U.S. DEPARTMENT OF COMMERCE

Maurice H. Stans, Secretary

ENVIRONMENTAL SCIENCE SERVICES ADMINISTRATION

Robert M. White, Administrator

RESEARCH LABORATORIES

Wilmot N. Hess, Director

ESSA TECHNICAL REPORT ERL 148-ITS 97

Comparison of Propagation Measurements

With Predicted Values in the 20

to 10,000 MHz Range

A. G. LONGLEY

R. K. REASONER

INSTITUTE FOR TELECOMMUNICATION SCIENCES

BOULDER, COLORADO January 1970

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D. C. 20402 Price S 1.00

FOREWARD

This document, the final report covering task 2. 8m , n & o,

is submitted by the Institute for Telecommunication Sciences,

Boulder, Colorado, in accordance with contract F04 701-68-F-0072.

The Air Force Project Officer was Captain M. A. Heimbecker of

Headquarters Space and Missile Systems Organization, SMQNL-3,

Air Force Systems Command, Norton Air Force Base, California.

The study was initiated on 1 July and completed by l February 1970.

Informat ion in this report is embargoed under the Department

of State International Traffic in Arms Regulations. This report may

be released to foreign governments by departments or agencies of

the U.S. Government subject to approval of Space and Missile

Systems Organization (SMSD), Los Angeles AFS, California, or

higher authority within the Department of the Air Force.

Publication of this report does not constitute Air Force

approval of the report• s findings or conclusions. It is published

only for the exchange and stimulation of ideas.

iii

TABLE OF CONTENTS

Page

1. INTRODUCTION 1

2. AREA PREDICTIONS COMPARED WITH MEASUREMENTS 3

2. 1 Gunbarrel Hill, Colorado, R-1

2. 2 Fritz Peak, Colorado, R-2

2. 3 Virginia Paths

2. 4 Wyoming, Idaho, and Washington

2. 4. 1 Wyoming area

2. 4. 2 Idaho area

2. 4. 3 Washington area

2. 5 Measurements at VHF

2. 5. 1 Colorado plains

2. 5. 2 Colorado mountains

2. 5. 3 Northeastern Ohio

2. 6 Summary of Area Predictions

3. POINT-TO-POINT PREDICTIONS COMPARED WITH MEASUREMENTS

3. 1 Gunbarrel Hill and Fritz Peak, Colorado

3. 2 Virginia

3. 3 Wyoming, Idaho,and Washington

3. 4 Measurements and Predictions at VHF

3. 5 Established Communication Links

4. CONCLUSIONS

5. REFERENCES

lV

4

13

19

25

26

29

33

38

39

43

43

50

51

53

63

67

75

90

98

102

COMPARISON OF PROPAGATION MEASUREMENTS

WITH PREDICTED VALUES IN THE 20 TO 10, 000 MHz RANGE

A. G. Longley and R. K. Reasoner

Predictions of tropospheric transmission loss over irregular terrain using the computer methods described

by Longley and Rice ( 1968) are compared with measure -ments, to determine their limits of applicability and define the boundary conditions for their use. Area

predictions for mobile systems where individual path

profiles are not available are compared with measure­ments made with low antennas in Colorado, Ohio, Virginia, Wyoming. Idaho, and Washington. Point-to­point predictions for fixed antenna locations are compared with measurements for each of these paths and for a large number of propagation paths in various parts of the world.

Key Words: Fixed point systems, irregular terrain, mobile systems, prediction methods, tropospheric

propagation.

1. INTRODUCTION

Predictions of tropospheric transmission loss over irregular

terrain using the computer methods described by Longley and Rice (1968)

are compared with a large amount of data to determine their limits of

applicability and define the boundary conditions for their use. The

computer methods may be used either with detailed terrain profiles to

predict the transmission losses expected for specific paths or for

11area11 predictions where path parameters that are representative of

median terrain characteristics for a given area are calculated. These

calculations are based on a large number of terrain profiles for widely

different types of terrain ranging from smooth plains to rugged mountains.

Median propagation conditions for a specific area are charac­

terized by a terrain parameter Ah expressed in meters. To obtain an

estimate of Ah, the inter decile range A h(d} of terrain heights above and

below a straight line (fitted by least squares to elevations above sea

level) is first calculated at fixed distances for a representative group of

terrain profiles. The median values of A h(d) increase with distance,

approaching an asymptotic value Ah that characterizes the terrain. When

an estimate of Ah is available, the median value of Ah(d} at any desired

distance may be obtained from the relationship:

Ah(d) =Ah [1-0. 8 exp (-0. 02d) J m, ( 1}

where Ah and Ah{d} are in meters, and the distance d is in kilometers.

When an estimate of the terrain parameter Ah has been

obtained the other essential parameters are: the radio frequency f in

MHz, the path distance d in km, and the transmitting and receiving

antenna heights above ground hgl and hgZ in meters. From these

required parameters the others used to calculate basic transmission

loss as a function of distance are derived. Some of the more important

additional parameters are the effective heights hel and heZ' the horizon

distances dLl and dLZ' and the horizon elevation angles 8 el and 8 eZ.

For area predictions, estimates of the effective heights depend

on the procedures followed in choosing antenna sites. When sites are

selected randomly with respect to hills or other obstructions, the

effective heights are assumed to be equal to the structural heights.

If antenna sites are chosen on or near hilltops to improve propagation

conditions, the effective heights are larger than the structural heights by

an amount that depends upon the terrain irregularity and the structural

heights. When antennas are high and the terrain is relatively smooth,

the effective and structural heights are almost equal, but with low

2

antennas over irregular terrain the improved propagation conditions

that can be achieved by careful site selection may be highly significant.

Because area predictions of basic transmission loss as a

function of distance do not depend upon individual path profiles, they are

particularly useful for military communication and surveillance, for

mobile systems including ground-to-ground and air-to-ground communi­

cation, for broadcasting systems, and for calculating preliminary

estimates of performance for system design.

When detailed profiles for individual paths are available, the

parameters for each separate path are obtained from its profile and

used in calculating the basic transmission loss. Such point-to-point

predictions are particularly useful in the design and operation of systems

with fixed antenna locations.

Both point-to-point and area predictions are compared with data

from several measurement programs carried out in the United States.

Point-to-point predictions are also compared with measurements recorded

over a large number of established communication links in several

countries. For convenience in handling, all measured values have been

converted to basic transmission loss, defined as the system loss that

would occur between loss-free isotropic antennas, free of polarization

and multipath coupling losses.

2. AREA PREDICTIONS COMPARED WITH MEASUREMENTS

Measurements of transmission loss with low antennas over

irregular terrain have been made in several areas in the United States

including Colorado, Idaho, Ohio, Virginia, Washington, and Wyo.ming.

These measurements cover a wide range of frequencies, from 20 to

9200 MHz, with structural heights ranging from less than a meter to

15 meters, in areas where the terrain characteristics range from

3

smooth plains to rugged mountains. Some of the geographic areas,

frequencies, and the number of paths in each area are described by

Barsis, Johnson,and Miles (1969).

Measurements made in Colorado in the frequency range from

230 to 9200 MHz, with support from the U. S. Army Electronics Command

and the U. S. Army Security Agency, are divided into four groups, each

group having a common receiving location. The Gunbarrel Hill and

Fritz Peak data (R-1 and R-2) are compared with predictions in this

report. The data recorded near Golden and southeast of Longmont,

Colorado, (R-3 and R-4) have not been completely analyzed and are

therefore not included. Only a partial analysis of the measurements in

Virginia has been made, but currently available data are considered.

Comparisons are made with measurements in Wyoming, Idaho, and

Washington that were sponsored by the U. S. Air Force Space and

Missile Systems Organization and with earlier measurements in

Colorado and Ohio sponsored by the U. S. Army Electronics Command.

Within each area median reference values of basic transmission

loss were calculated as a function of distance for each radio frequency

and antenna height combination, using an estimate of the terrain irregu­

larity. Comparisons of these area predictions with measured values

are discussed.

2. 1 Gunbarrel Hill, Coloradc (R-1)

Propagation experiments in the 230 to 9200 MHz range con­

ducted over irregular terrain in Colorado are reported by McQuate,

Harman,and Barsis (1968). The data for all frequencies were recorded

at a single common receiver site located near the summit of Gunbarrel

Hill (R-1) northeast of Boulder, Colorado. The site is in the open

plains about 15 km east of the foothills of the Rocky Mountains. All

measurements were conducted using mobile transmitters, and the

4

majority of the transmitting sites were selected to provide a clear,

unobstructed foreground in the direction of the receiver. The measure­

ment locations were arranged in roughly concentric circles around the

receiving site at nominal distances of 0. 5, 3, 5, 10, 20, 50, 80, and

120 k:m from the receiver. Of the 55 transmitter s ite s selected 10 are

located in the mountains, with the others in the somewhat rolling plains.

For seven of the transmitting sites a companion 11concealed11 site was

selected, where rows or clusters of trees are located in front of the

transmitter. The following discussion is concerned chiefly with the

paths where the foreground is clear and unobstructed.

All transmissions were continuous wave at frequencies of 230,

410, 751, 910, 1846, 4595, and 9190 MHz. The transmitting equipment

was housed in two mobile units, with the antennas fixed 6. 6 and 7. 3 m

above ground for t'.1.e three lower and the four higher frequencies,

respectively. The receiving antennas were mounted on a tower and

could be raised or lowered from 1 to 13 m above ground. A complete

description of the equipment, procedures, and experimental results is

given by McQuate, Harman, and Bar sis ( 1968).

Path profiles read from detailed topographic maps were

obtained for the 47 unobstructed paths, and for each path the terrain

parameter t::.. h was calculated. The median value, t::..h = 90 rn, was used

to characterize the terrain irregularity for these paths. Area predictions

were calculated for each frequency, transmitting antenna height, and

for integral receiver heights from 1 to 13 m. Figures 1 to 5 show predicted

values of basic transmission loss as a function of distance compared with

values derived from measurements for receiver heights of 1 and 10 m and

for frequencies of 230, 410, 751, 4595, and 9190 MHz. In each case

calculations were made assuming both randomly and very carefully

5

60

� 80 ....

.. ...

....

0

l'

c: .....

\� ....

120

140

160

180

200

60

80

100

120

140

:_, 160

j I I I

0

I I

•-- Random sites

- - - Selected sites

0

M�x. Meas. Loss j ....... ....... ........ ........ ................ ........ ·······• ....... ······•· •....... •

20 40 60 80 100

I hg2=10. Om

I I I

---�----�---

0

Figure 1. Basic transmission loss, measured and predicted,

common receiver site R-1, f1h=90m, f=230 MHz.

6

120

I I I I

1 I

·.r

,_, .�

.. ·

-·

.�

.....

()

0

160 �1 _u__J_�----1��+-=�-=--����-=------l-�--!-�-+�-0 ����-: I

180 �1 �-l-�-+-�-+-�---+-�0��- ��-P!!llo,,.,...=:-�-+-�-t---=L"I----:� '

200 l- M M ax. eas,

I ·�··r······� ······· ..... .

220 �'--�-1��-L��...L��.L_�__:.��-'-��_l_��...L.._��L-�--l.��-'-��� " ·-· 20 4:0 6'.) 80 100 � ;·-:-

60-, ���������������������--..��---.-��.....-��.--�� I

I

'

120. I

I I

140; 0 I

160, '

i 180:

zoo! 0

---

q

20 40

Free Space Loss --· ---1---- --- ___ .....,... ____ .

I .

I 0 I i

I o I i

80 �00

0 : q

Figure 2, Basic transmission loss, measured and predi°cted, common receiver site R-1, £lh=90m, f=410MHz.

7

c: -�

-� "' rr.

u ·-·

-� --· -�

-�

•r. �

I -, " .. . '/l

- � .. ., �

:.. -:..... <.'

..• ,,;. .•: .....,

220 J

60

'

80 p

' 1001

' 120'

I I 0 I 140-I

160i 0 I I '

180' I I I 200 ()

20 ·10

20 10

hg1

=6.6m

hg2

=1. Om

I :

' Max. Meas.

�--Random sites ·,- - Selected sites

80 100

Free Space Loss --- ,__ --- ---

0

80 1 00

Figure 3. Basic transmission loss, measured and predicted, common receiver site R-1, 6h=90m, f=751MHz.

8

l ,. l.

c:::; -;:; .... �, v-. 0

...:) ::! 0 ..... 10 ._,

� ·� i:; rJ ;... :..... L' i n

::i

,...., -;:; �

"' ·� '"'

� ::! ..... 'Jl 'Jl ..... � · � � , • ..i ;...

:--< u ..... .. � '";

C'.:l

100 ° l o +-- Random sites +- - Selected sites 120

140

160

180

200

220

240

100

140

FQ , hgz=l. Om ' • .1 I ! I I ! 1' -- I i I I I ' .\l��--4...------�.!....:.-=-:::-:::-� ---"--__,-. Free Spac L f- ---------� e o s s

0

I

20 40

____ I I r----0 !

I 0 0 l I

---- ---1---:----1 I

0

6C 80

I I h 2=10. Om

g I i

0 - +--'---- �

Max. Meas. Loss

I I I 100

. I I , --------�--_!ree Space Loss 1

, 0 I I ---- """'---r----�----1 I

160 l 0

I I I I ! 0

180

I 200 I I 220

i

240 0 20 40

0

6'.) '·

D�c:';-.-.c� in ��m

0

--1 -- o I o, - ----I Max. Meas. Loss

I I i ! 80 100

Figure 4. Basic transmission loss, measured and predicted, common receiver site R-1, .1h=90m, f=4595MHz.

9

(.)

�� -· --

�

,. .,.. .. , ,

.._,

�

'.'1 '" _ _, .. .. :::: r-...

:---; -·-.. �'

1401 I

_[_ I I I Random sites Selected sites

1 60 1�1 ___:i��-...Q..�---:.����@;.__�.'..-�-1-�-+-�-+-�-+-�-+�� I I

200:

240'

100

! 140;

I

160; I

180 I ' I

200 I

i 220 I

I

240 � "

0

I

I ... J� ..... ) - -

20 t;,O 60 80 100 ' ..,, ,, .l - -

hg2

=10.0m -'-�---+��-1-��1--�--+-�--1 I

0

20

)

8 I ; I I

i 0

Max. Meas. Loss

I 80 100

Figure 5. Basic transmission loss, measured and predicted, common receiver site R-1, �h=90m, f=9 l 90MHz.

10

___ J

o'

1. i -·

selected s i tes, as described by Longl ey and Rice ( 1968). Measurement

attempts that failed because the s ignal was 1"in the noise" are indicated

by a mark located at the l evel of the maximum measurable loss. In each

figure the upper graph shows measured and predicted values with a

receiver height of one meter, the lower graph presents the same infor­

mation with a receiver height of 10 m. A definite improvement in

propagation conditions with the increased receiver height is consistently

shown, particularly at the l ower frequencies.

