold climates.
-26-

45. G. Birnbaum and H. E. Bussey, "Measurement of

Variations in Atmospheric Refractive Index with an Airborne

Microwave Refractometer, " Jour. Res. NBS Vol. 51,

p. 171, October, 1953.

ABSTRACT

The cavity-resonator refractometer described is

essentially the same as that used for previous measurements

of 1951 (Birnbaum). Observations were made at heights

up to 10,000 feet; examples of strip records obtained are

reproduced. The variations were negligible for distances

less than 5 m. Large increases of refractive index were

observed on entering cumulus clouds, and intense fluctuations were noted within the clouds.

46. B. R. Bean and F. M. Meaney, "The Monthly

Refractive Gradient for the United States and Its Application to Predicting the Geographical and Annual Trend of

VHF Transmission Loss," Proceedings of the Conference

on Radio Meteorology, the University of Texas, November

9-12, 1953, Supplement III-2.

ABSTRACT

Climatic maps of monthly average refractivity gradient

are presented for the United States for the hours 0300 and

1500 GCT. These maps are shown to follow a regular

climatic pattern. The refractivity gradients as obtained

from individual monthly maps are then correlated with the

monthly median transmission loss of all available VHF

propagation paths. The usefulness of this approach for

the prediction of VHF transmission loss is described.

47. L. J. Anderson and E. E. Gossard, "Prediction

of the Nocturnal Duct and Its Effect on UHF," Proc. IRE,

Vol. 41, January, 1953.
-27-

ABSTRACT

A method is described for predicting diurnal variation

in UHF field strengths, which is based on the micrometeorology

governing the nighttime refractive -index profiles. Using

surface meteorological data from past years, predictions

are made of the probability distribution of the diurnal field

variations to be expected on 100 and 1, 000 Mc over CRPL

links in Colorado. The predictions are compared with fieldstrength observations taken in 1952, and the agreement is

encouraging.

48. D. L. Randall, "A Study of Some of the Meteorological Effects on Radio Propagation at 96. 3 Mc Between

Richmond, Virginia, and Washington, D. C. ," NBS Report

No. 2393, March 26, 1953; see also the Bulletin of the

American Meteorological Society, February, 1954.

ABSTRACT

This study was made to investigate the relationship of

surface meteorological data and corresponding surface

refractive indices to radio field strengths in the FM frequency band. For meteorological observations during which

wind speeds were equal to or greater than ten miles per

hour, and when fronts, low overcast clouds (less than 5,000

feet), rain, thunderstorms, and fogs were excluded, an

0. 70 correlation coefficient was found between hourly surface

refractive index and hourly median field strength over a Washington - Richmond path at a frequency of 96. 3 Mc.

49. Bradford R. Bean, "Prolonged Space -Wave Fadeouts

at 1046 Mc Observed in Cheyenne Mountain Propagation

Program, " Proc. IRE, Vol. 42, No. 5, pp. 848-853, May,

1954.

ABSTRACT

During the first year of continuous operation of the

Cheyenne Mountain propagation program, recording s of

1046 Mc fields at receiving locations within the radio horizon
-28-

have exhibitied ''fadeouts" or prolonged periods of attenuation often in excess of 20 db below the monthly median

level and lasting from a minute up to several hours. The

occurrence of these fadeouts has been found to coincide

with widespread superref raction, as evidenced by enhanced

signals beyond the radio horizon and ground modification of

the refractive index profile

.

50. B. R. Bean, "Estimation of the Annual Geographic,

and Terrain Variances of 100 Mc Transmission Loss,"

presented at the National Bureau of Standards Boulder Laboratories Dedication Program, September 8-14, 1954.

ABSTRACT

Regression lines are determined for use in predicting

the annual cycle and the geographical variations of monthly

median values of transmission loss on frequencies near 100

megacycles in terms of an atmospheric parameter, AN,

which is the difference of the values of refractivity at the

surface and at one kilometer above the surface.

Comment

This report is reproduced here as Supplement X under

the title, "Some Applications of the Monthly'Mean Refractivity Gradient in Tropospheric Propagation."

(d) Cosmic Radio Noise.

51. J. W. Herbstreit, "Cosmic Radio Noise,"

Advances in Electronics, Vol. 1, Academic Press, Inc.

Publishers, New York City, 1948.

ABSTRACT

The fact that cosmic and solar radio noise is arriving

at the earth with sufficient intensity to determine the lowest

usable field intensities for radio communication services

throughout a wide band of frequencies is now well established. This report reviews observations of cosmic noise
-29-

made up to the time of writing and presents in graphical

form estimates of effective noise figures for receivers

including effects of cosmic, ground, and receiver noise

using half -wave receiving antennas one -quarter wavelengths

above ground.

52. J. W. Herbstreit and Joseph R. Johler, "Frequency

Variation of the Intensity of Cosmic Radio Noise, " Correspondence. Nature, Vol. 161, No. 4092, April 3, 1948.

ABSTRACT

The intensity of cosmic radio noise (as received on

horizontal half -wave dipole antennas one -quarter wavelength above ground) has been measured at 25 Mc and 110 Mc

using identical noise diode calibration methods. Results

of these measurements are shown in a graph, and given at

110 Mc for antennas oriented both normal to and parallel

to the geographic meridian.

53. G. Reber, "Cosmic Static," Proc. IRE, Vol. 36,

p. 1215, October, 1948.

ABSTRACT

The results of a survey of the galaxy made at a frequency

of 480 Mc are compared with previous results for 160 Mc.

The apparatus used is described briefly. The principal

new findings are:

(1) a projection from Sagittarius in the direction

of the north galactic pole

(2) a supplementary small rise in Aquilla

(3) a splitting of the maxima in Cygnus and Orion

each into two parts.

54. H. V. Cottony, J. R. Johler, "Cosmic Radio Noise

Intensities in the VHF Band, " Proc. IRE, p. 1053, September,

1952. (Original -- May 23, 1951; Revised -- April 30, 1952).
-SOABSTRACT

During 1948 and 1949, the NB3 conducted continuous,

broad-directivity rr.easurements of the cosmic radio noise

intensities at frequencies between 25 and 110 Mc. Their

purpose was to evaluate the importance of this noise from

the standpoint of its interference with radio communication.

The results show a regular daily variation in noise corresponding to the movement of the principal sources of cosmic

radio noise across the antenna receiving pattern. This

normal cosmic noise intensity pattern was found to be

constant within the limits of the accuracy of the measurements.

It was found convenient to present the results in terms of

daily maxima and minima which bracketed the daily variations. No measurable change in these limits was observed

in the course of these measurements,

Besides the normal cosmic radio noise, periods of

abnormal high noise levels, generally associated with

periods of unusual solar activity, were observed and recorded.

(e) General.

55. K. A. Norton, "Propagation in the FM Broadcast

Band," Advances in Electronics , Vol. l,pp. 381-421,

Academic Press, 1948.

CONTENTS

(1) Introduction

(2) The Interference Due to Long Distance Ionospheric Propagation.

(3) The Effects of Radio Noise on Broadcast

Reception.

(4) The Effects of Antenna Height and Terrain on

the Effective Transmission Range Over a Smooth Spherical Earth.

(5) The Effects of Irregularities in the Terrain.

(6) The Systematic Effects of Terrain and of

Tropospheric Ducts.
-31-

(7) The Tropospheric Waves Resulting from Reflection at Atmospheric Boundary Layers,

(8) The Combined Effects of Ducts and of Random

Tropospheric Waves.

(9) The Calculated Service and Interference Ranges

of FM Broadcast Stations.

(10) The Efficient Allocation of Facilities to FM

Broadcast Stations.

(11) The Optimum Frequency for an FM Broadcast

Service.

56. "Extension of FM Broadcast Range, " NBS Tech.

News Bulletin, Vol. 32, No. 4, p. 37, April, 1948.

ABSTRACT

Experimental research conducted by K. A. Norton of

the National Bureau of Standards indicates that the reliable

service areas of FM broadcast stations using transmitters

now available may be extended far beyond the horizon. This

paper discusses ways of increasing service range.

57. "Bibliography of Reports on Tropospheric Propagation, " CRPL Report No. 2-3, July 23, 1948.

58. "N,ew Site for Radio Propagation Laboratory,"

NBS Tech. News Bulletin, Vol. 34, No. 3, p. 32, March,

1950.

ABSTRACT

Plans are noted for the building of a new radio laboratory

in Boulder, Colorado,

^9. "NBS Research in Navigation, " NBS Tech. News

Bulletin, Vol. 34, No. 6, p. 80, June, lO ^0.

ABSTRAC

This paper gives some idea ot the scope of the Bureau s work in the field of aids to navigation.
-32-

60. "URSI-IRE Meeting at NBS," NBS Tech. News

Bulletin, Vol. 34, No. 6, p. 91, June, 1951.

ABSTRACT

This is a brief review of the URSI-IRE meeting of

April 16-18, 1951, in Washington, D. C.

61. "Tropospheric Propagation Research," NBS Tech.

News Bulletin, Vol. 36, No. 8, August, 1952.

ABSTRACT

The Tropospheric Propagation Research program at the

Central Radio Propagation Laboratory is described in detail.

62. "NBS Boulder Laboratory," NBS Tech. News

Bulletin, Vol. 36, No. 12, p. 180, December, 1952.

ABSTRACT

The new Boulder, Colorado Laboratory for the Central

Radio Propagation Laboratory is described.

63. P. J. Short, J. W. Herbstreit, and P. L. Rice,

"Catalog of Available Tropospheric Field Strength Data,"

NBS Report No. 2915, October 28, 1953; (supersedes NBS

Report No. 2011, October 27, 1952).

ABSTRACT

A reference to tropospheric propagation data covering

approximately 200 propagation paths for distances from

33 to 616 miles and frequencies from 41 to 24,000 Mc is

presented in order to disseminate the information available

at the National Bureau of Standards.

64. "NBS Research in Radio Propagation," NBS Tech.

News Bulletin, Vol. 38, No. 4, p. 49, April, 1954.
-33-

ABSTRACT

This paper reviews the progress of research at the

Central Radio Propagation Laboratory, which is aimed at

better systems, more accurate standards, and more

reliable propagation forecasts for use by the government,

industry, and science.

65. "Dedication of NBS Boulder Laboratories," NBS

Tech. News Bulletin, Vol. 38, No. 8, p. 122, August, 1954.

ABSTRACT

Plans for the dedication of the National Bureau of

Standards Laboratories in Boulder, Colorado, are reviewed.

Scientific conferences on cryogenics engineering and on

radio propagation are planned for the same time.

66. "Annual Report of Central Radio Propagation

Laboratory, July 1, 1951-June 30, 1952," NBS Report 1962,

October 1, 1952.

67. "Annual Report of Central Radio Propagation

Laboratory, July 1, 1952-June 30, 1953," NBS Report 2793,

September 14, 1953.

68. "Semi-Annual Report of Central Radio Propagation

Laboratory, July 1, 1952-December 31, 1952," NBS Report

2405, March 31, 1953.

69. "Semi-Annual Report of Central Radio Propagation

Laboratory, January- June, 1953," NBS Report 2732,

August 12, 1953.

70. "Quarterly Report of Central Radio Propagation

Laboratory, January -March, 1952," NBS Report 1795,

July 17, 1952.

71. "Quarterly Report of Central Radio Propagation

Laboratory, April-June, 1952," NBS Report 1876, August 20,

1952.

72. "Quarterly Report of Central Radio Propagation

Laboratory, July-September, 1952," NBS Report 2090,

December 2, 1952.

73. "Quarterly Report of Central Radio Propagation

Laboratory, July-September, 1953," NBS Report 2936,

November 24, 1953.
-34-

B. Development of Theory and Prediction Methods,

(a) Propagation Parameters.

74. K. A. Norton, "A Formula for the Transmission

Loss of Space Waves Propagated Over Irregular Terrain,"

NBS Report No. 1737, June 16, 1952.

ABSTRACT

It is shown that the effects of irregularities in the

height of the terrain on space -wave intensity calculations

may be adequately described in terms of the coefficients of a second-degree polynomial fitted by the method of least

squares to an appropriate portion of the terrain between

the transmitting and receiving sites. The mean-square

residual height variation from such a polynomial provides

a measure, through Rayleigh's criterion of roughness, as

to the usefulness of the resulting field-strength formula.

If the frequency under consideration is sufficiently low to

satisfy this criterion, then the three coefficients in the

second-degree polynomial fitting the terrain are found to

play important roles in determining the effective heights of the

transmitting and receiving antennas, and the effective

curvature of the transmission path. A constant lapse of

refractive index with height may be taken into account by

a modification in the effective path curvature.

The utility of the formula on frequencies between 92 and

1,047 Mc is established by comparing the calculated and

measured fields for a variety of terrain in the vicinity of

the Cheyenne Mountain transmitting station of the NBS.

75. K. A. Norton, "Transmission Loss in Radio

Propagation," NBS Report No. 2044, October 31, 1952; Proc.

IRE, Vol. 41, No. 1, p. 146, January, 1953.
-35-

ABSTRACT

The utility of the concept of transmission loss in

radio propagation analysis is explored. The transmission

loss of a radio system is defined to be the ratio of the power

radiated from the transmitting antenna to the resulting signal

power available from a loss -free receiving antenna.

76. K. A. Norton, "Transmission Loss in Free Space,"

prepared for presentation at the 11th General Assembly of

the URSI at the Hague in August, 19 54.

ABSTRACT

The advantages of the concept of "transmission loss,"

L, in describing the characteristics of radio wave propagation

have been discussed in a recent paper by the author, A

brief review of this concept together with a few new definitions

is given here.

77. K. A. Norton, "Dependence of the Transmission

Loss in Tropospheric Propagation on the Angular Distance, " prepared for presentation at the 11th General Assembly of

the URSI at the Hague, August, 1954.

ABSTRACT

It is shown that the expected values of transmission

loss calculated for a smooth spherical earth by means of the

Bremmer-van der Pol diffraction theory and by a recent

version of the Booker -Gordon scattering theory are in

fair agreement with the observed transmission losses over

an actual rough earth when the angular distance, 8, is used

as the common parameter.

78. H. Fine, "An Effective Ground Conductivity

Map for Continental United States, " Proc, IRE, p. 1405,

September, 1954.
-36-

AB3 TRACT

The Federal Communications Commission has recentlyadopted a new effective ground conductivity map , presented

in this paper, representing estimates on measurements made

over approximately 7,000 paths throughout United States

and submitted to the FCC. The CRPL had previously made

a comprehensive study of effective conductivity, using paths

up to 25 rriles which were plotted on map overlays; from this

study the typical conductivity values for 144 of the 243

subsoil types were evaluated. The resulting conductivity

map was drawn freehand by the FCC, almost entirely from

the map overlays supplied by CRPL. The estimation of a standard error for this effective conductivity map is not an

attractive proposition because of the variable density of

the measurements, but if known would greatly enhance the

utility of the map.

79. K. A. Norton, "The Role of Angular Distance in

Tropospheric Radio Vvave Propagation," presented before

the 1953 ."/estern Flectronic Convention in San Francisco.

ABSTRACT

Angular distance is defined as the angle between the

ray from the transmitting antenna to its radio horizon and

the ray from the receiving antenna to its radio horizon,

determined in the great circle plane containing both antennas.

If a linear refractive index gradient is assumed over a smooth spherical earth, the angular distance is equal to

the distance between the transmitting and receiving antenna

horizons divided by the effective radius of the earth. It is shown how this parameter, to a good first approximation,

allows for the systematic effects of transmitting and receiving antenna heights and the effects of irregularities

in the terrain.

Comment

A revised and extended version of this paper is reproduced here as Supplement XV.
-37-

(b) Propagation Mechanisms; Comparison of Theory and Experiment.

80. J. Feinstein, "Reflection of Radio Waves from Meteor

Trails," CRPL Preprint, No. 50-19, February, 1950.

ABSTRACT

This is a brief discussion on a theory of N. Herlofson

of meteor trails having a core of dielectric constant zero

or less. Calculations proved that the effective dielectric

constant varied from unity on the surface to zero on the

axis of a cylinder.

81. H. E. Bussey, "Zonal Screening, A New Wave

Suppressing Technique, " CRPL Preprint No. 51-22,

February 5, 1951; see also "Reflected Ray Suppression"

Proc. IRE, Vol. 38, No. 12, p. 1453, December, 1950, and

NBS Tech. News Bulletin, Vol. 36, No. 1, p. 6, January,

1952.

ABSTRACT

A method is described for greatly reducing the reception

of a direct or a reflected wave. It employs a blocking screen

of such a shape as to cover about half of the area of the

first Fresnel zone at a place between the transmitter and

the receiver. For reflected wave suppression such a screen,

set on the ground, is cut in half; then, together with its

image, it behaves as a full screen and if correctly placed

it blocks the wave coming virtually from the transmitter.

Microwave measurements are described which confirm the

theory. The Fresnel diffraction pattern of a semicircular

area is derived analytically.

82. W. Miller, "Effective Earth's Radius for Radio Wave

Propagation Beyond the Horizon," Jour. Appl. Phys.,

Vol. 22, No. 1, p. 55, January, 1951.
-3 8

ABSTRACT

The geometrical optical arguments underlying the

equivalent earth's radius approximation are extended to

non-horizontal rays. The appropriate wave equation for

a non-uniform,, but spherically symmetric, region is

derived in a natural way. A formal solution is obtained

which contains the known solutions for a uniform medium.

For the non-uniform case, the solutions to the radial

equation are found by a technique due to Langer.

83, A. H. LaGrone, "Volume Integration of Scattered

Radio Waves, Proc. IRj£, Vol. 40, No. 1, p. 54, January,

1952.

ABSTRACT

A brief discussion on the geometry and integral equation

involved in the scattering theory. The general equation for

radio scattering developed by Booker and Gordon is extended

to a volume -integral equation, which gives the total scattered-power density at a receiver point relative to the power

radiated per unit solid angle by an isotropic source. The

propagation conditions assumed are stated,

84. G. Hufford, "An Integral -Equation Approach to

the Problem of Wave Propagation Over an Irregular Surface,"

Quart. Appl. Math., Vol. 9, No. 4, p. 391, January, 1952.

ABSTRACT

Theoretical discussion of the propagation of radio waves

over a surface whose radius of curvature is everywhere

much larger than a wavelength assumes that a scalar wave

phenomenon is involved and that a homogeneous boundary

condition applies at the surface. An integral equation is

derived for the attenuation function at all points on the

earth's surface, and a formal solution for the field at any

point above the earth is obtained. The analysis is applied

to the special cases of a plane earth and a spherical earth.

Agreement with the earlier work of Norton, van der Pol,

Bremmer, and Fock is noted.
-39-

85. J. Feinstein, "The Role of Partial Reflections in

Tropospheric Propagation Beyond the Horizon," NBS Report

No. 1447, February 6, 1952; see also NBS Tech. News Bulletin,

Vol. 38, No. 2, p. 17, February, 1952.

ABSTRACT

The continuous partial reflections, which must occur as

a consequence of the gradient of refractive index present in

the atmosphere, are evaluated on a hybrid-ray and wave

theory. It is found that the inhomogeneity associated with

the standard atmosphere is sufficient to account for the

anomalous field strengths found far beyond the horizon. The

wavelength, distance, and angular dependences associated

with this reflected energy are examined and compared with

observation. The extent to which the approximate methods

employed may be justified on a rigorous wave basis is

indicated. The mathematics of the conventional -mode treatment is examined with a view toward ascertaining the reason

for its neglect of this field contribution.

86. T. J. Carroll, "Internal Reflection in the Troposphere and Propagation Well Beyond the Horizon," NBS Report

No. 1416, January 22, 1952; see also Trans. IRE, PGAP-2,

p. 9, March, 1952.

ABSTRACT

A simple estimate of the feeble internal reflection from the

normal troposphere explains remarkably well long puzzling fields

well beyond the horizon throughout the VHF and microwave spectrum. Even in the absence of ducts, the continuous decrease with

height of the index of refraction under gravitational influence makes

the troposphere an inhomogeneous continuously stratified medium.

The effective earth's radius notion allows for the refractive effect

of this inhomogeneity in calculating the diffracted field beyond the

horizon, but not for internal reflections. A bilinear model for the

index profile of the normal atmosphere gives modes with db/mi

attenuation rates in approximate agreement with the experimental

one of roughly 1/7 db/mi at 50,400 and 3,000 Mc. To a considerable

extent, the internal reflection idea obviates the need for hypothesizing omnipresent atmospheric turbulence up to heights of several

miles in the troposphere, a phenomenon once erroneously thought

also to cause "angel" echoes on radars.
-40-

87. T. J. Carroll, "Normal Tropospheric Propagation

Deep Into the Earth's Shadow; The Present Status of Suggested

Explanation," Trans. IRE, PGAP -3, p. 6, August, 1952.

ABSTRACT

During the last seven years, experimental observations

of field strength measured well beyond the horizon from

high-power transmitters through the VHF and microwave

frequency range have shown much higher fields than conventional theory had predicted in the absence of ducts. The

three types of suggested explanations have been (a) scattering

by omnipresent turbulence in the atmosphere; (b) wave

scattering connected with earth roughness; (c) partial internal

reflections from the normal stratification of the troposphere

itself. No definitive judgment can yet be made concerning

the relative validity of these explanations, but the physical

ideas underlying each hypothesis and the claims of their

protagonists as of the end of 1951 will be summarized and

checked against supporting evidence in the hope of setting

the stage for the conflicts of views expected to develop later

in the meeting.

Independently of the explanation which ultimately wins

acceptance, it seems generally agreed that these fields will

have practical importance for reliable point-to-point

communication at ranges larger than formerly envisaged

at VHF and microwave frequencies.

88. T. J. Carroll, "Tropospheric Propagation Well

Beyond the Horizon," Trans. IRE, PGAP-3, p.84 , August,

1952.

ABSTRACT

Observed VHF and micro-wave fields well beyond. the

horizon from high-powered transmitters are attributed to

partial internal reflection from the normal troposphere

with its index of refraction decreasing smoothly and continuously with height. A simple estimate of such reflection

from the normal troposphere gives values well beyond the
-41-

horizon of the order of magnitude of the observed average

fields of frequencies throughout the VtFand microwave

range. The conventional effective earth's radius correction

for refraction fails to consider the tropospheric reflection

effect on the field beyond the horizon. This failure is

traced to the misbehavior of the linear index model at

great height. Either a bilinear model for the normal

troposphere with a unit index above 30,000 feet, or an

exponential model which falls asymptotically to unity at

great height, gives modes whose eigenvalues depend both

on the index gradient and on the total index change through

the atmosphere. Observations by Pickard and Stetson are

believed to give strong qualitative experimental support

for the importance of the total index change in a correct

wave theory of weak nonoptical fields. Comparison is

possible with the hypothesis of scattering from atmospheric

turbulence with respect to the following: height gain, pulse

shape preservation, antenna beam width and gain observations,

short-and-long term fading characteristics, divergence

factor considerations, and number of arbitrary parameters

involved.

89. A. H. LaGrone, "Cross Polarization of Scattered

Radio Waves," Proc. IRE, ONR Contract, p. 1120,

September, 1952.

ABSTRACT

The polarization of the signal reaching a receiving antenna

by the scattering mechanism proposed by Booker and Gordon

is investigated. Equations are presented which give the

response of dipole antennas oriented horizontally, vertically,

and axially, relative to a linear polarized source. The

relative response of the three antennas is calculated for

selected values of the scattering parameters and a comparison

made with the measured response of similar antennas to a 102.9 Mc signal arriving over a path length of 147 miles.
-42-

90. J. Feinstein, "Tropospheric Propagation Beyond

the Horizon," Jour. Appl. Phys. , Vol. 22, p. 1292, October,

1952.

ABSTRACT

Recent calculations of the field strength of A/HF waves,

based on a smooth -earth diffraction theory, give results far

below the observed values in the shadow region, even when

refraction produced by the standard atmosphere is allowed

for. But in these calculations the contribution made by

partial reflections, caused by the gradient of refractive

index in the atmosphere, has been neglected. A mathematical

treatment which accounts for these reflections is outlined,

and results deduced from it are shown graphically.

91. H. Staras, "Scattering of Electromagnetic Energy

in a Randomly Inhomogeneous Atmosphere," NBS Report

No. 1662, May 12, 1952; Jour. Appl. Phys., Vol. 23,

No. 10, pp. 1152-1156, October, 1952.

ABSTRACT

First-order perturbation theory is used to evaluate the

scattered power at a receiver due to random inhomogeneities

in the propagating medium. The integral expression for this

scattered power is identical with the expressions as used by

Pekeris and Booker and Gordon. However, instead of a space correlation function of refractive index variations,

this paper uses a time correlation function which permits

formal evaluation of the time average scattered power. It is shown that for large-scale turbulence, the frequency and

scattering angle dependence of the scattered energy is

affected greatly by the particular time correlation function

chosen.

Comment

Subsequent work by the author resulted in material

presented before the American Physical Society, June 30, 1952
-43-

in Denver, Colorado, under the title, "The Effect of Scattering

by a Turbulent Atmosphere on the Received Field Deep in

the Shadow Region."

92. C. R. Ammerman, "VHF Propagation Beyond the

Horizon," Penn State Engineer, November, 1952.

ABSTRACT

This is a short survey of theories concerning tropospheric

propagation well beyond the radio horizon.

93. J. Feinstein, "The Nature of Gradient Reflections,"

Trans. IRE, PGAP-4, pp. 2-13, December, 1952.

ABSTRACT

For a refractive index distribution which is an analytic

function of height, a development is presented which indicates

that the total effect of a gradient; is of the order of the

effective earth radius modification of the uniform atmosphere

theory. "When a discontinuity in any order derivative is

present, one obtains an inverse ^distance power law signal

dependence in which the magnitude of the power is a function

of the order of the derivative possessing the discontinuity.

94. H. Fine, "Some Notes on Theory of Radio Scattering

in a Randomly Inhomogeneous Atmosphere," Proc, IRE,

Vol. 41, p. 294, February, 1953 (Correspondence).

ABSTRACT

Booker and Gordon define an autocorrelation function

of pe rmittivity as a space correlation. Staras has proposed

the use of a time correlation function and derived an expression

for the average received power due to scattering, whereas

Booker and Gordon considered the instantaneous power.

From practical considerations it would seem that the average

power is the more useful, as the instantaneous power fluctuates greatly with time. A third definition of correlation is

proposed and discussed, with correlation in the time-space

domain.
-44-

95. George A. Hufford, "A Note on Wave Propagation

Through an Inhomogeneous Medium," NBS Report No. 1830,

July 28, 1952; see also Jour. Appl. Phys. , Vol. 24, p. 268,

March, 1953.

ABSTRACT

A few formal observations are made concerning wave

propagation through an inhomogeneous medium. A modification of Kirchoff's formula is suggested and an integral

equation derived which gives an estimate of the error made

in the usual approximate methods. Applications are indicated

to the equivalent earth's radius model and to the flat earth,

modified index model.

96. A. P. Barsis, "Comparison of Calculated and

Measured Fields Within the Radio Horizon for the 92 and 1000

Mc Range," presented at the Symposium on Tropospheric

Wave Propagation within the Horizon at US NEL, San Diego,

California, March 30 - April 1, 1953.

ABSTRACT

Propagation characteristics of space waves transmitted

over irregular terrain may be computed by replacing significant portions of the terrain by a smooth surface, determining

the fields by the usual methods applicable to smooth surfaces.

The deviation of measured fields over rough terrain from

computed smooth-earth values is investigated as a function

of Rayleigh's criterion of roughness. Evaluation of measurements available from the Cheyenne Mountain Experiment

suggests development of a formula correcting deviations of

measured from computed values of transmission loss with

corresponding values of Rayleigh's criterion of roughness.

Comment

This report is reproduced here as Supplement XI.
-45-

97. J. W. Herbstreit, K. A. Norton, P. L. Rice, and

G. E. Schafer, "Radio Wave Scattering in Tropospheric

Propagation," NBS Report No. 2459; 1953 Convention Record

of the IRE, Part 2, Antennas and Communications, pp. 85-91.

ABSTRACT

The scattering theory of Booker and Gordon has been

developed, assuming the correlation function C(r) = C(0) exp (-r/i), so as to be suitable for easy numerical

calculation of the transmission loss expected with this mode

of transmission; C(0) denotes the time variance of the

refractice index of the atmosphere, and i denotes the

scale of turbulence.

98. W. G. Albright and R. N. Ghose, "VHF Field

Intensities in the Diffraction Zone," Trans. IRE, Vol. AP-2,

p. 35, January, 1954.

ABSTRACT

A solution of the general wave equation is obtained

assuming a refractive -index versus height variation of

exponential form which fits the required boundary conditions.

An expression for field strength as a function of the height

and the separation of transmitting and receiving antennas

is derived. Calculated values of signal strength are compared

with measured values.

99. H. Staras, "The Statistics of Scattered Radiation, " presented at the National Bureau of Standards Boulder

Laboratories Dedication Program, September 8-14, 1954.

ABSTRACT

By means of a reformulation of the integrals that

appear in scattering theory, this paper derives explicit

mathematical expressions for many of the statistical parameters that appear in scattering theory, assuming isotropic

turbulence. Among the statistical properties discussed are
the statistical distribution of the received signal, the correlation of signals received on spaced antennas, and the

correlation of signals as a function of the separation of the

carrier frequencies.

Comment

See Report No. 100 in this list.

100. H. Staras, "A Mathematical Study of Beyond -theHorizon Scatter Transmissions," thesis submitted to the

Physics Department of the University of Maryland in partial

fulfilment of the requirements for the Ph.D. degree,

September, 1954,

ABSTRACT

In the past decade or so, it has been observed that the

frequency band between 50 Mc and 3,000 Mc, approximately,

could be used fairly reliably for long distance communication

(i.e., when the transmitter and receiver are well beyond

each other's radio horizon). The dominant characteristics

of these long-distance signals is their high signal strength

(as compared with any previously known theory) and their

severe fading. Because of these characteristics, a scattering mechanism was postulated. Booker and Gordon, using

an approach originally developed by Pekeris, were the first

to develop an appropriate mathematical approach for scattering of radio waves by random inhomogeneities in the troposphere,

It is the purpose of this thesis to extend their work by

deriving appropriate formulas for the statistical properties

of the scattered radiation in terms of the four-dimensional

autocorrelation function of the random inhomogeneities in

the troposphere. Both isotropic and anisotropic turbulence

are considered.
-47-

(c) Statistical Methods

101. K. A, Norton, Edna L, Schulz, and Helen Yarborough,

"The Probability Distribution of the Phase of the Resultant

Vector Sum of a Constant Vector Plus a Rayleigh Distributed

Vector," Jour. Appl. Phys., Vol. 23, No. 1, pp. 137-141,

January, 195 2,

ABSTRACT

Formulas, tables, and graphs are given of the cumulative

probability distribution of a function frequently occurring

in the theory and practice of radio wave propagation as well

as in the study of the influence of noise in modulation studies.

102. K. A. Norton, H. Staras, and M. Blum, "A

Statistical Approach to the Problem of Multiple Radio Interference to FM and Television Service," Trans. IRE PGAP-1,

pp. 43-49, February, 1952.

ABSTRACT

This paper presents a statistical analysis of the problem

of FM and television service in the presence of multiple

sources of interference, assuming that the received fields

vary in time and space as described in the FCC Ad Hoc

Committee report and its references C, D, and E. It is

believed that comparisons of national services which differ

because of different allocation policies maybe made with a sufficiently high degree of accuracy to warrant the use of

the methods developed in this paper.

103. P. L. Rice "A Comparison of Methods for Evaluating

Trends in Time Series of Tropospheric Radio Field Strength

Data," NBS Report No. 1742; Trans. IRE PGAP-3, p. 144,

August, 1952.
-48-

ABSTRACT

This paper presents a short review of several methods for

evaluating the "seasonal trend" in a series of hourly median

field strengths corresponding to one hour of the day. Two

tools of the statistician, the autocorrelation function and the

variate difference method, refine the analysis of time trends

to a point where a maximum amount of correlation with relevant

meteorological data is hoped for.

104. H. Staras, "Trend Analysis and Prediction in a Discrete Gaussian Stationary Process," in preparation

(presented at a Bureau of Standards symposium in August,

1953).

ABSTRACT

Under the assumption that a discrete time series

represents a Gaussian stationary process, this paper derives

the maximum likelihood estimate for the "trend" when no

functional form for the trend is known. In addition, this

paper obtains the probability distribution associated with

a future occurrence.

Comment

This paper is reproduced here as Supplement XIII.

105. J. Feinstein, "Some Stochastic Problems in Wave

Propagation," Trans, IR.£, Vol. AP-2, Parti, No. 1,

p. 23, January, 1954.

ABSTRACT

The effect of random height variations associated

with a conducting surface upon the characteristics of reflected wave energy is ascertained by the methods of

physical optics. Kve rage received power, its variance,

angular frequency power spectra, and the field correlation

pattern are determined in terms of the statistical parameters

of the surface. The results are applied to various problems

encountered in tropospheric and ionospheric wave propagation.
-4-9-

106. J. Feinstein, "Some Stochastic Problems in

Wave Propagation - Part 2," Trans. IRE, Vol. AV--2,

No. 2, April, 1954.

ABSTRACT

In Part I some of the properties of wave energy reflected

from surfaces subject to random height variations were

investigated.

Here we ascertain the effects of refractive index fluctuations within a volume upon the properties of waves traversing the medium. The results are applied to problems encountered

in tropospheric and ionospheric propagation.

107. J. Feinstein, "Some Information Theory Aspects

of Propagation tnrough Time Varying Media," 1954 IRE

Convention Record, Part 2, Antennas and Communications,

p. 87.

ABSTRACT

The channel capacity of a communications system which

utilizes wave propagation through a time varying medium

such as the ionosphere or troposphere is evaluated in

terms of the statistical properties of the medium and of the

noise. The signal fading in such a system reduces the

capacity.

Information theory concepts are broadened to include

the possibility of multiple reception at spaced receiving

sites, and the consequent increase in theoretical channel

capacity is computed as a function of the number of such

sites. Current practices in the use of diversity reception

and directional antennas are examined in the light of these

results.

1 108. K. A. Norton, P. J. Short, and W. Mansfield,1 "The Cumulative Probability Distribution of the Instantaneous

Resultant Amplitude of the Vector Sum of a Constant Component and a Randomly Phased Rayleigh Distributed Vector
-50-

Component," prepared for presentation at the 11th General

Assembly of the URSI at the Hague, August, 1954.

ABSTRACT

In this paper somewhat more accurate distributions than

those formerly available are derived for the case where one

component of a received field is large compared to the

remaining components. The median value and fading range

(interdecile range) of a signal composed of a Rayleigh

distributed component adding in random phase with a constant component are shown as functions of the ratio

between the power in the constant component and the average

power of the Rayleigh component.

Comment

This report is reproduced here as Supplement XVI.

109. G. McCrossen, "Long-Term Theoretical Cumulative Distribution Function for Tropospherically Scattered

Fields," in preparation.

ABSTRACT

In the analysis of radio trans rr.ission loss data it has

been convenient to tabulate data in the form of hourly

median values of trans miss ion loss ana to separately analyze

characteristics of the data within each hour. Defining x to be

the amplitude in volts of an instantaneous signal, it is

desirable to obtain a reasonable approximating cumulative

distribution function of x over an indefinitely long period

of time. It is the intent of this note to derive, unaer certain

restrictive conditions, such a cumulative distribution function

and to indicate how it can be evaluated to any prescribed

degree of accuracy.
-51-

(d) Estimating VHF, UHF, and Radar Coverage or Service Range,

110. X. A. Norton and A. C. Omberg, "The Maximum

Range of a Radar Set," Froc. IRE, Vol. 35, No. 1, p. 4,

January, 1947.

ABSTRACT

Formulas are derived which may be used to calculate

the maximum range of a radar set. It is shown that the

maximum range obtainable with a given radar set depends

upon (1) the energy in the pulse, i.e., the peak power times

the time duration of the pulse or the average power divided

by the pulse-recurrence frequency; (2) the transmitting

and receiving antenna gains; (3) the transmission line,

antenna, and transmit-receive-box losses; (4) the "effective

width" or time duration of the transmitted pulses; (5)

the "effective bandwidth" of the receiver; (6) the radio

frequency of the transmitted waves; (7) the recurrence frequency for the transmitted pulses; (8) the "noise figure" of

the receiver; (9) the cosmic, atmospheric, and man-made

noise picked up by the antenna; (10) the attenuation during

passage of the radio waves through the atmosphere due to

the absorption by the atmospheric gases and rain drops;

(11) the "effective echoing area" of the target; (12) the

directivity of the transmitting and receiving antennas in

elevation and azimuth; and (13) the effect of the ground, which,

in turn, is inextricably associated with the particular site

used, the height of the target above the ground, and the

polarization of the transmitted radio waves.

111. X. A. Norton and H. Fine, "A Study of Methods

for the Efficient Allocation of Radio Frequencies to Broadcasting Services Operating in the Range .Above 50 kc," CRPL

Report 4-5, August 1, 1949.

ABSTRACT

Methods are developed for describing the service provided

by a television broadcasting system. It is shown how the

service range of a clear channel television broadcasting

station is limited by receiver and cosmic radio noise and
-52-

formulas are presented for determining the field strength

required to provide a satisfactory television service in this

case.

112. H. Staras, "The Effect on Television Service of

Transmitting Antenna Height, Radiated Power, the Use of

Off -Set or Synchronized Co-Channel Carriers, and of

Correlation Among the Radio Fields Received from Several

Transmitters," CRPL Report 6-1 , October 10, 1949.

ABSTRACT

Calculations have been made which provide useful

information for consideration in the efficient allocation of

frequencies to television stations. These calculations show

that: (1) increasing, for all stations, either the transmitting

antenna height or the effective radiated power or both,

substantially improves the total service which can be

provided, particularly in those regions where service is

provided by only one or two stations; (2) synchronizing or

"off -setting" co-channel carriers almost doubles the efficiency

of service which can be provided to stations allocated in a triangular lattice network; and (3) the assumption of no

correlation among the desired and undesired fields leads to

results concerning efficiency of service which are quite

accurate.

113. K. A. Norton and L. Gainen, "A Study of the

Influence of the Geographical Distribution of Population on

The Coverage Obtainable from a National Television System, " a working document to the FCC Ad Hoc Committee for the

Evaluation of FM and TV Propagation Factors Between 50

and 250 Mc, October 27, 1950.

ABSTRACT

In the present paper some studies are made, in the light

of the actual distribution of the population in the WashingtonBaltimore area as determined by the 1940 census, of the

degree to which maximizing area of coverage is equivalent
-53-

to maximizing the number of people provided with satisfactoryservice. Having in mind that the radio field strength

required for a satisfactory television service is likely to

depend upon the density of the population in the neighborhood of the receiving location, this study is based upon a definition of satisfactory service involving required field

strengths which vary with population density.

114. K. A. Norton, "Addendum to Reference E, " a working document of the FCC Ad Hoc Committee for the

Evaluation of FM and TV Propagation Factors Between 50

and 250 Mc, November 16, 1950.

ABSTRACT

This addendum brings the analysis in Reference E to

the Ad Hoc Committee Report up to date and extends it in

several directions. It is emphasized that soundly conceived

definitions of service are basic to the development of a proper allocation, and the point is made that the FCC definition of three "grades" of television service appears to be

defective. Optimum methods of television station allocation

are described based on these alternatives: (a) maximizing

the coverage of area per station; (b) maximizing the coverage

of area per channel; or (c) maximizing the coverage of

people.

115. R. S. Kirby, J. W. Herbstreit, and K. A. Norton,

"Service Range for Air -to-Ground and Air -to-Air Communications at Frequencies Above 50 Mc," Proc. IRE, Vol. 40,

No. 5, p. 525, May, 1952.

ABSTRACT

Propagation aspects of air-to-ground and air-to-air

communications are analyzed. Contours of constant

received signal strength are shown in the form of lobes for

various frequencies. It is shown that for systems with
-54-

equivalent transmitted power, ground antenna height, and

transmitting and receiving antenna gain the service range

decreases as the frequency is increased. This is due

primarily to a decrease in the absorbing area of the receiving antenna and to a larger number of nulls in the lobe

structure arising from interference between direct and

ground-reflected waves. Ground station antenna height

diversity and tilted-array ground antenna systems are

discussed as a means of improving coverage as the operating

frequency is increased.

(e ) Radio Meteorology.

116, G. Birnbaum, "Millimeter "VV a velength Dispersion

of AA/ater Vapor," NB3 Report No. 1943, September 23, 1952;

see also Journ. Chem. Phys., p. 57, January, 1953.

ABSTRACT

Dispersion due to water vapor in the wavelength region

from infinity to 0.6 mm is computed by means of quantum

mechanical formulas. The dispersion is attributed to:

(1) the contributions of the 11 rotational lines in the region

considered; these are obtained with a dispersion equation

characteristic of collision theory specialized to sharp lines;

and (2) the combined contribution of all rotational lines of

shorter resonance wavelength. This is obtained with the

aid of the well-known shape factor (v" - v~) " , which is shown to be valid for sharp lines independent of any

special model. s

117. E. X. Smith, Jr. and Stanley Yi eintraub, "The

Constants of the Equation for Atmospheric Refractive Index

at Radio Frequencies," NBS Report No. 1938, September 19,

1953; Froc. IRF, Vol. 41, No. 8, pp. :035-1037, August, 1953.

ABSTRACT

Recent improvements in microwave techniques have

resulted in precise measurements at the National Bureau

of Standards, the National Physical Laboratory, and
-55-

elsewhere which indicate that the conventional constants in

the expression for the refractivity of air should be revised.

In much of propagation work, the absolute value of the

refractive index of the atmosphere is of small moment.

However, in some work it is important, and it seems highlydesirable to decide upon a particular set of constants.

Through consideration of the various recent experiments

,

this paper arrives at a relation

77.6 4810 e K (p + -— ) N = (n-1) 10 u

= T ^ T

Where

N - refractivity of air

n = refractive index of air

T - absolute temperature in degrees Kelvin

p = total pressure in millibars

e = partial pressure of water vapor in millibars

This expression is considered to be good to 0.5 per cent

in N for frequencies up to 30,000 Mc and normally encountered ranges of termperature , pressure, and humidity.

C. Use of Theory and Prediction Methods to Solve Specific

Problems.

(a) Air-to-Ground Communications,

118. J. W. Herbstreit and Harold Staras, "The Zffect

of Interference from a Co-Channel Station on Double Channel

Air-to-Ground Communication, A Preliminary Study,"

RTCA Paper 38-51/DO-31, March 26, 1951, (appendix),

entitled "Communication Frequencies Required within the

Band 118.1 -126.7 Mc, during the Period 1951-1953

Inclusive and Recommended Implementation Thereof,"

ABSTRACT

An estimate is made of the required separation between

ground stations and the required ground antenna height

necessary to provide various grades of service when taking
-56-

into account co-channel interference from one other ground

station. An evaluation of air-to-air interference encountered

in Single Channel Simplex and Double Channel Simplex

operation has also been made.

119. H. Staras, P. L. Rice, and J. W, Herbstreit,

"An Analysis of Propagation Phenomena as Affecting VOR

Communication Systems , " NBS Report No. 1038, June 19,

1951.

ABSTRACT

Graphs are presented giving the service to be expected

in the presence of interference from co-channel stations of

standard and short range VOR radio navigation facilities.

These graphs take into account the fluctuations of the received

field due to inhomogeneities in the atmosphere, irregularities of the terrain, and the random variation of directivity

associated with aircraft antenna patterns. Tables are given

of service range under various separations of co-channel

stations and altitudes of aircraft for two different grades

of reliability of service.

120. K. A. Norton and P. JL. Rice, "Gapless Coverage

in Air-to-Ground Communications at Frequencies Above

50 Mc," Proc. IRE, Vol. 40, No. 4, p. 470, April, 1952.

ABSTRACT

It is shown that there is an optimum ground station

antenna height for use in typical air-to-ground communications systems. When antennas lower than this optimum

are used, the maximum distance range is reduced at all

aircraft altitudes. When antennas higher than this optimum

are used, the interference between the direct and groundreflected waves causes gaps to occur in the coverage at

the higher aircraft altitudes. The minimum altitude at

which the gap in coverage occurs decreases with increasing

frequency and with increasing ground station antenna height.

The optimum antenna height decreases with increasing

frequency, and this, in turn, reduces the maximum distance

range for satisfactory communication as the frequency
-57-

increases. The curves presented are based on values

expected from theory for a smooth spherical earth. Such

curves have been found experimentally to approximate very

well the average practical operating results,

121. P. L. Rice, W. V. Mansfield, J. W. Herbstreit,

"Ground-to-Air Co-Channel Interference at 2900 Mc,"

NBS Report No. 1909, Trans. IRE PGAE-6, December, 1952.

ABSTRACT

Estimates are given of average ground-to-air interference for a ground installation utilizing a Bendix ASR-1

vertically polarized antenna operating at 2900 Mc. Coverage

is defined in terms of 0, 6, 12, and 18 db protection ratios

with respect to a similar installation sending out a desired

signal, with station separations of 10, 50, 100, and 150

miles being considered. "Coverage" here is not synonymous

with the usual concept of service, for no minimum signal

is taken into account, but only the ratio between desired and

undesired field strengths. Limitations of the estimates

are discussed, and their derivation is explained in an

appendix to the report,

(b) Point-to-Point Communications.

122. M. Blum and P. L. Rice, "Tropospheric Propagation Charts for 30, 400, and 600 Megacycles," NBS Report

No. 1007, May 10, 1951.

ABSTRACT

Propagation charts are given showing the time distribution of received radio field strengths as a function of

distance for various frequencies and transmitting antenna

heights, assuming a receiving antenna height of 30 feet. The

charts were computed by an extrapolation of the methods and

formulas derived by the FCC Ad Hoc Committee for frequencies from 50 to 250 Mc.
-58-

123. J. W. Herbstreit, "Propagation in the UHF-TV Band,"

IRE, Convention Record, p. 120 (abstract), 1954.

ABSTRACT

The Central Radio Propagation Laboratory of the National

Bureau of Standards has been conducting a program of research

at frequencies of 418 and 1046 Mc in conjunction with an

extensive 100 and 200 Mc program of measurements throughout the United States. Reception of 1046 Mc transmissions

400 miles from Cheyenne Mountain, Colorado has been

found possible at all times. By far the most important

factor determining the available signal power in the UHF band

is the effective absorbing area of the receiving antennas.

An estimate of expected service and interference ranges at

VHF and at UHF is included in the talk.

Comment

A written version of this talk presented before the 1954

IRE National Convention is included as Supplement XVIII to

this paper.

124. K. A. Norton, "Point-to-Point Radio Relaying

via the Scattering Mode of Tropospheric Propagation,"

prepared for presentation at the 11th General Assembly of

the URSI at the Hague, August, 1954.

ABSTRACT

Experimental data on the transmission loss far beyond

the radio horizon in the frequency range 100 to 1000 Mc are

extrapolated by means of the Booker-Gordon scattering theory

to transmission frequencies as high as 50,000 Mc. Similarly,

data and theories of the expected atmospheric absorption

presented by Bussey for relatively short paths are extrapolated to longer distance paths. These extrapolations provide

estimates of the feasibility of point-to-point radio relays in

the frequency range 100 to 50,000 Mc over distances ranging

from 100 to 500 miles of the following types of service:
-59-

60 words per minute frequency shift telegraphy, frequency

modulated voice, frequency modulated high fidelity music,

and U. S. standard television transmissions.