These five figures all show a wide scatter of the data when

plotted as a function of distance. Most of this scatter results from

differences in individual path profiles. If low values of transmission

loss are observed over a path at one frequency and receiver height,

consistently low values are observed at the other frequencies and heights.

For example, the low losses (plotted high in the figures) shown for paths

at d = 27. 5, 52. 5, 79, and 119 km appear at all frequencies and receiver

heights. An examination of the corresponding profiles shows that these

are either clear line - of- sight or isolated knife-edge diffraction paths.

On the other hand, the larger than average losses for paths at d = 5,

79. 5, and 119 km are all for two-horizon paths with rather large eleva ­

tion angles.

Such path-to- path differences, caused by differences in individual

profiles, are taken into account in the point - to - point predictions for

specific paths, as described in secti on 3 of this report. An area

prediction calculates the median transmission loss expected at each

distance, with an allowance for path- to - path or location variability.

In figures 1 through 5 with the receiver only one meter above

ground, the medians of data lie between the two curves for random and

carefully selected sites at the lower frequencies, but at the higher

frequencies the prediction curve for sel ected sites describes the medians

11

of data. With the receiver 10 m above ground the prediction for selected

sites agrees with the medians of data at all distances and frequencies

shown.

For several paths in this group the measurements were repeated

on three or more different days. In some instances two or three measure -

ments were made in the same month, but in others the elapsed time was

six months to a year. For some paths the results of the repeated

measurements agree closely with each other, but for other paths the re­

sults differ by 15 to 20 dB. Some of these differences represent commonly

observed seasonal differences in propagation conditions; others may

result from local atmospheric changes. In general the values measured

during the period April through June show less attenuation than those

measured in the period November through February. No detailed analysis

of these changes has been made.

The measurements at seven "concealed" transmitter sites were

compared with those at corresponding 11 open1' sites . These paths range

from 6 to 36 km in length. At all distances and receiver heights the

paths with concealed transmitters show larger values of transmission

l oss than the corresponding open paths. These differences range from

about 4 dB for the shortest path at 230 MHz to 35 or 40 dB for the longer

paths at 459 5 and 919 0 MHz, Even a rather thin screen of deciduous trees

increases the transmission loss 20 to 25 dB at 9190 MHz, while at the

three lower frequencies over the same paths the increased losses are 6 to

10 dB . At present the area predictions make no allowance for such surface 11 clutter 11 in a quantitative way. More measurements of this type are

needed as a basis for defining a 11 clutter factor" that would a llow for the

effects of natural and man- made objects.

12

2. 2 Fritz Peak, Colorado, R-2

Measurements in the 230 to 9200 MHz range were continued with

a common receiver site located in the mountains west of Boulder at the

foot of Fritz Peak. The peak shields the Site from the eastern plains, and

36 of the 44 transmitter sites are located in the mountains. These

measurements are described in detail in part II of the report by McQuate,

Harman, and Bar sis ( 1968). The data represent conditions in rough

mountainous terrain, where the ground cover is chiefly coniferous forest.

The immediate foreground at the receiver site is clear to a distance

of more than 50 m but is rather heavily forested beyond that distance.

The paths range in length from 2 . 5 to 120 km. The majority of the

transmitting sites were selected to provide an unobstructed foreground

in the direction of the receiver.

Path profiles were read from detailed topographic maps and the

terrain parameter calculated for each path. The median value, Ah = 650 m,

was used to characterize the terrain irregular ity for these paths.

Unfortunately, even though the common receiver is located in the mountains

the paths in this group do not have similar characteristics. The 3 to 10

km paths would be better represented by a much smaller value of Ah,

and several of the longer paths extend well out over the plains, with

transmission over relatively smooth terrain for the major part of their

lengths.

Figures 6 through 10 show the measured and predicted values of

basic transmission loss plotted as a function of distance. The wide scatter

of data, some 60 dB for the shorter paths, indicates that the characteristics

of these short paths show marked differences from each other. An exam­

ination of the terrain profiles for the 3 to 10 km paths shows that the

median value of A h is less than 200 m, and that most of these are line-of­

sight and knife-edge diffraction paths. In this group only two 3 km paths

13

---t --- ---

-0

u

h 6 6 Random sites gl= . m

I- Selected sites hg 2=1.0m -+-~~+-~-t-~~+-~-t-~---;

---t I Free Space Loss ---.,;..... ___ I --, --- ,..._. __

·- I •;, I

r~ 200 :,... --......----1

-..~

, .. ·-'" ~ ::>

._:i

c .... ·-·r. ·-. ) 1:. "~· ._, ~

u VJ -:-j

! I

220L' ~~.L._~-L.~~.1-~-L.~~..L-~-L~~-'--~---'-~~-'--~--'-~~-'--~-'

o 20 40 60 80 100 :zr;

160

180!

I I

200

I I

220 0

i ! ' ----+ I : --.--1------- --- Free Space Loss _......,._......, __

0 o I ; I

20 40

l I

0

Max. Meas. Loss

-u-'--80 lCO

Figure 6. Basic transmission loss, measured and predicted, common receiver site R-2, t.h=650m, f=230MHz.

14

: ..... ~

(..'

·r. -·

80.--~~~~~~...--~~~~,------~~~---.~~-.--~~~~.--~-r-~-,

6 Random sites

I. hgl =6. m

i--Selected sites ' I · . h -1 Om I I I ' cxr ' 2- · ·

I ' 100 '

'f=---L ___ I i ·. g i I' I: i I r ~--- , . 1 1

120 ,,·_ --4:+--.!.---·- --,--' ------;----=--==-«:...--_,,..~- Free Space Loss --....,·----' I

00 I ',i ii :, I . -------- I I , I -.-.---..-.r---~---i I . I , .

d 1 I I I i I

180

2oo i

160 I

180

I i

200 1 I I

i 220 ()

20

I

! 10

QI

Max. Meas.

(" 80

' q i 0 I

Max. Meas. Loss

I

0

--L ~ o · - . __ ,

~ 00

Figure 7. Basic transmission loss, measured and predicted, common receiver site R-2, 6h=650m, f=407MHz.

15

c .....

...., -:;

c ·-.,, ., ~

~ :::! ~

' 'f' ·-,. -"' c ··' :... ~

" --.. ,, ~ ~ ...

loo~-,~~----,.----.----.---..--~---....---,---,-.--___,.--___,....,.. __ _,_ _ ___, -1 hgl =6 · 6m .... __ Random sites 0o - -- 1 0 - - Selected sites - - h

2=. m . , _ ____ _,

120J '------!..., ___:::....-.~=------,-r-

1_-___ gr--- __ ;r;.:..:pace Loss j' ---.,--- ---

1401--.l.~0~+---l---+---+---r---i---+---+--+---+--+-----t

0 0 0

t· .. ···· ....... . ..................... . 200~1 __ ...._ _ ___,r-----,-;::-......:::-~---,---,+--.::....::0-----.r-:;;=-:---,t----,~---,---,.----,---,.----,--;

I --220!----+--J----t---+---+---.--..::::i-....... -=-+---+--+---4------,.

240 0

80

180 t

I 200 I

220 0

20 40 60 80 100 l 2C

I I i hg 2 =10. Om

-- I I I I -­ ._._....,.._ _,,_,,_ -~-

-....--.-

20 40 80 100

Dist:i.~cc i n km

Figure 8. Basic transmission loss, measured and predicted, common receiver site R-2, t.h=650m, f=751MHz.

16

'

I 1

• "l -,_ ~

c 0 .... '.!!

t"' ....

u

.... , . . , .. _, ., :... ~:

u ....

i20..-------r---.--.----,1---r----:-1--'j--.--~--~----....----,

I o ---- j I S 1 d . i --,' j 1· Random sites

~- • 1· ~-- e ecte sites .._._41111 ---- ! ' 1-. ---!----~--+--· ~~, ..... _..,,_.,.._,~· ~;;=::;='==-- F . ' I 140 1 I , -i"'"---·----t ree Space Loss -., rl· I I I h g 1=7. 3rn ---------1-----~----

160 '----l----1f----+----l;-- h g 2=1. 0 rn

I,@ I I i lso r~ J I

I \a... 0 c I 200 i \.. ";,,~ ,~ I I 0 0

l 0 ~ "'- ~ '- 0 I 0 I (1 (

2 20 ~ ~ •••• ·--~~.:::.~.~~ ·.:.::::.:t·····J········ ········~··•···· ........................ . j I .................. , - -- _ Max. Meas. Loss

240 l, --~-~--~_----_J[--~:J~==~::~::::~::~-:::--:::-±:--~-~-~-~-J. 260

0 20 40 60 80 100 120

100----..---..---.....---...-----.--~---.---...----.-------.----.---~

i i h~ 2=10. Orn

1201---'~-+---L---+---+---i=---·~--+---+---+----+---+------1

-- I I --t--- --- I 140 1 L. --+---T----l'---~~-..-;... .... .,,_c:l:::!::_,,,._=-_-1-_-__ F_:,ee Space Loss '

I -- ---r---- ---1

I d

0 0 0

~ 220r----+--~---r-~,___..,---=-'!!'"f).._......;.-=---+---+---+----.·---t--~

I. -- .....J 240 ~, ~~M_a_x_.~M_e_as_·_,_~.._____.~~~_._~__.._~__._~_._~-'--~

0 20 40 60 80 100 120

Fig ure 9 . Basic transmission loss, measured and predicted, common receiver site R-2, Ah=650rn, £=4595MHz.

17

and three 5-km paths have more than one horizon. The 20-km paths are

over highly irregular terrain, and six of them are transhorizon paths.

Ten of the longer paths are typical knife-edge diffraction paths and show

the expected low values of transmission loss.

Evei: though the measurements in this group were not all

made over rugged mountainous terrain, they sh0w clearly the improve­

ment in propagation that can be gained by careful site selection. At the

higher frequencies measurements at 20 km and beyond were successful

only over the line-of-sight and knife - edge diffraction paths, the other

values of transmission loss ex ceeding the maximum measura ble value .

Because of the unusually advantageous siting , and the non ­

homogeneous terrain, the area predictions with ~h = 650 m tend to

overestimate the transmission loss, especially for the lower r eceiver

height. Point-to-point predictions were also calculated for each individual

path and are discussed in the next section.

Some measurements at all frequencies were made with the

transmitter at 11 concealed11 sites, for paths 2. 9, 4 . 7, 11. 2, 20. 0, and

52. l km long. In this small sample the results are not completely

consistent, but in general they show increases in transmission loss of

10 to 20 dB for the concealed sites over the shorter paths. The results

for the longer paths are inconclusive because in about half the cases

the signal was "in the noise" .

2. 3 Virginia Paths

Measurements in Virginia were performed by the General

Electric Company under contract to the Institute for Telecommunication

Sciences (ITS). The results of these measurements have not yet been

completely analyzed, so no detailed descriptive report is available.

Some of the data are included in the previously referenced report by

19

Barsis , Johnson, and Miles (1 969 ). Thes e measurements were made

with seven common transmitter sites, and with receiving locations

arranged in roughly concentric circles about them at nominal distances

of 0 . 5 , 3, 5, 10, 20, 50, 80, and 120 km. In this area the terrain is

rolling, hilly, and partly covered by deciduous trees .

Terrain profiles have been read from topographic maps for

only about one-sixth of these paths . A median val ue of the terrain

parameter, ~h = 85 m , was obtained for these 51 paths, most of which

are rather short, but a few longe r ones a r e included.

Figures 11, 12, and 13 show predicted values of basic trans ­

mission loss as a function of distance compared with measured values

for frequencies of 76, 17 3, 409 , 950, 2180, and 8 395 MHz. The

prediction is for structural heights of 12 m and randomly selected sites.

The measurements were made with antenna height s of 11 . 3 and 15. 0 m

for the transmitters and 12 . 1 and 15. 0 m for the receivers. These

51 paths incl ude data from four of the seven transmitter sites . The

pl ots indicate that the area prediction, based on randoml y selected

sites, tends to overestimate the transmission l oss at the two lower

frequencies, describes the medians of the data at 409 MHz and tends to

underestimate the losses at the higher frequencies . This may result

from surface clutter in the form of deciduous trees in full leaf that

would cause considerabl y more attenuation at the h igher than at the

lower frequencies. This possibility will be further investigated when

more of the path profiles are available .

Because of current interest in the use of very low antennas,

a group of measurements was made with the receiving antenna 2 m

above the surface of the ground. For these 9 5 paths the transmitting

antennas were 11. 3 and 15. 0 m above ground. Figure 14 shows

predicted values of basic transmission loss compa r ed with measured

20

40 ,

C'.l 60~ -0 c .... :n 80 T.

~ c 0 .... !fl t~ ....

120 I 2 .,, I

·" I ... I :;) I .... i ~ 140 , u ! .... ·~

~ 160 , C0

180 ' 0

60

':::' 7

c ...... ·~ er. (")

~ I

c 120 I ,...

er. t'l ...... c: 140 ·~ ;.;

·~ :... c....,

160 u I .... l'l i ... . ,

;:o 180 i

200 1 0

i

f=76MHz

20 40 60

I I f=l 73MHz

I -- t I - -----~-.....,.-

20 40

hi =ll.3m. LJ ___ _ gl

h =12. lm. 15. Om g2

80 100

0

80 100

--~

0

; .:. :

Figure 11. Basic transmission loss, measured and predicted, 51 paths in Virginia, 6h=85m, f=76 and l 73MHz.

21

~ --:::'. ·-•n

:ll ,.,, -:i ,.. ::-... .. ·•1 ·-:: ., .... ~ :...

;....

·-·

......

-.:'

c: ·-· '.I:

'" ~

-:i -Ul

··~ -~

'-.. c t-: ;..

~ 0 ·-..

c;

80 I f= 409MHz

100 : I

I '

hg l = ll.3m,

hg2

: 12. Im,

I I

15.0m

15.0m - --'

120

I 140 I

- - Free Space Loss ____ ___ _, ~~r-----:-==~~-1--- ..... _ ..... ~-~

I

160

180

I

I

200 : I i I

220 ' v

80

100

120 1

I 140 1

160

I 180 1

200 1 :

220 0

I

0

0

20 40

20 40

60

i

f=950MHz

80

0

Max. Meas. Loss

100

---t -t --- ,--- __ ,!ree Space Loss _,,._,, _,,,_,,__ .......,._

0

Max. Meas . Loss I I I I I l

6'.) BC 100 ~ .. ~t;"_ ::~(! i~ km

Figure 12. Basic transmission loss , measured and predicted, 51 paths in Virginia , .1h=85m, f=409 and 950MHz .