Comment

This report is reproduced here as Supplement XVII,

D, Description of Equipment and Equipment Standards,

(a) Measurement of Field Strength,

125, F, M, Greene and M. Solow, "Development of

VHF Field Intensity Standards," NBS Journ, Res., Vol. 44,

No. 5, p. 527, May, 1950.

ABSTRACT

In many instances the accuracy with which the value of a physical quantity may be determined increases with the

simplicity of the method used to make the determination.

Such methods usually involve a theoretical calculation, or

an experimental observation, or both. In establishing the

"standard -antenna method" and the "standard-field method"

discussed herein, the methods were purposely made as elementary as possible for this reason. It is believed that

this enables the achievement of the maximum accuracy

possible or practicable at the present time between 30 and

300 Mc.

126, F, M. Greene, "The Influence of the Ground on

the Calibration and Use of VHF Field-Intensity Meters,"

Proc. IRE, Vol. 38, No. 6, p. 650, June, 1950.

ABSTRACT

VHF field strength measurements will be generally in

error if either the receiving antenna height or ground constants

are appreciably different from those existing when the fieldintensity meter was calibrated. These errors are discussed.
-60-

127, F, M. Greene, "Calibration of Commercial FieldStrength Meters at the National Bureau of Standards," NBS

Report No. 1019, July 11, 1951 e ABSTRACT

A brief description is given of the standards and methods

used in the calibration of commercial radio field strength

meters at the National Bureau of Standards in the frequency

range 10 kc to 300 Mc, A calibration consists in part of

measuring the overall linearity of the field strength meter

at one or more frequencies and r-f input voltage levels, and

of measuring the internal attenuator ratios at one or more

frequencies in terms of precision dissipative type step

attenuators as well as precision mutual inductance attenuators, depending on the frequency being used. The remainder

of the calibration consists of determining the so-called antenna coefficient or correlation factor of the set relating field

strength to the output meter reading. Below about 30 Mc

this is done only for sets using loop antennas in terms of a

quasi- static magnetic field produced by a single-turn balanced

transmitting loop. Above this frequency for sets using only

dipole antennas, a locally generated radiation field is used

and is evaluated in terms of the e e m,f, induced in a horizontal

receiving dipole. The accuracies of the various parts of

the calibration are discussed for different portions of the

above frequency range,

(b) Refractive Index Measurement and Computation,

128, G, Birnbaum, "A Recording Microwave Refractometer," Rev, Sci, Instr, , Vol„ 21, No, 2, pp, 169-176,

February, 1950; see also NBS Tech, News Bulletin, Vol, 34,

No, 4, p. 45, April, 1950,

ABSTRACT

An instrument designed to measure and record a small

difference between two cavity resonators is described, A

sweep frequency technique is used to generate the resonance
-61-

responses of the cavities. These responses are sharpened

and made to control the operating time of a trigger circuit,

whose average output is metered. Applications of the instrument are discussed, especially those relating to measuring

changes in dielectric constant, A simple extension of the

present instrument is suggested for simultaneously recording changes in dielectric constant and loss,

129. S, Weintraub, "Slide Rule for the Computation of

the Refractive Index of Air," NBS Report No. 2180, November 5,

1952; see also "Slide Rule Computes Radio Refractive Index

of Air," Electronics, January, 1953,

ABSTRACT

A slide rule method has been developed for the computation of the radio refractive index of moist air from temperature, pressure, and humidity data. The method attains good

precision with relative ease of calculation. It makes use

of two easily constructed slide rules,

130, W, E, Johnson, "An Analogue Computer for the

Solution of the Radio Refractive Index Equation," NBS

Report No. 2703, July 20, 1953; see also NBS Journal of

Research, Vol, 51, No, 6, p. 335, December, 1953.

ABSTRACT

The solution to the radio refractive index equation provides

information necessary to the research worker studying

tropospheric radio propagation in the VHF and UHF regions.

An analogue computer has been developed to solve this

equation:

N = (n - 1)10 6

= 77 * 6

( + 4810 e > where

N - refractivity of air

n = refractive index of air

T 5 absolute temperature in degrees Kelvin

p = total pressure in millibars

e = partial pressure of water vapor in millibars.
-62-

A unique feature of this computer is the modification of a linear ten-turn potentiometer so that its output to input

voltage ratio versus rotation closely approximates the exponential type curve of the saturated water vapor term in

the refractive index equation.

Comment

This computer is now in use at the Central Radio

Propagation Laboratory of the National Bureau of Standards

and has superseded other methods of calculating the radio

refractive index.

(c) General.

131. J. W. Herbstreit, "Extension of Signal Generator

Voltage Range to Lower Output Levels," NBS Report No.

1934, September 11, 1952; see also "Signal Generator for

Low Output Levels , " Electronics, Vol. 26, p. 218, January,

1953.

ABSTRACT

With narrow-band, crystal-controlled receivers in the

frequency range from 92 to 1047 Mc, useful measurements

have been made of available received signal energy at

170 db below one watt, corresponding to a 50-ohm signal

generator output level of only 0.022 microvolts. With a heterodyning system using two standard signal generators

and a crystal mizer, leakage fields from the signal generators

are effectively eliminated.

132. C. R. Ammerman and R, L. Riddle, "LowFrequency Modulator for Receiver Testing," Electronics,

Vol. 25, No. 9,pp. 240, 244, 248, September, 1952.

ABSTRACT

Modulation of signal generators at frequencies in the

order of 1 cycle is usually not feasible by ordinary methods.
-63-

A resonant circuit tuned at the modulating rate by a variable - speed motor is suggested, and the drawing of a resonator

suitable for use at VHF is included.

133. W. E. Johnson, "Semi-Logarithmic Rectangular

Coordinate Recorder," NBS Report No. 2288, February 6,

1953.

ABSTRACT

A new recorder consisting of two separate amplifying

and displacement systems uses standard 11 by 16 inch graph

paper in true rectangular coordinates and is controlled by

the amplitude and phase of an audio signal.

E. Subcontractors' Progress Reports

(Some of these reports predate the Signal Corps contract which

later supported the work.)

(a) Collins Radio Company

134. Report No. 1, November 3, 1949.

This contract No. CST-10783 with the CRPL of NBS,

deals with the measurement and recording of field strengths

at five different antenna heights, up to 500 feet, a frequency of

410 Mc over a non-optical path of about 100 miles, to be

performed near Cedar Rapids, Iowa. Much equipment to

be used on this project will be loaned to this company by

the NBS.

This report covers activities previous to the 3rd of

November, 1949, when measurements were made from the

27th of October to the 3rd of November at a receiving site

near Waukon, Iowa. Subjects discussed in this report are

the following:

(a) Purpose of project.

(b) Scope of project.

(c) Summary of work done, (very detailed), including data

in tabulated form in decibels above luv/m/kw for six days
-64-

(d) Results of measurements , (variations of field

strengths, 18 graphs).

(e) Plans for future operations, (equipment, receiving

site).

135. Report No. 2, December 1, 1949. (Author: S. C.

Shallon, Project Engineer)

This report covers activities during the period of the

4th to the 30th of November, 1949. Some propagation runs

were made, from the 16th to the 23rd of November, using a directional transmitting antenna beamed on the receiving

station at the WHO tower near Mitchellville, Iowa.

An explanation is given of the method used in analyzing

the eight days of recorded field strength signals, their conversion into tabulated data form, the 17 graphs for percentage

of time, and the final distribution curve. A correlation is

attempted with weather conditions.

In anticipation of future installation of a 50-channel timetotalizer, 50 Veeder-Root counters and their synchronous

drive motors were placed on a 24-inch square panel to

facilitate the simultaneous photographing of all fifty counters

once each hour. Six 10-channel time-totalizer chasses are

being constructed, one is a spare.

Explorations for a new receiver site will be necessary

during the next report period, due to the present modification plans at station WHO, to change the transmitting antenna.

136. Report No. 3, January 1, 1950. (Author: S. C.

Shallon, Project Engineer. )

This report covers the month of December, 1949, in

which two propagation runs were made, from the 5th to the

13th, and from the 16th to the 21st of December, using a directional transmitting antenna at the Cedar Rapids

Municipal Airport beamed on the receiving station at the

base of the WHO tower near Mitchellville, Iowa.
-65-

Improved equipment allowed most of the data to be

analyzed by photographic time -totalizer records. The schedule

of tables and curves to be submitted each month on the data

is the following:

A. Tables:

(1) Field strength in decibel units.

(2) Percentage of time the signal exceeds chosen

decibel levels.

(3) Hourly summary of field strengths.

B. Graphs:

(1) One graph on the 1%, 50%, 90%, 99% of time

the signal exceeded a decibel level for the

month,

(Z) Percentage of time the signal exceeded a decibel for each hour of each propagation run,

(3) Diurnal variation at 1%, 50%, 90%, and 99%

of the time.

The first chassis for the 10-channel time -totalizer was

completed and placed in operation on the 16th of December,

The frequency converter was completed and tested. Photographs and a circuit diagram of the time -totalizer are included

in this report.

Station WTAD-FM, 99.5 Mc, Quincy, Illinois, has an

antenna tower which is 750 feet high; this will be investigated

as a possible new location for the recording antennas of

this project,

137, Report No. 4, February 1, 1950. (Author: E. N.

Phillips, Project Engineer.

This report covers the month of January, 1950, in

which two piopagation runs were made: from the 6th - 12th,

and from the 23rd - 30th of January. The same equipment

and techniques were used as last month. The data is presented

as outlined in Report No. 3.
-66-

S. C. Shallon of Collins Radio Company, and G. R.

Chambers of CRPL, visited and conferred with the management of station WTAD-FM, Quincy, Illinois, with favorable

results, concerning use of their site and facilities for the

recording receiver to be removed from station WHO-FM,

138. Report No. 5, March 1, 1950.

Using the same facilities as mentioned in preceding

reports, two propagation runs were made this month, from

February 6-12 and 20 - 26, inclusive.

Five additional 10-channel time-totalizer chasses were

completed and tested, some persistent tube repair was

necessary, and modification of the receiver was begun this

month.

A thorough discussion is given in this report on the

equation upon which the data conversion is accomplished.

The scheduled tables and curves of the data are presented,

139. Report No. 6, April 1, 1950.

One propagation run was made during this period at the

WHO site, from March 6 - 12, using the same facilities and

techniques mentioned in previous reports. The scheduled

appropriate tables and curves are presented, and other

graphs of a summation comparison nature, as:

(a) A distribution curve of field strength for March

as compared with curves from previous reports on

November, December, 1949, and January, February,

1950.

(b) A family of graphs (12) are submitted on data

accumulated during the five months at this WHO

location.

(c) A graph on summation average of diurnal variation.
-67-

A test run was conducted at the site of the WTAD-FM

tower near Quincy, Illinois, from the 21st - 23rd of March,

1950, to assess the suitability of the site for the relocation

of the receiver. Four members of this project, with adequate equipment, went to Quincy on March 21 to start

operations. The received signal amplitude was great enough

to choose this site as a receiving terminal in the future.

If this permanent site at WTAD-FM does not give suitable

signals, it is planned to use portable equipment to measure

signal levels at different sites along the path from Quincy

to Cedar Rapids,

140. Report No, 7, May 1, 1950.

Two propagation runs were made during April, from the

10th - 17th and from the 24th - 30th, inclusive, at the WTAD-FM

tower site. The same equipment and techniques were used as

those previously, but only the recording from the 14th to

the 17th was used in this report. The scheduled conversion and

curves are submitted,

A detailed description is given on the present modification of the resnatron transmitter,

141. Report No, 8, June 1, 1950.

This is the concluding report of the series, covering

May, 1950. Using the same facilities as mentioned in report

No, 7, two propagation runs were made, from May 11 - 17, and

from 22 - 28, inclusive. The treatment of these data is

performed in the same manner as described in report No, 2;

the usual tables and curves of the data are presented.

The present location at the site of the WTAD-FM

transmitting tower near Quincy, Illinois, has proved to be

satisfactory.
-68-

(b) Federal Communications Commission,

142. FCC Report No. 1, May 15, 1951. (Author: E. W.

Allen, Project Director.

)

This report covers the period from March 1 through

April 30, 1951, although preliminary work of setting up

equipment began about February 16, 1951.

Log sheets of transmitter schedules will be submitted

by the transmitting stations each month to report any malfunctioning of equipment. The following is a list of the

recording sites, by state, and the number of stations monitored

by each.

a. California.

Livermore 3 stations

Santa Ana 3 stations

b. Florida.

Fort Lauderdale 1 station

c. Georgia,

Powder Springs 3 stations

d. Massachusetts,

Millis 3 stations

e. Maryland.

Laurel 4 stations

f. Michigan.

Allegan 3 stations

g« Nebraska.

Grand Island 3 stations

h. Texas.

Houston 1 station

143. FCC Report No. 2, July 13, 1951. (Author: W. C

Boese, Acting Project Engineer.)

All of the recording sites listed in Report No. 1 were in use between May 1 and June 30, 1953, except three;
-69-

a total of 58 Esterline-Angus chart rolls was fowarded

this month to the CRPL group in Washington to be scaled

by CRPL personnel.

The FCC Laboratory Division made calibration checks

on recording installations in Michigan and Maryland; enclosed

is a table of antenna factors.

144. FCC Report No. 3, July 1 through October 31, 1951.

Since July 1, 1951, the recorder charts have been

analyzed by the FCC Field Engineering and Monitoring

Division, usually at the recording sites. Tabulated sheets

for 49 months of analyzed data on 18 stations were forwarded

to CRPL in Washington at the same time as 39 chart rolls

were sent to be analyzed by CRPL personnel. An explanation

is given in this report of a new method of analyzing very

low signal strengths on charts; instead of hourly medians

being obtained, the number of minutes during the hour that

the signal exceeds certain predetermined levels is recorded.

Included in this report are lists of transmitter and path

characteristics for 26 monitored stations and fifteen different

receiver calibrations, giving the recommended antenna factors,

145. FCC Report No. 4, July 10, 1952. (Author: G. E,

West, Acting Chief, TID.

Three cumulative distributions are presented in this

report for data from July through December, 1951, hours

from 1900 to 2200, on 45 FM stations and 7 TV stations.

On February 11, 1952, 42 tabulated data sheets and 84

transmitter schedules on 19 monitored stations were sent to the

relocated CRPL in Boulder, Colorado,

146. FCC Report No. 5, July 16, 1952.

Ten new antenna calibration factors are given in this

report; 53 transmitter schedules and 60 tabulated data sheets

were sent to CRPL in Boulder, Colorado, February 11, 1952,
-70-

George Waldo, Project Engineer for the CRPJL--FCC recording

program, visited CRPL, and discussions were held on

equipment, methods of analysis, and future plans for this

project.

147. FCC Report No. 6, April 1 through June 30, 1952.

(Author: G. V. Waldo.)

This report covers data accumulated during April, May,

and June, 1952. Experiments are described which were

conducted at Livermore, California and at Laurel, Maryland

on the effects of terrain variations in regularly monitored

field strengths as compared with such variations affecting

fields from local transmitters.

A general review of the recordings from each monitoring

station is presented for all paths monitored during the fiscal

year ending June 30, 1952, and a table of transmitting

antenna heights is included.

148. FCC Report No. 7, July 1 through September 30, 1952.

This report describes the operation of recording facilities at each of the recording sites used by the FCC. In

accordance with the plans outlined in the proposal to CRPL

on June 5, 1952, a number of changes were made in the

installations at the recording sites before starting to record

the new paths listed in the proposal. A list is given in this

report showing the status of recordings at each monitoring

station.

(On January 5, 1953, 80 tabulated sheets of data for

26 stations were mailed to CRPL.)

149. FCC Report No, 8, October 1 through December 31,

1952.

A complete list is given showing the status of the recordings at each of the monitoring stations for the last
-71-

quarter of 1952. (On March 6, 1953, 63 data sheets were

mailed to CRPL, Each such sheet covers a recording period

of one month for one station.)

A list is given of 34 propagation paths for which terrain

profile charts are being completed by the FCC,

150. FCC Report No. 9, January 1 through March 31, 1953.

A status list is given of all stations recorded during

January, February, and March. On February 12, an inspection was made of technical facilities at the KMAR transmitter,

Bakersfield, California; there were indications that the transmitter and antenna systems were not up to par,

(May 21, 1953, data sheets for 21 paths were sent to

CRPL in Boulder.)

A complete description is given of a special mobile

field strength survey of three Fresno, California stations,

and three cumulative distribution curves are plotted.

151. FCC Report No. 10, April 1 to June 30, 1953.

This is the concluding report for the project, and

describes the operation of recording installations during

April, May, and June, 1953; this is a list including the

receivers used and the dates of termination of recordings.

Also included are lists of geographical coordinates of recording installations and a summary list of receiver antenna

factors for all antennas used in the project.

A detailed description is given of the effects of averaging

and sampling techniques in the measurement of rapidly fading

signals.
-72-

(c) United Broadcasting Company,

152. UBC Report No. 1, March, 1950.

Quite a detailed description is given in this report of

the necessary preliminary preparation of equipment needed

for the project. Of 29 available stations, the following were

selected for monitoring:

a. WHKC-FM, vertical and horizontal receiving antennas.

b. WCOL-FM

c. WVKO-FM

d. WXYZ-TV

153. UBC Report No. 2, April, 1950.

Charts were analyzed and hourly medians tabulated

for WVKO-FM, WHKC-FM, and WCOL-FM, all located in

Columbus, Ohio, and recorded at Hudson, Ohio. Problems

reported on include measurement of noise figures, air tempera*

ture control, building antenna supports, adjusting recorder

chart speeds and time constants to accommodate rapid signal

fading,

154. UBC Report No. 3, May, 1950.

The construction of a helix antenna to measure

circularly polarized fields from WHKC-FM is described.

Data are tabulated and a new setup to monitor WJR-FM is

reported,

155. UBC Report No, 4, June, 1950.

Data for five recording channels are tabulated, A

summary of the progress of the project is included in the

report.

156. UBC Report No. 5, July, 1950.
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Data for July are tabulated; general information about

equipment breakdowns and remeasurement of noise figures

is reported.

157. UBC Report No. 6, August, 1950.

Data for six channels are tabulated. The additional recorder

was set up on WKBN-FM, 98.9 Mc, due to the interference of

this station with WHKC-FM, 98.7 Mc

158. UBC Report No. 7, September, 1950.

Propagation measurements were made at the Hudson recorder site with the following channels:

a. Columbus -Hudson path:

(1) WHKC-FM, 98.7 Mc

(a) Horizontal dipole receiving antenna.

(b) Vertical dipole receiving antenna.

(c) Yagi.

(2) WCOL-FM, 92.3 Mc, horizontal dipole receiving

antenna.

b. Detroit-Hudson path:

(1) WJR-FM, 96.3 Mc , horizontal dipole receiving antenna,

(2) WXYZ-TV, 179.75 Mc , horizontal dipole receiving

antenna.

c. Youngstown-Hudson path: WKBN-FM, 98.9 Mc, horizontal

dipole receiving antenna.

A study of noise figures was continued.

159. UBC Report No. 8, October, 1950.

No changes except minor ones.

160. UBC Report No. 9, November, 1950.

One additional receiver was placed in service on the Columbus

Hudson path. Tabulated data is submitted for all paths. Three

noise measurement receivers were put in service this month.
-74-

161. UBC Report No. 10, December, 1950.

This is a very detailed report on: a. Performance of REL receivers,

b. Noise figure measurement,

c. Calibration of receiving equipment,

d. Service contour determination for station WHKC-FM,

Data for three paths are tabulated,

162. UBC Report No, 11, January, 1951.

Data for seven recordings is tabulated, (These data are

always in the form of hourly median field strengths.) Some

modifications were made and a few field calibrations were made

of receiving antennas.

163. UBC Report No. 12, February, 1951,

Noise figure measurements and field calibrations are

continuing. An eighth recording has been added, using a _ new high gain plane polarized antenna monitoring V/HKC-FM,

164. UBC Report No, 13, March, 1951.

Ten pages of recorded hourly median field data are

submitted on WHKC-FM alone, besides data for the other

four stations,

165. UBC Report No. 14, April, 1951.

A paper on the project was given at the URSI meeting in

Washington, D. C. Data are now reported in decibels above

one microvolt per meter for one kilowatt of effective

radiated power.
-75-

166. UBC Report No. 15, May, 1951.

A major part of the month was spent in preparing for

and making field strength measurements on 30 mile radius

circles around WHKC-FM, Columbus, Ohio, and WHK-FM,

Cleveland, Ohio. In addition, field strength measurements

were made on a radial from Youngstown to Hudson, The

usual propagation study continues, charts are analyzed, and

data are submitted.

167. UBC Report No. 16, June, 1951.

A mobile unit received from CRPL is being fitted out

to make field strength measurements on a regular tour of

twenty different locations; this is to be operated for one year.

The center of the arc along which the twenty sampling sites

are located is Columbus, Ohio, about 125 miles away. Otherwise, the regular program is continued.

168. UBC Report No. 17, July, 1951.

The mobile recorder unit is recording two channels,

tuned to WHKC-FM, 98.7 Mc and WCOL-FM, 92.3 Mc. The

regular recording program continues. Included in this progress

report is a graphical analysis of the diurnal variation for a

year of recordings of field strength from station WKBN-FM,

Youngstown. A detailed description of the mobile recorder

unit and its functions is included in this report,

169. UBC Report No. 18, August, 1951.

Recording and noise studies continue, A graphical

analysis of the daily variation of data as recorded at Hudson

is included in this report.

170. UBC Report No. 19, September, 1951.

Recording and analysis continues. Distribution curves

of data are included in this report.
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171. UBC Report No. 20, October, 1951.

Propagation measurements were made at the Hudson site

on eight receivers and with the mobile unit on two receivers.

Diurnal variation curves of data obtained at Hudson are

included in this report.

172. UBC Report No. 21, November, 1951.

The regular recording schedule was continued, noise

figure measurements were made on all receivers in operation

during the month. One antenna change was made at the Hudson

recorder site. Analyzed data and graphs are included in

this report.

173. UBC Report No. 22, December, 1951.

No changes,

174. UBC Report No. 23, January, 1952.

The program continues as previously set up except for

some trouble with antennas due to the weather. Data sheets

and graphs are submitted as usual.

175. UBC Report No. 24, February, 1951.

The Hudson recorder site and the mobile unit continue

recording. The channel used temporarily to measure the

field strength at No. 4 sampling site was changed to KDKA-FM

on the 25th of February.

176. UBC Report No. 25, March, 1952.

A resume of the recording project is given in this

report, KDKA-FM was recorded on the Pittsburgh-Hudson

path using one of the WHKC-FM antennas. Analyzed data

and graphs are included in the report.
-77-

177. UBC Report No. 26, April, 1952, UBC-T-30.

Propagation measurements of six stations with eight

receivers continue at Hudson. The mobile unit records

two stations on two receivers. A graphical analysis of the

diurnal variation of the hourly median field strength as recorded at Hudson is included in this report. The ratio of

simultaneous hourly median values of horizontal field

component to vertical field component is presented to

determine the condition of operation of the WHKC-FM

circularly polarized transmitting antenna.

178 UBC Report No. 27, May, 1952, UBC-T-31.

The regular schedule of field strength recording was

continued during May, In April a conference was held in

Washington with NBS personnel on the progress of the work,

179. UBC Report No. 28, June, 1952.

The regular schedule continued. Terrain profiles

have been prepared for the paths from WHKC-FM to each of

the twenty sampling sites used by the mobile unit. The

mobile unit concluded the twelve month period of sampling

field strength on the 125 mile radius arc. It is scheduled

to commence a similar program of sampling measurements

on an 85 mile radius arc, starting July 1, 1952.

180, UBC Report No. 29, July, 1952,

Propagation measurements are continued, and a change

from station KDKA-FM to WJAS-FM was made on July 3; it

became necessary to change back to KDKA-FM on July 22

because of interference on WJAS-FM,

The mobile unit was operated over a regular route

sampling twenty sites in North Central Ohio, stations WHKC

FM and WCOL-FM, This is the first month working on a new schedule of sampling at 85 miles from Columbus, Ohio,
-78"

A comparison is drawn between the 85 mile and 125 mile arcs,

The distance to each site on the two arcs is tabulated and

presented in chart form.

181. UBC Report No. 30, August, 1952.

No change.

182. UBC Report No. 31, September, 1952.

No change in schedule. A proposed modification of

the chart analysis would effect a simplification in the procedure; it is expected there would be a saving in time of up

to 50%, a reduction in errors, and a saving of about 50% in

the time spent in checking, (Later experience with these

methods modified these conclusions.)

183. UBC Report No. 32, October, 1952.

No change.

184. UBC Report No. 33, November, 1952.

Station WKBN-FM recordings were temporarily discontinued, pending installation of the WKBN-TV antenna. The

WKBN-FM recorder channel has been changed to WFMJ-FM,

105.1 Mc , Youngstown, Ohio. Noise figure measurements

continue.

185. UBC Report No. 34, December, 1952.

During the last half of December, a time totalizer was

used in conjunction with ordinary chart scaling methods.

186. UBC Report No. 35, January, 1953.

Hourly median values of six channels were taken principally from the totalizer record during January. Sampling

on the 85 mile arc is now done with one site change each

day; interference is experienced at certain sites.
-79-

This report includes a tabulation of the final measurements

made with the mobile unit on the 85 mile arc. Operation of

this phase of the project was concluded on January 31,

1953, after seven months data had been accumulated from

twenty sampling sites on the 85 mile arc.

Analysis with the electronic totalizer has not produced

the efficiency expected,

187. UBC Report No. 36, February, 1953, UBC-T-40.

A graphical analysis of the diurnal variation of the hourly

median field strength as recorded at Hudson is included in

this report. Propagation and noise figure measurements

were made on all receivers in operation during the month.

Some experimental work has been done in setting up a UHF recorder channel to measure WKBN-TV, Channel 27,

and WFMJ-TV.

188. UBC Report No, 37, March, 1953.

No change. Eight receivers are in operation recording

four different stations,

189. UBC Report No. 38, April, 1953, UBC-T-42.

No change,

190. UBC Report No. 39, May, 1953, UBC-T-43.

Each month since May, 1952, a statistical distribution

has been plotted of the ratio of the simultaneous hourly

median values of the horizontal field component to the vertical

field component of station WHKC-FM.

191. UBC Report No. 40, June, 1953, UBC-T-44

This is the 44th and final report on Contract No. CST10841 with the National Bureau of Standards, which terminated
-80-

on June 20, 1953, and in which propagation and noise, figure

measurements were made on eight different channels at

the Hudson recorder site and two channels on a mobile unit.

Appropriate data and curves on the recorded field strengths

are included in the report, A resume of the project is

also included.

(d) The Pennsylvania State College. (Author: C. R. Ammerman,

Assistant Professor, Electrical Engineering)

192. Penn State Report No. 1, April, 1951.

Preliminary work in instrumentation is described.

Exploratory recordings indicate relatively constant signal

from nearby stations. Studies of the available signal sources

are being conducted, and WHDL-FM, 90 miles, and V. RFL-FM,

115 miles, are suggested stations. Receiving equipment is

located in the Electrical Engineering Building on the Penn

State campus.

193. Penn State Report No. 2, May, 1951.

WHDL-FM, 95.7 Mc, Olean, New York, is being monitored.

194. Penn State Report No. 3, June, 1951.

A statistical study of receiver calibration variations was made

and they were found not to be excessive. A second antenna

was built and tuned to WJAS-FM, 99.7 Mc, Pittsburgh; recording was started on June 20. WHDL-FM data was studied

and compared with published information. On June 28,

WTPS, New Orleans, Louisiana, was received for a few

seconds over the WHDL-FM receiver.

195. Penn State Report No. 4, July, 1951.

A fourth recording was begun on July 31, monitoring

WEST-FM, 107.9 Mc, Easton, Pennsylvania at a distance of

140 miles. Data and diurnal variations for WHDL-FM and
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WJAS-FM are given for June and July. WTOP-FM, 96.3 Mc,

Washington, D, C. , has been chosen as the other eastern

station to be recorded. WTOP is about 135 miles away.

196. Penn State Report No. 5, August, 1951.

Four channels are now in operation. Hourly median

values of field strength are tabulated, diurnal variations

are studied, and terrain profiles of paths are shown for

WHDL-FM, and WEST-FM. Tuned doublet type antennas

were constructed for each channel, and some improvement

was noted in recorder sensitivity due to certain modifications,

197. Penn State Report No, 6, September, 1951,

A terrain profile is shown for WTOP-FM, Tabulations

of hourly median field strengths in decibels above one microvolt per meter for one kilowatt of effective radiated power

continue, and studies of diurnal variation and rate of fading

continue.

198. Penn State Report No. 7, October, 1951,

Exploratory meteorological correlations have not proved

significant.

199. Penn State Report No. 8, November, 1951.

The antennas have been checked and some weather protection added. Resistance standards were constructed to aid

in measurement of antenna standing wave ratios. Fading

studies are progressing. Variations in calibration are being

studied. Recording of data and calculations were carried out

throughout the month; hourly medians are tabulated.

Discussions were held with W. E, Gordon, L. H. Doherty,

J. W. Herbstreit, W. G. Albright, G. V. Waldo, and others

regarding the contract and propagation theory.
-82-

200. Penn State Report No. 9, December, 1951.

Recording continued throughout December, though difficulty is being experienced with interference of various kinds.

An analysis of receiver calibration stability is presented

which shows there is a marked improvement over earlier

operations; on this basis, the number of calibrations per

day has been reduced to approximately three. Values of

actual signal levels have been found to greatly exceed those

predicted for a smooth spherical earth, but they almost

never reach the theoretical values for a plane earth.

201. Penn State Report No. 10, January-February, 1952.

Recording and data analysis continue. Some antennas

have been repaired and equipment modified; overall accuracy

and stability is under constant study.

A severe external interference was located and eliminated.

Included in this report is a preliminary study on fading, a voluntary extra project not required by the contract. Attempted

correlation of field strength with certain meteorological

factors is continuing,

202. Penn State Report No. 11, March-April, 1952.

Data were recorded and analyzed. Improvements were

made in two receivers, and antennas were readjusted. A

comparison of fading with wind velocities was completed.

203. Penn State Report No. 12, May-June, 1952.

Recording and analysis continue , Data are being

studied for diurnal and seasonal trends,

204. Penn State Report No. 13, July-August, 1952.

All receivers are now crystal-controlled. Recording

and analysis of data show high signals now. Included in
-83-

this report is a copy of a published paper on the low frequency

modulator for testing receiver fading, by C, R, Ammerman and

R. L. Riddle.

205. Penn State Report No. 14, September-October, 1952.

A search is under way for suitable higher frequency

stations to monitor. An experimental receiver for monitoring Channel 10 on TV was assembled. A copy of the paper,

"VHF Propagation Peyond the Horizon," published in the

November, 1952, issue of the Penn State Engineer is included

in this report.

206. Penn State Report No. 15, November-December, 1952,

Two time totalizer recorders were received and put into

operation; a receiver for WNBF-TV, Channel 12, Binghampton,

New York, is under construction.

Recording proceeds as usual, and data are included in

this report. Previously reported studies are continued,

207. Penn State Report No. 16, January-February, 1953,

All four stations are being recorded on Esterline -Angus

charts. Two stations, WTOP-FM and WJAS-FM, are also

being recorded with the time totalizer and photo-record setup.

In analysis of the data, time totalizer records are used

whenever possible. Included with this report is a summary

description of procedures used in obtaining the hourly median

field strength values.

208. Penn State Report No. 17, March-April, 1953.

Recording of VHF field strengths continued throughout

April, the contract expiring April 30, 1953, Mr, Riddle

and a graduate student hope to continue some experiments,

A paper from this laboratory was presented at the current

URSI-IRE meeting in Washington, D. C. on the topic of signal

fading, (See Report No. 21 in this list.)
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(e) The University of Illinois. (Author: W. G. Albright,

EERL UI)

209. Illinois Report No. 1, May, 1950.

Since funds have not yet been established for work to

be done on project No, CST 10862, work accomplished by

equipment and personnel during this period is limited. No

recordings were possible through lack of equipment to be

loaned by NBS. Discussions were held as to the possible

locations of recording apparatus and the desire to have it

on the campus in the Electrical Engineering Building. Some

necessary facilities were installed.

210. Illinois Report No. 2, June, 1950.

Recorders and receivers arrived from NBS, and alterations are being made; receivers for TV channel studies will

have to be constructed. One receiver designed for aircraft

use was converted for use on TV channels.

211. Illinois Report No. 3, July, 1950.

Several NBS receivers are in use, with considerable

interference. New stations are being selected to eliminate

this problem. Variation of 20% in values obtained by scaling

Esterline -Angus charts was experienced by operators. Recordings were made of WXLW, WGNB, and KXCK, with some

difficulties.

212. Illinois Report No. 4, August, 1950.

During this period five recording units were installed.

Three units are recording FM and two TV signals. Six antenna towers have been designed, five are erected, and work

is proceeding on the sixth.

Stations selected for monitoring are:

a. KXOK-FM, St. Louis, Mo., 93.7 Mc, 146 miles.

b. WMBI-FM, Chicago, 111., 95.5 Mc, 126 miles.

c. WCSI-FM, Columbus, Ind. , 93.7 Mc, 139 miles.

d. WNBQ-Ch 5, Chicago, 111., 81.75 Mc, 126 miles.
-85-

213. Illinois Report No, 5, September, 1950.

Three FM stations have been recorded and hourly medians

obtained in decibels above one microvolt per meter. Calibrations were made once per week,

214. Illinois Report No. 6, October, 1950,

Monitoring of the three FM stations has continued, and

the hourly median values are included in this report. WGN-TV,

Channel 9, Chicago, Illinois is being monitored; because of

the low signal, a four-element Yagi antenna is being used,

215. Illinois Report No. 7, November, 1950,

Recording of three FM and one TV channel continues,

Tower construction is completed,

216. Illinois Report No, 8, December, 1950,

Station WNBQ-TV, 81.75 Mc, Channel 5, Chicago, Illinois

has been added to the list of stations being monitored; a seven-element Yagi is used for a receiving antenna.

217. Illinois Report No. 9, January, 1951.

During this period the field strengths of three FM

stations and two TV stations were recorded; medians are

included in this report for each hour of recording.

Some experimentation with calibration equipment is in

progress,

218. Illinois Report No. 10, February, 1951.

Previously listed recordings continue; WGN-TV is being

recorded on two antennas now, a folded dipole and a corner

reflector.
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219. Illinois Report No. 11, March, 1951.

Median FM field strengths are tabulated; TV data will

be submitted later. Antenna factors were measured for

each of the FM receiving antennas.

220. Illinois Report No. 12, April, 1951.

Effort is being made to correlate variations in atmospheric

conditions to changes in received signal strength from the

stations located in Chicago, Illinois.

221. Illinois Report No. 13, May, 1951.

Because of interference noted on the WNBQ recording,

monitoring of this station will be discontinued, and WBKB

will be substituted.

222. Illinois Report No. 14, June, 1951.

Recording and analysis continue . Meteorological data

are being collected and analyzed to study correlations with

field strength data over the Chicago-Urbana path.

223. Illinois Report No. 15, July, 1951.

Recording of WGN-TV has been discontinued until a REL receiver can be obtained. This station is to be monitored

at three different heights above the Electrical Engineering

Building, as well as at two different places in the horizontal

plane. Several repairs and changes in towers were effected

during this period.

224. Illinois Report No. 16, August, 1951.

Monitoring continues on three FM stations and one TV

station. Hourly medians are tabulated in the report.
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225. Illinois Report No. 1 on Contract No. CST 706,

September, 1951.

Recordings of three FM stations and three TV stations

are tabulated. One receiver monitors WBKB, 71.75 Mc,

Channel 4, Chicago, Illinois, with a standard dipole. Two

recording units monitor WGN-TV, 191.75 Mc by a standard

dipole with a ground plane, one at 25 feet and the other at

75 feet above the roof of the Electrical Engineering Building.

A receiver was installed to monitor WENR-TV, 179.75 Mc,

Channel 7, Chicago, Illinois, with a standard dipole thirtyfeet above the roof.

226. Illinois Report No. 2, CST 706, October, 1951.

Recording and tabulation of hourly medians for three

FM stations and three TV stations continue , Also included in the report are some curves obtained from the data.

Meteorological data from radiosonde ascents at Rantoul

and Joliet, Illinois, are being collected, as well as data

related to ground level atmospheric conditions at several

cities within a radius of 200 miles. A correlation of this

data with signal strength data is being attempted.

227. Illinois Report No. 3, CST 706, November, 1951.

Recordings of field strengths of WMBI-FM, WCSI-FM,

KXOK-FM, WBKB-TV, WENR-TV, and WGN-TV are continued.

WGN-TV is recorded with four antennas, three spaced 25

feet apart in the vertical direction and the fourth displaced

40 feet along the horizontal. Data and curves are included

in this report.

Fading was prominent during this period, making

Esterline-Angus chart scaling difficult. Four amplifiers

have been constructed to lessen this difficulty, taking

advantage of the totalizer circuits of the REL receivers and

fast chart speed EA recording. (Normal speed is three inches

per hour with a time delay circuit; fast speed is three inches

per minute with no time delay circuit.)
-88-

228. Illinois Report No. 4, CST706, December, 1951.

Each of the four units recording WGN-TV have had a second Esterline -Angus recorder added, operating at three

inches per minute. A chart inspector has been designed to

allow comparison of five charts simultaneously.

229. Illinois Report No. 5, CST 706, January, 1952.

The WGN-TV data is being studied for height diversity.

Otherwise no change in data and curves reported.

230. Illinois Report No. 6, CST 706, February, 1952.

No change.

231. Illinois Report No. 7, CST 706, March, 1952.

In this report the following tables and curves are

presented:

a. Hourly median signal strengths: 9 recordings

b. Cumulative distributions: 9 recordings

c. Daily signal strength: 9 recordings

Correlation was attempted between received signal

strengths and meteorological data.

232. Illinois Report No. 8, CST 706, May, 1952.

No change.

233. Illinois Report No. 9, CST 706, June, 1952.

No change,

234. Illinois Report No. 10, CST 706, July, 1952.
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Hourly median field strengths expressed in decibels

above one microvolt per meter for one kilowatt of effective

radiated power are tabulated, and curves are also contained

in the reports. Some difficulty with local interference from

the fire department is experienced on WENR-TV recordings,

235. Illinois Report No. 11, CST 706, August, 1952,

No change,

236. Illinois Report No. 12, CST 706, September, 1952.

Difficulty with the WENR-TV crystal oscillator necessitated deletion of data for the last half of the month for this

station.

237. Illinois Report No, 13, October, 1952.

July 1, 1952 WMBI-FM discontinued broadcasting.

More than one year's data has been obtained on stations

WCSI-FM andKXOK-FM, and it was decided that this was

sufficient for these frequencies. New stations are to be

chosen for these three recording units. A new crystal

was obtained for the recording on TV channel 7, which is

now being monitored again,

238. Illinois Report No. 14, CST 706, November, 1952.

Signals from each of the four WGN-TV receiving antennas

are being recorded at fast chart speeds for periods of fifteen

minutes, in addition to the regular slow speed recordings;

these fast speed recordings are made concurrently with

measurements of atmospheric conditions by radiosonde.

239. Illinois Report No. 15, CST 706, December, 1952.

During this month it was noted that temperature has a

large effect on rectifier components; some modification was

made to correct this.
-90-

240. Illinois Report No. 16, CST 706, January, 1953.

Preliminary recordings have been made of several

Chicago stations in order to find a satisfactory replacement

for WMBI-FM.

241. Illinois Report No. 17, CST -706, February, 1953.

Tabulated data and derived curves for six TV recordings

are submitted in this report. Station WFMF, 100.3 Mc, has

been selected to replace WMBI-FM.

242. Illinois Report No. 18, CST 706, March, 1953.

No change.

243. Illinois Report No. 19, CST 706, April, 1953.

No change except for trouble with the WBKB receiving

antenna.

244. Illinois Report No. 20, CST 706, May, 1953.

WBKB and WENR data are omitted because of antenna and

equipment trouble.

245. Illinois Report No. 21, CST 706, June, 1953.

Station WFMF has been chosen to be recorded at three

different sites along the propagation path; antennas and

receiving units have been built for this purpose.

246. Illinois Report No. 22, CST 706, July, 1953.

No change.

247. Illinois Report No. 23, CST 706, August, 1953.

During this period, signal strengths were recorded of

station WBKB -TV, as well as those of stations WGN-TV and

WENR-TV. Tabulated data and curves are submitted.
-91-

248. Illinois Report No. 24, CST 706, September, 1953.

No change except that WBKB-TV changed call letters and

frequency and WENR-TV became WKBN. This is the final

report on Contract CST 706.

(f) The University of Texas. (Author: DeForrest Metcalf,

Electrical Engineering Research Laboratory. )

249. EERL Report No. 1, March 10, 1949.

The scope of the measurement program is outlined, a channel study of FM stations in the State of Texas is presented, equipment for recording VHF field strengths is

described, and daily recordings for the month of February,

1949, of KPRC-FM are reported. Some analysis of diurnal

variations of these signals is also reported.

250. EERL Report No. 2, April 11, 1949.

Recordings of KPRC-FM for March, 1949, are reported.

Development of a totalizer is mentioned. Details of the

Houston to Austin path are listed. Receiving and calibrating

equipment is described. A bibliography is included.

251. EERL Report No. 3, May 12, 1949.

Hourly median field strengths, scaled manually from

Esterline -Angus charts, are tabulated for February, March,

and April, 1949. Equipment and methods of measurements and

analysis are described in detail. Within -hour Rayleigh

distributions for selected hours of recording of KPRC-FM

are shown. A bibliography is included.

252. EERL Report No. 4, June, 1949.

Recordings of KPRC-FM for May, 1949, are tabulated.
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253. EERL Report No. 5, July 13, 1949.

Recordings of KPRC-FM and KYFM are tabulated. The

effect of different time constants of two and five seconds

in smoothing the KYFM record is shown, and the KYFM signal

is described in some detail. Operation of totalizer equipment

is explained. A bibliography is included.

254. EERL Report No. 6, August 12, 1949.

KPRC and KYFM hourly medians are tabulated.

Accuracy of measurements is discussed.

255. EERL Report No. 7, September 14, 1949.

KYFM, KPRC-FM and WFAA-FM hourly medians are

tabulated. The receiving and recording installation is described in detail.

256. EERL Report No. 8, October 15, 1949.

KYFM, KPRC-FM, and WFAA-FM hourly medians are

tabulated. Data were collected to determine the hourly

frequency distribution of fading. Equipment changes are

discussed.

257. EERL Report No. 9, November 14, 1949.

A summary of absolute accuracy estimates (usually plus

or minus one decibel) is given for each set of tables of hourly

medians. The beginning of a study of meteorological correlation is indicated.

258. EERL Report No. 10, December 14, 1949.

Data about the propagation paths are tabulated. Some

preliminary results of a study of the correlation of meteorological factors with the radio measurements are discussed.

Certain matters pertaining to equipment are discussed.
-93-

259. EERL Report No. 11, January 11, 1950.

The circuit diagram of the broadcast monitor signal

strength analyzer is shown, as well as the diagrams of the

VTVM and its power supply. Other groups in EERL are (1)

developing instrumentation for computing correlation functions

of time series, and (2) studying tropospheric radio scattering.

260. EERL Report No. 12, February 15, 1950.

Field strength measurements made at Austin, Texas, of

FM broadcast stations in Dallas, Houston, and San Antonio,

Texas, are tabulated. These tabulations cover the months of

November, 1949 through January, 1950; in connection with

previously reported data, they round out ten months of field

strength recording on the Houston signal, eight months on

the San Antonio signal, and six months on the Dallas signal.

Preliminary estimates of the seasonal variations of tropospheric propagation over the Austin-Houston path are given

on the basis of these observations.

261. EERL Report No. 13, March 10, 1950.

This paper describes the results of signal strength

measurements of distant FM stations on two receivers using

antennas of different directivity. One antenna was a dipole

and the other was two horizontally-spaced dipoles separated

by one half wave length and fed out of phase. This second

antenna had a four decibel gain over the dipole in a horizontal

direction and a null in the vertical direction.

The ratio of the signal delivered by the two antennas

was found to be a function of the signal strength for stations

at 146 and 182 miles. For stronger signals, the directive

antenna showed its nominal gain over the dipole antenna.

However, for weaker signals the gain of the directive antenna

over the dipole was less, and for very weak signals the single

dipole indicated a stronger signal.
-94-

For an FM station at a distance of 73 miles, the double

dipole showed a consistent gain over the single dipole. These

data are explained in terms of the theory of scattering

recently proposed by Booker and Gordon.

262. EERL Report No. 14, April 14, 1950.

Propagation measurements made over a 146 mile path

at a frequency of 102.9 megacycles during the period April 7,

1949 to March 18, 1950 have been analyzed to determine the

seasonal effect on the signal as received at various times

of the day. The results are given in the form of graphs and

statistical tables.

It was found that the average signal strength was lowest

in winter and highest in summer, the extent of the difference

being around 20 decibels. The overall median signal level

was found to be about 9 microvolts per meter, with a standard

deviation of the order of 7 decibels, as determined by

statistical analysis of 4,670 hourly medians.

263. EERL Report No. 15, May 15, 1950.

Observations of FM field strengths made at the Electrical

Engineering Research Laboratory during February, March,

and April, 1950 are tabulated in this report for signals

arriving over 73,146, and 182 mile paths. These data are

presented in hourly median signal strengths. For the 146

mile case, the results together with previously reported

data cover 13 months of continuous recording. For the 73-

mile and 182-mile cases, the aggregates are 11 months and

8 months, respectively.

The concluding section of the report is a brief discussion

of the seasonal cycles as evidenced by the measurements thus

far made.
-95-

264. EERL Report No. 16, June 6, 1950.

The results of a year's continuous observation of FM

field strengths as received at Austin, Texas over 73- and

146-mile paths are summarized in this report. This takes

the form of (1) curves showing the smoothed seasonal

variations in field strength throughout the year, and (2)

statistical tables of percentiles based on hourly median field

strengths.

Observations over a 182-mile path have been made for

a period of nine months and provide comparison with results

obtained over the other paths for all but the early summer

months.

Computation of correlation coefficients for the signals

received via the two longer paths are described and some of

the results given,

265. EERL Report No. 17, July 12, 1950,

Tropospheric radio propagation characteristics observed

for the Central Texas area have been examined in conjunction

with meteorological measurements. A fair correlation was

found between atmospheric humidity at the ground level and

radio field strengths observed at Austin, Texas, for a 101,5

megacycle FM station in San Antonio. Somewhat better

correlation was had when upper air data in the form of curves

of refractive index versus height were utilized.

The influence of atmospheric ducts, substandard lapse

rates, etc. appears at least qualitatively to be the same for

the area studied as for other areas which have been reported,

266. EERL Report No. 18, August 10, 1950,

Tropospheric radio propagation characteristics at frequencies around 100 megacycles have been measured over

several paths in the Central Texas area during the months of

May, June, and July, 1950. These measurements, in the
-96-

form of hourly medians, are tabulated in this report for each

day of the three-month period. A brief description is given

of certain analyses of these data which are in process,

267. EERL Report No. 19, September 12, 1950.

Field-strength measurements have been made in Austin,

Texas, on WFAA-FM in Dallas, Texas, (frequency 97.9 Mc,

distance 175 miles) for a period of approximately one year,

and a summary of the results is presented. This takes the

form of (1) a smoothed curve showing the seasonal variations

of field strength from August 1949 through August 1950,

and (2) a table of statistical distribution data based on the

median levels as determined for each broaocast hour during

the year.

A comparative study of tropospheric propagation over the

Dallas -Austin path at frequencies of 97.9 Mc and 104,5 Mc

is summarized. Fairly good correlation was found for the

two frequencies during June, July, and August, 1950, the

correlation coefficient of the daily average levels being

computed to be 0.64, Field-strength measurements over

this path are continuing on 104.5 Mc,

268. EERL Report No. 20, October 11, 1950.

Radio field strengths observed in Austin, Texas, during

the month of September, 1950, on FM broadcast stations in

Dallas, Houston, and San Antonio, Texas, are reviewed in this

report. Various analyses of these measurements are currently

in progress and these are briefly described,

269. EERL Report No, 21, November 15, 1950.

Hourly observations of median tropospheric field strength

have been made during August, September, and October,

1950 at Austin, Texas, for FM broadcast stations in San

Antonio, Houston, and Dallas, Texas, The data are presented

in tabular form and in the aggregate amount to approximately

4,150 hourly entries. These complete some 21 months
-97-

of continuous monitoring of the Houston signal, 17 months for

the San Antonio signal, and 15 months over the Dallas -Austin

path.

270. EERL Report No. 22, December 12, 1950.

Simultaneous measurements of tropospheric field

intensities have been carried out with dipole antennas oriented

for the reception of:

(a) Horizontally polarized waves,

(b) Vertically polarized waves propagating horizontally,

(c) Vertically polarized waves arriving from higher

elevation angles, up to 90 .

Scatter diagrams showing hourly median signals received on

(b) and (c) plotted against (a) are included. These are briefly

discussed.

Routine observations of field strength made during

November, 1950, are reviewed. Operating experience with

the new Type 726 FM Receivers manufactured by Radio

Engineering Laboratories, Inc., is described.

271. EERL Report No. 23, January 8, 1951.

Observations of 101.5 Mc tropospheric propagation conditions over the 7 8-mile San Antonio -Austin path have been made

for the 17 -month period ending last October, 1950. These

data, in the form of hourly median field intensities, have

been statistically analyzed in various ways and the results of

this are presented in the form of seasonal graphs, statistical

frequency tables, and frequency curves. A 6-month cycle

seems to be present on the seasonal graph although it is

not especially pronounced. The over-all median field strength,

as scaled from the appropriate frequency curve, agrees

quite well with theoretical computations based on orthodox

diffraction in a standard atmosphere. Although rapid

short-time fluctuations were quite pronounced, especially

during the daylight hours, the dispersion (standard deviation)

of the hourly averages was found to be only 5 decibels.
-98-

272. EERL Report No. 24, February 14, 1951.

Hourly observations of median field strength have been

observed in Austin, Texas for FM broadcast stations in

Houston and Dallas, Texas, These data are tabulated for

the months November and December, 1950, and January, 1951,

and bring the current total up to 24 months of continuous

recording over the Houston-Austin path and 18 months over

the Dallas -Austin path.

273. EERL Report No. 1-25, March 12, 1951.

During recent months a number of new installations have

been made in the equipment being used for measuring, recording, and analyzing VHF field strengths at this Laboratory.

Two of the REL Type 726 FM Receivers have been in operation

since last December and have resulted in considerable improvement as regards measurement accuracy, calibration stability,

resolution of low field strength levels, and continuity of

operation. Automatic camera equipment has been in operation

since January and provides statistical data on a 24-hour daily

basis. This represents a 50% increase over the procedure

formerly used.

274. EERL Report No. 1-26, April 1 1 , 1951.

Project activity during March, 1951, under Contract

CST-10725 consisted in:

(1) Continuous recording of the signals received at this

Laboratory at three VHF frequencies from sources lying

at distances up to 175 miles.

(2) Statistical analysis on an hourly basis of the fluctuations of each of these signals.

(3) Computing and plotting graphs showing the secular

variations in field strength of each signal.

(4) A survey of concurrent sets of radio propagation

data and radiosonde data for several months during 1950, said

survey having as its objective the discovery of any significant

correlation as may exist between such observations. A summary

of these activities is presented in this report.
-99-

Also included are six supplemental sheets for attachment

to Reports 12, 14, 15, 16, 18, and 21. These provide information as to various corrections to be made on the material as presented in those reports. Although these have been noted

briefly in past reports, it has been thought desirable to issue

supplemental sheets in which these matters are given special

mention. The application of these corrections to our analysis

of the 102.9 Mc data in Reports 12 and 15 is discussed and the

results are reviewed briefly.

275. EERL Report No. 1-27, May 10, 1951.

Tabulations of hourly median field strength of VHF

signals received at this Laboratory over the Houston-Austin

and Dallas -Austin paths are presented in this report for

the months of February, March, and April, 1951. Information

regarding the transmitting and receiving installations is also

given and an estimate of accuracy is made, A brief review

of operational activities during the subject month is presented

and the report is concluded with a brief discussion of current

planning,

276. EERL Report No. 1-28, June 8, 1951.

Tropospheric radio propagation measurements made at

102,9 Mc over the 147 -mile Houston-Austin path are summarized

in this report for the 2-year period ending April 30, 1951.

This summary takes the form of:

(1) Smoothed seasonal graphs

(2) Statistical tables showing the frequency distribution

of the 9,729 hourly median levels observed during the course

of this study.

Current operational activities as of the end of the subject

month are also reported along with a brief account of plans

for June and July, 1951.
-100-

The appendix contains tabulations of some 900 hourlymedian levels observed at 59.75 Mc/sec for the Houston-Austin

path from March 2 through May 31, 1951. Discussion of

these is given in the concluding section of the report,

277. EERL Report No. 1-29, July 3, 1951.

Observational, operational, and analytical activities

carried on at this Laboratory during June, 1951 under Contract

CST-10725 are described. These include routine observations

of tropospheric propagation over four paths in the LouisianaTexas area at seven frequencies in the VHF band. In the

section dealing with the operational aspects of the project,

a brief account is given of equipment operation and of the

status of equipment under construction. Analytical activities for the subject month consisted in routine reduction of the

raw data to tables of hourly median field strength levels,

and statistical studies based on these hourly medians. Tables

of hourly median levels for the period April 25 - May 31, 1951,

are included at the end of the report. These data were obtained at a frequency of about 186 Mc for the 17 6-mile Dallas

Austin path.

278. EERL Report No. 1-30, August 8, 1951.

Observations of 100-megacycle propagation characteristics

for two Texas paths, (Houston-Austin and Dallas -Austin) are

presented in this report. These take the form of tables of

hourly median field strength levels and cover the 3 -month

period ending July 31, 1951. A brief description of the

measuring equipment and procedure is given and the magnitude

of experimental errors is estimated,

279. EERL Report No. 1-31, September 28 : 1951.

Continuous measurements have been made of the field

strength of six VHF broadcast stations as received at the

Electrical Engineering Research Laboratory near Austin

during the summer of 1951. The results of these are tabulated

in the present report and include data on frequencies ranging

from 60 to 186 Mc/sec and propagation paths ranging in length
101

from 147 to 275 miles, A brief description of the measuring

equipment and its calibration is presented, and an estimate

as to the accuracy of the tabulated data is made,

Some recent analytical studies of the influence of atmospheric turbulence on radio propagation through the troposphere

are presented in Section IV. The treatment here involves a

fresh approach to the subject and some very interesting

correlations are brought to light.

230. EERL Report No. 1-32, November 26, 1951.

The results of continuous observation of radio field

strength for six VHF broadcast stations in the LouisianaTexas areas are presented in this report. These observations

cover the period September 1 to October 31, 1951 and are

reported in terms of hourly median field strength levels for

each station. Some 6,000 such median values are tabulated

for the subject period.

The reduction process used in deriving these data is

described, and an accuracy appraisal of the data is given.

Also, a brief description of the receiving and transmitting

equipment is included, with specific data on items of particular interest to propagationists. The report is concluded

with a brief account of operational and constructional activities

connected with the project.

28L EERL Report No. 1-33, January 31, 1952.

Observations of VHF tropospheric propagation conditions

in the Texas -Louisiana area during November and December,

1951 are tabulated in this report in terms of normalized

hourly median field strength. These cover four propagation

paths and include frequencies in the range from 60 to 186 Mc,

A brief description of the measuring equipment is given, and

an estimate of data accuracy is made. Operational aspects

of the program such as equipment maintenance, etc. , are

discussed in the concluding section of the report.
-102-

282. EERL Report No. 1-34, March 28, 1952.

The results of continuous measurement of VHF signal

strengths at six frequencies over a variety of propagation

paths are presented for the months of January and February,

1952. A brief description of the measuring apparatus and

its accuracy limits is given, principally in the form of

citations from previous reports. Operational aspects of

the program are discussed in the concluding section of the

report,

283, EERL Report No. 1-35, May 28, 1952.

The results of continuous observations of radio field

strength for six VHF broadcast stations in the LouisianaTexas area are presented in this report. These observations

cover the period March 1 to April 30, 1952 and are reported

in terms of hourly median field strength levels for eachstation. Some 6,000 such median values are tabulated for

the subject period.

The reduction process used in deriving these data is

described, and an accuracy appraisal of the data is cited.

Also, a brief description of the receiving and transmitting

equipment is included, with specific data on items of particular interest in propagation studies. An account of nonroutine operational activities is given and the report is

concluded by a summary of some noise studies carried out

in conjunction with the regular field strength recording

work.

284. EERL Report No. 1-36, July 31, 1952.

Radio field strength measurements on six VHF broadcast

stations in the Texas -Louisiana area are reported for the

months of May and June, 1952. A brief account of the

measuring equipment used in this survey is given and some

comments regarding the reported data are included.

A two-year analysis of the 100 Mc Dallas -Austin propagation data has been completed and the results are presented
-103-

in the form of seasonal graphs and statistical frequencycurves.

2?5. EERL Report No, 1-38, September 29, 1952.

Tabulated data on hourly median radio field strength

observations are submitted with this report for the months of

July and August, 1952. These cover six frequencies in the

range 60 to 186 Mc/sec and four propagation paths ranging

in length from 147 to 275 miles. In the aggregate, the data

amount to about 6,500 hourly entries.

Section I, below, is a brief description of the measuring

equipment used in this study. Following this in Section II is a condensed discussion of the results concerning such

aspects as processing, accuracy, units of measurement, etc.

The concluding Section III summarizes our operational experience for the subject period.

286. EERL Report No. 1-39, November 25, 1952.

Observations of VHF radio propagation characteristics

are reported herein for the months of September and October,

1952, These cover six frequencies ranging from 60 to 186 Mc

and four propagation paths of length varying between 147 and

275 miles. The data are tabulated at the end of this report

in the form of median field strengths as determined for each

VHF signal for each hour of broadcast.

The textual discussion in the following sections is intended

to provide, within a brief scope, the necessary background

material required for a proper assessment and utilization of

the reported data. More detailed discussions have appeared

in earlier reports of this series, giving rather complete

descriptions of the measuring equipment, its construction,

calibration, and operation. Processing of raw data has likewise been dwelled upon at some length, and these earlier

reports should be referred to for amplification of the present

treatment.
-104-

287. EERL Report No. 1-40, January 29, 1953.

VHF radio propagation measurements made at a site near

Austin, Texas are submitted herewith for the months of November

and December, 1952. These cover path lengths ranging from

147 to 275 miles and frequencies ranging from 60 to 186 Mc.

Supplementing these data is a brief description of the measuring

equipment, the accuracies attained, and other factors.

288. EERL Report No. 1-41, March 31, 1953.

Bi-monthly summaries of VHF radio field strength data

are tabulated in this report, covering the months of January

and February, 1953, Four frequencies in the range of 60 to

186 Mc, as propagated over paths ranging in length from 147

to 275 miles, have been observed.

Beginning January 1 of subject period our recording load

was reduced from 6 to 4 channels. The equipment thereby

released from service is being reconditioned and will be

maintained for standby use,

289. EERL Report No. 1-42, May 29, 1953.

Radio field strength measurements are reported for the

period March 1 through April 30, 1953, in the form of monthly

tabulations of hourly median levels. Four frequencies have

been observed, ranging from 60 to 186 Mc, as propagated

over paths varying in length from 147 to 27 5 miles.

290. EERL Report No. 1-43, June 29, 1953.

VHF radio propagation data for the interval May 1 through

June 15, 1953, are presented herewith in the form of tabulations of hourly median field strength levels. These cover four

frequencies in the range of 60 to 186 Mc, for paths varying

in length from 147 to 275 miles.
-105-

After a brief description of the equipment and an account

of the data, operational notes covering the subject period are

included, along with correction notices for data submitted in

our Report No. 1-42, Since the interval covered by this report

is the concluding one for the project, a brief historical summary

has been presented,

(g) University of Washington, (Author: H, S, Swarm, Instructor,

Electrical Engineering Department.)

291. UW Report No. 1, May, 1951.

In this report the preliminary work of Contract No, CST481, with the NBS, is discussed, in preparation to recording

field intensity strengths of FM stations.

Upon consideration of the terrain between the transmitter

and the receiver, and because the initial tests show that among

six available stations, the least noise interference is on the

path of KOIN-FM, 101.1 Mc, Portland, Oregon, 148,5 miles;

this station has been selected to be recorded. The receiver

will be located in the Electrical Engineering Building on the

campus at this time, and a temporary antenna will be used,

94 feet above the ground.

Some equipment has arrived from NBS on loan; other

equipment is being built,

292. UW Report No, 2, June, 1951.

Recording of the field strength of KOIN-FM, Portland, for

18 hours per day was started June 22, 1951. The setup of recording equipment was completed early in the month; modifications

and repairs were made on the receiver to increase the sensitivity.

Included in this report are the following discussions:
-106-

(a) Receiver calibration procedure,

(b) Recording equipment.

(c) Antenna details. (The permanent antenna is completed.)

(d) Procedure of analysis of data,

(e) Noise.

(f) Further work on project.

293. UW Report No. 3, July, 1951.

The permanent dipole antenna was installed early this

month, one modification was made in the circuit of the receiver

to aid in detecting the noise level.

During the first part of July a local police FM transmitter

was found to be causing interference; this was easily adjusted

at the receiver.

The hourly median field strength of station KOIN-FM,

Portland, Oregon, as received in Seattle, Washington, is

presented in tabulated form; a distribution graph is included,,

294. UW Report No. 4, August, 1951.

The hourly median field strength as recorded in August of

KOIN-FM, was analyzed and put into tabulated data form,

as submitted in this report. Some data was lost this month

because of noise and interference.

A portable dipole antenna has been completed and will be

used in the investigation of variation of field strength with

location; possibly this will find a better location for the permanent antenna. Some modifications must be made on the

receiver to be used with this portable antenna,

A portable battery-operated field strength meter and a

loop antenna have been obtained, and will be used to aid in

locating the sources of local interference. This operation

should be ready in September, 1951,
-107-

295. UW Report No. 5, September, 1951.

The tabulated data of September hourly median field

strength, a distribution curve of these values, and a percentage of time curve are all presented in this report.

Since rainy weather has arrived, the average level of

the signal seems to be much lower than for previous months.

Two high periods occurred at approximately the same time as

the passage of a cold front diagonally across the transmission

path, A further investigation of this type of phenomenon is

planned,

296. UW Report No, 6, October, 1951,

The tabulated data of October hourly median field strength,

a distribution curve of these values, and a percentage of time

curve are all submitted in this report.

It has been observed that a high in hourly medians occurs

between 0700 and 0900 in the morning and again late in the

afternoon; this has been correlated with ignition noise from

rush hour traffic.

The high signal periods again show correlation with the

passage of a high pressure area across the transmission path,

297. UW Report No, 7, November, 1951,

The tabulated data and derived curves as previously reported

are submitted for this month.

The same daily peaks have occurred and are correlated

with rush hour traffic. The outage from November 18 to 23

was due to a defective receiver part; the receiver was properly

retuned on November 23, 1951,
-108-

Mr. Robert S, Kirby of NBS, Boulder, Colorado, visited the

University of Washington Laboratories concerned with this project

on November 28, 1951, bringing a considerable background of

information on tropospheric propagation research. Following

one of Mr. Kirby's suggestions, KOIN-FM, Portland, now

supplies information on any abnormal operation of their

transmitting station.

298. UW Report No. 8, December, 1951.

The tabulated data and derived curves as previously

reported are submitted in the report for this month.

During almost all of the month the signal was at noise

level, rising slightly only on three days: December 10, 11,

and 14.

Additional equipment has been received from the NBS,

which, with another receiver, will be installed in a University

truck to provide a mobile recording unit in the near future.

299. UW Report No. 9, January, 1952.

The hourly median field strength of KOIN-FM, Portland,

as recorded during January, 1952, is tabulated and presented

in this report; also the derived distribution curve and the

percentage of time curve.

On the 14th of January, 1952, the University of Washington

education FM broadcast station, KUOW , 90.5 Mc, began

regular daily operation; this caused considerable radiation

from receivers in the nearby dormitories and interference

trouble on the KOIN-FM recording project.

Modifications are being made on Cooke receiver which

arrived early this month.

The meteorology department is assisting in determining

the necessary meteorological conditions for favorable propagation.

Very good correlation of medium and high signal strengths has
-109-

been achieved with anticyclonic winds due to a high pressure

area west of the Pacific Coast, This weather condition gives

a positive temperature gradient and a negative moisture

gradient with increasing height and is favorable to a large change in the index of refraction, the necessary conditions for reception of KOIN-FM in the Seattle area.

300. UW Report No. 10, February, 1952.

The usual schedule of analyzing data and obtaining the

distribution curve and the percentage of time curve has been

carried out. The interference troubles due to broadcasting

by the University of Washington educational FM station, KUOW,

have been negligible.

Work is progressing on the modification of the Cooke

receiver. A correlation study is in progress concerning

field strength and meteorological conditions.

301. UW Report No. 11, March, 1952.

No change.

302. UW Report No. 12, April, May, June, 1952.

Tabulated data of analyzed hourly median field strengths

and the curves derived from the data are presented for the

months of April, May, and June, 1952, It is planned to issue

quarterly reports in the future.

Much time was spent on the modifications of the Cooke

receiver which is still not in satisfactory condition for continuous

recording. Erratic operation of the recorder has caused a

large portion of the data for May and early June to be deleted.

Normal operation was resumed in mid-June.

303. UW Report No. 13, July, August, September, 1952.
-110-

The hourly median field strengths as recorded of KOIN-FM

during the third quarter of 1952, and presented in tabulated

data form are included in this report, also the derived distribution curves of the data and the plotted graphs of percentage

of time for which the hourly median exceeds a given value.

During July and August, 1952, the equipment was maintained

in operation but no analysis was attempted, due to most of the

personnel being absent from the University of Washington.

In September the installation of some equipment in the

Mobile Laboratory was started.

304. UW Report No. 14, October, November, December,

1952.

The hourly median field strengths in decibels above one

microvolt per meter for one kilowatt of effective radiated

power for the three months of the last quarter are presented.

Three graphs are presented showing the diurnal distribution

of the hourly medians, and three other graphs show the

percentage of time the hourly median exceeded a given field

strength.

The preparation of the Mobile Electronics Laboratory

was completed with a few adjustments in the equipment. A field

trip was made and provisional points have been selected; preliminary tests suggest that better signals can be expected

away from the campus .

305. UW Report No. 15, January, February, March, 1953.

The hourly median field strength of KOIN-FM, Portland,

during the first quarter of 1953 is shown in tabulated form.

The distribution curves of hourly median values and of

percentage of time for which the hourly median exceeded a given value are presented in six graphs.
111-

This contract ended in January, 1953.

The Mobile Laboratory was used to secure data at two

additional sites away from the main recording site at the

Electrical Engineering Building. Two weeks of recording were

made at the top of Squak Mountain, and two weeks of recordings

were made on the roof of the Telephone Exchange Building in

downtown Seattle.

306. The Squak Mountain Report, November, 1951.

Four stations, KIRO, KOMO, KING-TV, and KRJ sponsored

a field survey of transmissions from the top of Squak Mountain,

in order to determine the best selection of VHF and UHF transmitter sites in the Seattle area. Actual field work was performed

on November 8 and 9> 1951 at recording sites along radials from

Squak Mountain through downtown Seattle. Recordings were

obtained on 49 . 5 Mc and 154. 57 Mc with omnidirectional antennas

and 3 5 watts of effective radiated power. A log was kept of

recording locations versus chart time.

This report goes into detail on the following:

(a

(b

(c

(d

(e

(f

(g

(h

Description of survey.

Transmitting equipment used.

Receiving and recording equipment used,

Calibration of recording equipment.

Data Analysis.

Interpretation of data.

Conclusions drawn.

Tables of radials used.

Included in the report are terrain profiles and photographs of

Seattle and of the recorder charts.

A supplementary list of technical reports will be found on

pages numbered 112 through 112q.
-112-

307. Kenneth A. Norton, " The Effect of Fading on the

Desired-to-Undesired Signal Ratio Required to Provide a

Specified Grade of Service for a Given Percentage of a Specified Period of Time, " CRPL Report 4-M-5, February

3, 1948.

ABSTRACT

It is the purpose of this memorandum to outline the

factors involved in determining the allowance for fading which

must be made in the allocation of two stations operating on

the same or adjacent radio frequencies in order to provide

a specified grade of service for a given percentage of a specified period of time. Factors accounted for include

transmitter powers, antenna directivities, propagation path

lengths, long-term and short-term fading, expected median

field strengths, and various possible definitions of grade of

service.

308. Kenneth A. Norton, " Sunspots and Very High

Frequency Radio Transmission, " CRPL Report 4-3, October

29, 1947; see also QST, Vol. 31, No. 12, p. 13, December,

1947.

ABSTRACT

At the present time, 1947, the activity of sunspots as

measured by Zurich sunspot numbers is at a higher level

than it has ever reached since the discovery of radio during

the latter part of the 19th century. A detailed discussion of

the expected increase in maximum usable frequencies leads

to the conclusion that the coming winter will afford many

opportunities for the amateurs to make new and interesting

long-range contacts using very low-powered transmitters on

the 50 -megacycle band.

309. " Extension of FM Broadcast Range, " NBS Tech.

News Bulletin, Vol. 32, No. 4, April, 1948.
-112aABSTRACT

Experimental research conducted by the National Bureau

of Standards indicates that the reliable service areas of

frequency modulation broadcasting stations using transmitters

now available may be extended far beyond the horizon. The

most effective way to increase the service range of an FM

broadcasting station is to increase the transmitting antenna

height rather than the power, since such a change increases

the service range more rapidly than the interference range,

resulting in a more efficient utilization of the channel. It seems, also, that there may exist an optimum frequency for

propagation to large distances beyond the horizon.

310. " VHF-UHF Range Tests, " letters to Wright Field,

November 6, 1947, January 29, 1948, and April 22, 1948.

ABSTRACT

These letters are technical memoranda with the object

of informing the Air Material Command of the progress of

CRPL on the problem of analyzing the propagation characteristics of VHF and UHF for use in air-to-air and air-to-ground

communication

Comment

The three letters, with associate figures, are reproduced

here as Supplement XIX.

311. R. S. Kirby, "Analysis of the Ground Wave and

Tropospheric Wave Field Intensity Variations at a Distance

Far Beyond the Line -of -Sight for an FM Broadcasting Station

Operating on 99.7 Mc, " CRPL working document for the

FCC Ad Hoc Committee, March 18, 1949.

ABSTRACT

For the purpose of obtaining a better understanding of

the nature of the variation in field intensities at large distances
-112bfar beyond the line-of-sight in the frequency modulation

broadcast band, field intensity recorders were installed at

the National Bureau of Standards in Washington, D. C,

late in 1947, and continuous recordings were made of the

field strengths of several FM broadcast stations. This report

analyzes one of the most complete sets of recordings, that of

WSAP-FM in Portsmouth, Virginia.

Comment

This report is reproduced here as Supplement XX.

312. K. A. Norton, 'Propagation Over Rough Terrain, " US NEL Symposium, July 25, 1949, NE 120301 Report 173

Problem NEL. 1A1, p. 101, U. S. Navy Electronics Laboratory,

San Diego, California.

ABSTRACT

It is intended here to describe some of the characteristics

of two important mathematical tools useful in statistical

predictions of ground-wave propagation, and to demonstrate,

by an example, their applicability to the description of radio

propagation over rough terrain.

Comment

This report is reproduced here as Supplement XXI.

313. J. H. Chisholm, "Measurements of Microwave

Diffraction Over Trees, " US NEL Symposium, July 25, 1949,

NE 120301, Report 173, Problem NEL 1A1, p. 114, U. S.

Navy Electronics Laboratory, San Diego, California.

ABSTRACT

Because many propagation paths, especially in the eastern

United States, contain tree foliage to heights of 70 and 100

feet, an investigation to determine quantitatively the effect
- 112c -

of such foliage upon microwave propagation was undertaken

by the Central Radio Propagation Laboratory. Controlled

experiments were conducted over a 4000 -foot path at a

wavelength of six centimeters; metal screens and actual

tree foliage were used as diffracting obstacles.

Comment

This report is reproduced here as Supplement XIV.

314. A. W. Straiton, D. F. Metcalf, C. W. Tolbert,

"A Study of Tropospheric Scattering of Radio Waves, " Proc. IRE, Vol. 39, No. 6, p. 643, June, 1951.

ABSTRACT

The theory of tropospheric scattering of radio waves

recently advanced by Booker and Gordon makes the

prediction that radio-frequency energy may arrive from

a ground-based VHF transmitter at angles well above the

horizon, and also that signals received as a result of

the scattering process will attenuate less rapidly with

distance if the polarization of the source is horizontal

than if it is vertical. Experimental observations made

at wavelengths of 3 meters and 3 centimeters have verified

these deductions.

315. "Study of Tropospheric Propagation of Radio

Waves, " Quarterly Progress Report No. 4, January 1, 1955 to March 30, 1955. NBS Report No. 3530.

316. A. F. Barghausen, M. T. Decker and L. J. Maloney,

"Measurements of Correlation, Height Gain, and Path Antenna

Gain at 1046 Megacycles on Spaced Antennas Far Beyond the

Radio Horizon, " IRE Convention Record, 1955, Vol. 3, Parti,

Antennas and Propagation.

ABSTRACT

Studies made and reported by the National Bureau of

Standards in 1953 on the correlation of 1046 Mc radio fields

on spaced antennas at distances far beyond the radio horizon

are supplemented by more recent measurements. In addition
- 112d -

to the correlation of instantaneous fields, the correlation of

hourly median fields and the diurnal variation of the received

signal are shown. Simultaneous measurements from a parabolic reflector antenna are used to indicate the loss in gain

relative to the expected free space gain of a large aperture

array.

317. "Survey of Propagation Characteristics of Sea Test

Range in Vicinity of the Naval Air Missile Test Center, Point

Mugu, " Progress Report No. 1, April 1, 1955, USNAMTC

Project TED EL-42036. NBS Report No. 3531.

318. "Large Reduction of VHF Transmission Loss and

Fading by the Presence of a Mountain Obstacle in Beyond

Line-of -Sight Paths, "letter to the editor, Rebuttal by

J. W. Herbstreit. Proc. IRE, Vol. 43, No. 5, pp. 627-628,

May 1955.

319. A. P. Barsis, B. R. Bean and K. O. Hornberg,

"Cheyenne Mountain Tropospheric Propagation Data February

March 1954," NBS Report No. 3536, May 1, 1955

ABSTRACT

This report describes tropospheric propagation measurements taken over the Cheyenne Mountain paths on frequencies

between 92 and 1046 Mc during February, 1954. The results of

the measurements are given in terms of cumulative distribution

of hourly medians (in units of basic transmission loss), diurnal

variations and interdecile range of hourly medians of transmission

loss, and dependence of the above quantities on the angular distance

©. Results of meteorological measurements on the 500 -foot tower

at Haswell, Colorado, are also shown together with radiosonde

data obtained at Denver, Colorado, and Dodge City, Kansas, during the recording period. A general description of the weather

during the measurement period is also given.

320. E. F. Florman, "A Measurement of the Velocity of

Propagation of Very-High-Frequency Radio Waves at the Surface

of the Earth, " Journal of Research, Vol. 54, No. 6, June 1955,

Research Paper 2596.
- 112e - ABSTRACT

The velocity of propagation of electromagnetic waves was

measured at the surface of the earth, using a radio-wave

interferometer operating at a frequency of 172.8 Mc. The

measured phase velocity, converted to velocity in vaccum, or

the "free-space" value, was found to be 299795.1 ±3.1 km/sec.

The accuracy with which the free -space phase velocity of

radio waves could be measured was limited primarily by the

accuracy to which the refractive index of air could be obtained

from measured values of pressure, temperature, and relative

humidity.

321. J. W. Herbstreit and M. C. Thompson, "Measurements of the Phase of Radio Waves Received over Transmission

Paths with Electrical Lengths Varying as a Result of Atmospheric

Turbulence, " Proc. IRE, Vol. 43, No. 10, pp. 1391-1401, October,

1955.

ABSTRACT

A system for the measurement of the variations in electrical

lengths of radio propagation paths is described. The observed

path-length instabilities are considered to be caused by the same

atmospheric turbulence responsible for the existence of very

high frequency and ultra high frequency fields far beyond the

radio horizon. Results obtained on 172. 8 Mc and 1, 046 Mc along

3/^-5 10-, and 60 -mile paths are reported.

322. K. A. Norton, L. E. Vogler, W. V. Mansfield and

P. J. Short, "The Probability Distribution of the Amplitude of

a Constant Vector Plus a Rayleigh -Distributed Vector, " Proc.

IRE, Vol. 43, No. 10, October, 1955.

ABSTRACT

Formulas, tables, and graphs are given for the probability

distribution of the instantaneous resultant amplitude of the sum

of a constant vector and a Rayleigh-distributed vector. It is

emphasized that two distributions are required to describe a Rayleigh-distributed vector: the distribution of its amplitude and
- 112f -

the distribution of its phase. References are made to ways

in which these distributions may be used to describe random

variables occurring in ionospheric, tropospheric, and

irregular terrain propagation problems. Finally, a discussion

is given of amplitude and phase distributions of two other random

vectors encountered in tropospheric propagation studies.

323. K. A. Norton, P. L. Rice and L. E. Vogler, "The

Use of Angular Distance in Estimating Transmission Loss and

Fading Range for Propagation Through a Turbulent Atmosphere

over Irregular Terrain, " Proc. IRE, Vol. 43, No. 10, pp. 1488-

1526, October, 1955.

ABSTRACT

A discussion is given of the transmission loss expected

in free space with various types of antennas, followed by a

description of theoretical prediction curves for the transmission

loss expected in tropospheric propagation on over -land paths.

Angular distance is shown to be useful for predicting the short

term within-the-hour fading range as well as the median transmission loss. Illustrations are presented of the theoretical

dependence of transmission loss on the angular distance, transmission path length, antenna height, radio frequency, and a parameter AN which is a measure of the vertical gradient of atmospheric

refractive index. The radio data indicate that the magnitude of the

scattering cross section decreases in inverse proportion to the

radio frequency in the range we have studied.

A new theory of obstacle gain is developed, and it is shown

that this is particularly useful for explaining some of the unusually

strong fields which have been observed just beyond the horizon in

over -land propagation.

Theoretical curves of the average value of the path antenna

gain to be expected in tropospheric forward scatter propagation

are presented as a function of the angular distance, the asymmetry

factor, and the free space gains of the transmitting and receiving

antennas.

324. K. A. Norton, P. L. Rice, H. B. Janes, and A. P.

Bar sis, "The Rate of Fading in Propagation through a Turbulent

Atmosphere," Proc. IRE, Vol. 43, No. 10, pp. 1341-1353,

October, 1955.
- H2g - ABSTRACT

Fading rate is defined to be the number of times per minute

that the envelope of the received field crosses its median level

with a positive slope. It is shown that this definition of fading

rate provides a quantity which is numerically related to the parameters of the propagation medium under certain conditions which are

normally satisfied in either ionospheric or tropospheric propagation

studies. The pertinent parameters of the propagation medium in

beyond -the -horizon transmission are the location and shape of the

scattering volume and the turbulent and drift velocities of the

scatterers. An extensive discussion is given of the shape of the

tropospheric scattering volume for beyond -the -horizon transmission.

An analysis is then given of some fading rate data obtained in the

National Bureau of Standards tropospheric propagation program in the

92 to 1046 Mc range of frequencies on transmission paths 70, 97, 226,

and 394 miles in length. Finally an analysis is given for within-thehorizon propagation. In this case it is advantageous to define fading

rate as the number of times per minute that the phase of the received

field crosses its median level with a positive slope.

325. M. T. Decker, "Propagation Aspects of TACAN System

Coverage," For ANDB Symposium on TACAN at Washington, D. C,

November 3-4, 1955, NBS Report No. 3556, October 27, 1955.

ABSTRACT

The propagation factors which affect the coverage volume of

a TACAN type facility operating in the 1000 Mc region are discussed

in this paper. Using theoretical and empirical methods, prediction

curves are derived which indicate the probability of receiving

satisfactory service in a given volume of air space.

326. Bradford R. Bean, "Some Meteorological Effects on

Scattered Radio Waves, " NBS Report No. 3561, December 15,

1955.

ABSTRACT

The long term variations of received scattered fields due

to atmospheric effects are estimated for frequencies of 100 to

50, 000 Mc and over propagation paths of 100 to 1000 miles. The
- 112h -

long term variations are presented in two parts: (1) empirically

derived variations excluding absorption and (2) theoretically

derived variations due to gaseous atmospheric absorption. The

absorption effects are obtained by following a scattered radio wave

through an actual atmosphere.

327. K. A. Norton, "Point-to-Point Radio Relaying Via

the Scatter Mode of Tropospheric Propagation, " NBS Report No.

3562, December 21, 1955.

ABSTRACT

Formulas are given for determining the transmitter power

required to provide a specified grade of service in point-topoint radio relaying of the following types of signals; television,

frequency modulation high fidelity music, frequency modulation

voice, frequency shift telegraph, and a just measurable signal.

Allowance is made for the antenna gains, the carrier frequency,

the systems bandwidth, distance, the antenna heights above the

ground and the effects of the terrain and the atmosphere along

the transmission path.

328. R. S. Kirby and F. M. Capps, "Correlation in VHF

Propagation over Irregular Terrain, " Trans. IRE, AP-4,

pp. 77-85, January 1956.

ABSTRACT

A study has been made of the correlation in transmission

loss observed over irregular -terrain paths. Simultaneous mobile

measurements were made of two pairs of VHF broadcasting

stations in Washington, D. C. -Baltimore, Maryland area. The

correlation coefficients derived from sample sets of transmission

loss data indicate that when reception is from opposite directions,

no significant correlation is evident, and when the paths of propagation are the same even though the frequencies are separated

considerably, the correlation appears to be significantly high.

329. R. S. Kirby, H. T. Dougherty, and P. L. McQuate,

"VHF Propagation Measurements in the Rocky Mountain Region, " NBS Report No. 3564, January 2, 1956.
- 112i - ABSTRACT

Mobile measurements of VHF propagation over various

irregular terrain paths have been made by the National Bureau

of Standards in the Colorado Rocky Mountain region in an effort

to evaluate terrain effects upon broadcast and point-to-point

communications at very high frequencies. Mobile measurements

of the varying path transmission loss were obtained in a continuous manner while driving along selected routes with a mobile

field strength recording unit, which consists of a modified

house trailer equipped with a telescoping mast and pulled by a

pick-up truck. The paths used ranged from relatively smooth

to very rough.

The results of the measurements are considered in the light

of current irregular terrain theory. The correlation of sector

median transmission loss for different frequencies over irregular

terrain tends to be high when the paths are nearly the same, becoming significantly less when the paths diverge. This would

indicate that the frequency selectivity of an irregular terrain

path is small.

330. First Annual Report of the Boulder Laboratories,

July 1, 1954 to June 30, 1955, NBS Report No. 3566.

331. H. T. Dougherty, Appendix E to "The Propagation

Characteristics of the Frequency Band 152-162 Mc Which is

Available for Marine Radio Communications. " ABSTRACT

To permit an estimate of the expected service range for

propagation paths over sea or fresh water in the frequency band

152-162 Mc, a nomograph is presented for a range of values of

height and separation of a transmitting and a receiving antenna.

This nomograph will permit an estimate of the expected service

range for propagation over a smooth spherical earth, through a

standard atmosphere.

332. "Cheyenne Mountain Tropospheric Propagation

Measurements August 1954, " Final Report, NBS Report No.

3568, February 6, 1956.
- H2j -

333. R. S. Kirby and A. P. Barsis, "Survey of Propagation Characteristics of Sea Test Range in Vicinity of the Naval

Air Missile Test Center, Point Mugu, " Progress Report No. 2,

NBS Report No. 3572, March 9, 1956.

334. A. P. Barsis and R. E. McGavin, "Report on Comparative 100 Mc Measurements for the Transmitting Antenna

Heights," Trans. IRE, Vol. AP-4, No. 2, April, 1956.

ABSTRACT

This report evaluates measurements taken during August,

1952, at a frequency of 100 Mc as transmitted from three

transmitting sites at elevations ranging from 6,220 feet to

14,110 feet above mean sea level. Six receiving sites were

used ranging in distance from approximately 50 miles to 620

miles from the transmitter sites. Results are presented in

terms of hourly medians of recorded field intensity and their

distributions, as well as the over -all median values and deviations derived from these distributions.

335. "Radio Studies of Atmospheric Turbulence, " by Section

83.60. NBS Report 3579, dated April 2, 1956.

ABSTRACT

Variations in the density and composition of the air in the

earth's atmosphere cause the phase velocity of propagation of a

radio wave to vary, in general, from point-to-point in the

atmosphere and at any given point, to vary with time. These

changes in velocity (or refractive index) act to produce two effects

which may be studied experimentally. The first of these effects

will be termed "scattering" and the second, "phase surface

distortion" or more simply, "phase distortion."

The value of scattering for long distance communication

systems has been clearly established and considerable experimental and theoretical work has been done to facilitate the

engineering design of practical systems. The phase distortion

effect of the atmosphere may be observed on relatively short,

within-line-of-sight paths.
- 112k -

This report has been divided into 11 sections which include

descriptions of the physical techniques, the instrumentation and

the treatment of data, and a final section in which the results are

summarized and interpreted. El even appendices containing supplementary discussions are included.

336. James R. Wait, "On the Theory of Propagation Along a

Curved Surface, " NBS Report No. 3583, dated May 5, 1956.

ABSTRACT

The method of solution is outlined for the problem of propagation of vertically polarized waves along a surface whose curvature and electrical properties have a discontinuity. The mutual

impedance between two short vertical antennas on either side of the

boundary of separation is considered to be the fundamental quantity

which is sought. It is shown that to a first order of magnitude, the

effect of the conductivity contrast and curvature change are additive

corrections to the mutual impedance between dipoles over a single

homogeneous spherical surface.

337. James R. Wait, "A Basis of a Proposed Method to

Measure the Characteristics of an Arbitrary Downcoming Radio

Wave, " NBS Report No. 3587, dated May 9, 1956.

ABSTRACT

It is the purpose of this note to outline a scheme for measuring

the angle of arrival, azimuth, and polarization of a downcoming

radio wave from measurements made on the ground.

338. NBS Boulder Laboratories Annual Report, NBS Report

No. 3592, dated June 19, 1956.

339. James R. Wait, "Transient Behavior of the Electromagnetic Ground Wave on a Spherical Earth, " NBS Report No.

3595, dated July 17, 1956, Presented at URSI meeting, University

of Florida, Gainesville, Florida, December 1955.

ABSTRACT

Some calculations are presented to show the nature of the

transient ground wave radiated from an electric dipole which is
- 1121 -

situated over a spherical earth. The moment of the dipole is

considered to vary with time in a linear manner. It is shown

that the departure of the leading edge of the radiation field from

a step function form is a consequence of diffraction and loss in

the finitely conducting ground.

340. M. C. Thompson, Jr., and M. J. Vetter, "A Microwave Refractometer for Use in Small Aircraft, " NBS Report

No. 3597, dated July 24, 1956.

ABSTRACT

The importance of an airborne microwave refractometer as

a tool in the study of tropospheric radio scattering has been recognized for some years. A considerable amount of work has been

done using both of the two types of instruments thus far developed

and some valuable knowledge has been gained concerning the nature

of atmospheric turbulence. The purpose of this work has been to

bring some of the development up to date with respect to circuit

techniques and components and to improve the design wherever

possible to increase useful sensitivity and reliability and at the

same time provide an instrument requiring less operator attention.

Experience gained from the use of previous models suggested, for

example, that there might be some significant advantages to the

use of smaller aircraft for this work, consequently one of the objectives of this design was to reduce weight, size, and power

requirements.

341. V. H. Goerke and R. S. Lawrence, "Galactic and Solar

Radio Emission as the Limiting Background Noise in Systems

Using Ionospheric and Tropospheric Scattering, " NBS Report No.

3598, August 3, 1956.

ABSTRACT

The background radio noise intensity produced by emission

from galactic and solar sources is evaluated as the limiting noise

for communication systems employing large-aperture antennas.

A procedure is given for estimating background intensities from

a sky map of galactic temperature contours. The maximum and

minimum expected radio noise levels are evaluated over a frequency

range from 25 to 10,000 Mc/s for various antenna apertures, and

are reported in graphs as noise intensity in decibels above kTQB

(T = 300° K).
- 112m -

Basic data have been obtained from published radioastronomy surveys, from solar measurements at the National

Bureau of Standards, and from measurements made with various

antennas used in the investigation of scatter propagation at VHF.

The expected variations and fluctuations in solar radio noise

emission are discussed.

Charts and tables enable the reader to estimate the background noise in any given antenna system.

342. A. P. Barsis and F. M. Capps, "Survey of Propagation Characteristics of Sea Test Range in Vicinity of the Naval Air

Missile Test Center, Point Mugu, " Progress Report No. 3, NBS

Report No. 5003, dated August 10, 1956.

343. R. W. Hubbard, "Study of Tropospheric Propagation

X-Band Propagation System Development, " First Quarterly

Progress Report March 1, 1956 - May 31, 1956, NBS Report

No. 5005, dated May 31, 1956.

344. B. R. Bean, "Survey of the National Bureau of Standards'

Application of Atmospheric Refractivity Measurements to Radio

Propagation Studies, " NBS Report No. 5007 dated August 20, 1956.

ABSTRACT

A brief general review is made of the National Bureau of

Standards' application of radio refractivity data to tropospheric

radio propagation problems. An appendix lists various groups of

radio meteorological data available at the National Bureau of

Standards.

345. R. W. Hubbard, "Study of Tropospheric Propagation

X-Band Propagation System Development, " Second Quarterly

Progress Report June 1, 1956 - August 31, 1956, NBS Report

No. 5015, dated August 31, 1956.

346. R. S. Kirby, "Measurement of Service Area for Television Broadcasting, " NBS Report No. 5020, dated October 19,

1956.
- 112n - ABSTRACT

It is proposed that the present definition of television service

in terms of iso -probability contours be abandoned. A new definition of service area, first proposed by Norton and Gainen in

1950, is recommended in its place. This provides a much more

useful measure of service and makes the estimating techniques

more tractable.

347. M. T. Decker, "Tacan Coverage and Channel Requirements, " NBS Report No. 5025, dated October 29, 1956.

ABSTRACT

Tacan is a radio air navigation system of the polar coordinate,

or rho-theta, type. The National Bureau of Standards has been

asked to estimate the number of channels which would be required

to implement the Tacan system in the continental United States

under certain assumptions. This report presents the essential

results of this study.

348. James R. Wait, "The Pattern of a Flush Mounted

Microwave Antenna, " NBS Report No. 5028, dated October 25,

1956.

ABSTRACT

The numerical results for the far zone radiation from an

axial slot on a circular cylinder of perfect conductivity and

infinite length are discussed. It is shown that the results for

large diameter cylinders can be expressed in a universal form

which is suitable for pattern calculations for arrays of slots on

a gently curved surface. The work is compared with a related

diffraction problem considered by Fock.

349. M. C. Thompson, Jr., and M. J. Vetter, "Single Path

Phase Measuring System for Three-Centimeter Radio Waves, " NBS Report No. 5035, dated December 19, 1956.

ABSTRACT

A system has been developed using the same general approach

previously employed at 1046 Mc, for measuring variations in

phase -of-arrival of 3 cm radio waves propagated along a line-of-
- 112o -

sight path. The techniques for obtaining the necessary frequencystabilization are discussed in detail together with some estimates

of the system performance.

350. R. W. Hubbard, "Development of an X-Band Field

Intensity Recording System for Tropospheric Propagation Studies, " Third Quarterly Progress Report September 1, 1956 - November

30, 1956, NBS Report No. 5036, dated November 30, 1956.

351. H. B. Janes and P. I. Wells, "Some Tropospheric

Scatter Propagation Measurements Near the Radio Horizon, " Proc. IRE, Vol. 43, No. 10, pp. 1336-1340, October, 1955.

ABSTRACT

Measurements of small variations in 100 Mc field intensity

within and just beyond the radio horizon are reported. The

measured fields are assumed to be the resultant of two field components, one having a constant amplitude and the other being a

rapidly -fading scattered component. Median values of transmission,

loss for the scattered component and for the measured signal are

plotted versus the angular path distance, 0. Measurement of

the correlation of field strengths received on two horizontally - spaced antennas within the radio horizon is reported. When the

spacing was varied from l/z to 20 wavelengths and the correlation

compared to other characteristics of the field, the correlation

was found to be as much a function of transmission loss and fading

rate as it was of antenna spacing.

352. Harold Staras, "Forward Scattering of Radio Waves by

Anisotropic Turbulence," Proc. IRE, Vol. 43, No. 10, pp. 1374-

1380, October, 1955.

ABSTRACT

This paper extends the theory of tropospheric scatter by

deriving the appropriate formulas for the important radio system

parameters under the assumption that the turbulence is anisotropic;

i.e., that the scale of turbulence in the horizontal dimension is

different from the scale of turbulence in the vertical dimension.

The frequency dependence of the scattered radiation is the same for

anisotropic large-scale turbulence as for isotropic. Furthermore,

those radio systems parameters which depend only on the rate of

decrease of scattered energy with elevation angle (such as the

vertical correlation function and height gain) remain unchanged
- 112p -

under the assumption of anisotropy while those parameters

which depend on the energy coming out of the great circle

plane (such as the horizontal correlation function) can be influenced quite substantially by anisotropy. Several other parameters such as the longitudinal correlation function, bandwidth

of the medium and effective antenna gain may also be influenced

by anisotropy but generally to a lesser extent. A comparison is

made between our theory and some recent NBS data indicating

that anisotropy does exist.

353. G. Birnbaum and H. E. Bussey, "Amplitude, Scale,

and Spectrum of Refractive Index Inhomogeneities in the First

125 Meters of the Atmosphere, " Proc. IRE, Vol. 43, No. 10,

pp. 1412 - 1418, October, 1955.

ABSTRACT

An extensive series of observations was obtained with two

refractometers and meteorological equipment installed on various

levels of a 128 -meter tower at the Brookhaven National Laboratory,

Long Island, New York. One of the refractometers was equipped

with a multiple cavity unit for the study of correlation between two

positions in the horizontal direction. The errors arising from the

exposure of the cavity to the atmosphere and its ventilation were

investigated.

The amplitude of the refractive index variations could be

correlated with various meteorological conditions. From the

experimentally determined cross -correlation coefficient, and

assuming that its variation with distance is given by the exponential

(Taylor) form, scales in the neighborhood of 60 meters were obtained. A crude analysis of the data indicated that the intensity of

the refractive index inhomogeneities varied, on the average, as

the 1. 6 power of their size.