22

120

120

::!) ~ -.... :i (/) ,... ~ c 0 .... !/)

'fl .... ~ 'J)

::: _. .;

i... ~

u ..... ~

M C'.l

c -· ::: .... ~ ·~ ("\

......l -0 ~,

".fl ·-c "

.-.; :... ~

u .... (/)

("j

""

80

f =2 180MHz h : 11. 3m, 15. Om - --1 ~---1---..+----'"---+----;--.---t-- gl

I I

160 1

I I

180 1

I I

200 · I I I

220 0

80

180 ' i I I

200 ' i I !

220 ')

20

20

h :12. lm, 15. Om g2

--- i ! I I I

----i----+----l---_Fr;e S ace Loss

---

I !

Meas . Loss

f=8395MHz

-- t ....... ----~_.,__ -r----.._._

I I

40

Dis t.~.~cc :.~. km

80 100

Max. Meas . Lo s s

h I

gl, z=l2rn

80 100

Figure 13. Basic transmission loss, measured and predicted, 51 pa ths in Virginia, t. h=85m, £=2180 and 83<)5MHz .

23

! ~ ')

1 :'.C

:".:! -.;:;

c ·-'" .. 0

..-1

0 ·-., (/) ·-,... ,. ., c l'J :.,

t-< ()

- ~

!,..~

~ ::::'.!

~" --;:;

~

:r. {..~ ~

,_..]

':'. ~

.. . , E ., ::: c; ;...

<;_;

u ·-<r. ~ ~

80

1 "-_

100 .

i h = 11. 3m, 15.0m

I f = l 7 3 MHz I g 1 · l h =2m

!

I T ---..- I I I ---~---~---_i,---~-Free Space Loss

120 : i I

- ~-- I t I i ii I g2 ' I .

I ! I ,....,.,.,._.,...,._....,.,_.,-.._,, --

~~--+---t---fZ!.-- I

'° ! 140

I

' I ' 160 i I I

180

200 !

01 I

I 0 20 40 80 100

80

120

I ___ J

I 140 1

I 160

180 I I I

200 '

I i

220 . 0 20 ?0 60 80 100

Figure 14. Basic transmission loss, measured and predicted, Virginia, all paths with hg

2=2m, f =l 73 and 409MHz .

24

!

values at frequencies of 173 and 409 MHz. The predictions were calcu­

lated assuming antenna heights of 15 m and 2 m, with randomly selected

antenna sites . The data are from all seven transmitting locations .

These plots show that the area prediction tends to overestimate the

transmission loss at 173 MHz but describes the median loss as a function

of distance at 409 MHz. No plots are shown for the higher frequencies

with this low receiver height because a large proportion of the attempted

measurements were in the noise, showing greater losses than the

maximum measurable values . A significant feature in this area is that

the path-to- path or location variability is considerably less tha n that

observed in either the R - 1 or R-2 data . This probably indica tes more

homogeneous terrain with fewer unusually good or bad propagation paths.

Point- to - point predictions for the paths where terrain profiles

are available are discussed in section 3. Further c om parison of

these data with predictions will be deferred until path parameters are

available for more of these measurements .

2. 4 Wyoming, Idaho, and Washington Paths

The measurement program conducted in Wyoming, Idaho, and

Washington was limited to two frequencies, 230 and 416 MHz, and to

very low antenna heights, from 0. 75 to 3 m above ground. Both the

transmitting and receiving units were mobile. The transmitting antennas

for both frequencies were fixed at heights of 0. 7 5 and 3 m above ground,

while the receiving antennas were raised continuously from 0 . 7 5 to 3 m.

Details of these measurements and the equipment used are described

by Hause, Kimmett, and Harman ( 1969).

This series of measurements differs from those previously

described in that no attempt was made to choose sites that would provide

good propagation conditions . With such low antennas the selection of

25

C:Q 'O

c ..... (/)

(/)

0 ...:I c 0 ..... (/)

(/) ..... E (/)

c "' I-< ~

0 ..... (/)

ct C:Q

(/)

(/)

0 ...:I c 0 ..... (/) (/) ..... E Ill c "' M ~

0 ..... (/)

"' C:Q

60

80

100

120

140

160

180

200 0

60

80

100

120

140

160

180

200 0

I I I I I I

• Partially obstructed path

h l 2 =0. 75m '- g • -,.

"-- I ---i--- I ~-.......... ~-..-,.-.. .... ---- Free Space Loss __ ,_

"'_,_ ----------·----..

' iD ,_ I'. ,,...,~ ....

\.:Ill IV Q -- .. ,_ __ ~ ) -- .. .. __

........_ - ,.... Q -- h =2m -- o- _u (:Y -- _U

~~ b--...... ~ 0 ---

.. __ e

• 'c 1--r--- ~

h - h -.. e g

• -10 20 30 40 50 60

I I I h 1 2=3m g •

' -'--..... ---- ---~--..-.. <D ~-..............

~-..... -.... Free Space Loss t---- __.._,,,.,_, __ .._.._,,,_,,_ ...-~.,. ~-...... --.......... ____ ' ( "' ~£ ~ ~ 'f:i- -.f\ ~O

\..UV ............. o-;:_&~--· 0 -- - cP - ... __

he =4 . Bm c • ~ . b • a- --. '"'"--• - -• - - • ---• • h =h -e g

10 20 30 40 50 60

Distance in km

Figure 15. Basic transmission loss, measured and predicted, Laramie range, Wyoming, £lh=l20m, f=230MHz.

27

c:Q "O c <II <II

,S c 0 .... <II rn .... s <II c ro "" E-< u .... <II ro

c:Q

c:Q "Cl c , ... rn rn 0 ~

c 0 .... rn rn .... s <II c ro

"" E-< u .... <II ro

c:Q

60

80

100

120

140

160

180

200 0

60

80

100

120

140

160

180

200 0

I I I I I

• Partially obstructed path h

1 2=0. 75m

g • ....... -...... .... --.. ·-~---- -..-....-..-.. ......... ._.. ... Free Space L o ss ...__..-.._ •-.-,,.., .. .,., ___ ---'

\)

' ~ ...... ~ \.

~ v - --~<§£

... ·-- 0 ( ~- ...

q ~ :)o•

,_ __ -- h e =2 rn

• ~ <e Oc -""ti- --r-@ --·--• ---- -• • ----- I --- h =h ~ e g

10 20 30 40 50 60

I I hgl, 2 =3m -+-~~-+-~~-+-~--1

--- .... _~-~-(J ---·-- --... F S L ' o ----i---- ___ }._:_:_pa c e o s s

• h =4 8 -...- e . rn _ --.,_

I -- .. --..._ • h =h -e g

I 10 20 30 40 50 60

Distance in km

F igure 16. Basic transmission loss, meas ured and predicted, Laram ie range, Wyom ing, ~h=l 20m, f =4 16MHz.

2 8

shows that the three paths that are more than 38 km long are all single

horizon knife - edge diffraction paths, where less than average trans-

mission loss is expected.

The path- to-path or location variability is not very large, with

a standard deviation of 9 or 10 dB . If care were exercised to select

only antenna sites with clear foreground terrain, the larger values of

transmission l oss could be avoided, even with these very low antennas,

and th~ path-to- path variability would be considerably reduced. For

many applications the variability introduced by low values of transmission

loss over unusually favorable line - of- sight or knife-edge diffraction

paths is much less important than that resulting from unusually poor

propagation conditions.

2.4.2 Idaho Paths

Measurements were made over some 31 paths in the lava flows

of Idaho. The area consists of extensive plains cut by stream valleys.

In the northeastern part much bare lava is exposed, while to the southwest

there is a considerable depth of soil in places with some sagebrush and

prairie grass cover. No detailed maps are available for most of the

test area and profiles were read from one by two degree maps with a

contour interval of 200 ft . Maps on this scale show only the gros s

features of terrain, so estimates of the terrain parameter, the horizon

distances, and the elevation angles are subject to considerable error .

For a few paths located in the southwestern part of the area, finer

scale maps are available. Information from these was compared with

that from the coarse-grained maps and for these few paths no major

differences were noted. This is relatively smooth terrain, with a

median value Ah= 60 m and an interdecile range of Ah from 25 to 116 m.

Figures 17 and 18 show measured and predicted values of

transmission l oss plotted as a function of distance for equal antenna

29

c:Q "Cl

c .... (/)

(/)

0 ....:I c 0 .... (/)

(/) .... 6 (/)

c ro I-< ~

0 ..... (/)

cd c:Q

(/)

(/)

0 ....:I c 0 ..... (/)

(/)

'§ (/)

c cd I-< ~

0 ..... (/)

cd c:Q

60

80

100

120

140

160

180

200 0

60

80

100

120

140

160

180

200 0

I I I I I

• Partially o b structed path h

1 2=0 . 75m

' g •

' I I --- ---... I I ... __ .... ___ Free Space Loss ------~ i... .............

~-..-.-.,.. ___ ..,.._,,_,_ __ .. _____ ,,,,_,_

i.--~-~,,,

~ . ";: :~ . - ::::::::::. ~ . -..

~ ... ·~.GO {9(01.. ~ ----- u ... -. .. ----...

() 4 h::6orn ···o ·oO ~ ,,. ... ---., ~

.... ········· ::=1----~ -9 ••••••. •••••• + 4 h::11 6rn I

~ ·-···· .J h:O rn •• ·······1-······· 10 20 30 40 50 60

I I h 1 2=3m g •

-, -.. ,.._ -- --- ...... -~ .. ---- _. ___ ,. 11-r-.---..- Free Spac e Loss

' _,,,,_,, __ ""',,_,._.,...."" ~., ...... , ---...-..--....... ..-., ... ·' ~ I', ~ ...... ~~ '0 . ...._ .......

- 0 -. ~ --: ••• u --

~----,9-.. ·•···· -- h =4. 7rn ·····O. ~· --...! ) --. --- !! ..• , --- ---It ········ D

~ .......... ········ 4 h ::6orn -···· l I .... ··--

4 h::Orn -·· ···· ········ I I

10 20 30 40 50 60

Distance in km

Figur e 17. Bas ic transmi ssion loss, m eas ured and predi cted, lava flows, I daho, m edian. Lih=60m, f:230MHz.

30

Cl "ti Cl .... VI VI

j d 0 .... VI VI .... E (/)

d I'd ....

E-l 0 ..... (/l

I'd Cl

VI VI (')

...:l d 0 ..... (/l (/l

60

80

100

120

140

160

180

200 0

60

80

100

120

140

160

180

200 0

I I I I I

• Partially obstructed path

h 1 2=0. 75m

g •

" - ...... "'! .... --... --- ~ ...... -..-....: ~-~-

..._ ___ . ... _..., ___ Free Space Loss _ ...,,, __ ....... ,,,_,,,

\ ~.~ ~ .. ~ - 0 ,.... .. 0 0

...., .. OoC ~ ... ~ (j•·· Oo ------····- '-' ()

4 h=60rn ,.... ·o .... ,_

• • •·•······ •······· ••••• 4 h ::o 01 -• ······--

10 20 30 40 50 60

I I h 1 2=3m g •

'

' -..... ---~-~-

~-...... -... ~-..... -.... -----..- w....,._..._.., Free Space Loss --~-.__,. -,,

' ~ nr. ~ 0

~~ ~oc ~ c o-•• v -

~ ········ ~ .6) (~

• ········ b 4 h::6orn Lr~-' ···-···· ········ I -. ••• :' h==Orn -· ····r··· •... ······••1

10 20 30 40 50

Distance in km

Figure 18. Basic transmission loss , measured and predicted, lava flows , Ida ho. median ~h=60m, f=41 6MHz .

31

60

heights of O. 7 5 and 3 m, at frequencies of 230 and 416 MHz. Three

curves of predicted basic transmission loss are shown in the upper

half of figure 17 for values of A h = 0, 60, and 116 m, assuming the

effective antenna heights equal to the structural heights of 0. 7 5 m .

These curves show the minimum, median, and upper decile of the

estimates of Ah for the 30 measurement paths. Note that as A h

increases from zero to 60 m , the predicted values of basic transmission

los s decrease, but that a further increase in A h results in an increase

in the predicted loss. For the paths in this area the median value

A h = 60 m is an optimum value for propagation, so with the lowest

height many of the measured values show more loss than predicted,

and the medians of data lie about halfway between the curves for Ah = 0

and Ah= 60 m . The lower half of figure 17 shows three prediction

curves, two with h = h = 3 m for Ah = 0 and 60 m, and one for e g

h = 4 . 7 m, Ah = 60 m . In this figure the curve drawn for effective e

antenna heights equal to the structural heights with the median

value of Ah describes the medians of the data. In figure 18, where

only the curves for h = h and for A h = 0 and 60 mare drawn, similar e g

results are observed.

Photographs from each site in the direction of the other

antenna show that in some cases the path is partially obstructed by a

nearby hill, or the immediate foreground is obscured by sagebrush.

These paths are coded in the figures, and show larger than average

values of transmission loss . Even in this comparatively smooth terrain

care in site selection can avoid unusually poor paths and reduce location

variability, but no great advantage can be gained from siting for un­

usually good propagation conditions because there are few isolated hills

or ridges .

32

2. 4. 3 Washington Paths

Measurements were made in three localities in Washington at

frequencies of 230 and 416 MHz. Fifteen paths were located in an area

of plains and low hills near Ritzville, where some of the acreage is

planted in wheat, and the rest is covered by prairie grasses. This

terrain is characterized by a value Ah = 70 m . A second group of

39 paths were chosen in rugged terrain with steep hills, coulees, and

deep canyons with almost vertical walls, where the principal ground

cover is sagebrush. The median value of the terrain parameter

Ah= 210 m for these paths is used to characterize the terrain in this

area. A third group of 14 paths were selected in the Spokane river

valley near Fort Spokane. These are short paths with a common re­

ceiver site in the valley and transmitter sites in the surrounding

mountains. The terrain is very rugged, characterized by a value

Ah = 305 m, and is largely covered by coniferous forest.

The measurements made near Ritzville and corresponding

predicted values are shown in figures 19 and 20. The predictions are

for randomly chosen sites, with the effective heights equal to the

structural heights . The results in this area are quite comparable to

those in Idaho.

Measurements made in the areas of rugged terrain are shown

in figures 21 and 22. Data from the few short paths in the Spokane area

are included with the larger sample. Although no specific attempt was

made to choose sites that would provide good propagation conditions,

an examination of the path profiles shows that most of the sites were

selected on hilltops and provide an unusually large number of line - of­

sight and single horizon paths . The curves showing predicted values are

drawn for selected sites with llh = 210 m . Using ~h = 305 m the predicted

values are a little larger than those shown by the curve . _ At both 230 and

33

60

i:Q "O

80

c ..... Ul 100 Ul

.3 c 120 0 ..... Ul Ul ..... E 140 Ul p Ill M

E-t 160 u ..... Ul c1I 180 i:Q

200 0

60

i:Q 80 "'O c "" Ul Ul 0

...:! c 0 ..... Ul Ul ..... E (/)

c Ill M

E-t u ..... Ul Ill

P'.l

100

120

140

160

180

200 0

I I I h l 2=0, 75m

g •

' I ' -~ ~--'--- ~-...... ...... -....... -.. Free Space tii---...,.-.... Loss -4-P-.... -----...-.. ,._,,,....,.,_

' ··N )

~ ··. ( .. --...... ... r----...~ .. .. D QO

,_ ····· (J"' ----"'·· ••• _c - - ei h:: 70n-i -······- (.)