354. B. R. Bean and F. M. Meaney, "Some Applications

of the Monthly Median Refractivity Gradient in Tropospheric Propagation, " Proc. IRE, Vol. 43, No. 10, pp. 1419-1431, October,

1955.

ABSTRACT

A consistent correlation has been found between the monthly

median values of 100 Mc transmission loss and an atmospheric
- 112q -

parameter AN which is determined from standard radiosonde

observations. AN is defined as the difference between the

refractivity at the earth's surface and at one kilometer above

the earth's surface. AN is determined from the midpoint of the

propagation path and is taken to represent an effective gradient

of the refractive index. It is found to yield correlation coefficients with transmission loss of about 0.7 even in the far scattering region. This correlation is also used to derive estimates of

the annual, geographic, and terrain variances of the transmission

loss. Six-year average values of AN are presented for the

United States and can be used as an aid in the prediction of the

annual cycle of 100 Mc transmission loss. The possibility of

using surface observations of N for times of day other than the

radiosonde observation hours is examined and found to be encouraging.

355. R. S. Kirby, H. T. Dougherty and P. L. McQuate,

"Obstacle Gain Measurements Over Pikes Peak at 60 to 1, 046 Mc, " Proc. IRE, Vol. 43, No. 10, pp. 1467 - 1472, October, 1955.

ABSTRACT

Radio transmission loss measurements made over four propagation paths approximately 100 miles in length show the effect of

a large mountain obstacle on VHF and UHF ground-to-ground

propagation. Recordings of transmission loss were obtained at

four sites as a function of receiving antenna height and by mobile

measurements along a route normal to the propagation path.

Measurements for propagation directly over Pikes Peak

exhibit the well defined lobing associated with four ray -path

diffraction theory. Theoretical approximations based on the

Fresnel-Kirchhoff scalar knife-edge diffraction theory predict

values of transmission loss and lobe structures which are in good

agreement with those observed.

Measurements for propagation to the east and west of Pikes

Peak are characterized by lower fields at all frequencies and

large fading ranges.

COMMENT

Additional publications in the Proc. IRE, Vol. 43, No. 10,

October, 1955, are numbered 321-324 in this supplementary list

of technical reports.
-112r356. B. R. Bean and R. L. Abbott, "Oxygen and Water Vapor

Absorption of Radio Waves in the Atmosphere, " to be published in

the July, 1957 issue of Geophysica Pura E Applicata.

ABSTRACT

Calculated values of the gaseous atmospheric absorption are

presented for the frequency range 100 to 50, 000 Mc at elevations

above ground up to at least 130, 000 feet, for average conditions

during February and August at Bismarck, N. D., and Washington,

D. C. Total radio path absorptions are presented for tropospheric

forward scatter communication links for distances of 100, 300 and

1000 miles. The total path absorptions were calculated by summing

the absorption contributed by each portion of the atmosphere traversed by a radio ray passing from a 60 foot parabolic antenna

resting on the ground to the scattering center and then to a similar

receiving antenna. A correlation of total path absorption with the

surface value of absolute humidity is developed, thus providing

estimates of the range of absorption values in different geographic

areas. Maps of average absolute humidity for the world are presented. Previous work on rain absorption is then combined with

the present study to provide estimates of the radio power loss due

to absorption expected to be exceeded 1 per cent of the time.

357. B. R. Bean and B. A. Cahoon, "The Use of Surface

Weather Observation to Predict the Total Atmospheric Bending of

Radio Rays at Small Elevation Angles, " NBS Report 5082, May,

1957.

ABSTRACT

The total bending of radio rays passing completely through

the earth's atmosphere has been calculated for the extremes of

observed refractive index profiles at eleven United States radiosonde observation stations plus those at Fairbanks, Alaska and

Truk, Caroline Islands. The significant level data of the radiosonde observations were used to allow for any possible effect of the

variation of the refractive index profile from the smoothed average

profiles commonly used for such studies. Even with allowance for

these departures from a smooth profile it is found that the surface

value of the refractivity alone may be used to predict the total bending with useful accuracy even for elevation angles of arrival or

departure as small as one milliradian.
-112s358. B. R. Bean and J. D. Horn, "On the World Wide

Variations of Radio Refractivity as Derived from Standard

Weather Observations, " NBS Report 5083, May, 1957.

ABSTRACT

World-wide maps of the monthly mean of the surface value

of the radio refractivity, Ns , are presented for the months of

February and August. A map is also given of the maximum range

of monthly mean values of N

g

. Annual cycles of Ng

are presented

for each of six major climatic types. It is estimated that geographic variations of monthly mean field strengths may be as

much as 25 db for identically equipped tropospheric forward

scatter systems and that annual cycles may be as large as 15 db,

due solely to correlation with the variation in surface refractivity.

359. "Bibliography on Tropospheric Propagation of UHF,

VHF and SHF Waves, " Meteorological Abstracts and Bibliography,

Vol. 8, No. 8, August, 1957.

ABSTRACT

A bibliography comprised of a listing (alphabetical by author)

of about 500 references to literature on the behavior of electromagnetic radiation in the UHF, VHF and SHF bands (30 to 30, 000

Mc or 10 m to 1 cm) in the troposphere and lower stratosphere:

i. e. any portion of the atmosphere below the ionosphere has been

prepared and will be published in the August or September issue

of Meteorological Abstracts and Bibliographies.

360. H. B. Janes, J. C. Stroud and M. T. Decker, "An

Analysis of Propagation Measurements Made at 418 Mc Well Beyond the Horizon, " NBS Report 5086, June, 1957.

ABSTRACT

This report presents the results of an analysis of transmission

loss measurements made at 418 Mc over the 135-mile path from

Cedar Rapids, Iowa to Quincy, Illinois during 1952 and 1953. The

data consisted chiefly of continuous simultaneous recordings of

signal level at several receiving antenna heights, ranging from 30

to 665 feet above ground. These data are reduced to tabulations of
-112thourly median values of basic transmission loss and fading range.

These valties, as well as the hourly difference in transmission

loss observed at two heights (height-gain) are also shown plotted

in scatter diagrams versus time of day for each of the 13 two-week

recording periods. The medians for each recording period of all

hourly values of median basic transmission loss, fading range

and height-gain are plotted versus time of year to show any seasonal

variation in these statistics.

The next page is 118.
-118-

II. STATUS OF PPvOJECTS AND FACILITIES.

A. Compilations of Data.

(a) Hourly Median Field Strengths.

Because of the large volume of radio transmission loss

data available in the Tropospheric Propagation Research

Section, it was decided to put all the hourly medians on IBM

punch cards for future processing. This task is almost

completed. It is believed that IBM methods of data processing

are particularly applicable to these data.

Methods of establishing a weighting system for all of

the data available are being devised, and IBM punch card

methods are to be used in developing such a weighting system.

Between seven and eight hundred station -months of data

which were incorporated into an equal number of graphs

showing average diurnal trends during a month have been

reproduced on microfilm, by request of Mr. Dickson of

the Office of the Chief Signal Officer.

At the end of the calendar year 1951, the following stations

were being recorded by the indicated contractors:

RECORDING AGENCY AND

TRANSMITTER FREQUENCY PATH LENGTH

Pennsylvania State College

State College, Pennsylvania

WHDL - Olean, New York 95.7 Mc 90 Miles

WJAS - Pittsburgh, Pa. 99.7 Mc 110 Miles

WEST - Easton, Pa. 107.9 Mc 125 Miles

WTOP - Washington, D. C. 96.3 Mc 145 Miles

University of Washington

Seattle, Washington

KOIN - Portland, Oregon 101. 1 Mc 140 Miles

-119-

Federal Communications

Commission

All egan, Michigan

W£NR - Chicago, Illinois 94.7 Mc 118 Miles

WKRC-TV - Cincinnati, Ohio 203.75 Mc 252 Miles

WFRO - Fremont, Ohio 99.3 Mc 109 Miles

Grand Island, Nebraska

KFOR - Lincoln, Nebraska 102.9 Mc 93 Miles

KMTU - Omaha, Nebraska 65.75 Mc 131 Miles

WOW-TV - Omaha, Nebraska 85.75 Mc 131 Miles

Ft. Lauderdale, Florida

CM21L - Havana, Cuba 102.7 Mc 240 Miles

Houston, Texas

WDSU-TV - New Orleans, La. 85.75 Mc 317 Miles

Laurel, Maryland

WABX - Harrisburg,Pa. 100.9 Mc 76 Miles

WCAU-TV - Philadelphia, Pa. 197.7 5 Mc 104 Miles

WIP - Philadelphia, Pa. 93.3 Mc 104 Miles

WEEU - Reading, Pa. 92.9 Mc 97 Miles

WNBF-TV - Binghampton, N.Y.209.75 Mc 205 Miles

Livermore, California

KVCI - Chico, California 101.1 Mc 139 Miles

KARM - Fresno, California 101.9 Mc 121 Miles

KGO - San Francisco, Calif. 179.75 Mc 38 Miles
-120-

Millis , Massachusetts

KC2XAK - Bridgeport, Conn. 535.75 Mc 116 Miles

WTIC - Hartford, Conn. 96.5 Mc 80 Miles

WKTV - Utica, New York 215.75 Mc 206 Miles

Portland, Oregon

KING -Seattle, Washington 98.1 Mc 145 Miles

Powder Springs, Georgia

WCAC - Anderson, S. C. 101.1 Mc 127 Miles

WFAM - Birmingham, Ala. 215.75 Mc 122 Miles

WMRC -Greenville, S. C. 94.9 Mc 146 Miles

Santa Ana, California

KMAR - Bakersfield, Calif. 92.5 Mc 131 Miles

KFMB - San Diego, Calif. 185.75 Mc 72 Miles

KFSD - San Diego, Calif. 94.1 Mc 84 Miles

University of Texas,

Austin, Texas

KXYZ-FM - Houston, Texas 96.5 Mc 147 Miles

KPRC -TV - Houston, Texas 59.75 Mc 7 2 Miles

KIXL-FM - Dallas, Texas 104.5 Mc 175 Miles

WFAA-TV - Dallas, Texas 185.75 Mc 175 Miles

KLTI-FM - Longview, Texas 115.9 Mc 235 Miles

KWKH-FM - Shreveport, La. 94.5 Mc 275 Miles

University of Illinois

Urbana, Illinois

KXOK-FM - St. Louis, Mo. 93.7 Mc 147 Miles

WMBI-FM - Chicago, 111. 95.5 Mc 126 Miles

WCSI-FM - Columbus, Ind. 93.7 Mc 139 Miles

WBKB-TV - Chicago, 111. 71.75 Mc 127 Miles

WENR-TV - Chicago, 111. 179.75 Mc 127 Miles

WGN-TV - Chicago, 111. 191.75 Mc 127 Miles
-121-

United Broadcasting Co,

Clevela nd, Ohio

Eight fixed recordings:

WHKC-FM - Columbus, Ohio 98.7 Mc 125 Miles

(Horizontal, vertical, circular, and high gain

receiving antennas.)

WCOL-FM - Columbus, Ohio 92.3 Mc 125 Miles

WJR-FM - Detroit Michigan 96.3 Mc 114 Miles

WXYZ-TV - Detroit, Michigan 179.75 Mc 114 Miles

WKBN-FM - Youngstown, Ohio 9 8.9 Mc 45 Miles

Two mobile recordings:

WHKC-FM - Columbus, Ohio 98.7 Mc Twenty sampling

sites,

WCOL-FM - Columbus, Ohio 92.3 Mc Twenty sampling

sites.

This work was supported in part by the National Bureau of

Standards and in part by the Department of Defense. A

complete summary of propagation paths for which data are

available at the National Bureau of Standards will be found in

NBS Report No. 2915, October 28, 1953.

Monthly summaries are made of data from each of the

Cheyenne Mountain Program's recording sites, and these summaries

are kept on file and used as a basic reference. Each monthly

summary of recordings from a given monitoring location

includes cumulative distributions of hourly medians for each of

eight three-hour periods during the day, starting at midnight,

a distribution of medians for all hours during the month,

and in some cases cumulative distributions within each hour

for extended periods of time,

(b) Terrain Profiles,
122-

The angular distance S is being obtained for paths where

contour maps are available, and other maps are being obtained

to complete as far as possible the list of terrain profiles for

both within-line-of-sight and beyond -line-of-sight paths.

About two thousand contour maps are presently on file; most

of these have already been used in plotting available propogation path terrain profiles.

(c) Meteorological Data.

A meteorological microfilm library has been built up

which contains all North American surface and constant

pressure charts for the years 1946 through 1951. These data

provide a ready check for unusual radio data due to unusual

meteorological conditions and form the basis for correlation

work with the observed transmission loss data.

Microfilm data were obtained from three Air Force

bases, giving radiosonde summaries for four times a day

during the years 1950 and 1951. These data are being

utilized in the study of the diurnal variation of refractive

index profiles.

Further consideration has been given to the use of IBM

facilities of the Weather Bureau Machine Tabulating Unit at

Asheville, North Carolina to make calculations necessary

for radio field strength correlation studies. The Weather

Bureau furnished IBM computations of (1) refractive index

gradients as derived from monthly average pressure,

temperature, and humidity data for each radiosonde station

for the period 1946 to 1951, and (2) daily values of refractive

index gradient for eighteen select U, S. stations. From these

data, cumulative distributions were made up showing the

statistical character of the variations of refractive index

pertinent to several FM and TV propagation paths for each

of several "time blocks," (see Supplement IX), and in some

cases, the values of angular distance for the propagation path

which would correspond to values of refractive index gradient
-123-

from the surface to one kilometer exceeded one, fifty, or ninety-nine per cent of the time were computed, (Attempts

to use this information in the analysis of data have not so

far been successful because of the amount of work involved

in refining analyses to this point.)

Emphasis is being placed on obtaining meteorological

data along some of the propagation paths in the Cheyenne

Mountain Experiment, including refractive index profiles

measured with the Birnbaum microwave refractometer and

also using the more conventional temperature and humidity

elements.

B. Facilities.

(a) Mobile recording units.

Several mobile units are available for making measurements

in the plains, foothills, and mountainous regions of Colorado.

Equipment is being readied to continue such measurements in

this region using a portable one hundred foot telescopic mast.

With this equipment it is planned to demonstrate more thoroughly

the behavior of some of the more recently proposed parameters

for analysis and description of VHF and UHF propagation over

irregular terrain.

In addition to the permanent transmitting facilities on

Cheyenne Mountain, transmissions are available from a mobile unit at the top of Pikes Peak during the summer months

and from Camp Carson at the base of Cheyenne Mountain,

(b) Cheyenne Mountain Experiment.

A paper entitled "Cheyenne Mountain Propagation Experiments" by A. P. Barsis, J. W. Herbstreit, and K, O. Hornberg

has been approved for publication as NBS Circular No, 554,

This circular describes the facilities of the National Bureau of

Standards Cheyenne Mountain Field Station, the type of measurements being taken, and gives a summary of the type of data
-124-

analyses being made. The circular is expected to be a basic

reference concerning the unique National Bureau of Standards

facilities available for tropospheric propagation measurements.

(c) Five hundred foot tower at Haswell, Colorado.

Pro^-ess in evaluating the Booker -Gordon scattering

theory as a function of frequency, antenna height, and terrain

is being made through the study of turbulence on a five hundred

foot tower erected at Haswell, Colorado, and also with special

airborne refractometer measurements made along the Cheyenne

Mountain Experiment's propagation paths. At present there

is a major emphasis on the design and development of

temperature compensated cavities. A five hundred foot

waveguide has been installed on the Haswell tower to permit

refractometer installation at several levels. In February,

1954, when a 158-foot length of waveguide had been installed,

refractometer cavities were installed at 15 and 158 feet,

and data were obtained for the last half of February,

Psychrometric data were taken over the height of the tower

in order to assess the reliability of the American Instrument

Company temperature and humidity elements.

(d) Airborne recordings.

In February of 1954, a two-week continuous radio recording program was sustained with five frequencies monitored

at Kendrick, Karval, Haswell, and Sheridan Lake, Colorado,

and a.t Garden City and Anthony, Kansas, this last site

being four hundred miles from Cheyenne Mountain. An Air

Force plane equipped with a refractometer made several

spirally ascending and descending flights to obtain refractivity

profiles. The plane was also flown in different regions of

space across the path in an effort to determine the regions

most responsible for the observed scattered fields. The

analysis that has been conducted so far has revealed that our

knowledge of the spatial distribution of radio field strength

is not adequate to explain the scattering patterns obtained
125-

during these flights. Accordingly, field strength measurements

made in August of 1954 were designed to supply the needed

information. The program included transmissions from Pike

Peak on 100 and on 1046 megacycles, alternating with transmissions from Cheyenne Mountain.

C. Projects.

At present, emphasis is being given to the more rapid

reduction of the large amount of data which has been taken in

the past and which is expected in the future. Some of the

projects proposed for the future are:

(a) The preparation of basic transmission loss versus

angular distance curves for frequencies between 50 and 10,000

megacycles,

(b) The derivation of adequate definitions of antenna

height over irregular terrain,

(c) A re-evaluation of basic parameters involved in the

Booker-Gordon scattering theory.

(d) An investigation of polarization effects in tropospheric

scattering,

(e) An investigation of path antenna gain effects. At

Garden City, Kansas, two complete receiving systems on

1046 megacycles were used simultaneously, one using a dipole receiving antenna and the other a parabolic reflector;

both antennas were at the same elevation above ground.

This was done to obtain data on loss in antenna gain with

respect to the theoretical free space gains, and to determine

the effect of antenna directivity on fading rate and fading

range,

(f) Trend analysis and correlation studies of radio and

meteorological data. Studies of the geographical distribution
-126-

of the refractivity gradient over the United States and the

effects of the refractivity gradient on the observed radio

transmission loss are expected to be useful in predicting

the annual and geographic trends of radio transmission loss

throughout the United States. Considerable progress has been

made in such studies.

(g) Derivation of terrain correction factors similar to

the FCC Ad Hoc Committee's M(d,f).

(h) Measurement and analysis of within-line -of-sight

scattering components. A gain stable receiver with a

differential amplifier was installed and operated at 100

megacycles at the Kendrick receiving site. About one week

of fast speed recording showed that at the within-line-ofsight location there was considerable instantaneous variation

of signal, although it was not evident on the regular recording receiver. This signal variation indicates that there is a measurable scattering component even for within-line -ofsight conditions.

(i) Study of prolonged space-wave fadeouts. An evaluation of the occurrence of prolonged space-wave fadeouts on

1046 Mc over the Cheyenne Mountain paths and on an overseas

path in the San Diego, California region is considered to be

important in the performance of air navigation facilities

proposed for the 1000 megacycle portion of the frequency spectrum.

Considerable progress has been made in determining the

extent of these fadeouts on the two paths under study, and

the data obtained are being used to evaluate their significance in determining the operational performance of air

navigation systems operating at 1000 megacycles.

(j) Irregular terrain studies. Recently, over 120 miles

of routes were traveled in making continuous irregular terrain

propagation measurements of each of three VHF broadcasting

stations, operating on frequencies of 59.75, 94,7 and 191.75

megacycles. In general, higher propagation loss and greater

ranges of variability are associated with the foothills terrain
-127-

than with the plains further east, and correlations between

observations of transmission loss tend to be mostly dependent

upon the degree of separation of the propagation paths and

much less dependent upon differences in frequency of operation.

(k) Measurements of phase variability due to slow changes

in the atmosphere, and measurements of phase instability

due to random inhomogeneities in the propagation medium.

Supplement I

CORRELATION IN VHF PROPAGATION

OVER IRREGULAR TERRAIN

By

R. S. Kirby and F. M. Capps

National Bureau of Standards

Boulder, Colorado

See No. 328, page 112h in the list of technical abstracts.

Supplerrent II

MICROWAVE PROPAGATION SURVEY IN

WASHINGTON, D. C. AREA

By

K. Tritabaugh and J. H. Chisholm

Supplement II MICROWAVE PROPAGATION SURVEY IN WASHINGTON, D. C. AREA

BY

Kenneth Tritabaugh and James H. C his holm

National Bureau of Standards

Boulder, Colorado

Microwave propagation conditions over several paths in the

Washington, D. C. area were investigated. Results of experimental

tests over the particular paths are given.

The following report on a series of radio propagation tests over

several proposed microwave radio relay paths has been prepared in

compliance with a request from the Plant Engineering Agency, Office

of the Chief Signal Officer, Department of Defense, for a preliminary

propagation survey of these paths prior to the establishment of a permanent microwave radio relay system.

Discussion of this problem in an informal conference at the

Pentagon, November, 1950, between Mr. J. H. Chisholm and Mr.

K. F. Tritabaugh of the Central Radio Propagation Laboratory,

National Bureau of Standards, and personnel of the Office of the Chief

Signal Officer, Department of Defense, resulted in an agreement by

this Laboratory to undertake a short-term propagation survey of the

proposed paths with the assistance of military personnel. It was

pointed out that the National Bureau of Standards had 4500-5000 Mc

AN/TRC-6 microwave radio relay equipment suitable for this purpose

and immediately available but that results from this equipment operating

in the 4500-5000 Mc range would not be directly comparable to that

expected from the proposed permanent installations operating near

2000 Mc with regards to path clearance and fading rates and fading

ranges. Since procurement of 2000 Mc equipment and modification

for recording would have required considerable time, it was agreed

to undertake these tests with the 4500-5000 Mc equipment on a shortterm basis as a useful guide for future installations. It was further

agreed that these tests would be limited to a few weeks on each path

in order to complete the survey as rapidly as possible although seasonal

variations would not be accurately represented.
-2- II

Mr. K. F. Tritabaugh of the Laboratory was assigned to devote full

time to this survey and with the excellent assistance and cooperation of

military personnel, established experimental microwave terminals and

recorded radio field intensity over the following paths:

6 February-19 February, 1951 - Quirauk Mt. to Sugar Loaf Mt.

28 February-11 March, 1951 - Sugar Loaf Mt. to Silver Hill

20 March -24 March, 1951 - Ft. Meade to Silver Hill

5 April -12 April, 1951 - Silver Hill to La Plata, Md.

Attached Figs. 1 through 4 show the profiles of these four paths

with earth curvature corrected for the refraction of radio waves in a standard atmosphere. The first Fresnel zone for a wavelength of 6.9

centimeters (4350 Mc) is outlined by broken lines on these profiles.

Complete clearance of this first Fresnel zone by intervening topography

is considered the minimum condition for a satisfactory microwave path

by most commercial radio relay system engineers. It should be noted

that tree foliage in the Maryland Coastal Region often reaches heights

of 80-100 feet and is not shown on these ground profiles. The effect

of obstructions by tree foliage will be more pronounced near the

terminals since the proportion of the Fresnel zone obscured by tree

foliage may become large as the zone decreases in area near the

terminals. The vertical width of the first Fresnel zone is proportional

to the square root of the wavelengths ratio or inversely proportional to

the square root of the frequency ratio (i.e. , for 2000 Mc, the vertical

dimensions would be 1/72000 or 1.48 times greater than shown).

/ v 4350

Under normal propagation conditions and with rough intervening terrain

a path loss of 6 db referred to the free space value would be caused by

obscuring one half of the vertical width of the first Fresnel zone. On

this basis, a 2000 Mc system should be only a few decibels poorer

than 4350 Mc for all four paths as shown under standard tropospheric

conditions. Experience has shown that fading rates and fading ranges

as a function of frequency as caused by varying non-standard meteorological conditions are complex in nature. In general, the fading rates and

range of fades appears to increase with frequency, although precise

quantitative data for a specific climatological area are too inadequate

to allow a firm conclusion. The range of fading, rapidity of fading,

and the median field strength of microwaves over extended distances

show pronounced diurnal and seasonal variations. Experience with

microwave radio relay systems in the Maryland- Virginia regions indicates
-3- II

that the summer median fields will be higher than winter and early

spring values but that fading will also be more pronounced, particularly

in the evening hours. However, an increase in path loss in summer

months may be caused by the increase in opaqueness to microwaves of

the tree foliage in full leaf and particular attention should be directed

to potential summer tree foliage obstructions near the terminals, as mentioned earlier. It is recommended that maximum use of towers at

each terminal be made to clear nearby foliage.

An analysis of the hourly median field strengths as shown in

Figs. 5-8, and in the accompanying tables, indicates that all four

paths are within a few db of the free space value (i. e. , closely

comparable to paths with an unobstructed first Fresnel zone) if one

ignores the tropospheric variations which are of the order of ten

decibels. A definite diurnal cycle is present on most days and will

probably be more pronounced in the summer months. The losses

recorded on the Quirauk to Sugar Loaf path on February 7, are believed

to be caused by snow and ice on the antenna system rather than tropospheric propagation effects. It should be noted that all data is referred

to free space as zero decibels and can be calculated in the following

manner:

Pt _ X

2

P- G+G. r

2 -t~r 4Tr

P = Power received by receiving antenna in watts under free space

conditions.

Pj. = Power delivered to the transmitting antennas in watts.

G{. = Numerical power gain of transmitting antenna relative to an

isotropic antenna.

G r = Numerical power gain of receiving antenna relative to an

isotropic antenna

R = Distance between terminals in meters.

X = Wavelength in meters.

Note: RF transmission line losses are not included in these calculations,

but are included in the threshold levels.

The threshold signal levels of the AN/TRC-6 radio relay for all paths

are shown as actually measured. The threshold is 42 db or more below

free space for the power radiated, antenna gains, receiver sensitivity,

and transmission line losses of this particular set, and each specific
-4- II

path distance. The threshold is defined in this report as the minimum

signal level that intelligible conversation can be maintained with the

AN/TRC-6 equipment. From prior experience with the AN/TUG-^,

it was found that this level is approximately six decibels above noise

for a single circuit althoiigh a completely quiet circuit requires a signal ten db above noise.

From these results, it is evident that AN/TRC-6 equipment would

furnish reliable communications over these single links with approximately 40 db margin for variation. This margin should be adequate

for all but extremely severe tropospheric variations and it is believed

that comparable commercial microwave systems would perform

satisfactorily. It is recommended that an on-the-spot survey of

tree foliage height near each terminal or other critical points along

the path be made in the summer months and added to the ground

profile.

It is hoped that this brief survey report will serve as a useful

guide for the permanent microwave installation. The National Bureau

of Standards will be happy to provide further details on these tests

upon request.
-5 II SUGAR LOAF MT. TO QUIRAUK MT.

Relative to free space.

Date Time Max. Min. Med.

February 6 1 2-1 pm

1:20-3

+ . 7 db

Power Off

- . 1 db + .5

3-4 + 1.7 + .4 + . 6

4-5 + 1.9 + .6 + 1. 6

5-6 + 1. 8 + .5 + 1.5

6-7 + 1.6 + 1. 6 + 1. 6

7-8 + 1.6 + 1.6 + 1. 6

8-9 + 1.8 + .8 + 1.6

9-10 + 2.4 + .6 + 1. 6

10-11 + 2. 5 + 1. 1 + 1. 6

11-12 + 2.5 -4.4 + 2. 2

February 7 12-1 -3.6 -9.4 -7.4

1-2 -3.7 -7.4 -4.6

2-3 + .6 - .4 + . 1 3-4 - .4 - .4 - .4

4-5 - .4 - .4 - .4

5-6 - .4 -1.4 - .9

6-7 - .9 - .9 - .9

7-8 - .4 -2.4 -1.4

8-9 - .4 -4.4 -2.5

9-10 -1.9 -4.4 -2.9

Heavy ( 10-11 -1.4 -3. 1 -1.9

Snow ( 11-12 -1.4 -10.4 -3.4

12-1 -1.4 -13.4 -8.4

1-2 -10.4 -13.4 -11.4

2-3 -8.4 -13.4 -10.4

3-4 -8.4 -10.4 -9.4

4-5 -8.4 -8.4 -8.4

5-6 -8.4 -10.4 -9.4

6-7 -7.9 -9.4 -8. 7

7-8 -8.4 -10.4 -9.4

8-9 -7.4 -9.4 -8.4

9-10 -7.4 -8.4 -7.9

10-11 -7.4 -7.4 -7.4

11-12 - .4 -13.4 -7.4
-6- II

Date Time Max. Min. Med.

February 8 12-1 -6 ,4 db -10. 4 db -9.9db

1-2 -1 .4 -7.4 -3.9

2-3 -2 4 -9.4 -7.4

3-4 -1 .9 -7.9 -6.9

4-5 -6 4 -7.4 -6.9

5-6 -6 4 -6.4 -6.4

6-7 -5,.9 -6.4 -6. 2

7-8 -5 .4 -6.4 -5.9

8-9 -4. 4 -6.4 -4.9

9-10 " * 4 -5.4 -3.9

10-11 -1. 4 -1.4 -1.4

11-12 TM"

* 4 -3.4 -1.4

12-4 Calibrate and power off

4-5 + . 5 - .4 + . 1 5-6 + . 6 + . 1 + .4

February 9 2-3 pm -1. 1 -2.1 -1.6

3-4 i 6 -1. 1 - .9

4-5 *"

i 1 -2. 1 -1.1

5-6 ""

* 1 - . 1 - .1

6-7 " 4 1 - . 1 - . 1 7-8 " 1 1 - . 1 - . 1 8-9 + . 4 - . 1 9-10 **

1 1 - . 1 - .1

10-11 + . 9 - . 1 + .4

11-12 + . 9 - . 1 + . 1 February 10 12-1 + . 9 - .8 - . 1 1-2 + . 9 - .8 + .4

2-3 + . 2 - .1 + . 1 3-4 + . 5 - . 1 + .2

4-5 + . 4 - .3 - . 1 5-6 + . 4 - . 1 + .3

6-7 + . 9 + .2 + .4

7-8 + . 4 - .2 + .3

8-9 + . 9 - .6 - . 1 9-10 + . 9 - .1 + .4

10-11 *" 1 1 -2. 1 -1. 1 11-4 Off for respairs

Power tr oubles at Sugar Loaf
-7- II

Date Time Max. Min. Med.

February 1

3-4 pm -1. 3db -3. 3db -3. 1 db

4-5 -2.3 -2. 3 -2.3

5-6 -1.1 -2.3 -1.8

6-7 -1.8 -1.8 -1.8

7-8 - .5 -1.8 -1.3

8-9 -1.3 -1. 3 -1.3

9-10 - .3 -1. 7 -1.3

10-11 + .2 -1.3 -1.0

11-12 - .9 -1.9 -1.3

February 12 12-1 -1.3 -2.3 -1.4

1-2 - .8 -1.8 -]. 3

2-3 -1.0 -2.4 -1.8

3-4 - .7 -3.3 -2.5

4-5 -1.9 -3.8 -3.0

5-6 -2.8 -5.8 -4.7

6-7 -2.8 -5. -3.2

7-8 -2.5 -3.8 -2.9

8-9 -2.3 -4. 8 -2.8

9-10 - .3 -2.8 -2.3

10-11 - .8 -2. 3 -1.8

11-12 -1.0 -2.3 -1.9

12-2 Calibrating

2-3 + 1.0 -1.5

3-4 + .5 + .5 + .5

4-5 + .5 + .5 + .5

5-6 + .8 + .3 + .6

6-7 + .8 - . 3 + . 1 7-8 + 1. 3 + . 3 + .5

8-9 + 1.5 + .5 + 1. 9-10 + 1.5 + 1. 5 + 1.5

10-11 + 1. + 1. + 1. 11-12 + 2.0 + 1. + 1. 1 February 13 12-1 + 2. + .5 + 1. 5 1-2 + 3. 2 - . 5 + 1. 5 2-3 + 2.2 + 1.5

3-4 + 2.0 - .3 + .5

4-5 + 1.5 + .5 + 1. 5-6 + 1.5 - . 5 + .3

6-7 + 1. 5 - . 5 + .5
-8- II

Date Time Max. Min. Med.

February 13 7-8

8-2

+ 1. 5db

Power Off

"" 9 3db + .4

2-3 -1.5 -3. 1 -1.6

3-4 -2.0 -2. -2.0

4-5 -2.0

Power Off

-2. -2.0

February 14 2-3 pm

3-4

Equipment

trouble

4-5 + .4 *" 4 5 - .2

5-6 + 1.0 + .5

6-7 + 1.0 +1. + 1.0

7-8 + 1.0 +1. + 1.0

8-9 + 1.0 + . 5 + .8

9-10 + 1.0 + . 5 + .8

10-11 + .5 -6. 5 - .3

11-12 + 1.3 + .6

February 15 12-1 +2.0 + 1. 5 + 1.7

1-2 + 1.6 + 1. 3 + 1.5

2-3 + 2.4 + 1. 3 + 1.6

3-4 + 2.5 + 1. 6 + 1.9

4-5 + 2.6 + 2. 2 +2.5

5-6 +3.0 + 2. 6 +2.8

6-7 + 3.0 + 2. 3 +2.6

7-8 + 2.5 + 2. 5 + 2.5

8-9 + 2.5 + 1. 3 + 2.2

9-10 + 2.5 + 1.5

10-11 +3. 7 + 3.0

11-12 + 2.7 + 2.5

12-1 -1.0

1-2 -1.6

2-3 Calibrate

3-4 -2.5

4-5 -2.5

5-6 -2.5

6-7 -2.5

7-8 -2.5

8-9 -1.9

9-10 -1.7

10-11 -2. 2

11-12 -1.7
-9- II

Date Time Max. Min. Med.

February 16 12-1

1-4

2-3

3-4

4-5

5-6

6-7

7-8

8-9

9-10

10-11

11-1

1-2

2-3

3-4

4-5

5-6

6-7

7-8

8-9

9-10

10-11

11-12

12-1

1-2

2-3

3-4

4-5

5-6

6-7

7-8

8-9

9-10

10-11

11-12

12-1

1-2

2-3

February 17

Calibrate

-1. 5 db

-1. 5 -1. 5

-1.

- , 5 +1. + 1. 6

+1. + 1. 5 +1. 7 + 2.

-1.

-1.

-1.

-1,

- . 7

- , 5

- , 5

- . 5

- , 5

- , 5

-1.

-1.

-1. 5 -2. 4

-3.

-8.

10.

12.

-7. 5 -5. 5 -5. 5 -5. 5 -4. 5 -4.

-1. 8

-2. 5
-10-

Date Time Max. Min. Med.

February 17 3-4

4-5

5-6

6-7

7-8

8-9

9-10

10-11

11-12

-2.5 db

-4.0

-4.0

-3.0

-2.5

-2.0

-2.0

-2.0

-2.0

February 18 12-1

1-2

2-3

3-4

4-5

5-6

6-7

7-8

8-9

9-10

10-11

11-12

12-2

2-3

3-4

4-5

Calibrate

Power Off

-1.5

-1.0

-1.0

-1.0

-1.0

-1.0

-1.0

-1.0

-1.0

-1.0

-1.0

-2.6

-2.5

-2.5

II
-11 II

Date Time Max. Min. Med.

February 18

February 19

February 20

5-6

6-7

7-8

8-9

9-10

10-11

11-12

12-1

1-2

2-3

3-4

4-5

5-6

6-7

7-8

8-9

9-10

10-11

11-12

12-1

1-2

2-3

3-4

4-5

5-6

6-7

7-8

8-9

9-10

10-11

11-12

12-1

1-2

2-3

3-4

4-5

5-6

-2. 5

-2. 5

-2. 8

-2, 3

-2,

-2.

-2.

-2. 8

-3.

-1. 5

-1. 5

-2.

-2. 1 -1. 5

-1. 2

-1. 2

-2. 2

-2. 5

-3.

-3. 7

-4. 3

-3. 8

-2.

-1. 7

-1. 5

-1, 5

-1. 5

-1. 5

-1. 5

-1. 5

-1. 5 - . 7 - . 5 - . 5 - . 5

-1.

-1.
12- II SUGAR LOAF MT. TO SILVER HILL

Date

February 28

Time Med.

March 1

March 2

3 -4 pm

4 -5

5 -6

6- 7

7 -8

8 -9

9 -10

10 -11

11 -12

Mid -1

1 -2

2 -3

3 -4

4--5

5 -6

6 -7

7 -8

8--9

9 -10

10--11

11 -12

Noon--1

1--2

2--3

3--4

4--5

5--6

6--7

7--8

8--9

9--10

lO--11

ll -12

Mid--1 1--2

2--3

-7. 2 db

-7. 2

-6. 9

-6. 9

-5. 9

-5. 9

-6. 3

-6. 3

-6. 5

-5, 7

-5„ 7

-5. 8

-5. 6

-5. 8

-6. 2

-7. 5

11. 4

11.

Power

14. 2

10. 9

-9. 6

-9.

-9. 7

-7. 2

-7. 1 -7. 3

-7. 4

-7. 2

-7. 1 -6. 8

-6. 6

-4. 7

-8. 2

-7. 9

19. 2
Date

-13 - II

Time Med.

March 2 3-4 -15.2 db

4-5 -14.2

5-6 -12.2

6-7 -11.2

7-8 -9.7

8-9 -8.3

9-10 -6.2

10-11 Cal.

11-12 Cal.

Noon-1 -4.0

1-2 -4.0

2-3 -3.9

3-4 -3.7

4-5 -2.7

5-6 -2.2

6-7 -2.6

7-8 -1.2

8-9 -1.7

9-10 -2.8

10-11 -3.0

11-12 -3.0

March 3 Mid-1 -2. 8

1-2 -2.2

2-3 -2.1

3-4 -2.4

4-5 -1.4

5-6 -1.3

6-7 -1.5

7-8 -2.0

8-9 -2.1

9-10 -1.6

10-11 Cal.

11-12 Cal.

Noon-1 -3. 2

1-2 -3.2

2-3 -3.4

3-4 -6.2

4-5 -7.4
-14- II

Date Time Med.

March 3

March 4

March 5

5-6 -9.2 db

6-7 -8.7

7-8 -9.9

8-9 -8.9

9-10 -8.8

10-11 -11.3

11-12 -9.7

Mid-1 -8.9

1-2 -7.9

2-3 -7.7

3-4 -7.6

4-5 -6.4

5-6 -6.5

6-7 -6.4

7-8 -7.5

8-9 -7.3

9-10 -7.4

10-11 -6.9

11-12 Cal.

Noon-1 -6.4

1-2 Power

2-3 Power

3-4 -6.4

4-5 -5.8

5-6 -5.4

6-7 -5.3

7-8 -5.0

8-9 -4.8

9-10 -5.4

10-11 -5.0

11-12 -4.5

Mid-1 -5.4

1-2 -5.4

2-3 -4.4

3-4 -4.6

4-5 -6.4

5-6 -8.4

Power Off
-15- II

Date Time Med.

March 5

March 6

March 7

11-12 -5.8db

Noon-1 -5.5

1-2 -6.

2-3 -6.0

3-4 -6. 1 4-5 -6.2

5-6 -5.

6-7 -3.6

7-8 -1. 8

8-9 -1. 8

9-10 -2. 6

10-11 -3.8

11-12 -3.7

Mid-1 -7. 1 1-2 -12. 2

2-3 -5.6

3-4 -1. 8

4-5 -5.2

5-6 -6.6

6-7 -6.7

7-8 -3.4

8-9 - . 8

9-10 -1. 1 10-11 -3.0

11-12 -5.9

Noon-1 -6.3

1-2 -5.9

Power off

Noon-1 -5.9

1-2 -6.6

2-3 -6.6

3-4 -6.6

4-5 -6.6

5-6 -6.4

6-7 -4.9

7-8 -4.0
-16- II

March 8

March 9

Time

8-9

9-10

10-11

11-12

Mid-1

1-2

2-3

3-4

4-5

5-6

6-7

7-8

8-9

9-10

10-11

11-12

Noon-1

1-2

2-3 3 -4

4-5

5-6

6-7 7 -8

8-9

9-10

10-11

11-12

Mid-1

1-2

2-3

3-4

4-5

5-6

6-7

7-8

8-9

9-10

Med.

-5. 1 db

-4. 3

-5.

-3. 6

-3. 6

-5. 5

-3. 3

-4.

-6. 7

-4. 7

-5. 5

-6. 6

-4. 2

-3. 4

-5. 3

Cal.

-4. 7

-4. 7

-5. 8

-5. 8

-5. 3

-5. 6

-4. 4

-2. 6

-1. 6

-2. 7

-2. 9

-2. 7

-3. 3

-3. 3

-3. 2

-3. 2

-3. 2

-3. 2

-3. 2

-2. 4

-3. 6

-4. 7
-17- II

Date Time Med.

March 9 10-11 -5. 2 db

11-12 -5.3

Noon-1 -5.3

1-2 -5.4

2-3 Cal.

3-4 -4.4

4-5 -4.2

5-6 -3.7

6-7 -2,9

7-8 -2.7

8-9 -2.3

9-10 -1.7

10-11 -2.0

11-12 -1.7

March 10 Mid-1 -1.7

1-2 -1.6

2-3 -1.5

3-4 -1.2

4-5 - .2

5-6 - .4

6-7 - .3

7-8 - .6

8-9 - .9

9-10 -1.8

10-11 -2.3

11-12 Cal.

Noon-1 -5.2

1-2 -4.7

2-3 -4.6

3-4 -4.7

4-5 -5.0

5-6 -4.2

6-7 -3.4

7-8 -3.1

8-9 -3.1

9-10 -3.2

10-11 -3.2

11-12 -3.2
-18- II

Date Time Med.

March 11 Mid-1 -3.2 db

1-2 -2.7

2-3 -2.7

3-4 -2.4

4-5 -2.3

5-6 -2.5

6-7 -2.5

7-8 -2.5

8-9 -3.5

9-10 -3.5

10-11 -4.2

11-12 Cal.

Noon-1 -4.4

1-2 -4.4

2-3 -4.4

3-4 Power

4-5 -3.7

5-6 -3.2

6-7 -2.4

7-8 -1.7

8-9 -1.4

9-10 -1.7

10-11 -1.8

11-12 -2.1

March 12 Mid-1 -1.3

1-2 -1.3

2-3 -1.2

3-4 -1.1

4-5 - .6

5-6 - .6

6-7 - .6

7-8 -1.2

8-9 -2.0

9-10 -3.1
-19- II

FT. MEADE TO SILVER HILL

Threshold = -46 db

Date Time Med.

March 20 Noon-1 -4.4 db

1-2 -3.9

2-3 -4.9

3-4 -4.9

4-5 -4.9

5-6 -4.5

6-7 -3.1

7-8 -2.3

8-9 -1.9

9-10 -1.7

10-11 -1.5

11-12 -3.5

March 21 Mid-1 -2.4

1-2 +1.1

2-3 +5.1

3-4 - .9

4-5 -3.5

5-6 - . 1 6-7

7-8 + .3

8-9 - .5

9-10 -3. 3 10-11 -5.1

11-12 -4.9

Noon-1 -4.9

1-2 -4.7

2-3 Power

3-4 + Cal.

4-5 -1.6

5-6 -1.8

6-7 -1.8

7-8 -1.-6

8-9 -2.0

9-10 -3.5

10-11 Power

11-12 Power
-20- II

Date Time Mllr

March 22

March 23

Mid-1 Power

1-2 -2. 1 db

2-3 - .9

3-4 + .6

4-5 + 4.4

(Power)

3-4 pm -3.7

4-5 -4.0

5-6 -3.5

6-7 -2.7

7-8 -2.3

8-9 - .5

9-10 -1.0

10-11 -2.3

11-12 -1. 1 Mid-1 + 1.8

1-2 - .5

2-3 -1.0

3-4

4-5 + 1.8

5-6 + 1.8

6-7 + .3

7-8

8-9 -3.5

9-10 -3.2

10-11 -2.9

11-12 -3.2

Noon-1 -3.2

1-2 -3.5

2-3 -3.5

3-4 -3.5

4-5 -3.4

5-6 -2.8

6-7 -2.9

7-8 -3.0

8-9 -3.0
-21- II

Date Time Med.

March 23

March 24

March 25

9-10 -3.0 db

10-11 -3.8

11-12 -4.0

Mid-1 -4.4

1-2 -4.4

2-3 -4.5

3-4 -4.5

4-5 -4.2

5-6 -4.2

6 -7 -3.8

7-8 -2.0

8-9 -2. 2

9-10 -2.3

10-11 Cal.

11-12 -1.0

Noon-1 -2.8

1-2 -3.5

2 -3 -3.5

3-4 -3.5

4-5

Paper

Jammed

-3.9

11-12 -4.2

Noon-1 -4.7

1-2 -4.9

2-3 -4.5

3-4 -4.7

4-5 -4.5

5-6 -4.2

6 -7 -2.7

7-8 -1.8

8-9 - .5

9-10 -1.3

10-11 -1.6

11-12 -1.7
-22-

Date Time

II

Med.

-2.2

March 26 Mid-1

1-2 - 2 - b

2-3

3-4

4-5

5-6

6-7

7-8

8-9

9-10

10-11

11-12

Noon-1

1-2

2-3

3-4 - 4 ' 4-5

5-6

6-7

7-8

8-9

9-10

10-11

11-12

March 27 Mid-1

1-2

2-3

3-4

4-5

5-6

6-7

7-8

8-9

9-10

-2.9

-2.9

-2.5

-2.5 - .9

-3.2

-4.5

-5.0

-5.5

Check Ant.

-4.7

-4.5

Cal.

-4.0

-3.5

-2.8

-1.5

-1.5

-1.5

-1.0

-1.0

-1.2

-1.0

-2.0 + 1.5 + 4.0 + 3.0 + 1.0

-1.5

-1.7

-2.3
-23- II SILVER HILL TO LA PLATA

Threshold = -48 db

Date Time Med.

April 5 3-4 pm -6.5 db

4-5 -6.5

5-6 -6.0

6-7 -4.5

7-8 -3. 2

8-9 -2.5

9-10 -2.5

10-11 -3.5

11-12 -4.2

April 6 Mid-1 -2.0

1-0 + 1.0

2-3 + 2.5

3-4 + 2.0

4-5

5-6 -1.6

6-7 -4.0

7-8 -6.0

8-9 -7.0

9-10 -6.4

10-11 Power

11-12 Off

Noon-1 -8.0

1-2 Cal.

2-3 -5.0

3-4 -5.5

4-5 -3.6

5-6 -3.7

6-7 -2. 1 7-8 + .2

8-9 + 2.2

9-10

10-11 -1.0

(Power Trouble)

April 10 3-4 pm -6.0

4-5 -5.6
-24- II

Date

April 10

Time

April 11

April 12

5--6

6- 7

7--8

8--9

9--10

lO--11

ll--12

Mid--1

1--2

2-3

3--4

4--5

5--6

6--7 7-.,1 8-9

9--10

lO--11

ll--12

loon--1

1--2

2--3

3--4

4--5

5--6

6--7

7--8

8--9

9--10

lO--11

ll -12

Mid--1

1.-2

2.-3

3.-4

4.-5 P ower Off

Med.

-5.0 db

-2.2 + .5 + 2.0 + 3.0 + 4.0 + 2.0 + .7 + 1.5

-1.0

-2.0

-3.0

-6.0

-6.0

-7.0

-6.8

-5.5

-4.2

Cal.

-3.5

-2.9

-1. 1 +++++

-1

-7.0

-2. 1 -3.3

-3.5
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FI6.8.
Supplement III

418 Mc PROPAGATION MEASUREMENTS

OVER THE CEDAR RAPIDS - QUINCY PATH

By

M. T. Decker and H. B. Janes

Supplement III

4-18 MC PROPAGATION MEASUREMENTS OVER

THE CEDAR RAPIDS-QUINCY PATH

By

M. T. Decker and H. B. Janes

National Bureau of Standards

Colorado Springs, Colorado

ABSTRACT

The transmitting, receiving and recording facilities used in

propagation measurements made at 418 Mc during the period May

to December, 1951 over the 133.9-mile Cedar Rapids -Quincy path

are described. The discussion of the received signal power data

includes an analysis of variations in instantaneous signal level, as well as analysis of diurnal and seasonal variations in hourly

median signal levels.

INTRODUCTION

A knowledge of the losses involved in the propagation of radio

energy is essential to the prediction of the range and reliability of

any radio communication system. In order to obtain data on the factors

which affect radio propagation in the frequency range from 100 to 1000

Mc, the National Bureau of Standards has been conducting and coordinating an extensive program for the measurement of losses in the transmission of radio energy over representative types of terrain throughout

the United States. To provide information on propagation characteristics

of the 400 to 500-Mc frequency range at distances far beyond the radio

horizon, the Central Radio Propagation Laboratory of the National

Bureau of Standards, with the assistance of the Department of Defense,

has been making field strength measurements between Cedar Rapids,

Iowa and Quincy, Illinois, a distance of 134 miles. A map indicating

the transmission path is shown in Fig. 1. In order to obtain reliable

information on the variations in signal strength at this distance, it is believed that measurements must be made over a long period of

time. For this reason seasonal as well as instantaneous and diurnal

variations in signal levels are being studied. The purpose of this

report is to present the method by which data were gathered and the

results of measurements made during the period April 30 to December

15, 195 1. This includes eight recording periods, each of roughly two

weeks' duration, during which simultaneous recordings were made of

the 418-Mc signal using two low receiving antennas having different

gain characteristics.
-2- III TRANSMITTING LOCATION

Transmission for this program was provided by the Collins

Radio Company of Cedar Rapids, Iowa, under contract with the National

Bureau of Standards. Transmitting equipment was located at the Cedar

Rapids Municipal Airport.

TRANSMITTER

The res natron transmitter used is capable of a continuous -wave

output on the order of 50 kw in the 400-M.c region. For the Cedar

Rapids -Quincy studies an unmodulated signal of approximately 23 kw

was fed to a moderately directional antenna beamed toward Quincy.

Since system frequency stability is a very important factor in this

program, the transmitter is crystal-controlled. Basic units of the

transmitter are 1) crystal oscillator, 2) frequency multipliers, 3)

intermediate power amplifier, and 4) final resnatron power amplifier.

The final amplifier tube is of particular interest due to its large

power handling capabilities at this frequency. The resnatron is a continuously pumped water-cooled tetrode with integral RF circuits— . The tube has high power gain combined with excellent RF shielding

characteristics. Physical dimensions include a length of 54 in, a diameter of 1 8 in, and a weight of 210 lbs. The directly heated

cathode requires 800 to 1000 amperes at 2.6 to 2.8 volts AC or DC.

Anode and screen of the tube are connected internally and are

operated at ground potentials. RF input power is fed through 3-1/8 in

coaxial transmission line, and the output is taken out through a 6

by 22 in wave guide, both at ground potential.

TRANSMITTING ANTENNA

The 6 by 2 2 -in wave guide from the transmitter is terminated in a pyramidal horn mounted on the roof of the hangar containing transmitting equipment. The axis of the horn is approximately 41 feet

above local terrain. Measurements made by theCollins Radio Company

indicated a gain of 14.5 db relative to an isotropic radiator—'.
-3- III RECEIVING LOCATION

The receiving location is the site of the WTAD-FM transmitter

near Quincy, Illinois. The selection of this site was made after a survey of several possible locations by the Collins Radio Company

under contract with CRPL, Preliminary measurements made in

March, 1950 showed that reception and recording of a 400-Mc signal

from Cedar Rapids was feasible. Advantages of the WTAD-FM

location included a 750-foot grounded tower and the availability of

space for recording equipment in the transmitting building at the base

of the tower. Recording at this site was carried on by the Collins

Radio Company through 1950 and results of this previous work have

already been reported.-'. In March, 1951 the operation of the receiving

site was begun by CRPL, while the operation of the transmitter in

Cedar Rapids was continued by the Collins Radio Company. Recordings were made during 1951 using antennas at low elevations, while

during 1952 and 1953 data are being obtained from antennas mounted

on the tower at various elevations from 30 to 665 feet. The latter

measurements -will be covered in future reports.

A block diagram of receiving equipment is shown in Fig. 2.

Description of the individual components follows,

RECEIVING ANTENNAS

One of the receiving antennas consists of a half-wave dipole in a corner reflector and the other a half -wave dipole mounted in a 10-

foot parabolic reflector. They are mounted side by side with a

horizontal separation of about 40 feet. Although they are situated

in the same horizontal plane, the ground has a considerable slope so

that the dipole in the corner reflector is 5.5 feet above the immediate

ground level and the dipole in the parabola is 8.5 feet above ground.

Both are matched to 50-ohm transmission line, and fed to receivers

with RG8/U coaxial cable. The gains relative to an isotropic radiator are 21.5 db for the parabola and about 10 db for the corner

A. I reflector. Measurements were made by the Collins Radio Company— . RECEIVERS

The 400 to 420-Mc field strength meters used for these measurements were built to CRPL specifications by the Polarad Electronics

Corporation of Brooklyn, N. Y. They are of the single superheterodyne
-4- III

type employing a variable local oscillator and an intermediate frequency of 36 Mc. A block diagram of the receiver is shown in Fig. 3.

The incoming signal is fed into a coaxial type cavity preselector

which serves to reduce response to spurious and image frequencies,

A pencil triode in a coaxial type mounting is then used as an RF amplifier. Crystal mixing is employed to convert t^the intermediate frequency of 36 Mc. The injection voltage is obtained from a 6F4

oscillator which may be tuned from 364 to 386 Mc to give the receiver

its range of 400 to 420 Mc. Coaxial cavity tuning is also used in the

oscillator as this method provides convenient circuit components at

these frequencies. Amplification of the intermediate frequency is

accomplished with four stages of pentode amplifiers. The band-pass

characteristic provides for constant gain to within 1 db for a carrier

frequency variation of 150 kc from the center of the band. The AVC

characteristic gives a receiver output which is approximately linear

with logarithmic signal input.

A detector following the last stage of amplification of 36 Mc

supplies three separate output circuits of the receiver. The first of

these is an audio amplifier which may be used for aural monitoring of

any incoming signal. The second is a dc amplifier used to operate a

to 5-miliiampere recording meter. The output of this circuit is

designed to provide critical damping for a type AW Esterline -Angus

recorder. A meter integral with the receiver allows monitoring of

this output with or without the external recorder. This recorder

provides a continuous plot of signal strength versus time. Examples

of this recording are shown in Figs. 4 and 5. A third dc amplifier

whose output range is from to -10 volts is used for the operation of

the time totalizing recorder.

TIME TOTALIZING RECORDER

The time totalizing recorder driven from the to -10 volt output

consists of 10 channels, each of which includes a dc amplifier, and

a bistable multivibrator that actuates a fast acting relay. The relay

in turn operates a motor which drives a revolution counter. The

multivibrator may be adjusted to operate the relay at various levels

of input voltage from the dc amplifier. Thus, the revolution counter

will indicate the total time that the signal exceeds a preset level.

Hourly readings of the counters were made with an automatically-
-5- III

actuated 35-mm camera. This equipment is of an advanced design

but similar to that described previously in connection with this recording program— . CALIBRATION

The magnitude of the incoming signal power at the antenna terminals was determined by the substitution for the antenna of a calibrated signal generator of impedance equal to the antenna transmission line impedance and with comparable output voltage. With

the relatively broad band pass of the receivers, commercially

available generators proved to be satisfactory for the purpose.

During the first portion of the measurement period (kay to September),

both receivers were calibrated with a Measurements Corporation

Model 84 generator, and for the remainder of the year, a General

Radio Model 1021 generator was used. The output calibrations of

both generators were checked against a third signal generator which

had been calibrated by the High Frequency Standards Section of CRPL.

The corresponding data were corrected to allow for the difference

from the calibrated standard.

RECORDING SCHEDULE

The schedule of field strength recording covered in this report

is given in Table I. Also shown is the total number of hours of useful

data obtained during each period.

CHARACTERISTICS OF THE TRANSMISSION PATH

In Fig. 6 a profile for each end of the transmission path has been

plotted. These profiles are based on a radius of four-thirds the

actual earth's radius in order to allow for standard atmospheric

refraction. Unfortunately, there are no topographic maps available

for the middle portion of the path. It will be noted that the radio

horizon is located approximately 11 miles from the trans mitting

antenna at Cedar Rapids, while the distance from the receiving

antennas to their common radio horizon is only approximately threequarters of a mile. Assuming standard atmospheric refraction, the

receiving antennas were located approximately 7100 feet below the

radio horizon of the trans mitting horn.

EXPLANATION OF UNITS

Although the signal power recording equipn ent was calibrated in

terms of available power from the receiving antenna^', the data
-6- III

presented in this report are expressed in terms of the ratio (in

decibels) of the power received at the receiving antenna terminals to

that which would be received in free space.

The conversion of available power at the antenna terminals to

the received power relative to that available in free space is given by:

received power in db below free space - 10 log, p f-rMcG

n

t \. 4-pd , t r a where P is the power input to the transmitting antenna

d is the distance between transmitting and receiving

antennas expressed in the same units asK,

Gx is the free space gain of the transmitting antenna

relative to an isotropic antenna

G is the free space gain of the receiving antenna relative

to an isotropic antenna

P is the measured available power from the receiving antenna,

For a frequency of 418 Mc and a distance of 133.95 miles, this equation

reduces to:

received power in db below free space -

10 log

1() Pt - 10 log

10

P

a

+ 10 log

10

Gt + 10 log

1() Gr

- 131.54

As was previously mentioned, G. was 14.5 db while G was 21.5

db for the parabola and 10 db for the corner reflector, P. was

determined for each hour by averaging the three transmitter output

readings for that hour contained in the transmitter log. This procedure was considered advisable since there was sometimes considerable variation in transmitter output from hour to hour.
-7- III GENERAL APPEARANCE OF THE SIGNAL

Figs. 4 and 5 show representative samples of received power

recordings made in Esterline -Angus graphic ammeter charts. A chart

speed of 3 in. per hour was used for all recordings. That there was a marked difference between the daytime and nighttime signals recorded

during the summer months is clearly shown in Fig. 4. Although the

short-term fading range appears to be quite similar for the day and

night signals, there is a considerable increase in median signal

magnitude during the night. In general, the strong nighttime signal

was accompanied by a decrease in the short-term fading rate. This

was not always true of the early winter signal. During November and

December there was often no clear-cut rise in signal strength during

the night. On the other hand, a relatively high signal during the

daylight hours, such as appears in Fig. 5 was not at all uncommon.

These effects will be more clearly illustrated by the diurnal

variation analysis which is included later in this report. It will

be noticed that the fading recorded by the two antennas separated

normal to the path by approximately 17 wave-lengths appears to be

almost perfectly correlated, at least so far as can be discerned at

this chart speed.

DISTRIBUTION OF SIGNAL LEVEL WITH TIME

Because of the characteristically rapid and violent fading which

is evident in these samples, it would have been difficult, if not

impossible, to obtain an accurate quantitative description of the

signal by analysis of the charts alone. For that reason time

totalizing recorders were used and totalizer counter readings made

each hour by the automatic photographic equipment mentioned

previously. By taking the differences between successive hourly

readings for each of the 10 channel counters, a distribution of

instantaneous signal levels is obtained for each hour. These hourly

distributions form the basis for all received power data presented

in this report. The Esterline -Angus charts are, of course, indispensable for displaying the fading rate and general appearance of the

signal, and for detecting equipment failures which might not be

discovered by analysis of the totalizer data alone.
-8- III

The information obtained from the hourly distributions has been

summarized in two ways. The first consists of a distribution of instantaneous levels recorded during two 3-hour periods of the day (3 to

6 AM, Noon to 3 PM) for each transmission period. These were obtained by determining the percent of time each of ten signal levels

(corresponding to the 10 totalizer channel settings) was exceeded for

all hours within a given 3-hour period during an entire transmission

period.

In addition, a distribution of hourly median signal levels was made

for each 3 -hour period of the day for each recording period. Examples

of these two types of distribution (i.e. instantaneous and hourly median

signal level) are shown in Figs. 7 to 14 for the parabolic receiving

antenna and Figs. 15 to 22 for the corner reflector receiving antenna.

The hours of 3 AM to 6 AM and Noon to 3 PM were chosen, since, in

general, the over -all median signal level was at its maximum and

minimum, respectively, during these hours; and they may therefore

be considered as representing the extremes in propagation conditions.

In Figs. 23 and 24 distributions of instantaneous levels for the

entire period from May to December are plotted for the same two

periods of the day. From these curves and from the curves in

Figs. 7 to 22, it will be seen that the slope of the 3 AM to 6 AM

distribution is in general steeper than that of the Noon to 3 PM

distribution, indicating a wider range of variation in signal during

the early morning hours. An analysis of this type does not, of

course, distinguish between short-term and long-term variations.

A study of short-term fluctuations in signal level about the hourly

median level is being undertaken and will be the subject of a subsequent report. Preliminary work indicates, however, that the

short-term fading for 418 Mc is essentially Rayleigh distributed

regardless of time of day or season of the year over this transmission

path.

Distributions of all hourly medians recorded during each transmission period are shown for both the parabolic and corner reflector

antennas in Figs. 25 to 32. Fig. 33 shows the distributions of all

hourly medians recorded with the two antennas during all periods

from May to December.
-9- I DIURNAL VARIATION OF MEDIAN SIGNAL LEVELS

Figs. 34 to 37 show the variation of signal levels exceeded by

10 per cent, 50 per cent and 90 per cent of the hourly medians versus

time of day for each recording period. These curves were prepared

from the distributions of hourly medians by 3-hour periods which

were discussed previously.

It will be noted that the magnitude of the diurnal variation shows

a marked decrease during the early winter months, the characteristic

shape of the curves obtained during the summer being almost unrecognizable during November and December. The lack of a clear-cut

diurnal pattern during the early winter is strikingly illustrated in

the samples of chart recordings shown in Figs. 4 and 5. It will be

seen that on November 29 the signal during the day reached much

higher median values than at any time the following night. As

pointed out previously, to apply the word "typical" to this sample

may be somewhat misleading since examination of the data for

November and December reveals that a high signal such as that

recorded from 10 AM to Noon on the 29th might occur at any time

of the day or night, and indeed, often did not occur at all for a period of several days.

In addition to the variation in the median value of the hourly

medians with time of day, there is also a diurnal variation in the

variability or dispersion of the individual hourly levels. This

can be seen in Figs. 34 to 37 by noting the difference between the

levels exceeded by 10 per cent and 90 per cent of the hourly medians

at various hours of the day. To illustrate this effect more clearly

Fig. 38 shows a plot of this difference between 10 per cent and

90 per cent levels (sometimes referred to as interdecile range)

for each receiving antenna and recording period. It should be

noted that the periods of greatest variability coincide, in general,

with the periods of strongest median fields. This can also be

seen in the chart samples in Figs. 4 and 5. During the night and

early morning hours when the median level is relatively strong,

the signal is still subject to deep fades which often reach the noise

level of the receiver.
-10- III

In Figs. 39 and 40 the median level of all the hourly medians recorded during the hours of 3 AM to 6 AM and Noon to 3 PM is plotted

versus time of year. The points are joined by a dotted line. For purposes of comparison, a plot (shown by the solid line) was also made

using the median levels obtained from the distributions of instantaneous

levels in Figs. 7 to 22. These curves serve to illustrate the fact that

the month-to-month variation in the weak early afternoon signal is very

similar to the variation in the strong early morning signal. It will be

noticed, however, that along with the increase in median signal level

during the summer months, there is also an increase in the difference

between the early morning and early afternoon signals. This effect is,

of course, also evident in the diurnal variation curves in Figs. 34 to

37. Figs. 41 and 42 show curves representing the levels exceeded by

10 per cent, 50 per cent and 90 per cent of all hourly medians recorded

during each measurement period. Superimposed on these curves is a plot of the average earth's radius factor k for each monthZ/. The

values of k were determined by B. R. Bean of NBS from meteorological measurements made at Joliet, Illinois, and Omaha, Nebraska.

These curves indicate a fairly close correlation between median

signal level and k.

COMPARISON OF MEASURED SIGNAL LEVELS

WITH COMPUTED DIFFRACTION FIELD

It is interesting to compare the measured median signal levels

with the computed values of ground wave field intensity obtained by

assuming diffraction over a finitely -conducting spherical earth. Using

the method developed by Norton—' , the power received from the diffraction field is computed as 156.91 db below free space for the parabola,

and 160. 62 db below free space for the corner reflector. In these calculations, the actual heights of the transmitting and receiving antennas

above local terrain were used for h, and hy, respectively. Also, a value of 1.405 was used for k, or the effective earth's radius factor.

This k was obtained by averaging the monthly k values shown plotted

in Fig. 41. From the over-all median signal levels shown in Figs,

41 and 42, it will be seen that the measured power levels are from

82 to 114 db higher than the computed levels for the parabola and

92 to 124 db higher for the corner reflector. It is evident from this
-11- III

that the ground wave component constituted only a small part of the total

received field. The major portion was apparently received from the

troposphere as a result of scattering!./ or some other propagation mechanism,

COMMENTS ON RELATIVE RECEIVING ANTENNA GAINS

As stated previously, the measured free space power gain of the

parabola was 21. 5 db, and of the corner reflector, 10 db. However, if the received power data from the two antennas are expressed in terms

of decibels relative to some common reference level (e.g., the power

output of the transmitter), it is obvious that the expected 11. 5 db difference in power levels is by no means realized. The average ratio of

power received by the parabola to the power received by the corner

reflector for the entire period from May to December is 6.1 db. Furthermore, there is possibly a seasonal variation in this effective relative

gain. Fig. 43 shows a plot of the average difference in power levels

received by the two antennas for each recording period. These differences were obtained by averaging the ratios of hourly median power

levels for all hours during which both recording systems were in operation.

The fact that the free space gain of the parabola relative to the

corner reflector was not realized may plausibly be explained on the

basis of tropospheric scattering. If we assume that the major portion

of the received field was contributed by scattering from atmospheric

discontinuities, it follows that this scattered signal could be expected

to arrive at the receiving antenna from a number of directions, depending upon the distribution of the scattering elements in space. Since the

major lobe of the parabola pattern is sharper than that of the corner

reflector, the effective gain of the parabola suffers more from the

scattering process than does the gain of the less directional corner

reflector. Assuming the correctness of the above explanation, the

seasonal variation of the relative effective gain of the two antennas

implies a very large variation in the height distribution of the scattering

elements with time of year.

ACKNOWLEDGEMENTS

The data presented in this report were processed and analyzed by

the Data Analysis Group of the Cheyenne Mountain Field Station in

Colorado Springs, Colorado. The authors wish to thank J. W. Herbstreit

and K. A. Norton for their very valuable advice and assistance in the

preparation of the report.
-12- III TABLE I RECORDING SCHEDULE

418 Mc Field Strength Measurements Between

Cedar Rapids, Iowa, and Quincy, Illinois, during 1951

Transmitting ,.. , £ TT Recording Period Number of Hours Period*

Parabola Corner Parabola Corner

Reflector Reflector

Apr 30-May 12 Apr 30-May 11 May 2-May 11 May 22-May 27 May 22-May 27 May 22-May 27

Jun 11-Jun 14 Jun 11-Jun 14 Jun 11-Jun 12

Jun 21-Jun 30 Jun 21-Jun 30 Jun 21-Jun 30

Jul 24 - Aug 4 Jul 24 -Aug 4 Jul 24 -Aug 4

Aug 13 -Aug 25 Aug 13 -Aug 25 Aug 13 -Aug 25

Sep 10-Sep 23 Sep 10- Sep 23 Sep 11-Sep 23

Oct 1-Oct 13 Oct 1-Oct 13 Oct 1-Oct 13

Oct 28 -Nov 10 Oct 28 -Nov 10 Oct 28 -Nov 10

Nov 26-Dec 15 Nov 26-Dec 3 Nov 26-Dec 10

Dec 10-Dec 15

329 285

252 228

231 229

257 230

225 202

249 238

279 266

249 297

*The transmitter was also operated during March 20-24 (0800-1700 only)

and April 2-13 (0500-2100 only). However, due largely to initial recording

equipment failures and adjustments, very few reliable data were obtained

during these periods.
-13- HI

REFERENCES

l/ "Very High-Frequency Techniques," Radio Research Laboratory

Harvard University, Vol. I, pp. 445-472, McGraw-Hill Book Co.

New York, 1947.

2/ I. H. Gerks, "Propagation at 412 Mc From a High-Power Transmitter, " Proc. IRE, Vol. 39, No. 11, pp. 1374-1382, November,

1951.

3/ R. P. Decker, "Notes on the Analysis of Radio Propagation Data,"

Proc. IRE, Vol. 39, No. 11, pp. 1382-1388, November, 1951.

4/ K. A. Norton, "Transmission Loss in Radio Propagation," Proc.

IRE, Vol. 41, No. 1, pp. 146-152, January, 1953.

5/ B. R. Bean, "The Geographical and Height Distribution of the

Gradient of Refractive Index, " Proc. IRE, Vol. 41, No. 4,

pp. 549-550, April, 1953.

6/ K. A. Norton, "Calculation of Ground Wave Field Intensity Over

a Finitely Conducting Spherical Earth," Proc. IRE, Vol. 29,

No. 12, pp. 623-639, December, 1941.

7/ J. W. Herbstreit, K. A. Norton, P. L. Rice, and G. E. Schafer,

"Radio Wave Scattering in Tropospheric Propagation, " 1953

Convention Record of the Institute of Radio Engineers.

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Supplement IV

PRELIMINARY REPORT ON PROPAGATION MEASUREMENTS

FROM 92 - 1046 Mc AT CHEYENNE MOUNTAIN, COLORADO

By

G. R. Chambers, J. W. Herbstreit, and K. A. Norton

Supplement IV

PRELIMINARY REPORT ON PROPAGATION MEASUREMENTS

FROM 92-1046 Mc AT CHEYENNE MOUNTAIN, COLORADO

By

G. R. Chambers, J. W. Herbstreit, and K. A. Norton

National Bureau of Standards

Boulder, Colorado

SUMMARY

A description is given of the facilities provided by the National

Bureau of Standards on Cheyenne Mountain in Colorado and in its vicinity

which are used for the measurement of the transmission loss on radio

transmission circuits operated in the frequency range from 92 to 1046 Mc

Some preliminary results of these measurements are presented together

with tentative theoretical explanations.

INTRODUCTION

The National Bureau of Standards Cheyenne Mountain Field Station

at Colorado Springs, Colorado, has been established to supply radio

propagation information which closely approximates transmissions from

an aircraft to distances far beyond the horizon. Information is being

obtained in such a way that results advance our over-all knowledge of the

factors influencing radio propagation in other parts of the world and in

other radio systems not immediately under study.

At the close of World War II, considerable effort was being made

in the air navigation field to develop a unified system of air communications and navigation in the frequency range 960 to 1600 Mc. This work

is now centralized in the Air Navigation and Development Board which is

administratively under the Civil Aeronautics Administration.

Very little quantitative information exists relative to the effects

of irregular terrain for transmission paths within the radio line -of - sight and still less at distances beyond the usual service range of

navigational systems where signals would be a source of interference

to nearby facilities operating on the same or adjacent frequency channels.
-2- IV

In order to expedite the program of research in tropospheric

propagation which is designed to determine propagation factors required for effective allocation and use of VHF and UHF frequencybands, particularly from an air navigation standpoint, the Air

Navigation and Development Board has been sponsoring a rapid

expansion of the tropospheric propagation research facilities of the

National Bureau of Standards at Cheyenne Mountain, including the

development, installation and operation of a system for studying

propagation factors at approximately 1000 Mc . This system

utilizes a transmitter which gives the highest continuous power

output of any 1000 Mc transmitter ever developed in this country

and specially developed very narrow bandwidth receivers capable

of measuring received signal powers much lower than usual receivers

for this frequency range. This high level of system performance is

necessary to obtain radio propagation data at great distances.

The United States Army Signal Corps, because of their vital

need for radio propagation information in the VHF and UHF frequency bands, have also been sponsoring the acceleration and expansion

of research facilities at Cheyenne Mountain. Military personnel of

the Signal Corps are participating in the work and are receiving

training in the methods of making VHF and UHF radio propagation

measurements

.

The Cheyenne Mountain measurements at frequencies between 92

and 210. 4 Mc, which are not in the proposed air -navigation band,

provide a means of studying climatic effects on tropospheric propagation in Colorado and vicinity, for comparison with many other

regions of the country where measurements have been made at these

presently -used air -navigation communications, FM and television

frequencies. A high system performance in the range 92-210.4 Mc

has been achieved through the use of stabilized transmitters, relatively high antenna gains and very narrow -band receivers.

A picture of the over -all VHF-UHF tropospheric field strength

program of the National Bureau of Standards may be obtained from

Fig. 1. This shows the numerous propagation paths over which

VHF and UHF field strengths are being measured.
-3- IV

SYSTEM SELECTION

When the National Bureau of Standards was requested to accelerate

its tropospheric propagation research program, a complete study of

existing facilities and equipment was initiated. System design, selection

of a suitable site, and establishment of the Cheyenne Mountain Field

Station followed. Some of the most important factors concerned with

the selection of the Cheyenne Mountain location and system design

employed are as follows:

A. Site

It was proposed to locate a site and install a system for long

term continuous radio-propagation measurements over air-to-ground

paths near and below the horizon. Use of aircraft for one terminal

was considered prohibitively expensive and impractical for long-term

continuous recording; moreover, their use would not permit the

obtaining of data under extremes of weather conditions. For these

reasons, ground installations which would simulate an air-to-ground

path were sought. Accordingly, after an extensive survey, a site

on Cheyenne Mountain near Colorado Springs, Colorado, was

chosen. This mountain, 9200 feet above sea level, rises abruptly

out of the eastern Colorado plains and provides an excellent

"airborne terminal" which is over 3000 feet above the adjacent

plains. The existing all-weather road and high-voltage power

facilities to the mountain summit were also important factors to

be considered. Receiving sites and paths with almost any desired

characteristics were available at the distances of interest, including

smooth, moderately rough and rough terrain, as well as some of the

most rugged terrain in North America. In addition, highway systems

extending eastward into Colorado, Kansas, and Arkansas, offered a number of approximately radial all-weather highways, suitable for

mobile recordings and convenient to fixed recording sites. The

location of the Army's Camp Carson and the Air Force installation

at Peterson Field in Colorado Springs were considered as making

future aircraft investigations and measurements practical.
-4- IV

B. Equipment

The preliminary objectives of the Cheyenne Mountain experiments are to measure radio field strength produced near and far

beyond the radio horizon with a carefully monitored transmission

and recording system which is divided into four equipment classes:

(a) Transmitting, (b) Receiving, (c) Recording, and (d) Calibrating. These are described generally as follows:

(a) Transmitting - The operating frequencies are 92, 100,

192.8, 210.4 and 1046. 4748 Mc. The available continuous

power output is 3 kw at 9 2 and 100 Mc and 4 kw at 19 2. 8,

210. 4 and 1046. 4748 Mc. During propagation measurements

the transmitted energy at each frequency is confined to a band

less than 50 cycles wide. This in combination with narrowband receivers insures the maximum "Margin of Detectability"

for a given receiver and provides data at maximum distances.

As pointed out in the description of system selection, the

detectable signal in a given system is essentially a function

of average power output, bandwidths, and thresholddetection factors. Reducing the receiver bandwidths or

detection factors by l/2 is effectively the same as increasing

the average transmitter power output by a factor of two.

As an example, if received signal power at some given distance

were recorded on a regular commercial FM operation at 100 Mc

where the receiver bandwidth is necessarily 150 kc and the

effective radiated power of the transmitter 10 kw, the

equivalent power for field- strength recording purposes could

effectively be increased to 3000 kw by reducing the transmitter

drift and incidental modulation to much less than 500 cycles and

the effective noise bandwidth of the receiver to 500 cycles.

The frequency stability of each transmitter is capable of

being maintained within ± 200 cycles of the assigned carrier

frequency. This insures that the transmitted signal power is

measured within the ± l/2 db flat-top response of the receivers.

The frequency-monitoring equipment for checking the transmitter frequencies utilizes a Hewlett-Packard frequency counter

in conjunction with a General Radio Primary Frequency Standard.
-5- IV

All transmitting antennas have moderate power gains.

Since the purpose of these studies was to observe propagation

over air-to-ground paths under conditions similar to those

of typical air -navigation systems, omni-directional transmitting and receiving antennas would have been most desirable.

However, a mountain is not a typical airborne terminal because

of other mountains to the rear and at either side. These

mountains are excited by the RF fields of the transmitting

antennas and reradiation occurs. In order to minimize this

reradiation from the adjacent terrain and to approach the

conditions expected for a typical air -navigation system some

moderate directivity is desirable. A careful survey of the

trans mitting sites resulted in a choice of an over -all solid

angle of radiation corresponding to ranges of 60 degrees in

azimuth and 15 degrees in elevation. Fig. 8 is a photograph

of the transmitting antennas at the summit site. The VHF

antennas at the base site are identical.

Modulation systems were provided in all transmitters

to assist in carrier identification and to provide facilities

for modulation studies.

(b) Receiving - The receiving equipment was designed to

measure accurately the transmission loss on each of the

five frequencies involved. It has several features to improve

its stability characteristics and make it adaptable to a narrowband recording system. General recording characteristics

of all receivers are approximately the same, but the design

and construction features of the VHF and UHF equipment

differ widely because of frequency.

Both the VHF and UHF receiving equipment are frequency

stabilized by multiplying the 100 kc output of a primary

frequency standard to the appropriate oscillator injectionvoltage frequencies. In locations where recordings are made

on all frequencies, one common primary frequency standard

is used for five receivers. The receiver circuits for feeding

the data- recording equipment are essentially the same for all

receivers. The equipment installation and facilities in the

mobile recording units are the same as those at the fixed

recording sites.
-6- IV

(c) Recording - Received power is recorded at all locations

on clock-driven charts, and at the more distant recording sites,

where fading makes analysis of chart data impractical, on

time -totalizing recorders. These time -totalizing recorders

are equivalent to a battery of clocks, each one recording the

total time that a certain pre -set signal level is exceeded.

Each clock is activated by the receiver when the appropriate

pre-set signal level is crossed. Readings of the clocks are

periodically recorded by an automatic camera system.

(d) Calibrating - The calibration of receivers and measurement

of the available signal power from the system is based on a comparison between that available from the receiving antenna

transmission line and that available from the output of a calibrated signal generator with the same impedance (50 ohms).

All signal generators used at various locations are related

to a standard and to transmitter power indication devices.

SYSTEM OPERATION

Propagation data at Cheyenne Mountain are collected on a continuous

twenty -four -hour-per -day basis. This schedule is limited only by loss

of time due to regular maintenance or equipment failures. Less than

60 per cent of this goal has been realized to date because of slow equipment deliveries, new equipment faults, and problems of perfecting

system operation, and the training of operating personnel.

As of March, 1952, however, all transmitters were operating on

a continuous schedule. The fixed sites at distances of 49. 3, 70. 2,

96. 6, and 226. 5 miles are visited and calibrated at least once each

day. The mobile sites have been operated for relatively limited

periods at several locations. It is not planned to make continuous

measurements at long distances but to take periodic samples of data

during typical seasonal climatological conditions. Some special recordings planned for the near future include samples of data at

distances equivalent to the fixed sites over several dissimilar paths

and recordings at many additional locations over line -of -sight paths.
-7- IV

SYSTEM RESULTS

Field-strength recordings have been made on all frequencies

at various distances frcm the transmitters. Recordable signals

have been received on 92, 100, 192. 8 and 1046 Mc as far as Anthony,

Kansas, a distance of 393.5 miles, and on 100 Mc at Fayetteville,

Arkansas, a distance of 616.3 miles. Recordings are now being made

at each of the four fixed receiving sites shown in Fig. 2 on a regular

basis in order to obtain measurements over an extended period of

time for the purpose of studying the effects of diurnal and seasonal

factors on the transmission loss (received field strength) as a function of distance, frequency, and antenna heights.
-8- IV

REFERENCES

1/ K. A. Norton and A. C. Omberg, "Maximum Range of Radar

Set," Proc. IRE, 35, January 1947, pp. 4-28.

2/ J. L. Lawson and G. E. Uhlenbeck, "Threshold Signals,"

Vol. 24, MIT Radiation Laboratory Series, McGraw Hill

Publishing Company.

3/ K. A. Norton, "Transmission Loss in Radio Propagation,"

report in preparation at the National Bureau of Standards.

4/ Federal Communications Commission Engineering Department.

Report on Very High Frequency Field Strength Measurements

1943-1944; Hearing in the Matter of the Allocation of Radio

Frequencies Between 10 kc and 30,000 Mc, September 28,

1944, Docket 6651. See also E. W. Allen, "Very-HighFrequency and Ultra-High-Frequency Signal Ranges as Limited

by Noise and Co-Channel Interference," Proc. IRE, 35,

February 1947, pp. 128-152.

5/ J. Feinstein, "The Interpretation of Radar Echoes From

Meteor Trails," Journal of Geophysical Research, 56, March 1951.

6/ A. C. B. Lovell, J. P. M. Prentice, J. G. Porter, R. W. B.

Pearse, N. Herlofson, "Meteors, Comets and Meteoric

Ionization," Physical Society, London, Reports on Progress

in Physics, Vol. XI, pp. 389-454, 1948.

7/ Federal Communications Commission Ad Hoc Committee For

the Evaluation of the Propagation Factors Concerning

Television and Frequency Modulation Broadcasting; Services

in the Frequency Range Between 50 and 250 Mc, Vol. I, May 31, 1949.

8^/ H. Fine and F. V. Higgins , "Long Distance Tropospheric

Propagation in the Ultra High Frequency Band," Federal

Communications Commission Report TRR 2.4.10, October 13,

1950.
-9- IV

9/ J. Feinstein, " Tropospheric Propagation Beyond the Horizon,"

Journal of Applied Physics, 22, October 1951, pp. 1292-1293.

10/ B. Ratner, "Upper Air Average Values of Temperature,

Pressure, and Relative Humidity Over the United States and

Alaska," U. S. Dept. of Commerce, Weather Bureau, Climate

and Crop Weather Division, "Washington, D. C. , May 1945.

11/ K. A. Norton, "Physical Reality of Space and Surface Waves

in the Radiation Field of Radio Antennas," Proc. IRE, 25,

pp. 1192-1202, September 1937.

12/ K. A. Norton, "Calculation of Ground Wave Field Intensity Over a Finitely Conducting Spherical Earth," Proc. IRE,

29, pp. 623-639, December 1941.

13/ H. J. Riblet and C. B. Barker, "A General Divergence Formula,"

Journal of Applied Physics, 19, pp. 63-70, January 1948.

14/ B. R. Bean, "Geographical and Height Distribution of the

Gradient of Refractive Index," National Bureau of Standards

report in preparation.

15 / K. A. Norton, "Propagation in the FM Broadcast Band ,

Advances in Electronics , Vol. I, pp. 406-408, Academic Press,

Inc. , New York, 1948.

16/ K. A. Norton, M. Schulkin, and R. S. Kirby, "Ground-Wave

Propagation Over Irregular Terrain at Frequencies Above 50

Mc," Reference C to the Report of the Ad Hoc Committee

of the Federal Communications Commission for the Evaluation

of the Propagation Factors Concerning the Television and

Frequency Modulation Broadcasting Services in the Frequency

Range Between 50 and 250 Mc , June 8, 1949.

17 / J. C. Schelleng, C. R. Burrows and E. B. Ferrell, "UltraShort-Wave Propagation," Proc. IRE, 21, March 1933, pp. 427-

463.


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Supplement V

TROPOSPHERIC PROPAGATION MEASUREMENTS WITHIN

THE RADIO HORIZON OVER CHEYENNE MOUNTAIN PATHS

By

A. P. Barsis
I*.
Supplement V

TROPOSPHERIC PROPAGATION MEASUREMENTS

WITHIN THE RADIO HORIZON OVER

CHEYENNE MOUNTAIN PATHS

By

Albrecht P. Barsis

National Bureau of Standards

Boulder, Colorado

SUMMARY

The tropospheric propagation measurements being conducted by

the Cheyenne Mountain Field Station of the Central Radio Propagation

Laboratory include several optical paths, over which continuous

recordings of field intensity are made on 100 Mc, 192. 8 Mc and 1046

Mc, Measurements at two fixed receiving sites located on a path

running 105° east of true north from the transmitter site on Cheyenne

Mountain are analyzed and the results of 12 months of continuous

recordings are presented in the form of charts showing diurnal and

month-to-month variations of hourly median values of received field.

In order to determine diurnal variations, values of hourly medians

for each month are grouped into eight three -hour periods, and monthly

distributions of hourly medians are determined for each of these periods,

as well as overall monthly distributions combining all diurnal periods

for each frequency at each site. The difference (in decibels) of hourly

medians exceeding 10% and 90% of the total numbers of hours for each

recording period may be termed the interdecile range of the received

hourly median, and its dependence on the overall median level, time of

day, and its change from month to month is investigated for each site

and each frequency.

The 1046 Mc signal shows occasional fades amounting to 5 to 15 db

and lasting from 20 minutes to several hours. A comparison is made

of the behavior of the signal on the lower frequencies during the times

these fades occur. Examination of the frequency of occurrence of these

"prolonged space-wave fadeouts" shows that they are substantially more

prevalent in summer than in winter, and that they occur principally at

night.
-2- V

1. INTRODUCTION ,

The Cheyenne Mountain Field Station of the Central Radio

Propagation Laboratory, National Bureau of Standards, conducts

continuous propagation studies on frequencies in the range from 9 2

to 1046 Mc. Fig. 1 is a pictorial representation of all facilities

used in these studies. The transmitters for continuous measurement

are located on Cheyenne Mountain near Colorado Springs, Colorado.

The transmitter power output is 2 kw for 92 and 210.4 Mc transmissions

from a location at approximately 7500 ft elevation. The antennas are

of the corner -reflector type. Similar transmitters and antennas for

100 and 19 2. 8 Mc are located at approximately 8800 ft elevation. In

addition thereto, a 4 kw UHF transmitter using a klystron final stage

is located at the 8800 ft elevation and transmits a 1046 Mc signal

employing a slot -fed horn type antenna.

All transmissions are continuous wave, and are horizontally

polarized.

The abrupt slope of Cheyenne Mountain simulates air-to-ground

communications, as the transmitters are from 2000 to 3000 ft above .. the relatively level prairie immediately east of Cheyenne Mountain.

Fixed receiving sites are located along a radial extending approximately

105 degrees east of true north from Cheyenne Mountain. The transmissions from the Cheyenne Mountain site on 100, 192. 8, and 1046 Mc

to the receiving sites at Kendrick (50-mile path) and Karval (70-mile

path) are within the radio horizon, and have, been carried out continuously

since January 1952 except for outages due to equipment failure. Results

obtained thereby are within the scope of this paper. Suitable VHF and

UHF receivers associated with dipole antennas, Esterline -Angus graphic

recorders and calibration standards are employed at these receiving

sites.

In order to point out a definite distinction in the appearance of

graphical recordings of optical and non-optical signals, Fig. 2 is

added to show the difference in the 100 Mc picture as received at

Kendrick and Karval from Cheyenne Mountain (optical) and the Camp

Carson site at the base of Cheyenne Mountain (non-optical). The

transmitters were operated alternate hours, and the distinction between

the signals is very clear, showing no appreciable short-term variations*

*Within the scope of this paper "short-term" variations are defined

as changes in signal intensity within each hour.
-3- V

in the received signal from Cheyenne Mountain summit, whereas

the signal from the Camp Carson site shows a substantial amount

of fading. The analysis of data collected over the period of one year

shows that with the equipment available, no short-term variations of

any importance are evident for any of the paths within the radio

horizon, except for prolonged space-wave fadeouts occurring on

1046 Mc which will be discussed later on.

2. METHODS OF ANALYSIS

Tropospheric fields within the frequency range covered in this

report exhibit short-term variations which may be described by

fading range and fading rate as well as long-term variations which

may conveniently be described by diurnal and month-to-month trends

in the variations of hourly median values. It has been pointed out

before that with the equipment available no appreciable short term

variations were determined. The hourly median, therefore, was

used as a basis of studying the variations in the received signal

occurring from day to day and month to month. The following procedures are followed in the analysis.

From the Esterlin^-Angus recordings (see Fig. 2 for an

example) the median value of the field for each individual hour is

determined by inspection. For each site and each frequency these

hourly median values are tabulated using suitable units. Allowance

is made for line losses at the transmitting and receiving end, antenna

gains as measured or assumed, and comparison of signal generators

used in calibration of the equipment to common standards. This

permits all median values to be expressed in attenuation relative to

the free space field. The value "A" which signifies attenuation relative

to the free space fields in decibels is taken as positive if the measured

field is less than the free space fields.

For each month the hourly median values for each path and each

frequency are divided into eight groups in accordance with successive

three-hour periods of the day. Thereby characteristic distributions

of hourly median values are obtained for eight periods within the 24

hour day, and used as a basis for diurnal variation analysis. The

distributions of all hourly medians over the period of one month serves

as a basis for determining month-to-month variations.
-4- V

From the tabulations of hourly median values, distributions

are computed, and plotted on probability graph paper. Samples of

such distributions are shown in Fig. 3, comparing for the month

of September (1952) a typical nighttime period (midnight to 3 AM)

to a typical daytime period (noon to 3 PM). It is shown that a diurnal

variation of the hourly median level on all frequencies is apparent,

and comparison of the distribution curves for the day and nighttime

period shows a difference in slope as well as a difference in median

level.

Similar distributions are drawn for all other three -hour periods

as well as for the aggregate hours of each month without regard

to the time of day. Each curve furnishes a monthly median value

which denotes the signal value exceeded by 5G% of all hourly medians

comprising the distribution, and a difference (in decibels) of the

values exceeded by 90% and by 10% of all hourly medians which may

be termed the interdecile range. This procedure was followed in

preference to determining a quantity like the standard deviation as

the distributions obtained from the data evaluation are only approximately

normal.

3. RESULTS OF ANALYSIS

Fig. 4 shows the diurnal variations of monthly medians taken

from the distribution curves for the eight three -hour periods for

three frequencies at both receiving sites within the radio horizon,

and compares results for a typical winter and summer month. It is significant that the diurnal variations are more substantial in

summer on the VHF frequencies, but the 1046 Mc data show not only

substantially less diurnal changes than the lower frequencies but also

seem to reverse the general trend of higher summertime signals.

This may be due to the choice of the months for which data are presented

here. The month-to-month trends will be discussed later.

Observed interdecile ranges taken from the aggregate distribution

curves for each month are shown in Fig. 5. Broken lines do not denote

extrapolations, but indicate that one or several months of data are

missing between others for which results are available. For March,

October, November, and December of 1952, no 1046 Mc data are

available but values for January 1953 were determined and serve

as endpoints of the broken lines. Fig. 6 shows (in solid lines)
-5-

the month-to-month trend of monthly medians for four three

hour periods which contain the hours 0200, 0800, 1400, and

2000 and are designated by these numerals. The use of these

particular periods is dictated by the availability of meteorological

data for these hours.

Although it has been planned to observe pertinent meteorological

data over the Cheyenne Mountain path simultaneously with field

strength measurements in order to correlate changes in field

with changes in atmospheric conditions, very little data of this

kind are available at the present time, However, observed

monthly distributions of the refractive index gradient determined

at Lowry Air Force Base near Denver, Colorado, were available

for the year 1951. Lowry Base is about 70 miles north of the

Cheyenne Mountain paths discussed in this paper, and it was felt

that in spite of the geographical separation and of the time difference

involved (1951 meteorological data and 1952/53 field strength

measurements) a study should be made to determine correlation,,

if any.

Expected values of field strength were computed for 100, 192„ 8,

and 1046 Mc using methods developed by Norton!/ and further

elaborated for the Cheyenne Mountain path by the author. The

resultant values of field computed for the median refractive index

gradient applicable to each month at each of the four daily periods

for which the JLowry data were available are shown in Fig. 6 by

the broken lines. In comparing the measured month-to-month field

strength data with the computed values based on the Lowry Field

meteorological data, it should be noted that meteorological data

were available for April, June, August, October, December, and

January only. Disregarding the absolute differences between

measured and computed monthly median values, correlation

coefficients between them may be determined for each frequency

at each site using only those months for which meteorological data

were available This was done with the following results£/;
Frequency Kendrick Karval

Correlation 90%Fidu- Correlation 90%FiduCoefficient cial Limits Coefficient cial Limits

IQOMc 0.034 -0. 314 to +0. 374 0.853 +0. 720 to* 0. 926

192. 8 Mc 0.697 +0. 449 to +0. 845 0.704 +0. 460 to -1-0. 849

1046 Mc 0.045 -0. 349 to +0. 463 0.284 -0. 159 to +0. 638

Although it may not be proper at all to draw conclusions from

a correlation of measured data varying over such a small range

with computations based on conditions of the previous year, the

high degree of correlation obtained on 192. 8 Mc at both sites

and on 100 Mc at Karval may be significant. The absence of

correlation on 1046 Mc at both sites is probably an indication that

characteristics of the atmosphere other than its linear gradient

are responsible for these changes in hourly median levels.

Signal variations observed at Kendrick on 100 Mc are often

small enough to be obscured by equipment instabilities and

calibration changes, and the absence of correlation in this

particular case may possibly be explained thereby.

Naturally a well coordinated meteorological program should

permit similar studies to be made with a much higher degree of

reliability.

4. PROLONGED SPACE -WAVE FADEOUTS ON 1046 Mc

While it may be stated that the signals within the radio horizon

may be described adequately by their hourly median values (in the

absence of any significant short-term variations), experimental

evidence is available which shows comparatively large fades of the

1046 Mc signal occurring at Kendrick as well as at Karval. These

fades last from several minutes to well over two hours and range

in magnitudes from 5 to more than 20 decibels below the average

signal before and after the fadeout. Fig. 7 shows samples of

recording charts for September 4, 1952, which not only show a characteristic fadeout occurring at both sites on 1046 Mc, but
-7- V

also the absence of any similar effect on the other frequencies.

These fades, however, do not always occur simultaneously at

both sites. A study of the frequency of occurrence shows that

the fadeouts are considerably more frequent in summer than in

winter (Fig. 8), and that more than 90% occur between the times

of two hours before sunset, and two hours after sunrise (Fig. 9).

Additional studies of this problem are in progress, and will be

reported separately.

5. CONCLUSIONS AND RECOMMENDATIONS

Although the data presented show certain diurnal and month-tomonth variations, it appears to be highly desirable to obtain .idditional

information in order to ascertain the character of diurnal variations

during successive years. What has been termed "month-to-month

variations" could probably more adequately be described as variations

due to changing air masses, and only a closely coordinated meteorological

program can provide the ultimate answer: namely, a method of predicting

the fields on the basis of weather information. This also points to the

necessity of having several years of measured data available in conjunction

with the meteorological information. Diurnal and month-to-month

variations of hourly median values and the interdecile range of the

received signals within the radio horizon are operationally not as significant as for larger distances. Overall variations are considerably less than

10 decibels, and the prolonged space-wave fadeouts observed in the

1000 Mc range do not occur on the lower frequencies.

Several possible explanations have been offered which should

account for the occurrence of prolonged space-wave fadeouts, but

they all depend on further meteorological studies which will be carried

out during the summer of 1953 by the Central Radio Propagation Laboratory

as well as by other agencies.
-8-

REFERENCES

\J K. A. Norton, "Transmission Loss of Space Waves,

Propagated Over Irregular Terrain," Trans. IRE Professional

Group on Antennas and Propagation, No. PGAP-3, August, 1952.