••••••• ;1 h ==O n-i I 0 ········ ········ -'r•••·-

10 20 30 40 50 60

I I h 1 2=3m g •

' ' -... ---... ·-~---~ .... -..... ~-~ .. ...... _ .... _

~-..-..-.. Free Space Loss ~-...... --- ,...,..,_ ,_,,_,..,_

" ,v

~ 0

~-~ r---p....__ .... 0 .. ... ......_ ••• k Oo - '1h::?on-i

'-.;I' .....

0 .......... ········ I 0

········ '1 h==On-i -··-... ········ ········ ~ ........

10 20 30 40 50

Distance in km

Figure 20. Basic transmission loss, measured and predicted, Ritzville area, Washington, 6h=70m, f =416MHz.

35

60

i:o 'O

c .... Ill Ill

.3 Cl 0 .... Ill Ill .... E Ul c nj

'"' r-c u .... Ul nj

i:o

Ill Ill 0 ~

c 0 Ill Ul .... E Ul c nj

'"' E-< u .... Ill nj

60 1 l I I • Spokane river data

80

100

h l 2=0. ?Sm

' g I

I -.... ...__. ---.._. _____ .. I

• .. _._._,... Free Space Loss -.... -.... i-. ___ __,,,, __

_,,,_,,,,, .. ~,-,,,,,_~,_,,,..- ,,,..._._,.... • c •b 120

140

160

.. ' 0 • .,... r--..• • , o -....

~-c (j.J 0 "<'. 9:, •• ""- OJ

~g 0 0 • otr ~- .. ~

h =2rn -c u -. ~-~ e 0 0 --. co 0 ru-- --. ... --

180

200 0 10 20 30 40 50 60

60 l l h 1 2=3m g •

~. "--o (b ... ---- -~-~ -~~ Free Space Loss

._. _ __.._ ~--...... - ~-----... ~ .. 0 ~~ .... - ------...... ,~-.. ~,,,---

•' 0 c Cb o1 0

' f:bO O°o :-~ '-- . Oo ~ ~ r - -- ... ~

)0 0 v

·-~ ' 0 0 !-€- ... 0 ·-- h =4 .8m

~ ( ~ .... :-_ ·-- e ~ ...., --... .;;:-:

80

100

120

140

160

(!'.) 180

200 0 10 20 30 40 50 60

Distance in km

F igure 21. Basic transmi ssion loss, measured a nd predicted, mountainous terrain, Washing ton, Ah=210 and 305m, f =230MHz.

36

co 'O

c ..... (/)

(/)

.3 d 0 ..... Ill (/) ..... E (/)

c "' i..

f--1 u ..... (/)

"' co

co 'O

c ..... (/)

CJ)

0 ~ c 0 ..... (/)

CJ)

E (/)

c "' lo<

f--1 u ..... CJ)

"' co

60 -----.~--..~--r~--r~-.-~.-~.,~-.-, ---,,r---y1~-r~-,

• Spokane river data

hg 1, 2=0. 75m ~----11--~--+-~~

200 0 10 20 30 40 50 60

60 I I

80 hgl , 2 =3m -+-~~-+-~~+-~--!

' --.. 100

' -..

Distan ce in km

Figure 22. Basic transmission loss, measured and predicted, mountainous terrain. Washington, ~h=210 and 30 5m, f =416MHz.

37

416 MHz the predicted values overestimate the transmission loss

especially for the higher antennas . Calculations based on very care­

fully selected sites would describe the medians of these data.

2. 5 Measurements at VHF

A series of measurements with low antennas at frequencies of

20, 50, and 100 MHz was carried out in the Colorado plains and

mountains and in an area in northeastern Ohio. This measurement

program was sponsored by the U. S . Army Electronics Command to

simulate net - type vehicular operations at frequencies up to 100 MHz

and with antenna heights limited to less than 10 m above ground. The

measurements in Colorado were made by personnel of the Institute for

Telecommunication Sciences (formerly the Central Radio Propagation

Laboratory of the National Bureau of Standards) and those in northeastern

Ohio by Smith Electronics under contract to CRPL. Details of geo­

graphical locations, experimental procedures, and cumulative distribu­

tions of the data are reported by Barsis and Miles (1965), while path

profiles and a complete tabulation of data are contained in a series of

reports by Johnson et al. (1967).

All measurements in the Colorado plains and mountains were

made from a common transmitter site northeast of Boulder. Receiving

sites were selected from a map study at nominal distances of 5, 10, 20,

30, 50, and 80 km from the transmitter site, which is close to the

plains-mountains boundary. All transmissions were continuous wave,

using vertical polarization at 20. 08 and 49. 72 MHz, and both vertical

and horizontal polarization at 101. 5 MHz.

The measurement program in Ohio was conducted in an area

surrounding Cleveland, using one central and five peripheral transmitters.

Receiver sites were selected in concentric circles around the .central

38

transmitter at distances of 10, 20, 30, and 50 km. All paths were in

hilly and partly wooded terrain, with none in urban areas. Transmission

was at 19.97, 49 . 72, and 101.8 MHz with vertical polarization, andat

101. 8 MHz with horizontal polarization.

In this report comparisons with predictions are shown for data

taken using vertical polarization. Comparisons with data at 100 MHz

using horizontal polarization are very similar to those using vertical

polarization. Most of the comparisons are with data for the 11 principal11

or randomly selected receiver site . An alternate site is the readily

accessible site within a 100 m radius of the principal site at which a

maximum value of field strength was recorded. An example of the

resultant improvement in propagation conditions in Ohio is included.

The measurements in Colorado were chiefly in the plains

but extended into the mountains . The paths were rather arbitrarily

divided into two groups, those in the plains and those in the mountains.

The separation is not clear - cut, as both groups include some measure­

ments in the foothills, and neither group can be considered as repre ­

sentative of homogeneous terrain.

Point-to-point predictions for all paths in Colorado and Ohio

have been compared with measurements and will be discussed in

section 3.

2. 5. 1 Colorado Plains

For paths in the Colorado plains the transmitting antenna

heights were 3. 3 and 4 m for 20. 08 and 49. 72 MHz, respectively, with

receiving antenna heights of 1. 3 mat the lower frequency and 0. 55 and

1. 7 mat the higher one. At 101. 5 MHz the transmitting antenna

height was 3. 15 m, with receiving antennas 3, 6, and 9 m above ground.

39

The common transmitting site is located in an open area with

level terrain and clear foreground. Most of the receiving sites show

clear foreground in the direction of the transmitter, but some paths

are partially obstructed by buildings or trees. Procedures were

planned to simulate completely random choices of sites by selecting

readily accessible sites at nominal distances from the transmitter

with a separation of at least 1 km between adjacent sites.

Measurements were made over about 190 paths in the plains

at nominal distances of 3, 5, 10, 20, 30, 50, and 80 km from the

common transmitter . At each of the shorter distances onl~· 13 paths were

used, with 18, 35, 43, and 52 measurements at nominal distances of

20, 30, 50, and 80 km, respectively. Values of the terrain parameter

calculated from profiles read from topographic maps for all measure ­

ment paths have a median value Ah = 90 m that characterizes terrain

for the area. Values of Ah, ranging from almost zero to 275 m , were

obtained showing the wide diversity of terrain in this group of paths.

Figures 23 and 24 show the median and interdecile range of

basic transmission loss derived from measurements at nominal distances

of 3, 5, 10, 20, 30, and 50 km and a curve of predicted values as a

function of distance assuming randomly selected sites. Figure 23 shows

the results of measurements at 20 MHz with antenna heights of 3 . 3 and

1. 3 m, and at 50 MHz with a transmitter height of 4 m and receiver

heights of 0 . 55 and 1. 7 m, and corresponding predictions of basic

transmission loss as a function of distance . Figure 24 shows data at

101. 5 MHz with a transmitting antenna height of 4 m and receiving

antenna heights of 3, 6, and 9 m, with corresponding predictions. In

both figures the interdecile range of data is rather large, often more

than 20 dB, but in most cases the medians show good agreement with

40

80

100

120

140

CQ 0 "O c ..... cn 100 (/)

.3 IC 120 0 ..... rn rn ..... E 140 en c ~

"" ~ 160 CJ ...... Ill ~

P'.l 0

100

120

140

160

0

I I I I I f =20MHz, hgl =3 . 3m, h = l. 3m

g2 -

.. ~

" ' --.. ~ -

0

10 20 30 40 50

I I I I I " f =50MHz , hgl =4m, h

2: 0 . 55m

\ g -

I I '

' ')~ '~-l

'' ~

· ·~ l'

10 20 30 40 50

I I I I I \ f =SOMHz, hgl =4m, hg2=l. 7m _

\ ~~

o~ ~ ...___

---l) '

10 20 30 40 50

Distance in km

Figure 23. Basic transmission loss, Colorado plains , llh=90m, £=20 an d 50MHz, showing median and interdecile range of values at each nominal distance.

41

the predicted values . Measurements at 101. 5 MHz and a distance of

80 kin are not shown in figure 24 but agree with predictions as well as

those shown at 50 kin.

2 . 5. 2 Colorado Mountains

About 46 of the measurement paths in Colorado extended from

the transmitter site on the plains into the mountains and were classed

as mountain paths. Of these paths 6, 10, 14, and 16 were at nominal

distances of 10, 20, 30, and 50 km, respectively. A median value of

the terrain parameter A h= 650 m was used to characterize the terrain.

Values of A h calculated from profiles of these paths rang\? from 260 to

17 50 m. The frequencies and antenna heights are the same as those

for the Colorado plains.

Figures 25 and 26 show the median and interdecile range of

basic transmission loss derived from measurements at nominal distances

of 10, 20, 30, and 50 kin, and a curve of pred icted values as a fw1ction

of distance assuming randomly sel ected sites . Figure 25 shows

predicted and measured values at 20 and 50 MHz, while figure 26 shows

values at 100 MHz for receiver heights of 3, 6 , and 9 m . These two

figures show a wide range of measured val ues at each distance and

frequency but a reasonably good agreement of their medians with

predicted values. The w ide range of measured values probably results

in part from the wide range in terrain irregularity, and in part from

the fact that sites were randomly sel ected, without regard for good

propagation conditions .

2. 5. 3 Northeastern Ohio

Measurements in northeastern Ohio were made with one central

and five peripheral transmitting locations. The receivers were located

on concentric rings about the central transmitter at nominal distances

43

100

120

140

160

~ 0 "O d ..... Ul

120 Ul

j d 0 140 ..... Ul Ul .... E 160 Ul d (1j

""' E-4 18 0 u ..... Ul

<II ~

0

100

120

140

160

0

I l I I I

~ f =20 M Hz, h =3 . 3m ,

g l hg

2=1. 3 m _

' ~ ~ I) ~

D \

I \ -

10 20 30 40 50

I I I I I \. f =SOMHz, hg 1=4m, hg

2=0 . 55m _

\ ~ I~

"""' ~ r--.. --I

j .J -

10 20 30 40 50

I l I I I f= 50MHz, hg l =4m, h g 2 =l. 7m _

\

" ~·~ --............ r----- r--- ---

1) 0

.I -I

10 20 30 40 50

Dis ta nce in km

F igur e 2 5. Bas Lc t ransmission loss , Colorado moun ta ins , 6h =650m, f=20 and 50MHz, s ho win g media n and interde c ile r a n g e of v a lues at each nominal distance .

44

I

120

140

160

180

o:l 0 'tl c: .... Vl 120 Vl 0

....:i c:

140 0 ..... Vl Vl .... E 160 Vl c: Id ,.. ~ 180 (J ..... Vl Id o:l

0

I 120

140

160

180

0

I 1 l

" hgl =4m, hg 2 =3m -

"'-....: ~ ............... ~ -

I

10 20 30 40 50

I h =6m .. g2

"' r-..... • ........ r.........._ .........._ ~

1)

•

10 20 30 40 50

I .. hg 2 =9m

"' ~ . , -~ r---

• )'"'--.

·~ . )

10 20 30 40 50

Di s tance i n k m

F igure 26 . Basic transmi ssion loss, Colo r ado mountains , tih=650m, f =lOl , 5MHz , showing median and interdecile range o f values at each nominal distance.

45

of 3, 5, 10, 20, 30, and 50 km. The transmitting antenna heights were

3. 3 mat 20 MHz and 4 mat 40 and 100 MHz. At 20 MHz the receiving

antenna height was 1. 3 m, at SO MHz heights of 0. SS and 1. 7 m were

used, and at 100 MHz heights of 3, 6, and 9 m were used. With six

different transmitter locations and a large number of receiving locations

at each distance, these measurements should closely simulate a situation

with randomly selected sites.

In this report we consider data from all transmitters, providing

a total of about 255 paths. Of these, 4S, Sl, 67, and 92 are at nominal

distances of 10, 20, 30, and SO km, respectively, from the transmitter.

Terrain profiles for all measurement paths were used to determine a

median value of the terrain parameter A h = 90 m. Values from

individual paths ranged from 20 to 270 m .

Figures 27 and 28 show the medians and interdecile ranges of

measured values at each nominal distance, with c..urves showing predicted

basic transmission loss as a function of distance . In all cases, good

agreement with medians of the data is noted with a rather wide range

of data at each distance. The downward arrows at the longer distances

indicate that several val ues were in the noise so the 90 percent level

could not be determined. The improvement obtained by selecting the

best receiving site within a 100 m radius of the principal site is shown

in figure 29. The only difference between the data in figures 28 and 29

is the choice of receiving sites. Some improvement is noted at all

distances and receiver heights but particularly with the lowest height

and at the longer distances. On figure 29 two prediction curves are

drawn for each set of data. The lower curve is for randomly selected

sites with the effective heights equal to the structural heights

hel, 2 = hgl, 2 . The upper curve is calculated assuming that the re ­

ceiving antennas are at carefully selected sites, he2

= 7, 10. 4,and 1 3. l m .

46

100

120

140

160

~ 0

'O

c (/)

Ill 100 0

.....:i

c 0 120 •-' (/)

(/)

E 140 (/)

c ro

"' E-< 160 u •-' (/)

ro ~

0

100

120

140

160

0

\ I I I l I f=20MHz, hgl =3. 68m, h =3 m

' g 2 -

'--11-......... r---- -

I I

0 -.

10 20 30 40 50

I I I I I \. f=50MHz, h

1 =4. 24m, h =lm

\ g g 2 -

" r---.... ............__ • u

'' -'

10 20 30 40 50

I I I I I \ £=50MHz, hgl =4 . 24m, h =3m

g2 -

\ i'...

~I

~ !""----. ...

) -•

10 20 30 40 50

Distance in km

Figure 27. Basic transmission loss , Ohio, Cih=90m, £=20 and 50MHz , showing median and interdecile range of values at each nominal distance.

47

100

120

140

160

l'.!1 't)

c .... VI VI 100 .3 c 0 120 .... VI VI

E VI 140 c nj lo<

r-. 160 0 ....

VI cd

l'.!1

100

120

140

160

I ' .

I I I I I f = lO l. 8MHz, hgl =4m, h =3m

' g2 -

' ~ I

~ 'I......

I

, ,,

0 10 20 30 40 50

I t. h =6m

'~ g2

""" ~ 4 ~

I --- -~

. 0 10 20 30 40 50

I \ h =9m

' g2

~ 1 ~ ............... - -

4 I -,,

0 10 20 30 40 50 Distance in km

Figure 28. Basic transmission loss, Ohio , 6h=90m, f =l O 1 . 8MHz, showin g median a nd interdecile range of values at eac h nominal distance.

48

i:Q "O c ..... (/)

(/)

j c 0 ..... (/)

(/) ..... E r.n c C1l

"" ~ u ..... (/)

rd i:Q

l l I I I 100 f :lO 1. 8MHz , hg

1 =4m, hg

2:3m _

\:-~ ~ ~ ~-~ ~-- -- h = 7m - ----· e --.,----·C ... ____ i..

120

140

h =h e g

I

160

0 10 20 30 40 50

I 100

.. h =6m

~ g2

~ 120

140

~ ~ ~--~ -~--

'-- he 2 =10. 4m • - -· ~-~- ~'....- -- ._ 160

h =h e g

I 0 10 20 30 40 50

l 1 (10

\ h =9m

~ g2

~ ~20 """ii:: ~-

......... ~ ~ -. hez =l3. lm

--~~ ... - ---140

h =h e g 160

0 10 20 30 40 50

Distance in km

Figur e 29. Basic transmission loss, Ohio, llh=90m, f =I O 1. 8MHz, using alternate receiving locations , vertica l polarization.

49

The observed improvement is slightly less than that predicted

for carefully selected sites. This is to be expected as the improvement

in each case is only at the receiving site .

2. 6 Summary of Area Predictions

Area predictions of basic transmission loss as a function of

distance are based upon an estimate of terrain irregularity in the area

and the way in which antenna sites are selected. Such predictions

depend upon median propagation conditions, where path parameters

that are representative of median terrain characteristics are calculated

from the terrain parameter Ah and the structural antenna heights,

with estimates of effective antenna heights depending upon the rules

followed in site selection. If the terrain in an area is homogeneous

so that values of Ah calculated for individual paths do not diverge

widely from the median value and antennas are all either advantageously

or poorly situated, the scatter of data about the median will be minimized.

In nonhomogeneous terrain a wide scatter of measured values may occur .

In some groups of measurements a range of 60 dB, or more, between the

highest and lowest values recorded over paths of the same length is

observed. Most of this scatter of data results from differences in

individual path profiles and in the way sites are selected. Some of the

scatter may also result from the fact that these are single "spot"

measurements . For the few paths where measurements were repeated

on two or more different days the measured losses differed by as much

as 15 to 20 dB over a single path.

Such path-to-path differences may be taken into account by an

allowance for path-to-path or location variability. For many applications,

the variability introduced by high values of field strength over unusually

favorable transmission paths is much less important than that resulting

from unusually poor propagation conditions. In such cases, care should

50

be exercised to select sites with a clear foreground, and no nearby

obstacle in the direction of the other antenna. With low antennas over

irregular terrain the improvement resulting from care in site selection

may be highly significant, as shown by the differences in measurements

over rugged terrain in Washington and Wyoming . In Washington the

majority of the sites were unusually well chosen for good propagation

conditions, while in Wyoming many paths were partially obstructed by

objects in the near foreground.

The prediction method used to calculate median basic transmission

loss as a function of distance was originally developed and tested against

the measurements at VHF made in Colorado and Ohio. The present

comparisons show that this computer method, described by Longley and

Rice (1968) applicable throughout the frequency range from 20 to

10, 000 MHz over terrain types ranging from smooth plains to rugged

mountains and for antennas less than a meter above ground. The

maximum antenna heights tested in this series are 15 m, but other tests

have shown that the methods may be used up to heights applicable for

air -to-ground communication and to distances much greater than any

used in the various measurement programs described in this section.

3. POINT-TO-POINT PREDICTIONS COMPARED WITH MEASUREMENTS

For all the measurement paths discussed in section 2 and for

a large number of established communication links, detailed terrain

profiles were read from topographic maps. For each path the following

parameters were calculated using methods described by Longley and

Rice (1968) and by Rice et al. (1967):

a an effective earth's radius in km, calculated as a function

of the minimum monthly mean value of the refractive

index of the atmosphere at the surface of the earth,

51

d

e

the path length in km,

the elevation angles eel and eel from each antenna to its

horizon, and their sum e , all expressed in milliradians, e

the angular distance between radio horizon rays in the

great circle plane defined by the antenna locations,

e = l 0 0 0 d I a + e mr, e

dLl, dLZ' dL the distances dLl and dLZ from each antenna to its

horizon, and their sum dL, all expressed in km,

the effective height in m of each antenna above terrain

along the great circle path between the antennas.

These parameters were used to calculate a predicted value of

basic transmission l oss for each path, using the computer methods

described by Longley and Rice ( 1968), and each predicted value was

compared with the corresponding measured value. Calculations were

made for more than 1300 individual paths, at several frequencies and

antenna heights . Because such a large amount of information is involved,

the path parameters and measured and predicted values of transmission

loss for individual paths are not tabulated here. Rather, for each group

of data, cumulative distributions of selected path parameters are tabu ­

lated. Similar distributions of basic transmission loss, predicted and

derived from measurements, and of their individual differences AL are

plotted in a series of figures . The groups of data are discussed in the

same order as in section 2 with the additional data from established

communication links considered last.

The point - to-point predictions depend upon values of Ah, d, dLl'

dLZ' e e, and estimates of effective antenna heights calculated for each

individual path, in contrast to the area predictions, which are based on

the median value of the terrain parameter A. h and estimates of median

values for each of the other parameters.

52

3. l Gunbarrel Hill and Fritz Peak, Colorado (R-1 and R-2)

Paths with common receiver terminals at Gunbarrel Hill and at

Fritz Peak are discussed in this section. The Gunbarrel Hill receiving

site is in the open plains about 15 km east of the foothills of the Rocky

Mountains. The receiver site at the foot of Fritz Peak is located in the

mountains and is shielded from the plains to the east. The majority of

sites for the mobile transmitters were selected to provide an unobstructed

foreground in the direction of the receiver . Transmission was continuous

wave at frequencies of 230, 410, 751, 910, 1846, 4595, and 9190 MHz, \:1.ith

antennas fixed at 6. 6 and 7. 3 m above ground for the three lower and

four higher frequencies, respectively. The receiving antennas, mounted

on a tower, were raised or lowered from 1 to 13 m above ground.

Tabl e l shows cumulative distributions of parameters for 48 11 open11

paths to Gunbarrel Hill and 43 "open" paths to Fritz Peak. In this and the

following tables the distances d, dLl, dL2

, and dL are in km, the terrain

parameter Ah, the antenna heights above ground h 2

, and the effective g l ,

heights h 1 2

are in m , and the sum of the elevation a n gles () is in mr. e , e

In both sets of data path lengths range from less than 3 to 120 km, with

a wide range in the terrain parameter Ah in both groups. The median

Ah for the R - 1 data is 92 m while that for the mountain data is 510 m,

with an interdecile range of more than 700 m in each area. These wide

ranges in Ah show that no clearcut differentiation between plains and

mountains was made in these two groups. The tabulated values of dLl,

dL2 ' dL, and () e are for a receiver height of 1 m . Raising the receiver

to 10 m makes little difference to the di stributions of these parameters,

but does result in a slight increase in median values of dL2

and dL. For

more than half of the paths large values of effective height are estimated,

especially for the R-2 paths . These values in most cases are subjective

estimates of the height of the antenna above average terrain in the

direction of the horizon object or of the other antenna.

53

Table l. Cumulative Distributions of Path Parameters, Colorado Paths

Para - Percentage

meter Min 10 20 30 40 50 60 70 80 90

Gunbarrel Hill, (R-1 ), 48 paths, hgl =6. 6 m, h =l m g2

d 0.5 3. l 5. 0 9.3 10. l 19.8 Z3. 3 49.1 58.7 92.2

Ah 2.2 35.9 60.8 70. 1 84.4 91. 8 101. 9 140. 9 187. 5 747.2

dLl 0.6 l. 1 2. 0 3.8 5. 7 7.4 9.6 14. 3 17.4 27. 7

dL2 0.03 0. 2 0. 3 l. 4 11. 4 16.3 26.4 31. 3 36. l 37 . 8

dL l. 3 3.2 5. 7 8. 5 17. 7 20.4 37 . 6 46.0 so. 5 58. 7

Be - 6.7 - 2. 8 -0.4 l. 0 3.0 7.7 15. 1 18. 1 40.5 58.9

h el 6. 6 6.6 7. l 16.S 16.6 18.6 26. 6 36 . 6 55. 1 150 . 6

he2 10. 0 10.0 10.0 15. 0 20.0 33. 5 35.0 45. 0 68 .0 210.0 (hg2=10)

12 line-of- sight, 13 1- horizon paths

Fritz Peak, (R-2), 43 paths, hgl =6. 6 m, hg2=1 m

d 2.9 3. 0 5. 0 9. 5 10. 1 19.6 20.7 50. 2 56. 5 91. 6

A h 159 . 9 251. 4 289 . 3 354. 8 432. 3 511. l 657. 0 718. 7 914. 4 1003. 4

dLl 0. 1 0.4 l. 8 3.3 4.8 5. 1 6.2 15. 6 37.6 63.9

dL2 0.02 o. 02 0. 1 o. 1 0. 1 0.2 2.6 5. 2 13. 1 18. 1

dL 0.06 2.9 4. 5 5. 2 5. 3 6. 3 17.2 28. 4 47.2 71. 9

8e 5. 5 57 . 0 86.9 99.6 132 . 0 172. 9 287. 3 336.5 429.0 546.9

hel 6.6 6. 6 36. 6 56.6 63.6 106.6 126.6 236.6 306.6 406.6

he2 10.0 10.0 10. 0 10. 0 (hg2=10)

48.5 60.0 110. 0 116. 0 205. 0 230. 0

4 line - of- sight, 11 !-horizon paths

54

All measured values of path loss were converted to basic trans ­

mission loss and compared with corresponding predicted values . Figures

30, 31, and 32 show cumulative distributions of basic transmission loss,

observed Lbo and predicted L , and of their differences AL = {Lb - L ) be c bo

in dB, for the Gunbarrel Hill {R-1) receiver site. In each case the values

plotted are for a receiver height 2 m above ground. Figure 30 shows

good agreement between predicted values and data at 230 and 410 MHz,

with a standard deviation of AL of about 9 dB. Figure 31 shows similar

results at 7 51 and 910 MHz, while figure 32 shows wider deviations

between observed and predicted values at 1846 and 9190 MHz. Referring

to the same data plotted in figures l through 5 with a receiver height of

l m we find a range at a single distance of some 80 to 90 dB, even at the

lower frequencies. Thus, the point-to- point predictions based upon

individual path parameters show considerably better agreement with

data than woul d be possibl e with an c.rea predicti on of basic transmission

loss as a function of distance and terrain type alone.

Figures 33 and 34 show cumulative distributions of deviations of

predicted from observed values, AL in dB, for receiver heights of 1, 3,

7, and 10 m. In all cases the deviations become more positive with

increasing antenna height, indicating that the prediction model tends to

calculate too much loss at the higher receiver heights . These height

differences are more pronounced at the lower t han at the higher frequencies ,

Figure 35 shows cumulative distributions of ~o and Lbc and of

their differences AL for the Fritz Peak {R- 2) receiver site. The

predicted losses are greater than those observed at 230 and 410 MHz,

with A L about 12 dB at the median. Unfortunately, at the higher fre ­

quencies more than half of the measurements were 11 in the noise11 so no

distributions of differences between observed and predicted values coul d

be prepared. Figure 36 shows cumulative distributions of AL for receiver

55

o:i 100 "d

s:: ..... If)

If)

0 ....:i

120

s:: 0 ..... If)

140 If) .... 6 f/)

s:: "' M

160 ~

u ..... If)

~ o:i

180

1 5

~ "d

s:: 20 ..... 0

..0 ....:i

0 u

..0 ....:i

II

....:i -20

<I

1 5

I I I I I

Observed ----- Predicted

I

I

~ l

I 47 paths

~

10

'~-

--~ ~ ' • ~ ~~OMHz ~ I I

' \ tlO MHz

\ ~-~~ \ I' ' ' ' ..

20 30 40 50 60 70 80

Percent of Paths

90 95

.... ... .... I ..... ~ ••• t

10

i-• .. , ~ .... ........... . ... ····· ....... _ .. ......

....... .. ""'······ .......... ····· i-•••

20 30 40 50 60 70 80 Percent of Paths

-... 410 MHz

I 230 MHz

90 95

99

99

Figure 30 . Cumulative distributions of basic transmis sion loss , observed and predicted, and of tiL, G unbarrel Hill, Colorado , R -1,

hg 2=2 m , f=2 30 and 410 MHz.

56

~ 100 "O ~ ...... (/)

(/)

0 120

....:i c 0 ...... (/) 140 (/) ...... 6 (/)

c ro f.<

160 ~

u ..... ({)

"' ~ 180

l

~ "O c 20

0 .D ' .-I

0 u

.D ....:i

II

....:i -20

~

1

Figure 31.

5 10

.......

5 10

I I

I Observed

I----- Pred icted I I I

I I

46 paths

MHz

M Hz

20 30 40 50 60 70 80 90 95 99

Percent of Path s

... .... ""--

, ..... -····t 910 MHz - -+--t "·· -. ... '·-...

751 MHz I

20 30 40 50 60 70 80 Percent of Path s

90 95 99

Cumulative distributions of basic transmission loss, observed and predicted, and of liL, R - 1, hg

2=2 m, £=751 and 910 MHz.

57

~ "O r::: ..... ~ <l .. (/)

Q) ::l

....... C'd

::> "O Q)

> $.! Q) (/)

..c 0 E 0 $.! .....

"O <I) ..., u .....