2/ George W. Snedecor, "Statistical Methods," The Iowa State

College Press, Ames, Iowa, p. 150, 1948.
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Supplement VI

PROPAGATION OF RADIO WAVES

OVER LAND AT 1046 Mc

By

A. P. Barsis, B. R. Bean, J. W. Herbstreit, K. O. Hornberg,

and K. A. Norton

Supplement VI

PROPAGATION OF RADIO WA VES OVER LAND AT 1046 Mc

(Report for the Air Navigation Development Board)

By

A . P. Barsis , B. R. Bean, J. W. Herbstreit, K. O. Hornberg, K. A. Norton

National Bureau of Standards, Boulder, Colorado

INTRODUCTION AND SCOPE

Background

The Air Navigation Development Board in discharge of its duties as expressed in its Charter, initiated an investigation of radio wave

propagation in the 960-1600 Mc frequency band and placed the supervision of such a project under the Central Radio Propagation Laboratory

of the National Bureau of Standards.

The most important aspect of this study of radio wave propagation

is its bearing on the problem of assessing the reliability of air-to-ground

communications or radio navigation. Most of the following report deals

either directly or indirectly with this important problem.

Furthermore, inasmuch as the frequencies to be used within this

band must necessarily be recurrent to conserve the frequency spectrum,

the distance between co-channel facilities must be determined by the

interference within the service area of one station by transmissions

from another station or stations on the same frequency. In view of the

fact that evidence existed wherein transmissions at these frequencies

did not behave strictly as line-of-sight but that interference fields

existed well beyond line-of-sight, the National Bureau of Standards

originated the Cheyenne Mountain Field Station in Colorado Springs,

Colorado to investigate the propagation phenomena associated with

simulated air-to-ground transmissions, not only at distances within

line-of-sight where the question of service reliability is involved,

but also at points far beyond the radio horizon which may be involved

in the solution of mutual interference problems.

The experiments conducted along these lines were to be the first

phase of a long range program and were to be of a continuous nature

for a period of at least one year to determine adequately the nature of

the diurnal and seasonal variations of the radio field intensity.
-2- VI

In view of the realization that climatological conditions varygreatly throughout this country and the world and that the propagation

data assembled over the Cheyenne Mountain path would have to be

very carefully interpreted for extension to other areas, a radio

meteorological program was considered advisable in conjunction with

the Cheyenne Mountain experiments. The meteorological phase of the

program is designed to test the accuracy of recent developments in

radio meteorology analysis and to improve these methods on a climatological basis .

The technical supervision of the ANDB project within CRPL was

assigned to Mr. J. H. Chisholm from the beginning of the project

until November, 1951, when he resigned from the National Bureau

of Standards. Mr. G. R. Chambers was then assigned the supervision

of the ANDB project in addition to the 100-1000 Mc program operating

concurrently. Upon the resignation of Mr. Chambers in June, 1952,

Mr. K. O. Hornberg was assigned the duties held by his predecessor

and is currently in charge.

Scope of this Report

The purpose of this report is to present the experimental data on

1046 Mc obtained at the Cheyenne Mountain Field Station for the period

February 1, 1952 through January 31, 1953. Continuous recordings were

not made prior to this period and consequently any previous data are not

considered. In addition, this report includes the analysis of diurnal and

seasonal variations in hourly median signal levels, the analysis of

variations in instantaneous signal levels and the analysis of prolonged

space- wave fadeouts within the radio horizon for the period investigated, an analysis of the effects of irregular terrain at points within the

radio horizon, an analysis of the scattered signals at points far beyond

the radio horizon, including estimates of the expected effective gains

of large antenna arrays, the required spacing for diversity arrays and

the effective intelligence bearing bandwidths of the propagation paths.

Finally, as a result of a recent investigation of propagation over high

mountain ridges, an analysis is presented of the "obstacle gains' 1 expected at 1000 Mc in mountainous terrain.
-3= VI

DESCRIPTION OF FACILITIES

Transmission Paths

The 1046 Mc Cheyenne Mountain project is shown pictorially in

Fig. 1 with the transmitting site located on Cheyenne Mountain at

an elevation of 8800 feet above mean sea level and several fixed and

semi-mobile recording sites in eastern Colorado, Kansas, and Arkansas,

Figs. 2a, b, and c show the terrain profiles along the transmission

paths from the transmitter to each of the three fixed recording sites

located at Kendrick, Colorado {49.3 mi), Karval, Colorado (70.2 mi),

and Haswell;, Colorado (96. 6 mi). Fig. 2d shows the terrain profile

out to Garden City and Anthony, Kansas. The definition is given on

Fig. 2d of an angle, 0, which we have used throughout this report to

characterize a particular transmission path. This is simply the angle

between the radio horizon lines in the great circle plane. Transmission

paths within the line -of -sight will be characterized by negative values of

while positive values of correspond to non-optical paths. The usefulness of the parameter in tropospheric propagation lies in the fact

that it can be used (largely independently of the antenna height h provided

h is sufficiently great) to describe fading characteristics and transmission

loss relative to free space, while at the same time it can be used to

extrapolate the results of propagation measurements to a terminal at

an arbitrarily high elevation. Fig. 2e demonstrates how the same angle

can characterize various transmitting heights h^., ht?

, and h^,, while

Figs, lie and 12e show how the experimental data can be described in

terms of the parameter 0, being largely independent of the heights of

the terminals. This principle is of great importance in engineering airto-ground communication and navigation systems. The method of calculating for transmission paths over irregular terrain is discussed

in Appendix I and the value of for our 1046 Mc transmission paths

are given in Table I, based on an assumed effective radius of the earth

equal to four -thirds of its actual value to allow for standard air refraction.

The terrain profiles of Figs. 2a, b, c, and d are based on standard

atmospheric refraction and show that the Kendrick and Karval sites are

within line-of-sight, while the Haswell site is just beyond line-of-sight

and in the diffraction zone and the Garden City location is well beyond

line-of-sight and considered out of the diffraction zone and in the scattering region for reception. An examination of these terrain profiles in the
-4- VI

light of Rayleigh's criterion of roughness indicates that the actual

terrain is quite rough compared to the wavelength of transmissions,

although the transmission path appears visually to be as level as one is likely to find in siting VHF ground terminals. The practical

significance of this roughness is discussed in detail in a later

section of this report.

The soil condition along the transmission path in eastern

Colorado and western Kansas is quite arid, being utilized for

cattle grazing and dry farming. In central Kansas, in the vicinity

of Garden City, the land becomes less arid and wheat farming

predominates.

The prevailing wind conditions are usually from the couth

with turbulence at all levels extending from the mountain region to

the Colorado-Kansas border. Wind velocities in the Colorado Springs

and Haswell, Colorado areas are generally in excess of 15 mi per

hr with gusts exceeding 50 mi per hr quite frequently. The area is

one of conflict between the settled conditions of mountain induced

subsidence and solar induced turbulence. The area is under intensive

study by meteorologists as the birthplace of tornadoes and the Geophysical Research Directorate is planning an intensive turbulence

study to be conducted in this area next summer. Although the site

for these propagation measurements was chosen primarily for a high mountain site, subsequent investigation has revealed the area

to be an ideal location for radio-meteorological studies due to the

heterogeneous meteorology available.

Transmitting Facilities

The 1046 Mc 4 kilowatt cw transmitter is located on Cheyenne

Mountain near Colorado Springs, Colorado with the transmitting

antenna at an elevation of 8760 feet above mean sea level or approximately 3000 feet above the average elevation of the plains at the base

of the mountain. Figs. 3a and 3b are photographs of the transmitter

site and a close-up of the antenna. Fig. 3c is a photograph of the

klystron transmitter. A block diagram of the 1046 Mc transmitting

facility is shown in Fig. 3d. A more detailed description of the

klystron transmitter can be found in NBS Report 1826. 1_/
-5- VI

The horizontally polarized transmitting antenna is of the slotfed-horn type and has a gain of 26 db with respect to an isotropic

radiator. This gain is obtained through the use of half -power

horizontal and vertical beam widths of 18 and 6 degrees, respectively.

Recording Facilities

The 1046 Mc transmissions are recorded continuously 24 hours

per day, seven days a week, at four fixed locations namely Kendrick,

Colorado: Karval, Colorado; Haswell, Colorado, and Garden City,

Kansas. Short term continuous recordings are made during midsummer and mid -winter at Anthony, Kansas and Fayetteville, Arkansas. Inasmuch as the Anthony and Fayetteville sites are far beyond

the radio horizon, less emphasis has been placed on this part of the

program.

Pertinent recording site data are given in Table I.

0) TABLE I >o

u

c <" ring ans.

JO< t ^ c « s K 2

f-l CO

Miles

frc

Transmi

Q

True

Bea

from

Tr

Elevatioi

MSL

- F

C

a

<

Antenna Above

G

Kendrick 49.3 -0.221° 105.569° 5260 Dipole 42.7

Karval 70.2 -0. 130° 97. 059° 5060 Dipole 42.7

Haswell 96.6 0. 102° 105.255° 4315 Dipole 42.7

Garden City 226.5 1. 532° 105. 247° 2855 Dipole 42.7

Anthony 393.5 3.422° 103.352° 1335 Parabol Lc 10.

Reflector

Fayetteville 616.3 5.638° 103.670° 1325 Parabol

Reflecto

Lcr 38.
-6- VI

Figs. 4a and 4b are photographs of typical fixed and mobile

recording sites, respectively. A block diagram of a recording

site is shown in Fig. 4c. Fig. 4d is a photograph of the recording equipment including receiver, calibrating signal generator,

frequency standard, chart recorder and time totalizing recorder.

A block diagram of the Brooklyn Polytechnic Research and

Development Co. , Inc. type 856-X narrow-band receiver is

shown in Fig. 4e.

Further details of the recording facilities are given in NBS

Report 1826, \I

RESULTS OF MEASUREMENTS

General Discussion

Results of continuous measurements on 1046 Mc for all

transmission paths are available in the form of Esterline-Angus

graphical records for all fixed receiving, sites while additional

microfilm records of time totalizer data are available for the

Garden City and Anthony sites. Figs. 5a to 5d are samples of

Esterline-Angus charts showing representative recordings for typical

night and afternoon periods during winter and summer at each of

the four fixed sites. Fig. 5e shows the only data available out of

a period of several weeks recordings at Fayetteville, Arkansas,

Although it has not been possible as yet to undertake a detailed

numerical study of fading rates at the various sites, inspection

of the chart samples indicates an increase in the fading rate with

distance from the transmitter beyond the radio horizon. The

rapid fading at Garden City makes analysis of the Esterline-Angus

charts quite difficult, and time totalizers are used for this reason

as they provide means for interpretation of rapidly fading signals.

At Haswell, which is some 20 miles beyond the radio horizon, the

amount and rate of fading has been found to vary with the time of

the day and the season, and is undoubtedly strongly influenced by

prevailing atmospheric conditions. Execution of the meteorological

program planner] will provide a basis for a detailed study of the

correlation between the character of the received signal, and the

status of the lower atmosphere.
-7- VI

Significant signal variations at the two sites within the radio

horizon appear to be iTTegular in nature, and, in general, are

not characterized by single fading rate for this range Observed

prolonged space-wave fad eouts will be discussed in a subsequent

portion of this report.

Hourly Medians

For purpose of data analysis and presentation, the hourly

nmedia-n value expressed in decibels below free space value was

used. This constitutes a measure of the field or power available

for 50% of -each hour for which recordings are available Hourly

median values are determined from the Esterline-Angus and time

totalizer records, and tabulated for each receiving site. In order

to determine diurnal variations of the received power, the hourly

median values for each month at each receiving site are separated

into eight three-hour periods (midnight to 3 AM, 3 AM to 6 AM,

etc. ) and data for each of the three hour periods have been investigated separately.

Figs. 6a to 6j show over-all distributions of hourly medians

for each month for which data were available. These distributions

are plotted on probability graph paper, and show the number of

hours of recordings which serve as a basis for each of the curves

shown. It is seen from the graphs that the curves approach lines

representing normal distributions with varying slopes. For each

month and each site, therefore, an over-all monthly median, and

the observed range of hourly median values may be determined, and

these serve as a basis for characterizing the seasonal variations of

these values art each site, and of the measured dependence of the

signal on the distance from the transmitter. The ratio of hourly

median values expeeded for 10% and for 90% of all hours is used

as a measure of the variance of the monthly signal*

Fig. 6k shows distributions of hourly medians for each site

for all hours of the entire year for which recordings were available.

Fig. 61 shows the distribution of hourly medians recorded at

the Anthony site during August, 1952.
-8- VI

Typical distributions for nighttime and afternoon diurnal

periods are shown in Figs. 7a to 7d. Distributions of hourly

medians during the months of February, June, and September

are shown for the periods 3 AM to 6 AM, and noon to 3 PM. It is believed that the larger variance of the transmission loss

during the early mm ning hours at Kendrick and Karval, particularly in September, is Id i gely due to the occurrence of prolonged

space-wave fadeouts at these locations. A monthly median for

each three-hour period, and a corresponding measure of its

variance may be determined from these distributions, and

equivalent graphs (not shown) drawn for all three-hour periods

for all months form the basis for Figs. 8 and 9.

Figs. 8a and b use the monthly medians for each threehour period to depict the diurnal change in the hourly median

values. Each set of curves shows the diurnal signal change at

the four sites for each month, and thus permit observation of

diurnal changes with distance, and over the season. Diurnal

changes were not shown in cases where sufficient data for individual three-hour periods were not available for a particular site

at a certain month. Similarly, Figs. 9a and b show the diurnal

changes of the variance of hourly medians as obtained from the

monthly distributions.

Fig. 10a shows the seasonal variation of median signal

levels comparing the over-all monthly values to the typical

night and afternoon periods. In studying this graph one should

bear in mind that no data at all were available for March, November, and December, and incomplete data for some of the

other months at several of the receiving sites.

Fig. 10b shows the seasonal trend of the variances drawn

for the same period as Fig. 10a. The same restrictions with

regard to the incompleteness of the data apply.

Finally s Figs. 11a and b show the over-all monthly medians

and their variances versus distance. The points shown for each

site are taken from the monthly distributions (Figs. 6a to j). The
-9- VI

line on the graph connects points taken from the aggregate yearly

distributions for each site (Fig. 6k).

Fig. lie shows the variatio"h of the median -attenuation for the

month of August relative to the free space value as a function of

the angular distance, 0. This illustrates, in the case of the 100

Mc data, how attenuations measured at different antenna heights

varying from 30' to 7800' above local terrain all lie on a single

curve when plotted as a function of 0.

Distributions of Signal Levels Within the Hour

The material discussed so far is based on the hourly median

of the received signal as its unit of evaluation; however, signal

variations occurring within the hour are important as well. They

may be described by fading range and fading rate. As detailed

studies of the fading rate are not yet available, the following

discussion will be restricted to fading range problems. It has

been found convenient to define fading range within each hour as

the ratio of power levels (expressed in decibels) exceeded for

90% and 10% of each hour.

The month of August, 1952, has been selected for detailed

studies of fading range. For all sites beyond the radio horizon

(Haswell, Garden City, and Anthony), distributions of signal

levels were obtained for each individual hour. These distributions

were tabulated with reference to the median value of signal observed

for each hour, and the distribution of deviations from the median was

averaged over the entire month for each hour, i. e. the 30 percentages

of time for each deviation level corresponding to the 30 days of

the month were averaged to determine a percentage typical of that

month and deviation level. These average distributions were then

plotted on Rayleigh graph paper. Samples of these average distributions are shown on Fig. 12a a together with a straight line representing the ideal Rayleigh distribution. From each distribution

the fading range is read off as the ratio (in decibels) exceeded for

90% and 10% of each hour, and compared with the range for an

ideal Rayleigh distributed signal (134 db). Figs. 12b, c s and d

show the diurnal variation of the hourly medians and of the fading

range for the three sites beyond the radio horizon. Fig. 12e shows

the variation of fading range with the angular distance, 0.
-10- VI

REFERENCES

1/ G. R. Chambers, J. W. Herbstreit and K. A. Norton, "PreliminaryReport on Propagation Measurements from 92-1046 Mc at Cheyenne

Mountain, Colorado," NBS Report 182b, July 23, 1952.

2/ P. A. Sheppard, "The Structure and Refractive Index of the Lower

Atmosphere," Meteorological Factors in Radio-Wave Propagation,

Report of a Conference Held on April 8, 1946, at The Royal Institution, London, by the Physical Society and The Royal Meteorological Society.

3/ K. A. Norton, "Transmission Loss of Space Waves Propagated Over

Irregular Terrain," Transactions of the IRE Professional Group

on Antennas and Propagation, PGAP-3, pp. 152-166, August, 1952.

Also NBS Report 1737, June 16, 1952.

4/ K. A. Norton, "The Calculation of Ground-Wave Field Intensity

Over a Finitely Conducting Spherical Earth," Proc. IRE, Vol.

29, pp. 623-639, December, 1941.

5/ H. G. Booker and W. E. Gordon, "A Theory of Radio Scattering

in the Troposphere," Proc. IRE, pp. 401-412, Vol. 38, No. 4,

April, 1950.

6/ Harold Staras, "Scattering of Electromagnetic Energy in a Randomly Inhomogeneous Atmosphere," Jour. App. Physics, pp.

1152-1156, Vol. 23, No. 10, October, 1952. Also NBS Report

1662, May 12, 1952.

7/ J. W. Herbstreit, K. A. Norton, P. L. Rice, and G. E. Schafer,

"Radio Wave Scattering in Troposphe ric Propagation," 1953

Institute of Radio Engineers Convention Record; also NBS Report

2459, April 15, 1953.

8/ W. E. Gordon, "Radio Scattering on Optical Paths," Paper presented at Symposium on Tropospheric Wave Propagation Within

the Horizon, Navy Electronics Laboratory, San Diego, Calif. , March 30-April 1, 1953.
-11- VI

9/ K. A. Norton, "Propagation in the FM Broadcast Band, " Advances

in Electronics , Vol. I, pp. 406-408, Academic Press, Inc.,

New York, 1948.

10/ K. A. Norton, "Propagation Over Rough Terrain," Report of

Symposium on Tropospheric Wave Propagation at the U. S. NavyElectronics Laboratory, San Diego, Calif., pp. 101-105,

July, 1949.

11/ S. O. Rice, "Statistical Fluctuations of Radio Field Strength

Far Beyond the Horizon," Proc. IRE, Vol. 41, No. 2, pp. 274-

281, February, 1953.

12 / Saburo Matsuo, "The Method of Calculating VHF Field Intensity

and Research on Its Variations," Report of the Electrical Communication Laboratory 621.39.001.6(047.3), Ministry of Telecommunications, Tokyo, Japan, August, 1950.

13/ J. C. Schelleng, C. R. Burrows and E. B. Ferrell, "Ultra Short

Wave Propagation," Proc. IRE, Vol. 21, pp. 427-463, March, 1933.

14/ K. A. Norton, "Transmission Loss in Radio Propagation," Proc. ~ IRE, Vol. 41, pp. 146-152, January, 1953.
-12- VI

APPENDIX I CALCULATION OF THE ANGULAR DISTANCE, G,

OVER IRREGULAR TERRAIN

We see by Fig. 2e that the angular distance 6 = a + (3 Q

is simplyequal, over a smooth spherical earth, to the distance between the

horizons of the transmitting and receiving antennas divided by the

effective radius of the earth, a:-*

d - dT f - d T „ G = Lt Lr

(1) a

Fig. 1-1 shows the geometry involved to take into account the effect

of irregular terrain on the determination of aQ

; a similar geometry

is involved in the determination of (3r . o From this geometry it may be shown that:-

d dLt

(h

ts " \s ) 2a a d t

, dT (h. - h ) _ d Lr _

v ts rs

c2

P ° ~2~a a " d

5 r (3)

where h - h Lt

* dLt

d 2

h - hT - Lr

8 r= _lf

Lr ~^T~ (5)

Lr

d - d T

. - d T 8 =a ip : ^ 1£ -6t -6

r

(6)
-13- VI

In the above dT and dT denote the actual distances to the radio

Lt Lr

horizons as determined from the terrain profiles plotted for the path,

h T L and hT denote the heights above sea level of the terrain at the

Lt Lr ° respective horizons, and h and h^. denote the antenna heights above

the same reference, sea level. The distance to the radio horizon,

d , is determined by plotting on linear graph paper the heights,

hT

(x), above sea level of the actual terrain at the distances, x,

corrected for the effects of the normal earth's curvature and of air

versus the distance. The farthest unobstructed P" 2~refraction, J h (x) - x

L sJ

point on the terrain, as determined on this modified plot, is the radio

horizon, and the distance to this point is denoted by d T

.; this is the same

procedure as that used by Norton—' in a recent paper.

*The symbol a is used for simplicity to denote k , where a denotes

the actual radius of the earth.

1/ Kenneth A. Norton, "Transmission Loss of Space Waves Propagated

Over Irregular Terrain," Trans, of IRE Professional Group on

Antennas and Propagation, No. PGAP-3, August, 1952; Also published

as NBS Report 1737, June 16, 1952.

GEOMETRY FOR IRREGULAR TERRAIN CALCULATIONS

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-35 -30 -25 -20 -15 -10 -5 *S

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Figure 15a <^BS>
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Supplement VII

THE RATE OF FADING IN TROPOSPHERIC PROPAGATION

By

K. A. Norton and H. B. Janes

National Bureau of Standards

Boulder, Colorado

See No. 324, page 1 lZf in the list of technical abstracts.

Supplement VIII

RADIO TRANSMISSION LOSS VERSUS DISTANCE AND

ANTENNA HEIGHT AT 100 Mc

By

P. L. Rice and F. T. Daniel

National Bureau of Standards

Boulder, Colorado

Published in Trans. IRE, Professional Group on Antennas

and Propagation, Vol. AP-3, No. 2, pp. 59-62, April, 1955.

See No. 35, pp. 20, in list of technical abstracts.

Supplement IX

RADIO TRANSMISSION LOSS VERSUS ANGULAR DISTANCE AND

ANTENNA HEIGHT AT 100 Mc

By

P. L. Rice, F. T. Daniel, W. V. Mansfield, and P. J. Short

Supplement IX

RADIO TRANSMISSION LOSS VERSUS ANGULAR DISTANCE

AND ANTENNA HEIGHT AT 100 MEGACYCLES

By

P. L. Rice, F. T. Daniel, W. V. Mansfield, P. J. Short

National Bureau of Standards

Boulder, Colorado

SUMMARY

This report derives prediction curves of radio transmission loss

and its long-term variability in time. The prediction parameters are

angular distance and transmitting or receiving antenna height, with one

antenna height fixed at 30 feet. The curves are based on observations

of transmission loss over propagation paths in the area of the United

States east of the Rocky Mountains, with data from the Pacific Coast

shown for comparison.

INTRODUCTION

The prediction curves derived in this report depend upon a longterm program of measurements which was undertaken by the Central

Radio Propagation Laboratory of the National Bureau of Standards, with

the assistance of the Department of Defense, the Federal Communications Commission, several universities, and other agencies. Transmission loss was recorded over particular paths for at least a year to

determine seasonal variations, whenever possible, and a number of

paths were studied for much longer periods of time to determine year

to year variability. The basic data for the analysis reported here are

hourly median values of transmission loss at frequencies between 92

and 108 megacycles.

This paper first defines transmission loss and angular distance and

then describes the data and methods of analysis used.

Transmission loss is defined as the ratio of total radiated power to

the resulting signal power available from the loss -free receiving antenna.

The advantages of this concept are explained in a recent paper by Norton_L-/
-2- IX

"Basic" transmission loss is defined as the transmission loss

expected between isotropic antennas. If the basic transmission loss Lu

is expressed in decibels and the frequency fmc in megacycles, then

a simple relationship exists between these quantities and the field strength

E expressed in decibels above one microvolt per meter for one kilowatt

of effective radiated power:

E = 139.37 + 20 1og10fmc - Lb

Values of basic transmission loss are presented in this paper as a function of the physical quantity "angular distance," which is the angle

between the ray from the transmitting antenna to its radio horizon and a ray from the receiving antenna to its radio horizon, determined in the

great circle plane containing both antennas. Angular distance was

determined assuming an effective earth's radius equal to four -thirds the

actual radius of the earth in order to allow for the effects of refraction

in a radio standard atmosphere.

Over a smooth spherical earth the angular distance, 0, is equal to

the distance between the transmitting and receiving antenna horizons

divided by the effective radius of the earth. For receiving locations at

radio line -of -sight, 9, is equal to zero, and beyond radio line -of -sight,

is positive.

The difficult problem of defining antenna height over irregular terrain

becomes less important when angular distance is used as a parameter

instead of the propagation path distance d. When is constant, any

increase in antenna height involves an increase in distance and in distance

attenuation. The height gain and distance attenuation work in opposite

directions, so that the net height gain for a constant is only a fraction

of the corresponding height gain at a constant distance. If there is more

distance attenuation than height gain, the net height gain for a constant

is negative.

Reference to two recent papers prepared at the National Bureau of

Standards 2, 3 will be required in order to understand the methods of

analysis described in this paper. Reference 2 shows how angular distance

enters into tropospheric propagation theory, and reference 3 describes

an interpretation of the Booker-Gordon scattering theory upon which the

analysis in this report depends. In this theory, angular distance is the

basic parameter.
-:- ix

The curves presented here are designed to reflect "average" smooth

earth conditions, not greatly affected by obstacle gain due to knife-edge

diffraction. Where a hill acting as the radio horizon of an antenna is

very high with respect to average terrain extending back to the antenna,

it is expected that smooth earth theory will not correspond very closely

to the physics of the propagation problem. A criterion for rejecting

data corresponding to such very rough terrain profiles and involving

"obstacle gain" is explained in Appendix II. It also explains how effective

antenna heights are defined. Cut of forty-two paths for which terrain

profiles were available, only four were rejected from the analysis, so

it may be seen that the present curves should be applicable to most

commonly occurring propagation paths.

The phenomenon of obstacle gain due to knife-edge diffraction is

treated in recent reports, by Dickson, Egli, Kerbstreit, and "."'"ickizer 4/ t by Kirby and McCuateJL > and by Dougherty_r_/.

2. DESCRIPTION OF DATA

A recent report on radio transmission loss versus distance and

antenna height at 100 megacycles 7

/

describes the data in detail. It has

been found that field strengths recorded at certain times of the day

and in certain seasons of the year are systematically stronger than at

other times. In order to allow to some extent for these systematic effects,

the year was divided into two parts and the day into four parts, making

eight "Time Blocks." Table I defines the time blocks used. The hours

of the day were divided in the fashion shown mainly because the low

point of the diurnal cycle in this type of data usually occurs between 1 PM

and 6 PM. The year was divided in half to distinguish between high

summer field strengths and low winter fields. Very few hourly medians

were available in time blocks 7 and 8.

TABLE I TIME BL,OCKS

1 Nov - Apr 6 AM .. 1 PM

2 Nov - Apr 1 PM - & PM

3 Nov - Apr 6 PM - 12 Mn

/;. May - Oct & AM - 1 PM

5 May - Oct 1 PM - 6 PM

b May - Oct 6 FM - 12 Mn

7 May - Oct 12 Mn - 6 AM

o Nov - Apr 12 Mn _ 6 AM
-4- IX

Once a division was made into time blocks, the basic data for

analysis were values chosen from the cumulative distributions of hourly

medians recorded during each of these time blocks over each path. Fig. 1 shows an example of such a cumulative distribution for station KXYZ-FM

Houston, Texas, as recorded by the University of Texas at Austin.

From the data for each time of block, year, and propagation path,

the transmission loss values exceeded 907c, 50%, and 10% of the hours

were determined. These values correspond to field strengths exceeded

10%, 50%, and 90% of the hours, respectively. The time block medians

were used to estimate the dependence of transmission loss on angular

distance and antenna height, and the other data were needed in order to

study long-term variability.

Appendix I gives pertinent information about the data used in the

analysis.

3. METHODS OF ANALYSIS

A mathematical basis for tropospheric radio scattering has been

formulated by Booker and Gordon 2±2/ and by StaraslL/. The development

of this theory for the purposes of the present analysis assumes a fourthirds earth standard atmosphere and simple isotropic scattering. The

theory is important to the analysis of these data because they all

represent conditions beyond the radio horizon, where tropospheric

scattering is important.

Within the framework of the theory described in reference 3, only

very simple assumptions with regard to meteorological factors are

justified. It is assumed that at any two points in space separated by a distance r, the covariance with respect to time of the refractive index

variations which give rise to scattering is of the following form:

C(r) = C(O) exp ( -r/i) , (2)

where C(O) is the time variance of the refractive index of the atmosphere

and i is the scale of turbulence of the atmosphere. The separation r may be in any direction, so the scattering is isotropic.

An estimate of the scale of turbulence was derived from data

obtained in Texas and in Ohio by von Rosenberg, Grain, and Straiton
-5- IX

of the University of TexasJ_i/ and on Long Island by Birnbaum, Bussey,

and Larson of the National Bureau of Standards^ /. Shown plotted in

Fig. 2 are values for the scale of turbulence used to define the empirical

relation: where SL is in meters and h is height

above ground in thousands of feet.

I = 7Uh

(3) h+ 0. 5

K

' Records of the variation of refractive index in time and space do

not always indicate that the correlation function C(r) is of the assumed

form given by equation (2), so in determining the scale of turbulence,

it was defined to be that value of JL which would make C(r)/C(0) = exp (-r/j2) equal 0.5 at the value of r where the actual normalized autocorrelation was 0. 5 in a record of refractive index fluctuations in space.

Scattering theory indicates that the power scattered from any volume

element of the atmosphere is directly proportional to the value of

C(0)/£ within the volume element. Radio transmission loss data were

used to determine a functional dependence of the mean value of this

parameter on the height above ground of the theoretical "center of

scattering." All the data used to determine the variation of C(0)/j2 with

height correspond to angular distances greater than 20 milliradians

(100 miles between radio horizons of the antennas). At these distances

scattering is thought to be the propagation mechanism usually dominant

at 100 megacycles.

Equation 24 in reference 3 shows how the parameter C(0)/j2 enters

into the scattering theory. Equations 15 and 25 in reference 3 define

the location of the "scattering center. " Equation 15 represents the

weakest link in this approach to the theoretical analysis of transmission

loss data, for the scattering centers given by this equation appear to be

too high. A substantial improvement of the estimates given by Equation 15,

however, will require a very elaborate theoretical analysis, which up to

the present time has not been completed. The prediction curves shown here

are largely determined by the experimental data and are little affected,

even in their extrapolated portions, by the precise form of the theory.

To determine a functional dependence of the parameter C(0)/£ on

height above ground, the methods of reference 3 were used. Each time

block median (the median of all hourly medians in a time block) was

corrected to correspond to transmission loss between isotropic antennas

500 feet high and 30 feet high by using the scattering theory.
-6- IX

The corrected data were used to obtain a curve for a 500 foot, 30 foot

combination of antenna heights, and then scattering theory was used to

extrapolate to other antenna height combinations. At short distances where

scattering does not predominate, predictions are based on the BremmerVan der Fol diffraction theory for a smooth spherical earth. Reference 2

describes the method used for combining the diffracted and the scattered

power at intermediate distances.

Both scattering theory and diffraction theory indicate that the ground

wave is propagated beyond the horizon as though guided by the surface of

the earth in such a fashion that energy spreads uniformly normal to the

great circle plane between the antennas, but is confined in the vertical

plane by the presence of a wave guide, the lower boundary of which is the

earth's surface. Thus the spatial decay of the energy with distance is as l/d rather than as l/d , which would be the case in free space. It follows that energy loss, or the basic transmission loss La. expressed

in decibels, will include a term equal to -10 log^d, resolving the

transmission loss into terms dependent separately upon the physical distance d and the angular distance 0. In the present analysis, therefore,

scattering theory was used to predict median basic transmission loss L^rn

minus 10 log-, n

d, rather than to fit curves through observed values of

L-, , The origin and development of this feature of the analysis will

be found in reference 2.

4. PREDICTION CURVES

Fig. 3 shows prediction curves of L-. - 10 log.^d as a function of Q 9 with one antenna ranging from ten to five thousand feet and with the other

antenna fixed at thirty feet. The circles in this figure are maximum and

minimum values of the time block medians obtained for each of the paths

used in the analysis. The X's in the figure represent maximum and

minimum, time block medians for three sets of Pacific Coast data rejected

from the analysis. (They were rejected by the criterion for obstacle gain

due to knife-edge diffraction which is explained in Appendix II). These

extreme values of time block medians were obtained from samples which

extend over several years in some cases and over a fraction of a year

in other cases. In Appendix I, one -half the difference between these

extremes is compared with the standard deviation of all the time block

medians available for each path. Also listed in Appendix I are the periods

of recording analyzed and the number of hours of data available in each

time block for each propagation path.
-7- IX

Fig. 4 shows height-gain curves with 8 a parameter; they extend over

a height range for one antenna from 10 feet to 100, 000 feet, with the height

of the other antenna fixed at 30 feet. The curves have been made to pass

through a reference point corresponding to a 500 foot, 30 foot combination

of antenna heights.

To simplify the explanation of this curve, let Z(h) = (L, - 10 log, d), , where the values of (Lbm ~ ^

^SlO ^ are estimates for the antenna

height indicated by the subscript h, with the other antenna height fixed

at thirty feet. Plotted in Fig. 4 versus the antenna height h, in feet is

the quantity

fyh^O) = Z(h

x

) - Z(500), (4)

An estimate of Z(h^) is obtained by adding Hc

to the value of Z(500) read

from the 500 foot curve of Fig. 3. These height-gain curves in Fig. 4

are designed for use where 8 is fixed and d is allowed to vary with hj.

Particularly to be noted in Fig. 3 and in Fig. 4 is the small

amount of height gain predicted by the scattering theory at a constant

value of the angular distance 8. Most of the data, other than that obtained

at the Cheyenne Mountain Field Station of the National Bureau of Standards

correspond to transmitting antenna heights near 500 feet.

Fig. 5 shows median basic transmission loss L>\)in versus antenna

height for a series of constant distances from 50 to 600 miles. These

curves assume a smooth four -thirds earth relationship between 6, d,

and the antenna heights h, and h2

: d=5.28G+J2h1 + J 2h2

, (5)

where d is in miles, 8 in milliradians, and hi and h^ are in feet.

Since all data are for 8>0, curves are not drawn in Fig. 5 within line of

sight of the fixed antenna height ho.

The basic prediction curves in Fig. 3 and in Fig. 4 were used to

obtain estimates of transmission loss for each path and each time block

for which data were available, and Fig. 6 shows the cumulative distribution of deviations of observed from predicted values of time block medians,

The predictions included some correction for time of day and season.

These corrections are discussed in some detail in Section 6 of this report.
-8- IX

An interesting point may be brought out about the comparison of

data with the prediction curves of Fig. 3. The standard deviation of

the departures from these basic prediction curves of all the time

block medians analyzed is a little over 4 decibels. This corresponds

closely with an estimate of variance due to terrain which was derived

independently in a recent report by Beani_i'

.

On the average, time blocks 2 and 5 show basic transmission loss

about two decibels greater, and time block 7 shows basic transmission

loss about three decibels less than that observed during the other time

blocks

.

Though the median deviation of these data from the prediction

curves is zero, it may be noted from Fig. 6 that extremely low fields

are more common than equally high values. The predictions shown in

Figs. 3 through 5 represent an "average" of all the data. Some time

blocks were not recorded for as many hours as some other time blocks,

and this "average" does not quite represent the expected median

transmission loss for all-day, all-year conditions. A discussion of

this aspect of the problem of prediction is presented in Section 6.

5. VARIABILITY IN TIME AS A FUNCTION OF

For each time block and each propagation path, a cumulative distribution was obtained of the hourly medians recorded, as illustrated in

Fig. 1. From the data for each time block, year, and station, the

transmission loss exceeded 90%, 50%, and 10% of the hours was determined. The convention is adopted that E(T) represents the field

strength exceeded T% of the hours and is expressed in decibels above

one microvolt per meter for one kilowatt of effective radiated power,

and that Lb(T) corresponds with E(T) and therefore represents the

basic transmission loss exceeded (100 - T)% of the hours.

Let yi equal the difference between 10% and 50% fields, and let y?

equal the difference between the 50% and 90% fields:

Yl = Lb

(50) - L

b

(10) = E(10) - E(50) (6)

y 2

= Lb

(90) - Lb

(50) = E(50) - E(90) (7)

Both y and y are always positive numbers.
The observed differences y^ Q and YZo as determined for each time

block, year, and station, were weighted. A weighted average was

computed for each propagation path, using for each average all of the

time blocks with data for that path. (This biases the results in favor of

the time blocks in which there were the most data).

There were 38 of these weighted average values of y, and y_ , and

these values are plotted in Fig. 7. This figure shows the estimates

of long-term variability of transmission loss versus angular distance

for an "average" time block, as obtained by weighted least squares curvefits of the data by certain functional forms.

In order to determine how to fit these functional forms to the data, a running average of the points taking five values of at a time was

plotted. A straight line was fitted to the y-, data and another to the

y^Q data from line-of-sight to where 9 = 12. 2 milliradians. A function

of the form y = A + B(0 - K logiQ0) was fitted to each set of data for

greater than 17 milliradians. The data at angular distances greater

than = 80 milliradians (obtained at one receiving location) seem to

indicate an increase of variance beyond this angular distance. Such

an increase seems unlikely, as scattering is occurring well up in the

stratosphere, so a restriction was placed upon the curve fit y = A + B(0 - K log n

6) to force the variance to decrease with increasing

out to 150 milliradians. K was fixed at a value of 345.39 = 150 Log 10

in order to force the curves to have a slope of zero at 150 milliradians.

Each curve was assumed to have a constant value independent of beyond

150 milliradians, where no data were available. On a smooth four -thirds

earth, = 150 milliradians corresponds to a distance of 79 2 miles

between the radio horizons of any two antennas. The curves in Fig. 7

may be used with confidence probably out to about 80 milliradians.

The two curve fits up to 12. 2 and beyond 17 milliradians were

blended together by taking a "firm grip on the pencil, " starting from

8 milliradians and extending to 25 milliradians to give a smooth

transition and to eliminate the end effects of the curve fits. The "firm

grip on the pencil" was guided to a considerable extent by the weighted

running average curves of the data in this range. The final curves of

y^(0) versus and -y?(0) versus were then plotted on a linear scale,

and are presented as Fig. 7.
-10- IX

6. DEVIATION OF PREDICTIONS FROM ALL-DAY, ALL-YEAR

CONDITIONS

Next, an evaluation was made of the departures AL of observed

median basic transmission loss L, (50) for a given time block, year,

and station from the predicted values L = L, (50) of Fig. 3. These

predicted values correspond to the "average" of the available data;

this average is biased relative to all-day, all-year conditions by the

fact that little data were available for the period from midnight to 6 AM.

It was noted that the deviations AL = L. - L, tended to be greatest

o bo b. °

at angular distances where the long-term variance is large, and as a

first approximation it was assumed that AL should depend upon in

the same manner as the function y,(0) defined by the upper curve in

Fig. 7. For each time block, a weighted mean value A of the

quantities AL /y.(0) was chosen to represent the average amount by

which transmission loss in the qth time block departs from the

prediction curves of Fig. 3. The deviation of the estimate of Lv (50)

for the qth time block from the L,(50) of Fig. 3 is then A y,(6), and

Lbq(50) = L

b

(50) + AqYl(0) = L

b

(50) + AL. (8)

In Fig. 8 the quantity AL = A-y^©) is plotted as a function of for each

of the eight time blocks.

Table II gives the values of A for the eight time blocks. Note that, as would be expected, the resulting predicted values of transmission

loss are larger for the winter time blocks than for the summer time

blocks and the transmission loss is greatest in the afternoon and least

in the midnight to 6 AM time blocks.

Also shown in Fig. 8, as a dashed curve, is the deviation of

all-day, all-year predictions of L(50) from the estimates obtainable

from Fig. 3; the method of obtaining this curve is explained below. The

dotted curve in Fig. 8 shows the deviation from the estimates of Fig. 3

corresponding (a) to all year, and (b) to the period from 6 AM to

midnight.
-11-

q = Time Block

Number

12

3

4

5

6

7

8

TABLE I I

A

q

Bi B ?2q

-.0061 1.0969 1.0817

+.1953 .9137 .8816

-.1051 1.0110 1.0965

-.4348 1.1867 1.0907

+.1521 .7689 .6993

-.2902 1.0437 .9425

-. 5999 1.1223 1.1737

-.1519 1.1711 1.1721

The observed differences yi_ and y? for each time block, year,

and station were fitted to functions of the form B,y,(6) and B 2

V2(6)»

where the smooth curves in Fig. 7 define y-i(0) and y?^). Values of

B, and B~ for each time block were weighted averages of quantities

y, /y (0) and y7o/y?^^ anc^ are listed in Table II. In order to obtain

a cumulative distribution for each time block at each of several values

of between and 110 milliradians, the following method was used:

Long-term cumulative distributions are almost log -normal, so

for the qth time block the quantity Biyj(6) was used to define the slope

of a log -normal distribution assumed to hold for field strengths exceeding the median, and B^Y-pi 0) defined the slope of another log-normal

distribution, assumed to hold for field strengths less than the median.

For instance, for time block q:

Lbq< 1 )= Lb

q

<50) - 1.815Blqyl(

e)

= Lb(50) + A

q

yj(0) - 1.815B lqyi(6) (9)

Next, at each value of 0, a combined distribution was obtained by

averaging the eight percentages at each of several convenient levels

of transmission loss; these combined distributions are believed to be

representative of what would have been obtained from data available all

day and all year from every propagation path. The averaging of

percentages was weighted in accordance with the possible number of

observations in each time block, not in accordance with the actual number
-12- IX

of hours of observation. All-day, all-year predictions of L(50) derived

from the dashed curves of Fig. 8 correspond to the median values of

these combined distributions. The dotted curve in Fig. 8 was obtained

in a similar fashion, averaging cumulative distributions for time blocks

1 through 6.

Fig. 9 presents the results of combining all of the time blocks as

a graph of y(T) versus G, where

y(T) = L(50) - L(T) = E(T) - E(50) (10)

Fig. 10 presents the corresponding graph for the period 6 AM to midnight.

7. USE OF THE CURVES

Most of the data upon which the prediction analyses are based

correspond to antenna heights near the 500 foot, 30 foot combination.

It is expected that the use of angular distance as a parameter will

make it possible to safely extrapolate to other antenna height combinations. Estimates of the time variance described as a function of

angular distance alone are expected to be valid over a wide range of

antenna height from beyond line-of-sight all the way back to where

= 0.

In order to predict the basic transmission loss L, (T) corresponding to field strengths exceeded T% of the time at an average location

over an average Z4-hour, lZ-month period, either Fig. 3 or Fig. 5

is used to find Li (50), and this is combined with estimates of £,L

from the dashed curve of Fig. 8 and estimates of y(T) in Fig. 9 in

accordance with the formula:

Lbp(T) = Lb

(50) + z*L -y(T) (11)

Estimates for the period 6 AM to midnight use the dotted curve of

Fig. 8 and the y(T) from Fig. 10.
-13- IX

8. COMPARISON \7ITH OTHER PREDICTIONS

The prediction curves in this report introduce the application of

the concept of angular distance to the analysis of data from all over the

country, and use of the scattering theory makes possible an extrapolation

of results to much higher antennas than are represented in the data.

Fig. 11 compares 500 foot, 30 foot, 100 megacycle 1% and 50% estimates

of basic transmission loss as obtained by the FCC Ad Hoc Committee

in 1Q49 H&jj/.and as derived by CRPL in 1953 7 /with the present 500

foot, 30 foot, 100 megacycle estimates. It will be noted that the 1%

estimates all agree closely out to 400 miles. Where the present

median estimates show more distance attenuation than the 1953

estimates at the larger distances, part of the explanation lies in the fact

that the manner of fitting an exponential function to C(0)/J2 in the region

beyond = 50 milliradians forces the curve to go about ten decibels

above data available at around 60 milliradians and ten decibels below

data available at around 100 milliradians (600 miles), while the 1953

curves were made to go through data available at 600 miles. The

FCC Ad Hoc curves depended upon 1% fields at the larger distances,

and the Ad Hoc 50% curves corresponded to an estimate of the difference

between the 1% and the 50r/ fields which was larger at great distances

than the present estimates.

It should be noted at this point that Figs. 9 and 10 show estimates

of the variability of hourly medians, not the variability of instantaneous

values. The variance of transmission loss values recorded at every

instant over a long period would also include within-the-hour variability.

"•/here tropospheric scattering is fairly "pure, " and Rayleigh distributions

of signal voltage are expected within short periods of time of the order

of ten minutes to a few hours, the variance of instantaneous values may

be more than twice as much as the variance of hourly medians.

Reference 16 gives a theoretical treatment of this subject by McCrosseni^/.

A description of within-the-hour cumulative distributions as observed

at 100 and 1000 megacycles in the CRPL Cheyenne Mountain Experiment

will be found in a recent paper by JaneslJ / . Theoretical reasons for

expecting Rayleigh-distributed fields in tropospheric scattering are

developed in a recent paper by Staras. 1& / and a paper by Norton, Short,

and Mansfield 19/gives the appropriate distributions in the region where

both diffraction and scattering are important.
-14- IX

1/ K.A. Norton, "Transmission Loss in Radio Propagation",

Proc. IRE, Vol. 41, January, 1953.

2/ K.A. Norton, "The Role of Angular Distance in Tropospheric

Radio Wave Propagation", in preparation.

3_/ J. W. Herbstreit, K.A. Norton, P. L. Rice and G. E. Schafer,

"Radio Wave Scattering in Tropospheric Propagation", 1953 Convention Record of the IRE, Part 2, Antennas and Communications

pp. 85-93.

4/ F. H. Dickson, J.J. Egli, J. W. Herbstreit, and G.S. Wickizer,

"Large Reductions of VHF Transmission Loss and Fading by

the Presence of a Mountain Obstacle in Beyond -Line -of -Sight

Paths", Proc. IRE, Vol. 41, No. 8, August, 1953, p. 967.

5_/ R. S. Kirby and P. L. McQuate, "Obstacle Gain at 60 Mc Over

Pikes Peak", in preparation.

hj H. T. Dougherty, "A New Technique for the Evaluation of the

Effects of Terrain upon Propagation at VHF and UHF", in

preparation.

7/ P. L. Rice and F. T. Daniel, "Radio Transmission Loss Versus

Distance and Antenna Height at 100 Megacycles", in preparation.

8/ H.G. Booker and W. E. Gordon, "A Theory of Radio Scattering

in the Troposphere", Proc. IRE, Vol. 38, pp. 401-412, April,

1950.

9/ W. E. Gordon, "The Scattering of Radio Waves by Turbulence in

the Troposphere", Research Report EE 163, Cornell University,

Investigation of Air-to-Air and Air-to-Ground Electromagnetic

Propagation Final Re port Part VI, September 15, 1953.

10/ Harold Staras, "Scattering of Electromagnetic Energy in a Randomly Inhomogeneous Atmosphere", Jour. Appl. Phys,

Vol. 23, pp. 1152-1156, October, 1952.
15. IX

11/ C. E. von Rosenberg, CM. Crain and A . W. Straiton,

"Atmospheric Refractive-Index Fluctuations as Recorded

by an Airborne Microwave Refractometer" , Univ. of

Texas EERL Report No. 6-01, February 6, 1953.

12/ George Birnbaum, H. E. Bussey, and R. R. Larson, "The

Microwave Measurement of Variations in Atmospheric Refractive Index", private communication, 1952.