"O Q) H

~ ..... 0

r::: 0 ..... ..., C'd ..... > Q)

0

20

0

- 20

1 5

20

0

- 20

1 5

20

230 MHz I .. ~- n .;.:,.

"~ g2 --- . ....._

lm -~

i-. __ -- ...::·· =-·:.:.: ---. .. 3 m .. ,.,,_,..,6' i-........: --· -- ~ ... --'&&-.. -.......... .......... --. ,._ __ ........ ........_ -----..

"'-10 20 30 40 50 60 70 80 90

Percent of Paths

~~-...... "'!

--~ ,~ ~ .... ~

" ---i.- ·-- '«:·· ............. -- :,,,,_ ...__ - .. ~ '• r.:-:.~--.... - -- r--.... ;= ..........

l"'-o...... -.....

10 20 30 40 50 60 70 80 90

•• ~ .. l'!ii.. ••

Percent of Paths

~······ .. ............... --~~.::~ .....

7 m -- · 10 m •••••••

95

410 MHz I

95

751 MHz

----

99

99

..........._ 1.-..:::llJ...~ ... __ _

0 l----+-----+----+-----+---+~~d-~--~ ...... ~--:!!!2*--··~··~··~----~---1------1---4 "'....._ -~ ... ..._... . -..:· ....... ' ,,

.... "' ' - 20 t---t-----t----f-----11----+--+---i--+-__,l----i----'~~l----+---4-~

1 5 10 20 30 40 50 60 70 80 90· 95 99 Figure 33. Cumulative dis t ributions of 6L showing the effects of

increasing receiver height, R-1, f= 230, 410, and 75-1 MHz.

59

~

II)

v ::::s ...... <d > "O v > "" v II)

..0 0 E 0

20

0

- 20

l 5

9 10 MHz ~-

h -~"'. g2

fl.!..• •• l m ........ ~

... _ ~~ .... 3 m _..,.._. __ ...__

;~= """"-- .... --......... ...,

~-=~= 7 m----,...__L ······ 10

10

-r-- ....._

20 30 40 50 60 70 80

Percen t of Paths

m·········· -...........

--

90 95 99

4595 MHz

~ - 20 1----1~~~-~~~~-+~-+~+-~l---+-~+-~+-~~+-~-t-~~t---t

"O v ...., u .....

"O v

"" Cl. ..... 0

c 0 ..... ...., <d ..... > v

Cl

1 5

20

0

- 20

1 5

10 20 30 40 so 60 70 80

Percent of Pat hs

~

10

~ ~ ~ ~ ~

~ ~

20 30 40 50 60 70 80 Percen t of Paths

90 95 99

9190 MHz

90 95 99

Figure 34. C umulativ e distributions of LI L showing the effects of i n­creasing r eceiver hei ght, R-1 , £=9 10 , 45 95, and 9 190 MHz .

60

Observed

- - - - - Predicted

P'.l 100 'O 3 7 paths c: .... C/l C/l 0

120 ...:I c: 0 .... C/l 140 C/l ...... E C/l c "' H 160 E-l u ·-C/l

"' P'.l 180

l 5 10 20 30 40 50 60 70 80 90 95 99

Percent of Paths

co -0

c 20

-0

~~: .. I I ··:·. '"'i.• I • j-· •. ···it.

.D ...:I

0 u

.D ...:I II

...:I -20

I ... • • .. i- •• .. ·· . ... .

•• ••• 4 .. ... 230 MHz .. .... I

4 10 MHz ...... • •• •4

• •.

~ 1

l 5 10 20 30 40 50 60 70 80 90 95 99 Percent of Paths

Figurc3 5. Cumulative distributions of basic transmission loss , observed

and predicted, and of ClL, Fritz Peak, Colo. , R - 2, hg 2

=2 m,

f =230 a nd 410 MHz .

61

-0

.:t u .0

...::1

II

...::1 <J

40

20

0

- 20 1

40

20

0

- 20 1

40

20

-0 -

-- 20

I

l

~ . ~, ~ '"~· 230 MHz , . .;..,.

.......... -~ ~~ -... ~ .. -· ...... -~ ~ ~~

!'-: ~"' ""'~···-~'\

5 10 20 30 40 50 60 70 8 0 90 95

Percent of Paths

~ ' It~~ " ~

I

~ 410 MHz

~ ~ 19...

"' ~ ~ ~ ~ ~

5 10 20 30 40 50 60 70 8 0 90 95

Percent of Paths

~ ... ~ ...... ~4 ~· ••

~ .. I

\:• . 751 MHz ...

' ,.

h \ ' .. g2 ' ••

~ ,.

lm \·. 3 m •1 ,,_,.,,_

'~ • •

7 m ---10 m ..........

I I

5 10

•. \\

\ 20 30 40 50 6 0 70 80

Percent of Paths 90 95

99

99

99

Fig ure 36. Cumulative distribution s of 6L showing the effects of in­creasing receiver height, R-2, f-230, 410, and 751 MHz .

62

heights of 1, 3, 7, and 10 mat frequencies of 230, 410, and 751 MHz.

In this area a l so the deviations become more positive with increasing

antenna height. At the higher frequencies no such comparisons coul d be

made because more than half of the measurements were in the noise.

For both the R - 1 and the R - 2 data an unusually large proportion

of the paths are either line - of- sight or one - horizon diffraction paths .

The lack of agreement with increasing antenna height and the large

predicted losses for the R - 2 data suggest that the models for line - of­

sight and one-horizon diffraction paths should be re - examined and

possibly modified.

3. 2 Virginia Paths

The results of measurements made in Virginia have not been

completely analyzed. Terrain profiles have been read for 51 of the

rather short paths . Of these 30 are line-of-sight paths and 5 are one­

horizon paths . No tabulation of parameters is included for the 2 1 trans­

horizon paths, as they would probably not be truly representative of the

l arge number of measurement paths from seven transmitter sites in

this area.

The measurements reported here were made with transmitter

heights of 11. 3 and 15. 0 m and receiver heights of 12. l and 15. 0 m.

Figures 37, 38, and 39 show cumulative distributions of basic trans ­

mission loss observed and predicted and of their differences for the

51 paths for which terrain profiles are available . These figures show

good agreement between predicted and observed values, with a tendency

to predict too much loss at 76 MHz and not enough at 2180 and 839 5 MHz.

In this area there is considerable forestation for which no allowance is

made in the present prediction model. Such surface clutter would cause

much more attenuation at the higher than at the lower frequencies, and

63

'° 80

"d s:: .... (/) (/)

100 0 ....:i s:: 0 .... (/)

(/) 120 ....

E (/)

s:: C1l i...

t-< 140 u .... CJ)

ro

'° 160

l

c:'.:l "O c 20 ....

0 .D

....:i 0

u .D

....:i

II

....:i - 20 ~

1

Observed

----- Predic ted

51 paths

5 10 20 30 40 50 60 70 80 90 95

Percent of Paths

•••••••• ··-~ ···-........ --.......... .... ······ ....

5 10

... ····· .. "'····

. .. ····· 76 ······ MHz ····· •••••••• 1 .... .. .l ······· .. ·········· ····-173 MHz ····· I

20 30 40 50 60 70 80 Percent of Paths

90 95

99

99

Figure 37. Cumulative distributions of basic transmission loss, observed

and predicted, and of t.L, Virginia, £=76 and 173 MHz .

64

i:Q 100 "Cl

c ..... Ill (/)

0 ....l c 0 ..... (/)

(/) ..... E Ill c Cl!

120

140

~ 160

180

CQ "O

c 20 ..... 0

.0 ....l

0 u

.0 ....l

II

....l - 20 ~

l

.

l

5 10

I Ob se~ve d I----- Pred icted I

20 30 40 50 60 70 80 90 95

Percent 0£ Paths

I ..... ··.:·4 ••• ••

5

~- .. ..• -.. .... ... •• .... I~ -i:.~~: .... ...... 409 MHz ..... . .

I -·· .. ········ 9 50 MHz ...... t ..... ...

10 20 30 40 50 60 70 80 Percent of Paths

90 95

99

99

Figure38. Cumulative distributions of basic transmission loss , observed and predicted, and of tiL, Virginia, £=40 9 and 9 50 MHz

65

may be the explanation of these differences. This possiblity should be

further investigated when more of these paths have been studied.

3. 3 Wyoming, Idaho, and Washington

The measurements in Wyoming, Idaho, and Washington were

limited to frequencies of 230 and 416 MHz, with very low antennas.

The transmitting antennas were fixed at 0. 7 5 and 3 m above ground,

while the receiving antennas were raised continuously from 0. 75 to 3 m.

Both transmitting and receiving units were mobile, and sites were chosen

without regard to propagation conditions.

Cumulative distributions of parameters for 47 paths in Wyoming

and 30 paths in Idaho are listed in table 2. The parameters listed are

for transmitting and receiving antenna heights of 0. 7 S m. Increasing

both antenna heights to 3 m has little effect on the path parameters

dLl' dL2' dL, and (Je. However, with the lower heights we assume that

the effective heights are equal to the structural heights, while with the

3 m antennas effective heights are estimated. These effective heights

exceed the structural heights for about half of the paths in Wyoming,

and for a few paths this increase is more than 30 m. The estimated

effective heights in Idaho exceed the structural heights for about one­

third of the paths.

The computer model is limited to situations where the distance

from each antenna to its horizon is not less than one-tenth of the

corresponding distance dLSl, 2 over a smooth earth. With antenna heights of 0. 75 m, dLSl, 2 �3. 5 dB and their sum dLS �7 dB. Table 2

shows that for many paths, especially in Wyoming, the horizon distances

are less than one-tenth of these smooth earth values. The prediction

67

Table 2. Cumulative Distributions of Path Parameters, Wyoming and Idaho

Para-Percentage

meter Min 10 20 30 40 50 60 70 80 90

Laramie Range, Wyoming, 4 7 paths, h =h =O. 75 m gl g2

d 3. 6 6.0 7.8 8.8 10.0 13. 9 1 7. 6 19.8 21. 9 26. 1

�h 53.8 65. 5 8 7. 8 99.4 112. 0 120.4 136. 7 159. 2 18 3. 4 204.0

dLl 0. 1 0.2 0.4 o.6 1. 3 1. 5 1. 7 2.9 4.4 8.8

dL2 0. 1 0.2 0.3 0.4 0.6 1. 1 2.0 3. 1 4.9 7. 8

dL 0.2 0.7 1. 8 2.0 2 • .3 2.9 4.2 5.6 8.4 15.8

(j -3. 0 12.5 19. 5 2. 3. 3 28.9 36. 6 49.4 53.0 71. 7 88.4 e

2 line-of-sight, 8 1-horizon paths

Idaho, 30 paths, hg1=h

g2=o. 75 m

d 10.8 15.0 1 7. 1 18.4 20.4 20.8 21. 4 23.4 27.2 32.8

�h 8.6 24.8 46.6 52.8 59.2 62.8 70. 4 81. 3 102. 4 116. 2

dLl 0.3 1. 2 2.0 2.4 3. 7 8.0 11. 1 13.9 15.2 19.8

dL2 0.4 1. 3 1. 5 2.4 3. 6 5. 1 6. 6 8.4 10. 2 13. 2

dL 4.7 5.0 10. 5 12.3 13. 0 14.8 16.2 17. 6 20. 5 24.0

(j -3. 4 -0. 1 1. 8 3.9 7. 0 11. 5 15. 3 1 7. 3 20.2 24.2 e

1 line-of-sight, 9 I-horizon paths

6 8

model was mo dified to allow for this as follows:

AL = 0 dB. c

(2a)

(2b)

Then for low antennas (less than 3 m) over irregular terrain, the

calculated median basic transmission loss is mo dified by adding AL to c

the computed value Lbc

for trans horizon paths.

Figures 40 and 41 show cumulative distributions of basic trans -

mission loss observed and predicted, and of the differences AL between

these values for each path for frequencies of 230 and 416 MHz in Wyoming.

Figures 42 and 43 present the same information for the paths in Idaho.

For both the 0. 7 5 and 3 m antennas the predicted values show good

agreement with measurements. In all cases the standard deviation of

AL is about 9 or 10 dB. This represents the location or path-to-path

variability caused by factors not included in the prediction model. In

Idaho the predicted values with Cl;_ntenna heights of 0. 7 5 m tend to under -

estimate the transmission loss. The reason for this is not clear at

present.

The measurement paths in Washington fall naturally into two

groups, the first consisting of 15 paths near Ritzville where the terrain

is relatively smooth farm land, the second of 53 paths in rugged and

mountainous terrain. Of the latter group 14 paths have a common

receiver site in the Spokane river valley near Fort Spokane and extend

into the surrounding forested, moun !ainous terrain, while the remaining

paths are in rugged country west of Ritzville where steep hills, coulees,

and deep canyons with almost vertical walls occur. Distributions of

parameters for these two groups of paths are listed in table 3. In the

69

'° "tj c ..... C/l I/) 0

...:i d 0 ..... C/l C/l ..... E !/) d ro I-< f-i

CJ ..... en tU

a:)

co "tj

100

120

140

160

180

l

I I I I I I

I Observed

I I

I -----Predicted

I I I

I :

I !

I � "' � I ,__ _ .

� � � ..... ,__

,._�� ,_

�� "" ....... .... .. � � "" ..... � """"' ..._ ....... � ..... -

... , ...... .. -� ... 3m ' ...... ....... � ' � I r---. � .. ....... 0. 75 m

5 10 20 30 40 50 60 70 80 90 95 99

Percent of Paths

d 20 t---+---�t----+-----;.---1---+--+--+--+---+-----+----+----+--� ..... -0 ..0 ...:i

t) ..0 ...:i

""······ .... ······.

. ....

. .. ········

····· 0 1---i���������··�·�- ·�--=i-·-··-·::pt...· �,---+�-+��-t-��t-�-+�--1 ,..... . ...

l 5 10

... ... ····It· ··•···· .. :�··· ······

20 30 40 5 0 60 7 0 80 Percent of Paths

•• .. .. ..

90 95

3m

0. 75 m

99

Figure 40. Cumulative distributions of basic transmission loss, �bserved

and predicted, and of 6L, Laramie range, Wyoming, £=230 MHz.

70

i:o 100 "C d .... Ul Ul 0 120

...:i d 0 .... t/) 140 Ul

6 Ul d ro S.. 160 r.. (.) ..... Ul ro

11'.l 180

l

i:o "CJ d 20 ....

-0 .D �

0 (.) .D

...:i II

...:i -20 <I

l

I I I I -, I I I Observed I I I I I - - - - - Predicted I I

I I ' I

I ! r I

lo..

��� I

"' -- -' I "'" - -� .. � � ..

"' �� ...... ... � � --........ I' -

� ' '· � r---..... � � ...... � 3m � """'

� I ......_ ...... _ "lii;"'0.75m-

5 10 20 30 40 50 60 70 80 90 95 99

"·

�-:� . ••

5

Percent of Paths

. ........ -.. .... ""···· .... ······

10

.. ····· .. ·- . ••• •• 4 . . •• .... .. .. ..... .... , · ··-

········ � ......

20 30 40 50 60 70 80 Percent of Paths

... ,

...... 3 m -······· 0.75 m_

I 90 95 99

Figure41, Cumulative distributions of basic transmission loss, observed and predicted, and of L'lL, Wyoming,. f=416 MHz.

71

I ' ' I •

Observed

l ----- Predicted

c:Q 100 "O d I ..... I/) I/) 0

...4 120

p 0 .... I/) 140 I/)

'� � -----.... 6 ....... ---::: � -I/) cl ro "" 160 E-i u .... I/) ro

c:Q 180

.... ..... � !'.::: - ... - - ... ""' . ...... .. _ ...... - �- -

-........... ::.-- 3 m - .. --· --.... I'--- -- ... � I ......___ � ' �o . 75 m _

"' �v -

1 5 10 20 30 40 50 60 70 80 90 95 99 Percent of Paths

c:Q "O d 20 .....

0 � .. ... .0 ...4

0 u .0

...4 II

...4 -20

-··· .... .. ••• -···· ······ .... � � ..... •• • "···· .. . ...

" • • .. ... . . ••••

.. ... 3 o. 75 m ····· ····· m

........ ······ �

1 5 10 20 30 40 50 60 70 80 90 95 99 Percent of Paths

Figure 42. Cumulative distributions of basic transmission loss, observed and predicted, and of L\L, Idaho, £=230 MHz.

72

CQ 100 "O c .... U) U) 0

....:i 120

p 0 ..... U) 140 U) ..... 8 ti) p cd J.-4

160 f--1 (J ..... U) cd

i:Q 180

1 5

P'.l '1j p 20 .....

0 .D �

0 (J .0

....:l II

....:l -20 ci

l 5

I I I I

Observed I I

-----Predicted I I I

� I "'

r-...�--...... � � .. - _ !'--. I ..... - �---- I ...... , ..... _ � ..... ' -�

- !'--. - -� --· 3m ......... �. - , I r--...... r--_."""- "' I

� P'�o. 75 m . -

I I 10 20 30 40 5 0 60 70 80 90 95

Percent of Paths

i. ••••• ... ••

······ ·•. ........ .. ... _

... ..•. . . .. . .. ... i. •• •••• . .. • .. ·····

.. ..... � .... ······ ..... ,

10

•

20 30 40 5 0 60 70 80 Percent of Paths

•• •• ..

3 m o . 75 m

90 95

99

99

Figure 43. Cumulative distributions of basic transmission loss, observed

and predicted, and of 6L, Idaho, f=416 MHz.

73

Table 3. Cumulative Distributions of Path Parameters, Washington

Para- Percentage

meter Min 10 20 30 40 50 60 70 80 90

Ritzville, 15 paths, h =h =0. 75 m gl g2

d 9 . 4 9.9 11. 4 18.6 19. 8 22.3 22. 8 23. 7 29.6 49. 0

�h 19.6 29. l 44.2 65. 4 67. 6 70.0 7 8. 8 80.3 139. 0 19 5. 0

dLl 1. 5 1. 7 2. 0 2.0 2. 3 2. 5 3. 7 4.5 7. 5 9.7

dL2 0. 2 0. 2 0.9 l. 7 3. 3 6.4 7. 6 9. 5 12.9 14. l

dL

l. 7 2.6 6. 4 9.9 10.2 11. 2 1 1. 8 12.6 14.9 16. 4

(Je 0.9 0.9 l. 6 2. 4 3. 0 4.0 8. 3 12.4 16. l 19. 4

no line-of-sight, 3 !-horizon paths

Rugged terrain, 53 paths, hgl

=hg2

=0. 75 m

d l. 4 3.2 9. 0 12. 6 17. 5 22.6 24. 5 26.8 31. 9 37. 3

�h 2. 3 85. 4 128.2 178.7 193.4 257. 5 321. 4 378.3 424.6 500, 0

dLl o. l 0.5 o. 8 l. 0 1. l l. 8 2. 1 3. 1 5.6 13.7

dLZ 0. l 0.2 0.6 l. 2 2. 0 3.4 8. 1 12. 0 15. 8 20. 5

dL

0.9 l. 7 2. 3 3.6 5.4 8. 7 12.2 17. 3 22. 4 29.0

8e -2. l 5. 0 11. 4 15. 2 32.6 42.0 50. 8 58. 5 70.2 157. 4

1 line -of-sight, 15 !-horizon paths

74

first group terrain ranges from rather smooth to quite hilly, with a

median value Ah = 70 m. The terrain in the second group ranges from

hilly to mountainous, with a median Ah value of 260 m. The terrain in

the latter group is more rugged than that in the Wyorr.ing area, while

the former group is rather comparable to the measurement area in

Idaho. The group of paths in rugged terrain contains an unusually large

proportion of one-horizon paths where the obstacle is an isolated hill or

ridge. The parameters tabulated are for antenna heights of 0. 75 m.

Raising the antennas to 3 m increases the horizon distances slightly and

causes some reduction in median values of 8 . Estimates of the effec-e

tive antenna heights exceed the structural heights for more than half of

the paths in rugged terrain and become quite large in a few cases.

Cumulative distributions of observed and predicted values of

basic transmission loss and their differences are shown in figures 44

through 4 7. The 15 paths in the Ritzville area are rather too small a

sample from which to draw conclusions but, as with the Idaho paths,

they show that the predicted values are less than the observed values of

transmission loss at both frequencies. The paths in rugged terrain on

the other hand show less loss than is predicted. In the latter case the

high proportion of single horizon paths suggest that the model for such

paths should be revised.

3. 4 Measurements and Predictions at VHF

A large measurement program with low antennas at frequencies

of 20, 50, and 100 MHz was carried out in the Colorado plains and

mountains and in northeastern Ohio. All of the measurements in

Colorado were made from a common transmitter site, northeast of

Boulder. Receiver sites were chosen at nominal distances from the

transmitter without regard to propagation conditions. The measurements

75

� 100 'U s::: ..... Ul Ul 0 120

...:i p 0 .... Ul 140 Cf) ..... .... c Cf) s::: ro I-< 160 E-1 u .... Ul ro

CQ 180

1 5

CQ '"d s::: 20

0 .D

..4 0

<.: .D ...:i II

...:i -20 <S

l 5

1 -, ' I I

Observed ----·Predicted

I I

--� "-... __ _ .... _ � '

--� ' � --- ... � r--=:::.::: K� - 1' � .. _ � --- -� 1/ 3 1 �- � -1 - -..._ -

I ... "'-, ...... , I .

r-...� '

r--...... � �o . 75 m

10 2.0 30 40 so 60 70 80 90 95 Percent of Paths

� .. ... ::·····-

10

....... 4 �4:,�·· .... •• ., .... ...... 3 .... ........... m ...... -..-:.-.·-··· ·····

20 30 40 50 60 70 80 Percent of Paths

0. 15 m

90 95

99

99

Figure44. Cumulative distributions of basic transmission loss, observed and predicted, and of tiL, Ritzville, Washington, £=230 MHz.

76

o:i 100 '"d d ...... (/) (/) 0 120

...1 d 0 ...... (/) 140 (/) ..... ,.., c:: If) d rd I-< 160 t-i u ...... (/) rd

c:Q 180

1 5

c:Q '"d d 20

0 .D

...1 0

u .D ...1

II

...1 -20 �

1 5

I I I I I I

Observed I ----·Predicted I I I I I I

I

I

I

' � -· - -�I ..... ...... '

�, ' ' � - -"""" � ' �, - I --.. --

"""" ,---- - .

" r----. .........

�/3 1m

-�o. 75 m -

10

10

-.....

I 20 30 40 50 60 70 80 90 95

Percent of Paths

---. �, .... ····· .... .. ····· ... "'···· 3 m � . - .... ······ ········ ...... ....... Iii••······ o.

20 30 40 50 60 70 80 Percent of Paths

75 m I

90 95

99

99

Figure 45. Cumulative distributions of basic transmission loss, observed and predicted, and of L.lL, Ritzville, Washington, £=4 1 6 MHz.

7 7

co 100 "O s:: .....

(/) (/) 120 0

....:i s:: c (/) 140 en

E u: s:: ro � 160 f--i u ..... (/) rd

CQ 180

l

C'.l "O c 20 .....

c ..c

....:i 0

u ..c ....:i II

....:i -20 <I

1

-1 I I I I Observed I -----Predicted I I .. I "' I I

I "' ' � """'--�" ........ ,..__ \'

0 � ' � � ' ... ..... � ' ... �- -.. I .......... � "- -� ' !' .... ,�� �-.. __ 3m

O. 75 m/ ___..: ... , ......_ .. , -�

- .

� -............

5 10 ·20 30 40 50 60 70 80 90 95 Percent of Paths

....... ····· ..... ······ . -······· •• .. . .... ... ······It-. .. ••

5 10

·-....

··• • 1 •• ······ ••

········ •, �. •• •. ······

20 30 40 50 60 70 80 Percent of Paths

. . ..

3 m ··-

. ..

·······

o. 75 m

I 90 95

99

99

Figure46. Cumulative distributions of basic transmission loss, observed and predicted, and of 6L, Rugged terrain, Washington, f=230 MHz.

78

o:::i 100 "O

d ..... Ul Ul 0 120

....:1 d 0 Ul l40 !/J

..... 6 Ul d rd i.. 160 f--1 0

..... (/) rd o:i

180

l

o:::i "O d 20

..... -

0 .D

....:1 0

0 .D ....:1 11

....:1 -20 <I

1

I Observed

- - - - • Predicted

5 10 20 30 40 50 60 70 80

Percent of Paths

-. ········� •

• .. ••••• It , ••• ··· ·-

5 10

.... ····· ..... ......

• •

...... . ..

. .. •• ....... •• 1ri ••••••• I ····· ..

•• •• ••

........

20 30 40 50 60 70 80 Percent of Paths

m

90 95

3 m ...... �

... .. .... 0,75 m

I 90 95

99

99

Figurc47, Cumulative distributions of basic transmission loss, observed and predicted, and of 6L, Rugged terrain, Washington, £=416 MHz.

79

in Ohio were made from one central and five peripheral transmitters to

receiver sites similarly selected at nominal distances from each trans-

mitter.

Path profiles were read for about 490 paths and parameters

calculated for each of them. Point-to-point predictions were then

calculated for each path at each frequency and antenna height combina­

tion used in the measurement program. Tables 4, 5, and 6 show

cumulative distributions of parameters for the following paths: 184 in

the Colorado plains, 48 in the Colorado mountains, and 255 in north­

eastern Ohio. In all cases the parameters are for randomly selected

11principal11 sites, and where more than one receiver height was used

the lower height is represented. Table 4 lists distributions of parameters

in the Colorado plains for 184 paths with a median length of 50 km at

100 MHz, and 132 paths with a median length of 30 km at the lower

frequencies. In this area the terrain is somewhat rolling, with a median

value of the terrain paran1eter .oCI. h � 9 5 m but with a total range of nearly

300 m which corresponds closely to the terrain characteristics of the

Ohio area. The Colorado mountain paths are over the most rugged area

considered in this report, with a median .oCl.h �580 m and values ranging

over 1500 m. The advantageous siting of the transmitter in the Colorado

plains is indicated by the median dLl

' which is much larger than the

median dL2 for the randomly selected receiver sites. The same

advantage is observed in the mountains paths, but to much less an extent

in Ohio where six transmitter sites were chosen.

Figures 48 through 53 show cumulative distributions of basic

transmission loss, observed and predicted, and of their differences

at frequencies o'f 20, 50, and 100 MHz for each group of paths. In each

case the measurements with vertical polarization are considered, and

at 100 MHz receiver heights of 3 and 9 m are shown. The data at

80

Table 4. Cumulative Distributions of Path Parameters, Colorado Plains

Para-meter

d

..6. h

dLl dL2 d

L

(} e

d

..6. h

dL ()

e

Percentage

Min 10 20 30 40 50 60 70 80

100 MHz, h g 1 == 4 n1, h

g2= 3 m, 184 paths

0. 6 5.0 13. 0 26. 6 30. 2 49.6 49. 9 50. 4 80. 0

l. 0 57. 9 68. 7 78.7 87. 0 96. 5 106. 7 128. 8 151. 7

l . 0 2. 6 9. 0 10. 3 11. 3 12. 1 16. 2 21. 6 24. 8

0. 5 0. 5 1. 0 1. 5 2. 0 3. 5 6.2 10.0 19.0

2.0 9.5 12. 1 13.7 19. 2 22. 6 28. 2 30. 2 37. 6

-6. 5 -3. 4 -1. 6 0. 1 3. 6 5. 6 8.6 12. 1 16. 9

26 line-of-sight, 34 l -horizon paths

50 MHz, h gl

==4 m, hg2==0. 55 m, 132 paths

0. 6 5.0 9.6 19. 6 20. 0 30. 0 30. 2 49. 6 49. 8

1. 0 47. 3 69. 6 81. 4 90.0 97. 8 107.2 120. 1 147. 2

2. 0 5.0 9. 8 12. 1 13. 7 18. 6 22. l 29. 0 30. 1

-4. 5 -2. 0 o. l 2. 0 5. 2 9.4 11. 2 17. 0 22. l

22 line-of-sight, 28 !-horizon paths

20 MHz, hgl

=3. 3 m, hg2:::1. 3 m, 132 paths

2. 0 5.0 9.9 12. 4 14.4 19.3 22.6 29. 3 30.2

-4.5 -2.2 0. 4 2.6 5.6 8.9 11.0 16.3 20. 7

24 line-of-sight, 30 I-horizon paths

81

90

80.3

197. 2

29. 4

28.8

49. 8

25.2

50.0

187. 8

39. 3

34.2

41. 0

34.6

Table 5. Cumulative Distributions of Path Parameters, Colorado Mountains, 48 Paths