13/ Bradford R. Bean, "Estimation of the Annual, Geographic,

and Terrain Variances of 100 Mc Transmission Loss",

presented at the National Bureau of Standards Boulder Laboratories Dedication Program, September 8-14, 1954.

14/ Report of the Ad Hoc Committee for the Evaluation of the

Radio Propagation Factors Concerning FM and TV, FCC

Mimeos Nos. 36728, May 26, 1949; 36830, May 31, 1949;

and 54832, July 7, 1950.

15/ E. E. Allen, W. C. Boese, and H. Fine, "Summary of Tropospheric Propagation Measurements and the Development of

Empirical VHF Propagation Charts (Revised), Reference D

to the Report of the Ad Hoc Committee for the Evaluation of

the Radio Propagation Factors Concerning FM and TV, FCC

Mimeo No. 36728, May 26, 1949.

16/ Garner McCrossen, "Long-Term Theoretical Cumulative

Distribution Function for Tropospherically Scattered Fields",

in preparation.

17 / H. B. Janes, "An Analysis of Within-the-Hour Fading in 100-1000

Mc Transmissions", in preparation.

18/ Harold Staras, "The Statistical Properties of a Tropospherically

Scattered Radio Signal", presented at the joint meeting of

URSI-IRE, May 3-6, Washington, D. C. ; manuscript in preparation.

19 / K.A. Norton, P.J. Short and William Mansfield, "The Cumulative Probability Distribution of the Instantaneous Resultant

Amplitude of the Vector Sum of a Constant Component and a Randomly Phased Rayleigh Distributed Varying Component",

in preparation.
-16-

APPENDIX I

IX

Path No, Transmitter

1* KFOR, Lincoln, Nebr.

2* WCAC, Anderson, S. C.

3* WEEU, Reading, Pa.

4* WIP, Philadelphia, Pa.

5*# WMRC, Greenville, S. C.

6* WTIC, Hartford, Conn.

7*# WEST, Easton, Pa.

8* WMBI, Chicago, 111. 9*# WCOL, Columbus, Ohio

10* WHKC, Columbus, Ohio

11* WKBN, Youngstown, Ohio

12*# WVKO, Columbus, Ohio

13* WDKA, Pittsburgh, Pa.

14*# KIXL, Dallas, Texas

15*# KLTI, Longview, Texas

16*# KPRC, Houston, Texas

17 # KRBC, Abilene , Texas

18*# KWKH, Shreveport, La.

19*# KXYZ, Houston, Texas

20*# WFAA, Dallas, Texas

21* CRPL, Cheyenne Mt.

Colorado Springs, Colo.

22* CRPL, Cheyenne Mt.

Colorado Springs, Colo.

23* CRPL, Cheyenne Mt.

Colorado Springs, Colo.

24*# CRPL, Cheyenne Mt.

Colorado Springs, Colo.

25*# CRPL, Cheyenne Mt.

Colorado Springs, Colo.

26* CRPL, Cheyenne Mt.

Colorado Springs, Colo.

27*# CRPL, Cheyenne Mt.

Colorado Springs, Colo.

Receiver

FCC, Grand Island, Nebr.

FCC, Powder Springs, Ga.

FCC, Laurel, Md.

FCC, Laurel, Md.

FCC, Powder Springs, Ga.

FCC, Millis, Mass.

Pa. State College, State College, Pa.

Univ. of 111. , Urbana, 111. United Broadcasting Co. .Hudson, Ohio

United Broadcasting Co. , Hudson, Ohio

United Broadcasting Co. , Hudson, Ohio

United Broadcasting Co. , Hudson, Ohio

United Broadcasting Co. , Hudson, Ohio

University of Texas, Austin, Texas

University of Texas, Austin, Texas

University of Texas, Austin, Texas

University of Texas, Austin, Texas

University of Texas, Austin, Texas

University of Texas, Austin, Texas

University of Texas, Austin, Texas

CRPL, Kendrick, Colorado

CRPL, Karval, Colorado

CRPL, Haswell, Colorado

CRPL, Garden City, Kansas

CRPL, Anthony, Kansas

CRPL, Haswell, Colo.

CRPL, Garden City, Kansas
-17- IX

APPENDIX I (continued)

28*# CRPL, Cheyenne Mt.

Colorado Springs, Colo.

29*# CRPL, Cheyenne Mt.

Colorado Springs, Colo.

30* CRPL, Camp Carson, Colo.

31* CRPL, Camp Carson, Colo.

32* CRPL, Camp Carson, Colo.

33*# CRPL, Camp Carson, Colo.

34*# CRPL, Camp Carson, Colo.

35*# CRPL, Camp Carson, Colo.

36*# CRPL, Pikes Peak, Colo.

37*# CRPL, Pikes Peak, Colo.

38*# CRPL, Pikes Peak, Colo.

CRPL, Anthony, Kansas

CRPL, Fayetteville, Arkansas

CRPL, Kendrick, Colorado

CRPL, Karval, Colorado

CRPL, Haswell, Colorado

CRPL, Garden City, Kansas

CRPL, Anthony, Kansas

CRPL, Fayetteville, Arkansas

CRPL, Garden City, Kansas

CRPL, Anthony, Kansas

CRPL, Fayetteville, Arkansas

* Refers to data used in investigating variability in time as a function of

# Refers to data used in deriving an expression for C(0)/jg as a functipn

of
-18- IX

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10 125.0 19.4 98.7 620 718 31

11 44.9 3.6 98.9 490 592 30 +0.1

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13 96.7 12.2 92.9 540 736 30

14 175.9 32.3 104.5 520 553 32 +0.2

15 227.2 40.4 105.9 320 305 32 +0.3

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22 70.2 4.1 92 30 1742 37 + 1.3

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29 617.1 98.3 100 55 2002 38 -1.3

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-19- IX

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-25- IX

APPENDIX II

DEFINITION OF ANTENNA HEIGHT

The angular distance which was used as a parameter in this

analysis contains the major effects of both path distance and antenna

height. The height gain realized from the directivity of the lobe

structure at each end of the path needs to be taken into account.

This height gain is a second-order correction.

In order to calculate this correction, effective antenna height

is defined as the height of the antenna above an equivalent smooth

spherical four -thirds earth fitted by least squares to the central

eight-tenths of the terrain along the great circle path which extends

from the antenna to its four -thirds earth radio horizon. The initial

one-tenth of the terrain is ignored because it is assumed that in the

lower regions of the scattering volume, lobery is unaffected by the

terrain near the antenna. The final one -tenth of the terrain is omitted

because it is assumed that the critical lobery is unaffected by terrain

irregularities in the immediate vicinity of the radio horizon.

This definition of effective antenna height was not satisfactory

for most receiving antennas. Their height above ground was small

with respect to the average terrain irregularities. In such cases,

some effective heights were found to be an order of magnitude or

more greater than the structural antenna heights. The structural

height was used, therefore, for receiving antennas, and the more

complicated definition of effective antenna height was used only for

transmitting antennas, which were in general much higher than the

receiving antennas.

Although much further work needs to be done to obtain an

adequate definition for the "effective antenna height" over irregular

terrain, it should be noted that the use of angular distance, 0, has

made this less urgent, since these "effective antenna heights" enter

into the calculations only in connection with second-order corrections.
-26 IX

CRITERION FOR REJECTING DATA

The curves in thi^ report are designed to reflect "average" smooth

earth conditions, not too seriously affected by obstacle gain effects.

Where the hill which acts as a radio horizon is very high with respect

to average terrain extending back to the antenna, it is to be expected

that the smooth earth theory used in this analysis may not correspond

very closely with the physics of the problem. Accordingly, a criterion

was adopted for rejecting data where the geometry of a terrain profile

indicated that smooth earth theory might not be adequate for analyzing

transmission loss over the propagation path. A smooth spherical

four-thirds earth curve was fitted to the central eight-tenths of the

terrain from each antenna to its four-thirds earth radio horizon, and

a second such curve was fitted under the restriction that it had to pass

through the radio horizon. The angle between the radii of these two

curves was added to the corresponding angle obtained from curve-fits

at the other end of the path, and the sum of these two angles, c^ + c r , was adopted as a criterion for the reliability of the smooth earth theory.

Whenever c f + c exceeded ten milliradians, the data corresponding

to that propagation path were rejected from the analysis on the assumption

that obstacle gain effects might be large.
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Supplement X

SOME APPLICATIONS OF THE MONTHLY MEDIAN REFRACTIVITY

GRADIENT IN TROPOSPHERIC PROPAGATION

By

B. R. Bean and F. M. Meaney

National Bureau of Standards

Boulder. Colorado

See No. 354, page 112p in the list of technical abstracts.

Supplement XI

COMPARISON OF CALCULATED AND MEASURED FIELDS

WITHIN THE RADIO HORIZON FOR THE 92 TO 1046 Mc RANGE

By

Albrecht P, Barsis

Supplement XI

COMPARISON OF CALCULATED AND MEASURED

FIELDS WITHIN THE RADIO HORIZON FOR THE

92 MC TO 1046 MC RANGE

By

Albrecht P. Barsis

National Bureau of Standards

Boulder, Colorado

SUMMARY

Propagation characteristics of space waves transmitted over irregular

terrain may be computed by replacing significant portions of the terrain by

a smooth surface, and determining the field by usual methods applicable

to such smooth surfaces. The deviation of actually measured fields from

the computed values is investigated as a function of Rayleigh's criterion

of roughness in the range of frequencies from 92 to 1046 Mc. The data

analyzed appear to indicate that Rayleigh's criterion 4-rr Ah sinijj R = _ must be less than 0. 1 for the earth to be considered smooth in radio

field intensity calculations. Thus, even the relatively smooth terrain

encountered in the eastern Colorado plains usually appears to be rough

to radio waves with frequencies of the order of 100 Mc and above.

INTRODUCTION

Transmitting and permanent receiving facilities for the Cheyenne

Mountain paths have been described previously** f/. The transmission

paths from the upper site to receiving sites at Kendrick (49. 3 miles),

and Karval (70. 2 miles) are optical, permitting the use of the 100,

192. 8 and 1046 Mc data in conjunction with other, special measurements

in order to determine the deviation of measured fields from calculated

smooth-earth fields.

In order to obtain additional data, a number of points at about 30

miles distance from the transmitter have been selected, extending in

azimuth up to 45 degrees north and south of the center line of the

antenna beams (oriented about 105 degrees east of true north). All

these points are within the radio horizon of both Cheyenne Mountain

transmitting sites, and permit evaluation of the fields by simple ray

theory. Measurements at all points have been made on the frequencies
-2- XI

of 92, 100, and 192. 8 Mc. It is planned to supplement the data bymeasurements on 1046 Mc as well as frequencies in the 200 to 300

Mc range. Consideration also has been given to measurements in

the 40 Mc range. This report presents results obtained on 92, 100, and

192. 8 Mc for eleven special points, and on 100, 192. 8 and 1046 Mc at

Kendrick and Karval.

EQUIPMENT AND PROCEDURE

Fig. 1 shows the truck used for making the measurements at the

eleven special points in a typical set-up. Dipole antennas mounted at

30 foot elevation were used to receive the signals from Cheyenne

Mountain. They were placed so as to minimize the effects on each other

and also to reduce the effect of the truck and mobile engine -generator

on the dipole patterns. The signal from the dipoles was fed to receivers

through RG-8/U coaxial transmission line. Power to the receivers and

auxiliary equipment was supplied through a voltage regulator from an

engine generator mounted in a trailer. Calibration of the receivers was

accomplished using a Measurements Corporation Model 80 Signal

Generator, which had been checked against similar units in the laboratory.

At each point and for each frequency the receiver was first calibrated,

then the signal was recorded for a period of about thirty minutes, then

the receiver was recalibrated. The signal was recorded by means of an

Esterline-Angus graphic ammeter. All recording was performed during

daytime hours in December of 19-2 and January of 1953.

At each location the antenna match was checked by means of a General

Radio Admittance Meter, and the losses introduced by the transmission

lines were measured for each frequency. These values were taken into

account at the time of analysis of the measurements. For the purpose of

analysis of the data, it was assumed that the receiving dipoles (which were

always oriented broadside to the transmission path) had the theoretical

gain value of 2. 15 db relative to an isotropic radiator. The gain of the

transmitting antennas toward the various receiving locations was determined from previous computations and measurements performed in part

on model antennas.
-3- XI

METHOD OF COMPUTATION

In accordance with the method indicated by K. A. Norton 3 /

profile graphs were drawn from each of the receiving sites to the

transmitters. Fig. 2 shows the profile from the Kendrick fixed

site to the Cheyenne Mountain summit transmitter; Fig. 3 shows the

profile from Karval to the same transmitter; and Fig. 4 shows profile

graphs drawn from four of the eleven special points toward the

summit transmitter site. The geometry involved in calculating space

wave fields may best be followed by studying Fig. 3, which shows the direct

and the ground reflected ray and the grazing angle involved, and gives

an indication of the terrain roughness. The Kendrick and Karval

profiles were drawn on the basis of standard atmospheric refraction

(k = 4/3), whereas the profiles on Fig. 4 are based on average

atmospheric conditions along the paths for the winter months corresponding to a value of k = 1. 261. An inspection of Figs. 2 and 3

shows that the terrain between the transmitter and the receiver

horizon (neglecting the fact that a small part of Cheyenne Mountain in

the vicinity of the transmitter is "seen" by the receiving antennas) is

not illuminated by the receiving antennas, and therefore, presumably

does not influence the field received at the receiving site. Thus the

significant portion of the terrain contributing to the received field is

considered to lie between the receiving antenna and its horizon. The

terrain in the vicinity of the transmitter, and the directional characteristics of the transmitting antenna are such that no appreciable contribution to the received field would originate from that part of Cheyenne

Mountain which is "seen" by the receiving antenna. A second-degree

curve was fitted to each profile for a distance extending from the

receiving site to a point beyond the receiver horizon by an amount of

10 per cent of the distance between receiver and its horizon. This

approach removes any bias in the fitted curve due to the fact that the

horizon itself is necessarily an unusually high point of the terrain,

although the 10 per cent value itself is arbitrary. The actual fit was

done by the method of least squares, taking the actual terrain at sufficiently frequent equally- spaced intervals. The second degree curves

representing the least square fit are shown on Figs. 2, 3 and 4.

The profiles shown on Fig. 4 serve to illustrate some of the practical

difficulties encountered in this method of analysis. For instance, the

second degree curve fitted to the terrain extending from Point No. 3

toward the transmitter site as far as the receiver horizon at nine miles,
-4- XI

would not provide a physically realizable solution, as the receiving

antenna would be located several feet below the smooth curve representing the terrain, and no reflection off that curve would reach the

receiving antenna. A second fit extending only to a closer horizon

at 1 . 5 miles does provide a solution, but the nine-mile horizon itself

will undoubtedly produce an additional contribution at the receiving

point. On the other hand, it can be shown that the first Fresnel

zone for all frequencies includes the entire nine-mile distance, so

that it is not feasible to talk of distinct and independent reflections.

For Point No. 5 the horizon appears to be at three quarters of a mile. The profile is virtually the same toward the summit transmitter site (100 and 192. 8 Mc) as toward the base site (92 Mc).

However, the terrain fit as shown, and computed by the method of

least squares does not provide a physically realizable solution on

92 Mc because, due to the lower elevation of the 92 Mc transmitting

antenna, the reflection point is pushed out to almost one mile from

the receiving antenna, where the terrain fit, as computed, is no

longer valid.

Similarly, Point No. 9 does not provide a solution for the 92 Mc

field, as the curvature of the fitted smooth curve is such that no

reflection will reach the receiving antenna.

For all cases where solutions of the field were obtained by the

above method the value of Rayleigh's Criterion of Roughness, R, was

obtained. This criterion may conveniently be expressed by the

equation:

4-tt Ah SIN^j

where i|j denotes the grazing angle, X the wave length of the signal,

and Ah was taken as the root mean square of the deviations of the

smooth curve from the actual terrain over the region where the least

square fit was obtained.
-5- XI

RESULTS OF COMPARISON OF EXPECTED AND MEASURED FIELDS

Fig. 5 shows the actual deviations of measured from computed fields

plotted versus Rayleigh's criterion as defined above. In this graph positive

values correspond to measured fields being higher than computed fields.

It is immediately apparent that there is no frequency dependence beyond

that expressed by the X in the denominator of the formula used. Although

the points appear widely scattered, there is a suggestion of a trend which

might be confirmed by additional measurements. A deviation of computed

from measured fields of up to two decibels could be expected due to

measurements errors, and the limitations of the method of computation.

Fig. 5 indicates that only for values of R less than 0.1 is there consistently

less than two decibels difference between the computed and measured

values. The conclusions to be drawn from this rather limited set of

data are, therefore, as follows: only for very smooth terrain with R

less than 0. 1 may agreement of computed and measured values be expected; and for R between 1 and 2 the expected deviations will increase

to the order of ten decibels or more. It may also be concluded that the

smooth-appearing terrain of the eastern Colorado plains usually is

quite rough to radio waves with frequencies of the order of 100 Mc and

above
-6- XI

REFERENCES

1/ G. R. Chambers, J. W. Herbstreit, and K. A. Norton, "PreliminaryReport on Propagation Measurements from 92 to 1046 Mc at Cheyenne

Mountain, Colorado," National Bureau of Standards Report 1826,

July 23, 1952.

2 / A. P. Barsis, B. R. Bean, J. W. Herbstreit, K. O. Hornberg,

and K. A. Norton, "Propagation of Radio Waves Over Land at

1046 Mc (Report for the Air Navigation Development Board), "• National Bureau of Standards Report 2494, May 1, 1953.

3 / K. A. Norton, "Transmission Loss of Space Waves Propagated

Over Irregular Terrain, " Trans. IRE Professional Group on

Antennas and Propagation, No. PGAP-3, August 1952.
Figure <NBS>
GEOMETRY FOR SPACE WAVE CALCULATIONS

FOR PATH BETWEEN SUMMIT TRANSMITTER

SITE AND KENDRICK RECEIVING SITE

RAY PATHS SHOWN ARE FOR 1046 Mc TRANSMISSIONS

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k \CHEYENNE M r SUMMI T \

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7200

7000

6800

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6400

6200

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5800

5600

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5200

5000

4800

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DISTANCE IN MILES

(FROM RECEIVING SITE)

FIG. 2
GEOMETRY FOR SPACE WAVE CALCULATIONS

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Supplement XII

AN ANALYSIS OF WITHIN-THE-HOUR FADING IN

100-1000 Mc TRANSMISSIONS

By

H. B. Janes

National Bureau of Standards

Boulder, Colorado

See No. 14, page 10, and also No. 324, page 112f - 112g,

"The Rate of Fading in Propagation through a Turbulent

Atmosphere, " by K. A. Norton, P. L. Rice, H. B. Janes,

and A. P. Barsis, in the list of technical abstracts.

Supplement XIII

TREND ANALYSIS AND PREDICTION IN A DISCRETE

GAUSSIAN STATIONARY PROCESS

By

H. StaraS

Supplement XIII

TREND ANALYSIS AND PREDICTION IN A DISCRETE

GAUSSIAN STATIONARY PROCESS

Harold Staras

National Bureau of Standards

Washington, D. C.

SUMMARY

Under the assumption that a discrete time series represents a Gaussian stationary process, this paper derives the maximumlikelihood estimate for the "trend" when no functional form for the

trend is known. In addition, this paper obtains the probability

distribution associated with a future occurrence.

INTRODUCTION

There are many situations in which physical or chemical theory

indicates that there should be a simple relation between two variates

X and Y, However, in any actual experiment, experimental errors

may enter which make it impossible to measure either X or Y exactly,

or sometimes neither can be measured exactly. If the physically

indicated relation between X and Y is of the form Y = f(X; a, . . . a ),

where a.-, . . . an represent a set of parameters, then the technique

of least squares is commonly used to estimate the parameters

al

• • • an

^rom a sequence of measured values {X-, Yj}. However,

there are many occasions when one observes a time sequence of

data {Yj} and it appears that a "trend" exists; yet, no functional

form for this trend is known. Under these conditions, many investigators assume some functional form for the trend and then estimate

the parameters by the method of least squares. Common functional

forms to assume for such a situation are a few terms of a sequence

of orthogonal polynomials or a few terms of a Fourier series. Still

other investigators may use the method of moving averagesJL/ or

the linear operator technique 2 / . It is the purpose of this paper to

point out a new technique for estimating the "trend" in a normally

distributed random but auto -cor related sequence.
-2- XIII

BASIC CONCEPTS

In this paper, a trend of a correlated random sequence {Y^} is

considered to be another correlated random sequence {X^} rather

than a well-defined function. The trend sequence {X-}, however,

has a smaller variance than the measured sequence {Y^} and is

more highly auto -correlated than the measured sequence, i.e. the

normalized correlation coefficient between X- and X- .-^ is greater

than the normalized correlation coefficient between Y^ and Y^i^.

whenever each of them is not zero. Oftentimes this is a more

realistic assumption than the assumption that the trend has a welldefined functional form. In particular, this paper investigates the

possibility that the measured sequence {Yj} may be considered to be

composed of a "trend"sequence {X^} and a purely random sequence

(.€•}, where the purely random sequence has the characteristics of

"white noise. " A potentially useful application of this point of view

may be the following: Let the measured sequence {Y-} represent

hourly median tropospheric field strengths. Let another measured

sequence {r\^ } represent an appropriate meteorological parameter.

One question of immediate interest is whether or not the two

sequences {Y^} and {r^ } are correlated. Disappointingly, the

measured correlation coefficient between the two sequences may

turn out to be small, say 0. 3. The next question that arises is:

"Is it possible that the low correlation between {Y-} and {r^} is due

to the fact that both sequences contain "white noise?" Furthermore,

if it were possible to extract the respective "trend" sequences {X^j

and {£• } may it not turn out that these two sequences are highly

correlated? We next develop a method for estimating the trend

sequence, as here defined, from a given measured sequence {Y^}

under the assumption that we are dealing with a Gaussian stationary

process.

THE POAVER SPECTRUM AND THE AUTO -CORRELATION FUNCTION

If the measured sequence {Y^} is sufficiently long, a satisfactory

estimate can be made of its auto-correlation function, Ry (k), defined

by N

Ry(k) = lim _1_ V Y. Y

N— co 2N+1 L

i=-N
-3- XIII

We define the purely random sequence {e ^ } to have the following

correlation function

R€ (k) = (r e2

k, o Where 5j4 is the Kronecker delta. cr is at the moment stixl unknown.

We can estimate it, however, by means of the power spectrum analysis,

The power spectrum 3 / , P(9)» for a discrete process is related to the

auto -correlation coefficients R(K) by

CO

P(G) = R(0) 12 y R(k) co

k=l

s k 9 (1)

Since, by assumption, the process {X-} is independent of the "white

noise" {e^} we have Ry(k) = Rx

(k) + cr 2

8k

Using this relation in (1 ) we obtain

Py( 9 ) = Px< > +%2

By definition of a power spectrum, P(6) must be non -negative for all

values of between and it. Furthermore, since Rv

(k) will become

zero and stay zero for k larger than 10 (say) we can actually plot

Py(0) as a function of 6. If PV

(B) is zero or very nearly so for any

value of 6 between zero and it, then there is almost no "white noise"

in the sequence {Y^}. If, however, Py(0) is sufficiently positive

for all values of 9 (it may look like Fig. 1, for example), then it may

be considered to contain "white noise" with a value of cr as indicated

in the Fig.

P

y

( Q )

TT

Fig. 1
-4- XIII

THE MAXIMUM-LIKELIHOOD METHOD.!/

Having estimated the variance of the purely random component in

the sequence {Y^} we are in a position to estimate the trend sequence

\X^}. If we reduce our data to have a zero mean, the likelihood

function for the sequence Y- is

L <l_3n i= exP { -l

\/ttct. \ZTrCT J .1 r> Z yLj yLj

e / .( D

J

Where cr 1 JillJ is the inverse of the covariance matrix cr- • which ,_ J 1 J.J I can be obtained simply from Rx

(k) = R

y

(k) - cr^ 6^. Q and D is the

determinant of ] j cr- -

] [. It should be noted that since {Y^} was assumed

to be the Gaussian stationary process, it is natural to expect {X-}

and {c-} to be Gaussian and stationary. The likelihood function is

merely the probability density of obtaining what actually was obtained.

Under our assumptions, the probability of obtaining the sequence

IS

f'^-Vr ±=. exp {.}LY a«X.Xj}

i»j

While the probability of obtaining the sequence {e.} = {Y^ - X-} is

n \TM— .._ , L \ ,„ v , 2

) — expt-^ > (Yj-Xj) 2

}

\ Zircr,. /

e l

Since these two probabilities are independent, the likelihood function

is as given. The sequence {X-} which maximizes L would be the

maximum-likelihood estimate of the trend. To maximize L we take

its logarithm and maximize that by the usual method.

N N

In L = -N In Ztto-

€ - lnJTT- \- \ tr^ XjXj - ~^Z ^ < Y1 " Xi^

i, j=l i=l
-5-

Differentiating with respect to X-. , we obtain

"Z

ffkj x

j + p: < Y

k

" X

k> ° K , 1, 2 ~~ N

j or

N v

J(-

kJ + V 5kJ ) -£ k=l,2 N

J- 1

Multiplying both sides of the above equation by cr--. and summing over k

the results

N N N

K- <rkJ + ~" cr ik 6 k# .) X. = -p- Y - ik Yk

i . 1 . - N

LJ % €

1 k=l i^l k=l

Performing the summation over k for the left hand side and multiplying

both sides by o"g , we obtain

N N

Y K

25

i,j +(rij

)Xj = £ ^Yk i=l,2—-N (2)

j=l k,l

Thus we must solve a linear set of equations for the Unknown, Xj.

Should it be desired to predict the value of a future occurrence, the

double sum v

_, would be considered to go from 1 to N and

-

lj XiX

j

i»j

N+n while the sum would terminate at N. The linear

"

(T, - X.)

2

i set of equations to be solved would then be:
-6- XIII

J &e2

6ij +

-ij (1 " SN+nj }

) "J X. = £

cr ik Yk

i . 1,2 —~ N,N+n (3)

J k

with Y-njij^ taken to be zero. The probability distribution associated

with a future occurrence at the instant N+n would then be a normal

distribution with a mean, Xj^j.^ , as determined from the solution

of the linear set of equations (3), and a variance equal to cr 6

. From the above we see that a solution of one set of linear

equations gives all the values of the trend sequence as well as a prediction for the future. This is in contradistinction to the linear

operator method_£_/ which requires, that after solving a linear

set of equations, one apply the linear operator to the observed data

in order to obtain one term of the trend sequence. One must then reapply the linear operator to obtain each additional term of the trend

sequence. In addition, the inherent difficulty with the linear

operator method when there are missing data does not apply to

the maximum -likelihood method described in this paper.
-7- XIII

REFERENCES

1 / M. G. Kendall, "The Advanced Theory of Statistics," Vol. 2

Chap. 30, Charles Griffin and Co., 1946.

2/ N. Levinson, "The Wiener RMS Error Criterion in Filter

Design and Prediction," Jour, of Math and Phys. 25, No. 4,

Jan., 1947, pp. 261-278.

3/ Herman Wold, "A Study in the Analysis of Stationary Time

Series," Chap. 2, Sec. 17, Almquist and Wicksells

Boktryckeri A.B., Uppsala 1938. Note that our P(0) is

Wold? s W^x).

4/ A. M. Wood, "Introduction to the Theory of Statistics,"

Sec. 8.3, McGraw-Hill Book Co. , 1950.

Supplement XIV

MEASUREMENTS OF MICROWAVE

DIFFRACTION OVER TREES

By

J. H. Chisholm

Originally presented at U.S. NEL Symposium,

July 25, 1949, NE 120301, Report 173, Problem NEL 1A1, p. 114, U.S. Navy Electronics

Laboratory, San Diego, California.

Supplement XIV

MEASUREMENTS OF MICROWAVE DIFFRACTION OVER TREES

By

J. H. Chisholm

National Bureau of Standards

Boulder, Colorado

When the performance of microwave links is calculated from the

terrain profile and is compared with the actual performance of such links,

it is often found that the actual performance is inferior to the calculated

in cases where heavily foliated trees are present in the transmission path.

Because many transmission paths, especially in the eastern United

States, contain tree foliage to heights of 7 to 100 feet, an investigation

to determine quantitatively the effect of such foliage upon microwave

propagation was undertaken by the Central Radio Propagation Laboratory,

Controlled experiments were conducted over a 4000-ft path at a wavelength

of 6 cm; metal screens and actual tree foliage were used as diffracting

obstacles.

The experiments sought to determine the nature of the diffraction

pattern behind tree-foliage barriers. The experimental approach to the

problem was quite simple in that attempts were made to duplicate the

classic optical experiment and to secure knife-edge diffraction patterns

at the 6-cm wavelength. It should be noted, however, that in the optical

case it is assumed that any obstacle in the path is absorbing and that

there is no reflection.

It was found that only under certain circumstances could the characteris

tic knife-edge diffraction pattern be duplicated at 6 cm. In most cases

where there was any ground reflection, it was found that instead of a typical single -wave diffraction over a knife edge, a strong interference

pattern resulted in the diffracted zone. This interference pattern was

quite different from the knife-edge pattern and was characterized by

very deep minima, A method of calculation that gave good agreement

with the observations considered the signal received behind the knife
-2- XIV

edge as the resultant of four components. This idea, of course, is not

new, but (at microwaves) the general tendency has been to neglect

the effect of ground reflection. This gives rise to false results, for

there has been found not only a direct wave which is diffracted but, in

addition, a wave which is reflected on the transmitter side of the screen

and then diffracted. Each of these components, in turn, gives rise to a direct and reflected wave.

Figure 1 shows the results of the initial experiment in which the

attempt was made to duplicate the results of the knife-edge optical

experiment over a 200-ft path. The dashed curve of figure 1 represents

the result derived from simple diffraction theory. The solid and dotted

curves were obtained experimentally by running the receiver up and down

the tower. The obstacle was a 16- by 50-ft, 18-mil, copper screen.

The horns had a beam width of approximately 15 degrees and therefore

discriminated almost entirely against ground reflections. However,

deep in the diffracted zone, there is a departure from the single

diffracted-wave result, and a characteristic interference pattern is

apparent. These effects occurred because, at that point, the horn no

longer discriminated against the ground wave.

In an effort to determine the magnitude of the ground reflection for

the type of terrain (fairly rolling with a high, grassy stubble about 6

to 8 inches high) over which the experiment was conducted, a series of

reflection coefficient tests were made. The results of these tests are

shown in figure 2. For angles up to 3 and 4 degrees, the effective

reflection coefficient varied from 0.6 to 0.95. The reflection coefficient

is seen to vary quite rapidly with the change of angle. Little difference

is noted, however, between horizontal and vertical polarization for these

conditions in which the grazing angles were in most cases less than 4

to 5 degrees.

Figure 3 shows the results obtained for a path in which a wooded

area, 400 to 500 feet deep and 60 to 70 feet high, was used as an

equivalent dull knife edge. From the illustration it should be noted

that again horizontal and vertical polarization give practically the same

pattern. There was a slight difference in the spacing and depth of the

minima but not enough to be important.
-3- XI

Y/hen the experiment was repeated in the presence of a light breeze,

the fluctuations in the minima were more pronounced than those in the

maxima. When points above the shadow region were investigated, it was noted that the fluctuations due to the leaf motion were less pronounced.

An effort was also made to determine the seasonal effects. On a calm winter day, the characteristic diffraction pattern was again obtained,

and found to be only slightly displaced from that observed in the summertime. However, the average signal level was higher.

Again in the presence of a light breeze, the characteristic fluctuation

was observed, and upon moving deeper into the diffraction zone, the

fluctuations became more rapid. No pronounced difference between

horizontal and vertical polarization was noted.

Figure 4 shows a pattern calculated on the four-path basis. A

reflection coefficient of 0.8 was used. It may be noted that the characteristic shape of this curve is quite similar to the results obtained by

experiment, and does seem to explain very adequately the effect of the

reflection. If the reflection coefficient is changed, the depth of these

minima is not influenced greatly, but their position is shifted,

A military viewpoint might be taken of the results of the experiments

conducted by CRPL, If it were necessary to operate in a severely

diffractive region, it might not always be possible to cut down the interfering trees and it might be impossible to install towers to a height of

300 feet. In cases such as these, there always exists the possibility of

employing some type of diversity and of determining the optimum antenna

spacing experimentally. This method of approach might be of value because

of the shifting up and down of the minima.

One other point should be mentioned. As has been shown in the heightgain patterns, the field is very irregular, and a small horn was used. The

question may be asked whether or not a large dish in such a field would

give the desired gain. As a matter of record, it should be stated that

one does not get the desired gain when a dish is used. Experiments

along these lines have not been completed but some rather surprising

results have been observed.

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Supplement XV

DEPENDENCE OF THE TRANSMISSION LOSS IN

TROPOSPHERIC RADIO WAVE PROPAGATION

ON THE ANGULAR DISTANCE

By

Kenneth A. Norton

National Bureau of Standards

Boulder, Colorado

See No. 77, page 35, and also No. 323, page 112f,

"The Use of Angular Distance in Estimating Transmission

Loss and Fading Range for Propagation Through a Turbulent

Atmosphere over Irregular Terrain, " by K. A. Norton,

P. L. Rice, and L. E. Vogler, in the list of technical abstracts.

Supplement XVI

THE CUMULATIVE PROBABILITY DISTRIBUTION OF THE

INSTANTANEOUS RESULTANT AMPLITUDE OF THE

VECTOR SUM OF A CONSTANT COMPONENT AND

A RANDOMLY PHASED RAYLEIGH DISTRIBUTED

VARYING COMPONENT

By

K. A. Norton, P. J. Short, and W. V. Mansfield

National Bureau of Standards

Boulder, Colorado

See No. 108, page 49, and also No. 322, page 112e,

"The Probability Distribution of the Amplitude of a Constant

Vector Plus a Rayleigh-Distributed Vector, " by K. A. Norton,

L. E. Vogler, W. V. Mansfield and P. J. Short, in the list

of technical abstracts.

Supplement XVII

POINT-TO-POINT RADIO RELAYING VIA THE

SCATTERING MODE OF TROPOSPHERIC PROPAGATION

By

K. A. Norton

National Bureau of Standards

Boulder, Colorado

See No. 327, page HZh, in the list of technical abstracts.

Supplement XVIII

PROPAGATION IN THE UHF-TV BAND

By

J. W. Herbstreit

Supplement XVIII

PROPAGATION IN THE UHF-TV BAND*

By

J. W. Herbstreit

National Bureau of Standards

Boulder, Colorado

The propagation factors influencing the performance of TV in

either the VHF or UHF portion of the frequency spectrum have been

some of the biggest bugaboos in determining the rate of development of a nation-wide TV service in this country. In the case of

VHF -TV, the lack of knowledge concerning the propagation factors

was responsible for about four years of delay in obtaining a nationwide TV allocation which is now well on the way to being implemented

in the VHF bands. Because of the lack of many operating stations

in the upper portion of the spectrum, our knowledge of the propagation factors influencing TV performance in the UHF band is still

rather meager; however, it is the purpose of this paper to be

informative concerning our present-day knowledge of the propagation factors in the UHF-TV band and to attempt to evaluate them

in terms of TV coverage to be expected in the presence of noise

and interference.

The Central Radio Propagation Laboratory of the National

Bureau of Standards in cooperation with the Department of Defense

and the Air Navigation Development Board has been conducting

a program of research at frequencies of 418 and 1046 Mc in

conjunction with an extensive 100 and 200 Mc program of measurements throughout the United States. The extensive 100 and 200 Mc

network of measurements provides us with the best available

method of extrapolating our 418 and 1046 Mc measurements to

estimate the nation-wide performance on these higher frequencies.

On Fig. 1 are shown the propagation paths over which propagation measurements have been made. Measurements in the VHF

bands have been made in the southern portion of the country by

the University of Texas, in the northwest by the University of

*Talk presented by Mr. Herbstreit at the IRE National Convention

held in New York City March 23-25, 1954.
-2- XVIII

Washington, in the midwest by the University of Illinois, and

the United Broadcasting Company, in the northeast by The

Pennsylvania State College, and the Federal Communications

Commission has provided data from many of its monitoring

stations located throughout the country. The National Bureau

of Standards has obtained 418 Mc propagation data from the

operation of high power resnatron transmitter by the Collins

Radio Company at Cedar Rapids, Iowa and 100, 200 and 1046 Mc

data from the NBS operations of the Cheyenne Mountain Field

Station. In this program, most emphasis has been placed on

obtaining data beyond the radio line of sight; however, the region

within the radio horizon has not been neglected.

The type of data collected and the nature of the analyses

completed will be illustrated by a series of figures relating to

the National Bureau of Standards program of research being

conducted at the Cheyenne Mountain Field Station. Fig. 2

illustrates the geographical layout of facilities being used in this

program. Transmitters operating on frequencies of 100, 192. 8

and 1046 Mc are located at the summit of Cheyenne Mountain at

an elevation of 8800 feet above sea level, approximately 3000

feet above the relatively flat plains to the east. Transmitters

on 92 and 210. 4 Mc are operated at a second site on the mountain

at an elevation of 7700 feet. A mobile 100 Mc transmitter has

been operated at an elevation of 6200 feet at the base of the

mountain and also at the summit of Pikes Peak, elevation 14, 110

feet above sea level and 9000 feet above the plains. Field

strength recording receivers have been operated at a number of

locations at distances ranging from 50 miles out to as far as 61

6

miles from the transmitters. Reception of all transmissions,

including the ones on 1046 Mc , has been found possible at all

times at all locations out to and including the 400-mile receiving

site at Anthony, Kansas. It may be appropriate to mention that

exceptionally high field strength recording system performance

is obtained in this program through the use of narrow band

techniques. Although the same degree of television system

performance would be extremely difficult to achieve because

of the much larger bandwidths involved, propagation factors

derived from the narrow band system employed in this research

program are applicable to television systems. Studies have been
•3- XVIII

conducted of the frequency dependence of propagation from 100 to

1000 Mc, including the attenuation with distance, and the magnitude of signal strength variations as a function of both time and

location.

Figure 3 shows sample recording charts of Cheyenne Mountain

transmissions on frequencies of 100 and 1046 Mc received at

Garden City, Kansas, at a distance of 225 miles from the mountain.

Signal strength calibrations are given in terms of basic transmission loss, which is the equivalent propagation path loss

encountered between the transmitter and receiver assuming

isotropic antennas. Thus, "basic transmission loss" implicitly

contains the reduced effective absorbing area of non-directional

antennas at the higher frequencies. When going from a VHF

frequency of 63 Mc to a UHF frequency of 700 Mc, this amounts

to an automatic increase in basic transmission loss of 21

decibels. It may be noted from Fig. 3 that the observed

difference in basic transmission loss between 100 and 1046 Mc

is about equal to the 20 decibels which would be expected just

on the basis of the reduced effective absorbing areas of nondirectional antennas for the two frequencies. Another observation which may be made from Fig. 3 is that the rate of fading

at the 1046 Mc frequency is approximately ten times that

observed at 100 Mc.

Figure 4 illustrates one type of analysis of data which has

been conducted for all of the field strength data taken in both

the VHF and UHF portions of the spectrum. These particular

data are the hourly medians of the 1046 Mc transmission loss

taken at Haswell, Colorado, 100 miles from the transmitter during the month of April 1953. The values of loss not exceeded by

10%, 50% and 90% of the measurements are shown as a function

of time of day.

In the National Bureau of Standards program of tropospheric

propagation research, approximately a quarter million hourly

median values of transmission loss have been analyzed for a great variety of frequencies, distance, antenna heights and

geographical locations. In these analyses it has been found

desirable to express distance in terms of a parameter G which
-4- XVIII

is defined in Fig. 5 for actual paths under study, as well as for a smooth spherical earth. The terrain profile in the great circle

plane between transmitting and receiving antennas is plotted on the

basis of an earth radius four-thirds times the actual radius, therebytaking into account standard atmospheric refraction. The angle

between lines drawn from the transmitting and receiving antennas

tangent to the actual horizons is the angle 0. When equals zero,

the two horizons coincide a condition commonly termed the line

of sight condition. It is seen that is also a measure of the

scattering region which is thought to be responsible for the

existence of signals far beyond the radio horizon. A paper describing the application of the principles of tropospheric scattering was

presented at the IRE 1953 National Convention and appears in the

1953 Convention Record. The term "angular distance" for the angle

is derived from the fact that for a smooth spherical earth it

constitutes the distance between horizons expressed in radians.

Fig. 6 shows the results of our analyses of the 100-Mc Cheyenne

Mountain data as a function of the angle for a wide range of

antenna heights, obtained by transmitting from an effective

antenna height of only 30 feet at Camp Carson, Colorado and

from the top of Pikes Peak. Also shown on this figure is the

expected transmission loss versus computed in accordance

with the diffraction theory in the region of less than about 10

milliradians , and in accordance with the tropospheric scattering

theory in the region greater than 10 milliradians. It is in the

region- of 10 milliradians that the scattering mechanism becomes

predominant. The degree to which the measured transmission

loss agrees with the computed values and the fact that both of

these are virtually independent of antenna height when plotted as

a function of angular distance, are well illustrated in this figure.

Another propagation factor of importance in television system

performance is the variability of tropospherically propagated . signals. Fig. 7 shows the results of our analyses of the longterm variability of transmission loss versus for the nation-wide

100 Mc study. The ratio between the 10% and 50% fields are given

by the upper curve and the ratio of the 50% and 90% are given by

the lower curve. The spread between the two curves gives a measure of the variability. It is evident that maximum variability

occurs at an angular distance of approximately 18 milliradians
-5- XVIII

which is just beyond the point where the scattered and diffracted

fields have become equal as indicated in Fig. 6. Beyond this

point the variability becomes less, presumably because the predominant scattering is taking place in a higher, less variable

portion of the troposphere. At this time the long-term signal

strength variability as a function of frequency in the range 63 to

1000 Mc is assumed to follow the values determined for 100 Mc

and depicted by Fig. 6, based principally on our data for the

Cheyenne Mountain path which agrees with scattering theory.

In Fig. 8 are shown, as a function of distance in statute

miles, the 100-Mc results of the National Bureau of Standards

analysis for antenna heights of 500 feet and 30 feet, and for

transmission loss levels not exceeded for 1% and 50% of the time.

Also shown are the tropospheric propagation curves derived by

the Ad Hoc Committee for the FCC in 1949 from the limited data,

then available. It may be seen that the new and old 1% curves

are essentially identical; however, considerable modification is

indicated by the new data for the 50% curves beyond about 80

miles, amounting to about 14 decibels at a distance of 1Z5 miles.

Based on the results of our analyses described in the

preceding, Fig. 9 shows basic transmission loss versus for

the TV frequencies at 63 and 700 Mc , and for antenna heights

of 30 feet at one end of the path and 50, 500 and 5000 feet at

the other end of the path. Again the independence of transmission

loss on antenna height may be noted when plotted as a function

of angular distance. The frequency dependence is also illustrated,

the 700-Mc basic transmission loss in most regions being

approximately 20 decibels greater than at 63 Mc.

Fig. 10 shows the same information as Fig. 9, but plotted

as a function of distance in miles over a smooth spherical

earth rather than in terms of angular distance. While the

analysis of data in terms of angular distance is facilitated by

reducing the effects of antenna heights and irregular terrain,

a plot of transmission loss versus distance re-emphasizes

the effects of antenna height as is illustrated here. For example,

essentially free-space fields may be expected out to 70 miles at

700 Mc with a very high 5000 ft antenna, while at 63 Mc free -space
-6- XVIII

fields would be expected only to about 20 miles with a similar height

antenna. Again the lower loss for 63 Mc is evident in this figure.

The curves shown here are for propagation over a smooth spherical

earth and additional analyses have been made in order to take into

account the effects of irregular terrain.

Fig. 11 shows data relating the median time varying fields to a median location in the presence of irregular terrain. Here the

connection with the theoretical median smooth earth basic transmission loss is given for distances beyond line of sight as a function

of frequency as derived from our most recent collection of data.

Also shown is the correction presented in Reference C of the work

of the 1949 FCC Ad Hoc Committee for distances greater than

37. 5 miles. It may be seen that our more recent 1000 Mc data

indicate that the 1949 correction factor is too severe in this

frequency range and the suggested tentative estimate is proposed

to replace the original curve at frequencies above 100 Mc.

Fig. 12 shows the terrain correction factor as a function of

distance for 63 and 700 Mc for transmitting antenna heights of

500 and 2000 ft. The data shown in Fig. 11 have been used for the

region beyond line of sight and the methods used by the FCC Ad

Hoc Committee have been used for the region within line of sight.

Up to this point, our latest knowledge of a number of the

important propagation factors for VHF and UHF television

frequencies has been discussed, including the basic transmission

loss versus angular distance, the basic transmission loss versus

distance in miles, the variability of transmission loss with time,

and the variability of transmission loss with location. The

question now arises, what do all these propagation data mean in

terms of television servece? Excellent methods were evolved by

the FCC Ad Hoc Committee for developing criterea of service

from a knowledge of the propagation factors which have just

been presented. These methods are contained in Reference E to

the FCC Ad Hoc Committee Report and will not be discussed here.

However, Fig. 13 has been prepared using these methods and the

most recent radio propagation data to determine the relative

number of locations receiving acceptable television service on 63

and 700 Mc for at least 90% of the time on the line between two
-7- XVIII

cochannel stations. The following system parameters were

assumed in the development of these results: effective radiated

power of 100 kw on 63 Mc and 1000 kw on 700 Mc; transmitting

antenna heights of 500 feet and receiving antenna height of 30

feet; half-wave dipole receiving antennas with 50 feet of RG 59/U

co-axial cable on both frequencies; and the same conditions of

signal-to-noise and signal-to-interference ratios to provide

satisfactory service as were developed by the FCC Ad Hoc

Committee. The required field strength in decibels above one

microvolt per meter for 63 Mc is 47 db and for 700 Mc is

75 db. The 28 db difference in required fields for the two

frequencies is made up of the 21 db difference in effective

absorbing areas of the dipole receiving antennas, 3.4 db

difference in noise figure, and 3. 6 db additional transmission

line loss at 700 Mc. The relative number of receiving locations

receiving service is proportional to the height of the curves and

the total number of receiving locations is proportional to the

total area under them. For each frequency, service is shown

for two situations - one corresponding to that limited by noise

alone, and the other corresponding to the service obtained on

the line between two cochannel stations of equal power and

antenna height at geographical spacings specified in the FCC

rules for Zone I stations. The small relative number of locations receiving service on UHF is strikingly evident on this

figure. Spacing UHF stations only 1 55 miles apart even reduces

this service. If UHF stations were spaced 200 miles apart,

the service would essentially return to that limited by noise

alone. It is quite evident from the propagation factors alone

that, from a "number of locations" standpoint, UHF stations

with 500-foot antennas heights will be at a considerable disadvantage with respect to 500 foot VHF stations even though the

UHF stations use one megawatt of effective radiated power.

There is a UHF propagation factor that may be taken

advantage of to improve this situation. It is the height gain

within the line of sight obtained at UHF that was pointed out

previously. Fig. 14 shows the same type of information shown

in the previous figure, but for transmitting antenna heights of

2000 feet instead of 500 feet. Here it is indicated that the

relative number of locations receiving service on UHF with
XVXII

the Zone I 155-mile separation is greater than that obtained on

VHF with Zone I 170-mile separation. Again 200-mile separation

on UHF would provide the additional service indicated which is

essentially limited by noise.

In conclusion, the propagation factors dictate that high power

and high antennas are mandatory for UHF to obtain any semblance

of equal coverage in the two frequency bands.
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Supplement XIX

WRIGHT FIELD LETTERS

Supplement XIX

WRIGHT FIELD LETTERS

No. 1 November 6, 1947 14.4

Colonel S. A. Mundell

Air Materiel Command

Electronic Subdivision

Engineering Division

Wright Field

Dayton, Ohio

Attention: TSELC5C2

Dear Colonel Mundell:

Subject: VHF-UHF Range Tests

Work is progressing on a theoretical propagation study concerning the above subject on the basis of the information supplied in

your letter of September 5, 1947.

Assuming that 6 watts are actually radiated from the transmitting antenna and that the antenna actually has a directivity

characteristic equivalent to that of a half wave dipole in free space,

the free space field intensity in the direction of maximum radiation

from the antenna will be 10,600 microvolts per meter at one mile.

Assuming that the receiving antenna actually has an absorbing

area equivalent to that of a half wave dipole and that all of the available

absorbed power is actually delivered to the receiver input, it follows

that a field intensity of 24. 9 microvolts per meter is required at

328 Mc to deliver a voltage of 3 microvolts across the receiver

input impedance which is assumed for these calculations to be 50 ohms.

(This value of impedance was not included in the September 5 letter

and we should be informed if the assumed value of - ohms is correct).

From the above, the calculated free space maximum range is

(10,600/24.9 = 428 miles; the observed air-to-air range of 200 miles
-2- XIX

at 17, 000 feet implies, if we neglect the presumably negligible

effects of ground reflection, that the assumption in the above paragraphs are optimistic by only 6.6 decibels.

In order to obtain more precise results, the following information would be useful:

(a) The measured radiation in the horizontal plane (free space

field intensity at one mile) from the aircraft antenna. This could be

measured by comparison with the radiation from a standard field

generator.

(b) The measured field intensity required to deliver a voltage of

3 microvolts across the receiver input impedance. This could also

be measured by means of a standard field generator.

(c) The transmission line lengths, impedance, and loss

characteristics per unit length; also the probable mismatch losses

for transmission and reception.

The calculations of the expected air-to-ground performance

involving the ground reflection lobes is not yet complete but the

results so far appear to bear out the conclusions tentatively reached

at the meeting here at CRPL. However, because of the rough terrain

along the propagation path quantitative agreement cannot be expected. For this reason it is considered to be of great importance

to plan air-to-ground tests of this equipment at some location where

the terrain within 3 miles of the ground station antenna is more

nearly level than that near Wright Field.

Expected air-to-ground performance over a smooth earth is

now being calculated for several ground antenna heights and for

both 328. 2 and 139. 14 Mc; these data will be furnished as soon as

completed.

Very truly yours,

hi

Kenneth A. Norton, Chief

Frequency Utilization Research Section

Central Radio Propagation Laboratory
-3- XIX

No. 2 January 29, 1948 14.4

ColonelS. A. Mundell

Air Materiel Command

Electronic Subdivision

Engineering Division

Wright Field, Dayton, Ohio

Attention: TSELC5C2

Subject: VHF-UHF Range Tests

Dear Colonel Mundell:

This letter is written with the object of informing you of our

progress to date on the problem of analyzing the propagation characteristics of VHF and of UHF frequencies for use in air-to-air

and air-to-ground communication. This project was started as a result of a conference held at CRPL on August 14, 1947 discussing

the significance of the comparative measurements made at Wright

Field of the ranges of similar VHF and UHF equipment. The

conclusions reached at that conference have been substantially

verified by our subsequent calculations. Thus we have reached

the following conclusions:

(1) The free-space-range for non-directive antennas will

decrease in direct proportion to the frequency provided the

receiver sensitivity and transmitter power are the same for

the various frequencies. This decrease in range is due to a decrease with increasing frequency in the absorbing area

of the non-directional receiving antenna. Since it is undoubtedly impracticable to use much, if any, directivity on the aircraft antennas it follows that the service range

for the UHF equipment can be made equal to that on the

VHF band only by using additional transmitter power in

direct proportion to the square of the frequency. Thus a

6 watt transmitter on 120 Mc/s will have the same freespace-maximum range as a 54 watt transmitter on 360

Mc/s. This conclusion is modified to some extent by the

effect of the ground as discussed below.
-4- XIX

(2) The reliable air-to-air maximum range will be very

nearly equal to the free-space-maximum range. The

waves reflected from the ground will tend to cause the

received field to fade (as the aircraft change their distance

or direction from each other)but the signals received in an

airplane from another airplane well above the line-of -sight

would be expected to be usable for more than 90% of the

time at a distance corresponding to half of the distance to

the free-space-maximum range and for more than 60% of

the time at the free-space-maximum range. Curves showing the air-to-air ranges to be expected for various

percentages of the time will be supplied in a later letter.

In the meantime reference may be made to our letter of

November 6 in which it was stated that the calculated freespace-maximum range on 328 Mc/s is 428 miles; this

calculated value was based on the assumption of no losses

throughout the system. If we allow 6 db for transmission

line or mismatch losses, the expected free-space-maximum

range will be only 214 miles. Thus the calculations indicate

that satisfactory air-to-air signals (greater than 3 microvolts) will be available across the receiver terminals for

more than 90% of the time at a distance of 107 miles and

for more than 60% of the time at a distance of 214 miles.

In your letter of September 5, 1947 the measured maximum reliable range on 328 Mc/s for aircraft at 17, 000 and

30, 000 feet was given as 200 miles; this value is considered to be in good agreement with the theory especially when

it is considered that the 6 db assumed loss may be somewhat too large. The measured decrease with increasing

frequency in the reliable air-to-air range from 200 miles

at 328 Mc/s to only 150 miles at 400 Mc/s is slightly more

than inversely proportional to the frequency; this slight

additional decrease in range, over and above the inverse

frequency variation expected because of receiving antenna

absorbing area changes, also is in accord with the theory

because of the slightly larger receiver noise figures and

system losses to be expected at the higher frequencies.
-5- XIX

(3) The ground-to-air (or air-to-ground) problem is more

complex and the situation in this case can best be understood by carefully studying the four figures enclosed with

this letter. Figures 1 and 2 show the expected ground-toair range over a smooth spherical earth with a transmitting

and receiving antenna pattern similar to that of a half-wave

vertical dipole. Figure 1 shows the expected coverage of a

6 watt transmitter operatingon-138 Mc/s. For example,

an airplane flying at an altitude of 30, 000 feet will receive

signals in excess of 12 microvolts out to a range of about

80 miles at which distance the received signals may be

expected to drop to 8 or 10 microvolts. At greater distances

the signals again increase and remain above 12 microvolts

out to a distance of 12*. miles. Between 120 and 150 miles

the received signals will drop down to 2 or 3 microvolts but

again increasing with increasing distance out to 200 miles

at which a received signal of 12 microvolts is expected.

Beyond 200 miles the signals again deer ase, finally dropping

below 3 microvolts at 240 miles, which is the expected

maximum range for an aircraft flying at 30, 000 feet over a smooth earth. It should be emphasized that the coverage

contours shown on this figure as well as on igures 2 and 3

are for antennas which have transmission and reception

characteristics symmetrical about the horizontal plans. The

vertical pattern of both the ground and aircraft antennas submitted with your letter dated January 13, 1948 indicate substantial differences in radiation for similar angles above and

below the horizontal. Thus the direct wave and ground reflected

wave radiation will be different and this will have the effect

of decreasing the coverage at angles near those corresponding

to the maxima of the lobes and will increase the coverage at

angles near those for the lobe minima. Reference to the

antenna pattern submitted will indicate that this unsymmetry

in the vertical plane will not be a large factor in the coverage

except for the region more than about five degrees above the

horizon.

Figure 2 shows the expected coverage of a 328 Mc/s system

with the same transmitter power and antenna height. The

difference between the coverage on 328 Mc/s and 138 Mc/s can
-6- XIX

best be appreciated by considering the lowest lobes on

figures 1 and 2 within which a signal in excess of 1

2

microvolts may be expected. On figure 1 this lowest

lobe has a maximum extending to 235 miles while the

corresponding maximum on figure 2 is only 100 miles.

It is quite clear from figures 1 and 2 that the coverage

on the higher frequency is much more spotty and generally

less dependable. In one respect the theory does indicate

that the higher frequency system is almost as good as

the lower frequency system and this is with respect to

the absolute maximum range over a smooth earth, i. e. , the distance, at the same height, to the point on the bottom

of the lowest lobe at which a signal of 3 microvolts is

expected. On 138 Mc/s this distance is 240 miles for an

aircraft at 30, 000 feet and is 233 miles on 328 Mc/s.

Figures 1 and 2 are for a smooth earth and standard

atmosphere. Reference to figure 4 shows that the terrain

involved in the Wright Field tests was far from being

sufficiently smooth to expect the coverage diagrams of

figures 1 and 2 to be applicable. Shown on figure 4

are the distances (for the two frequencies) out to the

centers of the Fresnel zones within which the ground

reflection can be considered to take place for aircraft

flying at some point near the maximum of the lowest lobe

when the propagation is over a smooth spherical surface.

These effective reflection zones begin several miles short

of the indicated zone centers and extend several miles beyond these centers. According to the paper "The Maximum

Range of a Radar Set", Proc. IRE, January 1947, page 24,

the allowable deviations in terrain height, Ah, must be less

than one-fourth of the transmitter height over the entire

Fresnel zone if the first lobe of coverage is to be well

developed. V/e see by figure 4 that the actual variations

within this zone are much greater than the permissible

3 feet and we conclude that the actual propagation will

deviate significantly from the predicted smooth earth values.

Irregularities in terrain will tend to reduce the ranges to

be expected at angles near the maximum of the lobe and to

increase the ranges to be expected at angles near the lobe

minima. Theoretical curves for the ranges to be expected

in very rough terrain are now being prepared and will be given

in a later letter.
-7- XIX

The observed air-to-ground range for an aircraft at

30, 000 feet was stated to be 220 miles and this is only

slightly less than the 240 miles expected for a smooth

earth as shown on figure 1. This small difference

between measurement and theory might easily be caused

by irregularities in terrain such as those on figure 4;

it should be noted that the irregularities in terrain would

be expected to affect the lower frequency somewhat less

because the Fresnel zone of reflection occurs nearer

to the transmitting antenna and covers a smaller area.

On 328 Mc/s the observed reliable air-to-ground range

for an aircraft at 30, 000 feet was stated to be only 90 miles

with spotty reception beyond that distance. Reference to

figure 3 indicates either that irregularities in terrain must

have had serious effects upon the four lowest lobes or that

the system loss for this particular flight test was unusually

high. Calculations indicate that the Fresnel zone for propagation to the middle of the fourth lobe extends from 0. 23 to

0, 99 miles from the base of the antenna and reference to

figure 4 indicates that the terrain is very flat over this

range of distances; permissible height deviations are, however,

only about 3 feet (actually one thirty-sixth of the transmitting

antenna height) for this fourth lobe Fresnel zone and thus

place a severe requirement on the site required to realize the

conditions postulated in the theory. Nevertheless, it does

seem surprising that the effective air-to-ground range on

328 Mc/s was not greater than 90 miles; further measurements

to confirm this unexpectedly low range are suggested.

(4) One practicable method of improving the air-to-ground

range on 328 Mc/s is to use a ground station antenna with

directivity in the vertical plane. For example, the use of

four vertically-stacked half-wave dipoles will be non-directional

in the horizontal plane but will tend to concentrate the radiation

near the horizon in such a way that the power gain for either

transmission or reception will be 2.62 times the value for a single half-wave dipole. The air-to-ground coverage for

such an antenna is shown on figure 3 and we see that the

coverage of such a system is considerably improved. The

long dashed curve on this diagram is the envelope of the 12
-8- XIX

microvolt lobe maxima and we see that the use of this

vertically directive antenna produces a gap in coverage at

an angle of 3 above the horizon. This gap extends for

several miles at the higher heights and might be considered

undesirable; however, such a gap is inevitable with

vertically directive antennas and represents the price

which must be paid for the added range at angles nearer to

the horizon.

(5) Coverage over a smooth earth almost identical to that

shov/n on figure 1 for 138 Mc/s may be obtained on 328 Mc/s

by decreasing the transmitting antenna height in proportion

to the increase in frequency, i. e. , to a height h = 115 x

(138/328) = 48 feet and simultaneously increasing the

effective transmitter power in proportion to the square of

the frequency, i. e. , to a power = 6 x (328/138) 3 34 watts.

V/ork is now in progress on the problem of computing the

expected coverage on 328 Mc/s for this case but it is known

in advance that it will be closely similar to that shown on

figure 1 for 138 Mc/s.

It is considered most desirable that further tests be conducted on the 328 and 138 Mc/s transmission from a site which is

sufficiently smooth to make possible a check of the calculated smooth

earth ranges and from another site sufficiently rough so that random

ground reflections can be considered in the calculations. The proper

interpretation of such tests can be made only from continuous

records of the received field intensity. Thus a requirement for

such tests is the availability of a transmitter which may be operated

continuously for several hours. Ideally this should -be an airborne

transmitter, but, if only a ground transmitter is available the field

intensity recording might be done in the airplane.

The additional calculations mentioned above will be supplied

as soon as they become available. In the meantime it will be
-9- XIX

appreciated if you will keep us advised of the results of any further

measurements made of either the ranges or of the transmitter,

receiver or antenna characteristics.

Very truly yours,

/s/

Kenneth A. Norton, Chief

Frequency Utilization Research Section

Central Radio Propagation Laboratory
-10- XIX

No. 3 April 22, 1948 14.4

ColonelS. A. Mundell

Air Materiel Command

Electroni c Subdivision

Engineering Division

Wright Field

Dayton, Ohio

Attention: TSELC5C2

Subject: VHF-UHF Range Tests

Dear Colonel Mundell:

This letter is written with the object of informing you of

further progress in the analysis of the air-to- air propagation

characteristics of the UHF and VHF frequencies used in air-toair and air-to-ground communications. Reference is made to a letter from Mr. K.A. Norton of this office dated January 29,

1948, which contained the primary results of the air-to-ground

portion of the analysis and a preliminary analysis of the

relative air-to-air performance in the VHF and UHF bands.

The results of further study of the air-to-air portion

of the problem are presented in the attached figures 5 and 6

wherein the calculated performance on both 138 Mc/s and 328

Mc/s for two aircraft flying at the same altitude are shown.

These figures show the regions within which (a) well defined

lobe structure would be expected, (b) the transition regions

between well defined lobe structure and Rayleigh distributed

ground reflected waves, and (c) the region where the space-wave

is made up of a direct wave and a Rayleigh distributed ground

reflected wave. These regions are calculated for irregular terrain

wherein height deviations from smooth earth conditions are as great as 100 feet particularly within the first Fresnel zone.

For larger irregularities of terrain and on higher frequencies

the regions of well defined lobe structures and the transition

regions would be a smaller fraction of the total coverage area.
-11- XIX

The solid line range reliability curves shown in the upper region

give the percentage of the time that three microvolts across the

receiver input terminals would be expected considering the received

field to be made up of a direct wave and a Rayleigh distributed

ground reflected wave. These curves are shown dashed in the

transition region and apply only if the terrain is sufficiently

irregular to produce Rayleigh distributed ground reflected waves

in this intermediate region. The radio line-of-sight, shown

as a dashed line on the figures, is the height at each end of the

transmission path of a plane tangent at the mid-point of the path

to the spherical earth with a radius 4/3 of the actual radius of

the earth to allow for average air refraction.

The method ordinarily employed for calculations of received

UHF field intensity well within the line-of-sight involves the vector

sum of a direct wave and a ground reflected wave which is assumed

to be reflected from a smooth spherical earth. Calculations using

this method result in well defined "lobe structures" as has been

illustrated in figures 1,2, and 3 of Mr. Norton's previous letter,

and which have been found to exist in VHF and UHF air-to-ground

propagation. However, when the limitations given in the paper

"The Maximum Range of a Radar Set" are applied in calculations

for very high antennas on each end of the path (communication

between two high flying aircraft) to determine the minimum

deviations in the height of the terrain within the principal region

from which the signal from the ground is reflected, it is found that

unless only small variations in the height of terrain exist, the

lobes will not be well defined in a large portion of the coverage

region. The limiting irregularities of height for well defined

lobes vary with altitude, distance and frequency.

A new theoretical approach to the problem of calculating

range reliability of air-to-air communication was employed in

arriving at the reliability contours shown in figures 5 and 6.

In this approach it is assumed that the terrain involved is

sufficiently irregular so that the received space-wave field

is made up of a conventional direct wave and a random phased

ground reflected wave, the intensity of which is distributed in

accordance with the Rayleigh distribution. The Rayleigh distribution
-12- XIX

is that which would be expected when a large number of signal components arrive at the receiving location in random phase as might

result at UHF and VHF from reflections from irregular terrain

consisting of hills, valleys, trees, buildings, and the like. The

combination of the random phased Rayleigh distributed ground

reflected wave with a direct wave has resulted in the statistical

spatial representation of communication reliability shown for the

two frequency bands in the two upper regions on figures 5 and 6.

(Not?: for stationary objects at the altitudes and distances indicated,

instead of percentage of time, the charts would read the probability

that the field intensity would be sufficient to produce 3 microvolts

across the receiver input terminals. ) When the terrain is sufficiently irregular to produce ground

reflected path length differences deviating from the smooth earth

conditions by as much as X-/8, the lobe structure begins to break

down. When this irregularity is sufficient to produce ground reflected path length deviations of one wavelength from smooth earth conditions and the irregularities are at random, the phase of the ground

reflected portion of the space-wave is assumed to be random and

its intensity Rayleigh distributed. These two conditions are

shown on the figures for deviations in terrain height of 100 feet

from smooth earth conditions as the lower and upper boundaries

respectively of the transition region. Deviations in terrain height

are particularly important in the first Fresnel zone, the size of

which depends upon the antenna heights, distance, and frequency.

Some idea of its magnitude can be gained by taking an arbitrary case

of two aircraft at 10, 000 feet 100 miles apart. Here it can be shown

using the equations from "The Maximum Range of a Radar Set, " that the dimensions of the first Fresnel zone ellipse are 7. 2 miles

long and 0.24 miles wide at 328 Mc/s and 11.3 miles long and 0.37

miles wide at 138 Mc/s. Referring to figure 4 of Mr. Norton's

letter of January 29, 1948, a perfunctory examination of the

terrain to the west of Wright Field, Ohio, would indicate that 100

foot variations in height within the first Fresnel zone is a reasonable

figure for the illustrated terrain contours west of Wright Field.
-13- XIX

The conclusions reached with regard to the relative merits

of the two frequencies for plane to plane communications based

on the above new theoretical approach to the VHF-UHF air-toair problem are given in paragraph (2) of the January 29 letter.

Figures 5 and 6 just give the detailed results of the calculations

mentioned in that letter.

It should be emphasized that the above mentioned new theorecical approach upon which figures 5 and 6 are based is tentative

and to our knowledge only meager experimental data exists that

may be analyzed to substantiate it. At a meeting held .April 6, 1948

between members of the Army Air Forces, Navy Department and the

Central Radio Propagation Laboratory, results of recent air-to-air

VHF-UHF tests made for the Navy by Collins Radio Corporation

were made available to the CRPL for analysis. A preliminary

analysis of the over-land air-to-air recordings indicates that the

data are in general agreement with the irregular terrain theory.

Further study of these data is in progress and other results will be

furnished as obtained particularly as regards the application of

similar statistical approach to air-to-air VHF-UHF propagation

over smooth terrain. In view of the sparceness of experimental

data on air-to-air VHF-UHF propagation, it may be desirable for

your organization to instigate an experimental study designed to

test this new approach to the problem in cooperation with the

Central Radio Propagation Laboratory. It is not feasible for CRPL

alone to carry out experiments of this type since required equipment

and aircraft are at present not available.

In paragraph (5) of the January letter, it was mentioned that

air-to-ground coverage over a smooth earth on 328 Mc/s almost

identical to that shown on figure 1 for 138 Mc/s could be obtained

by decreasing the transmitting antenna height in proportion to the

increase in frequency (from 115 to 48 feet) and simultaneously

increase the effective transmitting power in proportion to the square

of the frequency (from 6 to 34 watts). Figure 7 has been computed

for these conditions (ground antenna height above average terrain

s 48 feet; the effective transmitting power 13 x 4. 29/1. 64 : 34 watts)

and it may be seen that this coverage pattern for 328 Mc/s is

practically identical to that shown in figure 1 for 138 Mc/s as was

expected. In this computation, the ground antenna is assumed to
-14- XIX

be a four element colinear array with a power gain of 4. 29 over

an isotropic antenna; with its use the free space maximum range

for 328 Mc/s was made equal to that of 138 Mc/s by increasing

the power by a factor of 2. 16 as compared with a factor of 5. 65

necessary if half-wave dipoles had been assumed for both frequencies.

A null at 30 above the horizon is the price paid for using a colinear

array instead of a higher power transmitter.

It will be appreciated if you will keep us advised of the results

of any further measurements made of either the ranges of the

transmitter, receiver or antenna characteristics. It is considered

most desirable that further well planned measurements be made

as previously suggested. If you so desire, arrangements may

be made to have a member of CRPL familiar with the theoretical propagation aspects of the air-to-air /air-to-ground communications problem visit your laboratory for further discussion

and assist with future measurements and tests.

Very truly yours,

Is/

Jack W, Herbstreit

Frequency Utilization Research Section

Central Radio Propagation Laboratory
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Supplement XX

ANALYSIS OF THE GROUND WAVE AND TROPOSPHERIC WAVE

FIELD INTENSITY VARIATIONS AT A DISTANCE FAR BEYOND THE

LINE-OF-SIGHT FOR AN FM BROADCASTING STATION

OPERATING ON 99.7 Mc

By

R. S. Kirby

Supplement XX

ANALYSIS OF THE GROUND WAVE AND

TROPOSPHERIC WAVE FIELD INTENSITY VARIATIONS

ATA DISTANCE FAR BEYOND THE LINE-OF-SIGHT FOR

AN FM BROADCASTING STATION OPERATING ON 99.7 Mc

By

Robert S. Kirby

National Bureau of Standards

Boulder, Colorado

For the purpose of obtaining a better understanding of the nature of

the variation in field intensities at large distances far beyond the lineof-sight in the frequency modulation broadcast band, field intenisty

recorders were installed at the National Bureau of Standards in

Washington, D. C. , late in 1947. These recorders consisted of

Hallicrafters' Model S X-42 AM-FM receivers so modified that the

input signal voltage could be recorded on an Esterline Angus recording milliameter. Calibration of the recordings was effected by the

use of a suitable signal generator, several types of which were used.

Continuous recordings were made of the field intensities of several

frequency modulation broadcast stations. One of the most complete

records is that of frequency modulation broadcast station WSAP-FM

in Portsmouth, Virginia, broadcasting on a frequency of 99. 7 Mc and at

an airline distance of 151 miles from the receiving location at the

National Bureau of Standards. The terrain profile over this path

is shown in the attached figure. The center of the WSAP-FM transmitting array is 356 feet above sea level, and the average terrain

in the direction of Washington, D. C. , is essentially water at sea

level to a distance of about 11 miles. The effective radiated power

(i.e. radiated power times antenna power gain relative to a half wave

dipole) in this direction was 49 kilowatts to July 17, 1949, and from

this date on, 100 kilowatts. At the receiving end a three-element

Yagi array was used with a gain of 9.3 decibels with respect to an

isotropic antenna; this was erected on the roof of the Northwest

building of the National Bureau of Standards. This receiving array

was 80 feet above the ground level as shown in the figure. On
-2- XX

September 10, 1948 a recording site was set up in the West building,

and the records obtained from this site were used from this date on. The receiving antenna here consisted of a half-wave dipole about

15 feet higher above sea level but again only about 80 feet above the

ground which was about 15 feet higher at the latter location. This

location was approximately 200 yards to the southwest of the original

location.

The calibration technique consisted of comparing the meter deflection

from an unknown input voltage with that of a known input voltage from

the signal generator and applying a calibration factor to obtain readings

in terms of microvolts-per-meter.

The data were analyzed by tabulating the median field intensity for

each hour. A total of 3 071 hours were thus analyzed for the WSAPFM transmissions between April 30, 1948 and January 28, 1949. The

hours used are shown in the tabulation at the end of this report.

The distribution with time of the hourly median field intensity was

plotted separately for each hour of the day and then an overall distribution was determined from these separate hourly distributions by

giving each hour for which distribution curves were available equal

weight, regardless of the number of days for which measurements

were made at the various individual hours. In all cases shown in the

tabulation the value of field intensity used refers to an effective

radiated power of 100 kilowatts. For the period in which the effective

radiated power was 49 kilowatts, a correction factor was applied to

the data. The results of this analysis are tabulated in terms of the

value of field intensity that was exceeded for the given percentages

of time. This particular analysis of these data was prepared to

assist in the work of the Ad Hoc Committee appointed by the FCC

to study VHF field intensity propagation.

The following memebers of CRPL participated actively in obtaining and analyzing these data:

Mr. M. Blum

Mr. H. Bussey

Mr. J. H. Chisholm

Mr. E.G. Cowen
-3- XX

Mr. J. Harman

Mr. L. C. Huffman

Mr. V. LaBolle

Dr. W. Miller

Mr. E.Y. Mitoma

Mr. D.L. Randall

Mr. H. Staras

Mr. K. F. Tritabaugh

Mr. W.W. Warren

Mr. J. W. Whitmore

Mr. W. P. Witkowski
-4.

Number of days field intensity record of WSAP-FM was analyzed

by hour of day during the period April 30, 1948 to January 28, 1949.

Hour Apr. May June July Aug. Sept. Oct. Nov. Dec. Jan, Total

00-01 5 7 01-06 Off the Air

19 22 22 24 18 23 16 156

06-07 4 7 16 24 22 25 19 25 17 159

07-08 4 7 16 25 22 25 19 25 17 160

08-09 6 8 18 29 23 29 22 27 19 181

09-10 1 15 8 19 28 22 29 24 28 19 193

10-11 1 15 9 18 29 22 31 24 28 18 195

11-12 1 15 9 21 29 21 31 26 28 18 199

12-13 1 15 9 20 29 22 31 26 28 18 199

13-14 1 14 9 20 29 22 31 25 28 15 194

14-15 1 14 9 21 29 24 31 25 27 17 198

15-16 1 12 9 20 29 23 30 24 26 18 192

16-17 1 14 9 21 29 23 23 19 16 8 163

17-18 1 14 9 21 30 23 21 0* 1 0* 120

18-19 1 14 9 20 30 23 20 0* 0* 0* 117

19-20 1 14 9 21 30 23 20 0* 0* 0* 118

20-21 1 14 9 22 30 22 20 0* 0* 0* 118

21-22 1 14 9 22 30 22 20 0* 0* 0* 118

22-23 6 8 22 30 22 20 0* 1 0* 109

23-24 4 7 22 30 23 30 23 26 17 182

Total 13 213 160 379 541 426 491 294 337 217 3071

* Record not available at these hours during these months

because of interference from WCFM operating on 99.5 Mc.
-5- XX

Distribution of hourly median values of field intensity for 100 kw

transmission from WSAP-FM, Portsmouth, Va. , 99.7 Mc . as received at National Bureau of Standards, Washington, D. C.

Hour 1% 10% 50% 90% 99%

00-01 520 98 27.5 9.1 3.5*

01-06 Off the Air

06-07 255 106 29.5 7.8 2.8*

07-08 222 109 29.0 8. 1 2.7*

08-09 380 128 28.5 8.8 3.0*

09-10 395 102 22.0 8.3 3.0*

10-11 27 74 21.0 7.3 2.7*

11-12 182 60 17.5 6.2 2.6*

12-13 148 53 16.0 6.0 2.7*

13-14 123 50 15.0 5.7 2.8*

14-15 121 56 13.9 5.4 2.4*

15-16 138 57 15.2 5.9 2.9*

16-17 180 57 14.3 4.8 2.1*

17-18 186 38 13. 1 4.6 2.1*

18-19 440 42 12.5 5.0 2. 1*

19-20 155 45 14.7 4.9 2.2*

20-21 180 53 15.5 4. 1 1.8*

21-22 320 52 18.0 5. 1 2.3*

22-23 180 67 23.0 6.0 2. 1*

23-24 440 87 22*5 7.6 2.6*

Total distribution of hourly median values of field intensity (giving

equal weight to each hour)

1% 10% 50% 90% 99%

250** 71 18.5 5.9 2. 2*

*Extrapolated values.

**3ome extrapolated points used to obtain this value.

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Supplement XXI

PROPAGATION OVER ROUGH TERRAIN

By

K. A. Norton

Originally presented at U.S. NEL Symposium,

July 25, 1949, NE 12030 1 , Report 173, Problem NEL 1A1, p. 101, U.S. Navy Electronics

Laboratory, San Diego, California.

Supplement XXI

PROPAGATION OVER ROUGH TERRAIN

By

Kenneth A. Norton

National Bureau of Standards

Boulder, Colorado

It is intended here to describe some of the characteristics of

two important mathematical tools useful in statistical predictions

of ground-wave propagation, and to demonstrate, by an example,

their applicability to the description of radio propagation over irregular terrain. It should be stressed at the outset that this is

but an interim report on y. lo-I.; which have been found useful in a

field in which new and better methods of analysis are being developed

almost daily. The methods to be described have been useful in

stimulating thinking on this subject and are passed along at this

time merely as a progress report and not as completed research.

The Rayleigh Distribution

Lord Rayleigh solved the problem of determining the probability

distribution of the intensity and phase of the resultant vector, E , obtained by adding together, with random relative phase, a large

number of vectors, Ei, E ?

, and so forth up to E , as shown in

figure 1. If E is a constant, i.e., the mean energy in the reflected

? 2

wave is a constant, E^ a « E for i = 1 to n, the phase of each

component vector E- is random, and n is sufficiently large, then

(1) the probability that the resultant E g will be greater than x is

given by the cumulative Rayleigh distribution, P(E g > x) = exp

(-x /E r

), and (2) the phase of the resultant vector E will also be

random.

Figure 2 shows the result of the deviations from one of the above

four requirements: the effect of reducing the number, n, of the

component vectors. This particular graph paper has been constructed
-2- XXI

in sur a way that a Rayleigh distributed vector of amplitude, E , will be represented by a straight line with a slope of -1. The

distributions shown here are for n unit vectors added with random

relative phase. Thus, the root-sum-square value in each case

is equal to the square root of n. The ordinate gives Eg divided by

this root-sum-square value. It can easily be shown that the rootmean-square value of E s is equal to \/n. The maximum amplitude

of the resultant of n vectors is, of course, simply equal to n. The

rapid approach to a Rayleigh distribution is clearly shown by the

curves for n = 2, 3, and 4. Throughout the range of this particular

graph, that is, from a value of 0.01 per cent up to 99.99 per cent,

the distribution for n - 10 deviates from the true Rayleigh distribution

by less than the width of the line. It is important to notice that

a complete specification of a Rayleigh distributed wave can be made

in terms of a single parameter which is, in effect, a measure of the

total energy in the wave. This single parameter might be the rms

value which is exceeded by 36.8 per cent of all the values which

the amplitude of E s may have. A Rayleigh-distributed amplitude

could equally well be defined in terms of a value exceeded for

some specified percentage of the time; for example, the median,

or 50 per cent amplitude is equal to 0.8326 times the rms value of Es

Figure 3 considers the distribution of the instantaneous voltage,

v, to be expected from a Rayleigh-distributed vector with amplitude,

E s , and random phase [u.t + §) . If p(E > x) = exp -(x /E 2), then

co

p (v > X) = -i—

\ exp (-y 2 /2)dy.

\/2tt

(Xv/2/E.)

We find that this voltage is distributed in a normal distribution with

a mean value of zero and a standard deviation E / N/2, where E is

the rms value of E g

,

In many radio propagation studies, the received fields are

rectified before being recorded, and thus continuous recorders

ordinarily provide records of the variations of the inherently positive amplitudes, E , of the envelope rather than of the instantaneous

voltage, v, which may be either positive or negative. For this
-3- XXI

reason, in the remainder of the discussion of the Rayleigh distribution, no further mention will be made of the instantaneous voltage v. This

brief discussion of the normal distribution of instantaneous voltage

was presented because ir is sometimes confused with Rayleigh

distribution of the amplitude of E , and in this paper only the latter

distribution will be used.

Application of the Rayleigh Theory

The application of the above theory to a problem of ground-wave

propagation over irregular terrain can now be discussed. It is well

known that the resultant field, E, to be expected in propagation over

a smooth earth at points within the line-of-sight, may be considered

to be the vector sum of a direct wave, ED , plus a ground-reflected

wave, Ea , as shown in figure 4a, Over a smooth spherical earth,

the ground-reflected wave will be weaker than the direct wave, not

only because some of its energy is lost by absorption, but also because

of a divergence of the energy on reflection at the curved surface of

the earth.

O'-er a rough earth, it is convenient to consider the groundreflected wave to be the resultant of a large number of component

vectors with random relative phases as indicated in figure 4b. Thus,

each component vector may be considered to have its phase determined

by the length of the path from the transmitting antenna to the corresponding bounce point and thence to the receiving antenna. The bounce

points on the rough reflecting surface, corresponding to the several

component vectors, are the locations on the surface for which the

phase is stationary; that is, the path length is either a minimum or

a maximum. When the earth is sufficiently rough, the frequency

sufficiently high, and the angle of incidence sufficiently small--that

is, not too near to grazing incidence--it will be found that the relative

phases of the individual component vectors will be comparable to or greater than 2rr radians. Under these circumstances, all values of

the relative phase between the component vectors are equally likely.

The above description of the ground-reflected wave over a rough

earth is simply that of a Rayleigh distributed wave. It has already

been seen that such a wave is completely described by its rms amplitude, E r , If there were no additional loss in the ground-reflected
-4- XXI

wave energy due to roughness, this rms amplitude, E r

, would simply

be equal to the amplitude, E„, of the wave reflected from the smooth

earth. For the present, it will be sufficient to let E r

= kE^ = Ej 2 + E 2

2 + E

3

2 + E 4

2 + E

5 + E^ 2

, where k is a constant, usually

lees than unity, which denotes the energy in the rough-earth groundreflected wave relative to that in the direct wave.

It might at first sight appear that the vector sum of the direct

wave, E , plus the Rayleigh-distributed, rough-earth, groundreflected wave would also be distributed in a Rayleigh distribution,

but this does not follow because of the fact that the component vector,

E , is, in this case, not small compared to the root-sum-square value

of all of the components.

In figure 5 is shown the expected distribution of a resultant when

the energy of one of the individual component vectors, represented by

E S is not small in comparison to the total energy represented by

(E 2 +E r 2

), It will be noted that the resultant, E, is Rayleighdistributed only for very large values of k, that is, only for very

large values of multiple -component, Rayleigh-distribution energy

compared to the single -component, direct-wave energy. Such large

values of k would be expected only in an unusual situation where the

direct wave is suppressed, for example, by means of a transmitting

array directed away from the actual receiving antenna toward the

center of gravity of the images of the receiving antenna in the rough

ground.

As k becomes smaller and smaller, that is, as the random energy

becomes small in comparison to the direct wave energy, the slope

of the distribution becomes smaller. This should be noted in connection with later experimental results.

The results shown here can also be used in the case where the

individual component vectors do not have completely random relative

phases. Consider, for example, the situation where the individual

vectors have phases which vary at random only through a restricted

total range of phase variation much less than 2tt, In this case, each

individual component vector can be resolved into two other components,
-5- XXI

one of which can be considered to consist of coherent, specularly reflected energy, and the other to consist of scattered energy. The

coherent components can be added to give the vector designated at E

(in figure 5), while the root-sum-square value of the incoherent components is simply E . Thus, it becomes possible to determine the

distribution of the amplitude of a wave reflected at a moderately rough

surface, simply by identifying a specularly reflected component, E

and a scattered component, Er

.

Experimental Applications

Some of the concepts just described can best be illustrated by

applying them to the explanation of the results of a propagation experiment

illustrated in figure 6, In this experiment, two aircraft flew away from

each other at an altitude of 9800 feet. Field intensity measurements were

made in one of the aircraft by the Collins Radio Company of the simultaneous transmissions from the other on 123 Mc and 328 Mc, Two

flights were made, one with the midpoint of the transmission path on

land in the Midwest, and the other with the midpoint on Lake Michigan,

Calculations indicated that regular fading was occurring at the rate

which would be expected for interference between a direct and a groundreflected wave. Under these caidi tions , the field intensity maxima should

be equal in amplitude to the sum of the direct wave amplitude plus the

ground-reflected wave amplitude, and the observed minima equal to

the difference in these two amplitudes. By measuring these maxima

and minima, it is possible to calculate the value of the ground reflection

coefficient. A separate value of this ground reflection coefficient can

be obtained from each maximum and succeeding minimum.

Figure 7 shows the distribution of the ground-reflection coefficients

determined in this way for these two distance ranges. The lines having

the slope of -1 are the Rayleigh distributions determined from the rms

value of the reflection coefficient and are given by p = 100 exp

[j(E-/En) /(Ep/Eq ) |. It will be noted that the measurements are in

good agreement with the theory at the shorter of the two distai ce ranges

corresponding to more nearly oblique incidence on the ground (the

angle at the earth's surface is 3 degrees). The data at the larger range

did not agree as well with the Rayleigh distribution, presumably because

of the larger angle of incidence, nearly 89 degrees in this case. Thus,
-6- XXI

it appears that the ground is beginning to appear more nearly smooth

to the radio waves at this grazing angle of only about 1 degree. By

using the curves shown in figure 5, it is possible to estimate from the

slope of this curve the relative amount of the energy scattered and

specularly reflected. In this particular case, it has been determined

that the energy received by specular reflection is about six times the

scattered energy. It should be noted that the rms reflection coefficient

is somewhat larger at the larger range.

The magnitudes of the ground-reflection coefficients will now be

considered. In figure 8 the points plotted represent rms values of the

ground-reflection coefficients. Each point is the rms value obtained

from about 40 separate determinations. The circles joined by a dashed

curve denote values measured over land on 328 Mc, while the crosses

joined by a dotted curve represent values measured over land on 123

Mc. The upper solid curve corresponds to a reflection coefficient

calculated on the assumption that the earth is smooth and may be

represented by a dielectric constant equal to 30; thus, these values

correspond to the product of a plane-wave reflection coefficient multiplied by a divergence factor to allow for the effects of earth's curvature

in spreading the energy in the reflected wave. The low values of

reflection coefficient at the shorter distances are caused by earth

absorption near the pseudo-Brewster angle, while the low values at

large distances are due to the larger divergence expected near grazing

incidence. The lower solid curve corresponds to Lambert's law of

reflection from diffuse surfaces; thus, according to this law, the energy

reflected is proportional to the cosine of the angle of incidence. Lambert's

law does not specify the magnitude of the reflection; this has been assumed

in these curves to be the plane -earth reflection coefficient. Thus, it is assumed that the divergence factor, D, over a smooth sphere should

be replaced by the factor, ycos^, for a perfectly rough earth, the

latter corresponding to a much greater divergence of the energy due to

scattering. For the transition between the perfectly smooth and perfectly

rough calculations,

|

', ^2 ?. , 4tt Ahcos j> %

, 4uAhcoscl> */

2

|R| = LD'-cos^ ( ^ =-) +cos ^ sm^ \ J_J
-7- XXI

In figure 9 are values similar to those of figure 8, but representing

propagation over Lake Michigan, In this case, it was assumed that the

dielectric constant should be 80, and it is noted that the pseudo-Brewster

effect occurs now at a larger range. The large value of £h= 10 ft,

which seems to agree best with experimental data, is difficult to believe

unless Lake Michigan was unusually rough. However, it is not known

how far out over the lake the measurements were made, and it may be

that shore reflections played a large part in the measured results.

THE RAYLEIGH DISTRIBUTION OR RANDOM WALK

Ef -Ef+ ••• Ef+---+ES

2

if (I) E r is a constant, i.e. the mean energy in the

reflected wave is a constant

and (2) E* << E* for i = I to n

and (3) The phase of each component vector Ej is random

and (4) n is sufficiently large

then (I) The probability that the resultant Es will be greater

than X is given by the cumulative Rayleigh distribution:

(E

S >X) e

and (2) The phase of the resultant vector E s will also be random

NBS NATIONAL BUREAU OF STANDARDS

CENTRAL RADIO PROPAGATION LABORATORY MAY 1949

Figure I
THE RESULTANT OF n UNIT VECTORS WITH RANDOM RELATIVE PHASE

-_Ls

"fn

10

7

5

3

2

I

0.7

0.5

0.3

0.2

0.1

0.07

0.05

0.03

0.02

0.01

NATIONAL BUREAU OF STANDARDS CENTRAL RADIO PROPAGATION LABORATORY ~

VALUES OF X DISTRIBUTED ACCORDING

TO THE RAYLEIGH DISTRIBUTION

-X

2 p=iooe

WILL BE ON A STRAIGHT LINE WITH SLOPE OF -1

" ^

> n=4

n=3

rl-JI

\\\<>.

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0.01 0.1 I 5 10 30 50 70 90 95 99 99.9 X

99.99

EXPECTED PERCENTAGE OF THE RESULTANTS WITH A FIELD INTENSITY

GREATER THAN THE ORDINATE

Figure 2 JVBS.
THE NORMAL DISTRIBUTION OF VOLTAGE, OT,

DERIVED FROM A RAYLEIGH DISTRIBUTED

VECTOR OF AMPLITUDE E„

NATIONAL BUREAU OF STANDARDS CENTRAL RADIO PROROGATION LABORATORY

JULY 1949

tr** Es cos (00t + ^)

-(X/'E?)

if (I) p(EQ >X) = e

r

then p(^>X) = ^=

and (2) all values of (00t+^) are equally likely. ooe-v

2/2

dy

(XiT/E r

) mean value of or =

standard deviation of v = root- mean-square voltage = E

r /"(2

E r = root- ian-square value of the amplitude E s

Figure 3 <NBS>
VECTOR REPRESENTATION OF DIRECT AND

GROUND -REFLECTED WAVES FOR SMOOTH OR ROUGH EARTH

Direct Wave E,

E n Ground-Reflected

Wave

E Resultant Wave at Receiving Antenna

Q. SMOOTH EARTH

Direct Wave E

Multiple Ground-Reflected Waves

o o p p o p ! Er

-- £; * ef* e;* e,+e;+e;)

E Resultant Wave at Receiving Antenna

b. ROUGH EARTH

Figure 4

NATIONAL BUREAU OF STANDARDS

CENTRAL RADIO PROPAGATION LABORATORY MAY 1949
THE SUM OF A DIRECT WAVE PLUS A RAYLEIGH DISTRIBUTED

GROUND- REFLECTED WAVE

10

7

5

3

2

I

0.7

0.5

0.3

0.2

0.1

0.07

0.05

0.03

0.02

0.01

i NATIONAL BUREAU OF STANDARDS

- CENTRAL RADIO PROPAGATION LABORATORY - MAY 1949 SZ(

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|E(k = 0.l)l

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lE(k = 0.5)|

|E(k = 0.8)|

|E(k=5)l

|E (k = 2)|

0.01 0.1 I 5 10 30 50 70 90 95 99 99.9 99.99

EXPECTED PERCENTAGE OF THE RECEIVING LOCATIONS WITH A RESULTANT

INTENSITY GREATER THAN THE ORDINATE VALUE

NBS.

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Supplement XXII

OBSTACLE GAIN MEASUREMENTS OVER PIKES PEAK

AT 60 TO 1046 MC

By

R. S. Kirby, H. T. Dougherty and P. L. McQuate

National Bureau of Standards

Bouldero Colorado

See No. 355, page H2q, in the list of technical abstracts.

I .S. DEPARTM ENT OF COMMERCE /^f2^,

Frederick H. Mueller, Secretary Iff ££ ^S\

NATIONAL BUREAU OF STANDARDS W^EW A. V. Astin, Director ^i^j^

THE NATIONAL BUREAU OF STANDARDS

The scope of activities of the National Bureau of Standards at its major laboratories in Washington, D.C., and

Boulder, Colorado, is suggested in the following listing of the divisions and sections engaged in technical work.

In general, each section carries out specialized research, development, and engineering in the field indicated h\

its title. A brief description of the activities, and of the resultant publications, appears on the inside of the front

cover. WASHINGTON, D.C.

Electricity and Electronics. Resistance and Reactance. Electron Devices. Electrical Instruments. Magnetic Measurements. Dielectrics. Engineering Electronics. Electronic Instrumentation. Electrochemistry.

Optics and Metrology. Photometry and Colorimetry. Photographic Technology. Length. Engineering

Metrology.

Heat. Temperature Physics. Thermodynamics. Cryogenic Physics. Rheology. Molecular Kinetics. Free Radicals Research. Atomic and Radiation Physics. Spectroscopy. Radiometry. Mass Spectrometry. Solid State Physics. Electron Physics. Atomic Physics. Neutron Physics. Radiation Theor\ . Radioactivity. X-rays. High

Energy Radiation. Nucleonic Instrumentation. Radiological Equipment.

Chemistry. Organic Coatings. Surface Chemistry. Organic Chemistry. Analytical Chemistry, inorganic

Chemistry. Electrodeposition. Molecular Structure and Properties of Gases. Physical Chemistry. Thermochemistry. Spectrochemistry. Pure Substances.

Mechanics. Sound. Mechanical Instruments. Fluid Mechanics. Engineering Mechanics. Mass and Scale. Capacity, Density, and Fluid Meters. Combustion Controls.

Organic and Fibrous Materials. Rubber. Textiles. Paper. Leather. Testing and Specifications. Polj - mer Structure. Plastics. Dental Research.

Metallurgy. Thermal Metallurgy. Chemical Metallurgy. Mechanical Metallurgy. Corrosion. Metal

Physics.

-Mineral Products. Engineering Ceramics. Glass. Refractories. Enameled Metals. Constitution and Microstructure.

Building Technology. Structural Engineering. Fire Protection. Air Conditioning, Heating, and Refrigeration. Floor, Roof, and Wall Coverings. Codes and Safet) Standards. Heat Transfer. Concreting Materials.

Applied Mathematics. Numerical Vnalysis. Computation. Statistical Engineering. Mathematical Physics.

u Data Processing Systems. SEAC Engineering Group. Components and Techniques. Digital Circuitry.

Digital Systems. Analog Systems. Application Engineering.

• Office of Basic Instrumentation. • Office of \\ eights and Measures. BOULDER, COLORADO

Cryogenic Engineering. Cryogenic Equipment. Cryogenic Processes. Properties of Materials. Gas Liquefaction. Radio Propagation Physics. Upper Atmosphere Research. Ionospheric Research. Regular Propagation

Services. Sun-Earth Relationships. \ III-' Research. Radio Warning Services, Airglow and Aurora. Radio

Astronomy and Arctic Propagation.

Radio Propagation Engineering. Data Reduction Instrumentation. Modulation Research. Radio Noise. Tropospheric Measurements. Tropospheric Analysis. Propagation Obstacles Engineering. Radio-Meteorology. Lower Atmosphere Physics.

Radio Standards. High Frequencj Electrical Standards. Radio Broadcast Service. High Frequenc) lmpedance Standards. Electronic Calibration Center. Microwave Physics. Microwave Circuit Standards. Radio Communication and Systems. Low Frequencj and Very Lovi Frequencj Research. High Fre- quency and Verj High Frequenc) Research. I Itra High Frequency and Super High Frequencj Research. Modulation Research. Antenna Research. Navigation Systems. Systems Analysis, field Operations.
NBS