Para- Percentage

meter Min l{) 20 30 40 50 60 70 80 90

100 MHz, h gl

=4 m, h =3 m gZ

d 5.0 9.8 19.6 19.7 29. 3 30. 1 30.4 49.8 50. 0 50. 2

.Ah 253. 4 362. 4 429.9 477. 3 508.9 579. 5 629. 1 720. 5 811. 6 957. 8

dLl 3.4 4.4 4. 5 4. 5 6.6 7.8 9.2 11. 4 13. 5 15. 3

dL2 0.5 0.5 0. 5 1. 0 1.4 l. 5 2. 5 3.0 5. 8 10.4

dL

4.9 5.0 6.6 8. 1 10. 1 11. 6 12.8 15.0 16.8 22. l

0 e 22. 9 56. 0 60. 7 75.6 112.2 139. 4 155.2 166. 1 198. 6 298.4

no line -of-sight, 5 !-horizon paths

50 MHz, h gl

=4 m, h g2

=0. 55 m

dL

4.9 5.0 6.6 8. 1 10. 1 11. 5 12. 8 15. 0 16.8 22. 1

0 23. 3 57. 3 62.5 77. 2 e 115. 9 140.4 158.9 168. 0 203. 0 302.0

no line-of-sight, 5 !-horizon paths

20 MHz, h gl=3. 3 m, h 2=1. 3 m

g

dL 4.9 5.0 6. 6 8. l 10. l 11. 5 12. 8 15. 0 16. 8 22. l 0 23.4 57. 3 62.l 76.8 e 115. 2 140. 2 157. 8 166.9 202.l 301. 0

no line -of-sight, 5 !-horizon paths

82

Table 6. Cumulative Distributions of Path Parameters, N.E. Ohio, 255 Paths

Para- Percentage

meter Min 10 20 30 40 50 60 70 80 90

100 MHz, hgl =4 m, hg2=3 m

d 9.8 10.0 19.9 20.0 29.8 30.0 30.2 50 . 0 50. 1 50. 3

A h 15.7 50.5 63.8 77.0 85 . 9 94.7 107.3 124.8 143.8 169.8

dLl o. 5 1. 5 2. 5 4.0 4.5 5. 0 8. 5 14.7 20.5 25.0

dL2 0. 5 0. 5 1. 0 1. 0 2.0 3.0 4.5 6.3 11. 0 16.2

dL 1. 0 4.0 5. 5 7. 0 10.0 15.0 19. 1 23. 3 28. 1 34.6

ee -3. 3 0. 1 3. 2 5. 3 7. 1 8.8 10.8 13.4 19.0 31 , 3

22 line-of-sight, 2 5 1- horizon paths

50 MHz, h gl =4. 2 m, hg2=l m

4.0 5. 5 6. 5 9 . 9 15.0 19. 1 22.9 26.8 33. 9

0. 1 3. 7 5.6 7. 5 9.6 11. 9 14.8 19.8 32.8

1 7 line-of- sight, 2 5 ! -horizon paths

20 MHz, h gl=3.7m, h =3 m g2

dL 1. 0 4.0 5. 2 6. 7 10.0 15.0 19. 1 23. 2 27.9 34.6

e e -3. 3 0. 1 3. 2 5. 4 7 . 2 8. 8 10.9 13. 5 19.2 31. 3

83

o:i 100 'O ~ ..... Ul Ul 0

120 ~ c 0 ..... (/) 140 (/) ..... E CJ)

c rd 1-<

160 E--1 u ..... (/)

rd CQ

180

l 5

CQ 'O c 20

0

~ .... ····· :~,---.D ~

0 u

.D ~

II

~ - 20 <f

1 5

Observed

I I ----- Predicted

I 132 paths

MHz

10 20 30 40 50 60 70 80 90 95 99

Percent of Path s

-···· ·==:····· ····· ·····

10

.... ..... . ... 20 MHz -··· ····· -··· ~ ...... .... ... ····· ... ······ ··-

50 MHz ········ ······· ······· I

20 30 40 50 60 70 80 Pe rcent of Paths

········

90 95

····· ······

99

Figure 48. Cumulative distributions 0£ basic transmission loss. observed and predicted. and of tiL . Colorado plains. median s tih=95 m. f=20 and 50 MHz.

84

l:Q 80

"C1 c .... !/) (/} 100 0 ~ c 0 .... (/}

(/} 120 .... E (/}

c rd M

f-1 140 u ..... (/}

rd a:i

160

1

l:Q "C1 c 20 .... - ::::: ~-~---:.:::

0 .D ~

0 u

.D ~

II

~ -20 ~

1

Observed ----· Predicted

184 paths

5 10 20 30 40 50 60 70 80 90 95 99

Percent of Paths

~·:...... ----...;,; ::: ........

5 10

....... ~~ 1-.... ..... .... ~ I'"<• ......

~-. ............ :::_ ....... _ -........

3 m

20 30 40 50 60 70 80 Percent of Paths

9 m

r--·---~ ;;::-.·~. ~

90 95 99

Figure 49. Cumulative distributions of basic transmission loss , observed and predicted, a n d of 6L, Colorado plains, median 6h=95 m, £=100 MHz .

85

CQ 100 "Cl

d ..... (/)

(/)

0 120

...:l d 0 ..... (/) 140 (/) ..... E (/)

d cd I-<

160 r-i () ..... (/)

cd CQ

180

l 5

CQ "O

d 20 ..... ..... -0 .D

.4 0

()

.D ...:l

II

...:l -20 ~

l 5

I Observed ----· Predicted

I

41 paths

10 20 30 40 50 60 70 80 90 95 99

Percent oi Paths

---..... 1---... .._...__ ~

10

-........ -.. ~--

' :::::: ::-....... ·-20 MHz --...;: ~-..... ~

20 30 40 50 60 70 80 Percent of Paths

50 MHz :-..-...... .. I

-1--· 90 95 99

Figure 50 . Cumulative distribution s of basic transmission loss , .observed

and predicted, and of tiL, Colorado mountains , median tih=580 m ,

£=50 and 20 MHz.

86

O'.l 120 "O

s::: ..... !/)

I'll 140 0

...:i s::: 0 ..... !/)

160 !/)

E !/)

s::: ro !-<

180 E--4 u ..... !/)

ro ~

200

1 5

O'.l "O ~ 20 .....

0 ..0

...:i 0

u ..0

...:i

II

...:i - 20 ~

1 5

I I I I

Obs erved - ----Predicted

I I

I I I I

I 48 pa ths

'-I

I

~~ i I

I

I

~ I """' ~

3 a nd 9 m

~ / ~' ~ ......_ ....,..., 9 m

~ -- 3 m ......

10 20 30 40 50 60 70 80 90 95

Percent of Paths

~ ...... .,

10

--- ' •-"' ...... ~ ~ .... ~ ...... 9m .... , ...... , ,

~-... .... ___ 3 m

20 30 40 50 60 70 80 Percent of P aths

I 90 95

99

99

Figure 51. Cumulat ive d i stributions of basic transmission loss , observed and predicted, a nd of llL , Co lorado moun tains , media n b.h =580 m ,

f = lOO MHz .

87

~ 100 "O c ..... (/)

en 0 ~

120

c 0 ...... en 140 en ..... E en c I'd

'"' E-1 160 u ...... en rO ~

180

1

~ 'O c 20 ...... -0

""--....... ~~ .. ~··

.D ~

0 u

.D ~

II

~ -20

~

l

Observed -----Predicted

50 MHz 255 paths ' 20 MHz 232 paths

-...... --

5 10 20 30 40 50 60 70 80 90 95

Percent of Paths

-~ 50 MHz ---........ --·-·--. '"-·~. -·---.......

5 10

--~ -· --~ 20 MHz ....__,. ..........

zo 30 40 50 60 70 80 Percent of Paths

90 95

99

99

Figure 52. Cumulative distributions of basic transmission loss, observed and predicted, and of 6L, northeastern Ohio, median 6h=95 m,

f=20 and 50 MHz.

88

O'.l 100 '"d

a ..... (/)

Cll 120 0

..:i d 0

====== '-...

......

~-... __

~- ,.....,__ ..... (/) 140 (/) ..... 6 (/)

d

"' ,.. 160 E-4

(J ..... (/)

~

O'.l 180

1

O'.l 'O

d 20 ..... -.. .. .__ .... -0 .D

..:i 0

(J .D

..:i

II

..:i -20 ~

1

' I ' I

Observed

- - - - • Predicted I

I

255 paths

~ ~ ---- ~ 9m -- ~ ..........

~ ~ ~ ~ ~ .. __ -

~

\f --I

3 m

5 10 20 30 40 50 60 70 80 90 95 Percent of Paths

--.. ... -........ .. ~' , __

r-~

5 10

~~ 9m ~ ..... , ~~, ..... ~ .... ~....._ 3 m . ....._ ..

20 30 40 50 60 70 80 Percent of Paths

90 95

99

99

Figure 53. Cumulative distributions of basic transmission loss. observed and predicted, and of tiL , northeastern Ohio, median flh=95 m,

f=lOO MHz .

89

provide needed information. For each path the coordinates of antenna

locations are accurately known; path profiles have been carefully read

from detailed topographic maps and used to determine the required

parameters for each path. A report on these paths and the long-term

variability of transmission loss is in preparation.

Cumulative distributions of parameters for each group of paths

are shown in table 7. In each group a range of frequencies from 40 to

nearly 10, 000 MHz, terrain types from smooth to mountainous, and a

wide range of path lengths are represented. For the line-of-sight paths

distributions of effective antenna heights are also shown, as this parameter

is particularly important for these paths.

Values of basic transmission loss were calculated for each path

using the methods described by Rice et al.(1967) and the computer

methods described by Longley and Rice (1968). In each case these

calculated values were compared with the long-term median value of

basic transmission loss derived from measurements. Figures 54 through

57 show cumulative distributions of basic transmission loss, observed

and predicted by both of these methods, and their differences AL.

Figure 54 shows that for known line-of-sight paths the earlier

method calculates values that are too small by as much as 13 dB at the

median� while the later "computer method11 agrees well at the median

but overestimates the loss by a wide margin for many of these paths.

Sever al possible modifications of the methods we re considered. Of

these the best agreement with data was obtained by calculating the

attenuation below free space A cs

as a function of the terrain parameter

Ah, frequency f, effective antenna heights he

l, 2, and path length d.

This attenuation is added to the free space loss to give calculated values

of basic transmission loss:

(3a)

91

Para-meter

f

d

Ah

hel

he2

min. of h

e l , 2

f

d

Ah

f

d

Ah

f

d

�h

Table 7. Cumulative Distributions of Path Parameters, for Established Communication Links

Min

40

11. 9

2

3.9

l. 5

l. 5

53

10.4

29

41

22

2

42

76

4

10

76

18.6

18

18.3

5. 8

5.8

60

50.9

73

60

75

5

65

150

2Z

Percentage

20 30 40 50 60

84 line-of-sight paths

100 187 210 516 952

27.5 42.7 69.0 80.5 100

22 46 56 88 126

48.3 70.0 210 342 599

13. l 25. l 38 41 50

12. 2 18.3 19 38 41 · · - - - - -

46 one-horizon diffraction paths

90 160 190 230 570

76.0 76.4 98 101 113

76 84 89 90 93

83 two-horizon diffraction paths

92

80

46

92

19 5

38

98

94

73

101 160

118 126

96 102

340 scatter paths

97

205

65

107 190

225 265

95 105

92

190

138

116

400

29 5

135

70

1310

113

191

831

67

47

1000

122

114

210

152

126

580

335

175

80 90

4650 6825

125 143

302 454

985 1021

124 286

63 86

2860 7270

128 195

160 415

492 1046

184 228

135 285

950 2100

365 480

250 345

···--

i:o 100 "O c:! ..... Ul Ul 120 0

....:i s:l 0 ..... Ul 140 Ul ..... E Ul c ro ,...

160 E-1 tJ ..... Ul ro

i:o 180

l

i:o 't) � 20 .....

-0 .J:l ....:i

•• •• 0

tJ .J:l ....:i II

....:i -20 ct

1

Observed •••••••••• Predicted, Rice et al.

·- "-.·· •• - - - Predicted, Longley, Rice � . .. -""""'

� � .. ....:· •• ........ :····· ' .:.:

5

'- . ... ,

• ······ -

5

'-····· •••

' ' ••

"� ••• i-• •• ••

� �. •• ........ • ..

"'. � ........... � ..... • • ' ..

••• .. . ......

"- •• ,, • ••

'" .. ·-� •• � ••• � ' '-'· """' ..... ... ' "" - -

10 20 30 40 50 60 70 80 90 95

Percent of Paths

... , '· .... _ Rf evised prediction

� ....._ ········· -...........

... ............ •• ........__ •• ..

10

-· ····· ••••• '····-i---· .. ...

20 30 40 50 60 70 80 Percent of Paths

------�

... ······••· 90 95

' ....

99

��

99

Figure 54. Cumulative distributions of basic transmission loss, observed and predicted, and of b.L for 84 established line-of-sight pa.ths.

93

c:Q 100 'U � ..... (/) (/) 120 0

� -� 0 .... .. 0 (/) 140 (/) ..... E (/) 0 ro M

160 � u ..... (/) ro

� 180

l

c:Q 'O s::: 20 ..... ·--0 ······ .D

� 0

u .D � II � -20 �

1

I I I I I I I I Observed

•••••••••• Predicted, Rice et al. --- Predicted, Longley, Rice -

• � "' -.... ... � • .. ·-� � .....

�· .... � �� , .... . K·· • ""' ' •• •. ' � •• ' ••

' ..... ••••

,, �- � ......

io....- .. r..... ... -

5 10 20 30 40 50 60 70 80 90 95 99

Percent of Paths

'-� t--- -

'-..,! ......

--........ � ,_ ...... ..... ..

5 10

� .... , Revised prediction_ ..... ,

�"-� -""r--. � � ..... .. ............. ...

20 30 40 50 60 70 80 Percent of Paths

••• 4

-.. __

� , ...... ..

"'----.. -•• 90 95 99

Figure55. Cumulative distributions of basic transmission loss, observed

and predicted, and of CIL for 46 established one-horizon

diffraction paths.

94

CQ 120 "'O p ....

"·· �·,, (/) (/) 140 0

� p 0 .... (/)

160 (/) ...... 6 (/) p ro J.<

180 b () ..... (/) ro CQ zoo

l

CQ "'O p 20 �

..... -0 ..0 �

0 () ..0

� II

� -20 �

l

I I I I I I I Observed

••••••••• Predicted, Rice et al.

- - - Predicted, Longley, Rice_

--"""llilli

� "

5 10

--...... �� ""

5 10

� � l"-- -I� ��

� � "'-

-� ..

�

20 30 40 50 60 70 80

Percent of Paths

-.-, �-�=-· ... -- .::·· ... ·.:.:: . ::, .. ..:: ...

20 30 40 50 60 70 80 Percent of Paths

--...;,,;;,

'-:• ---... ' , ...... . _ � ..... . . •• ...__.

90 95 99

...

�� � ...... ..... . ··---.. .... .....

90 95 99

Figure 56. Cumulative distributions of basic transmission loss, observed

and predicted, and of 6 L for 83 established two-horizon

diffraction paths.

95

O'.:l "O c

160

U) 180 U) 0 ....:i c 0 ..... U) 200 U) ..... E U) c I'll M 220 � u ..... U) I'll

O'.:l 240

C'.:l "d c 20

0 .D ....:i

0 u .D ....:i

II

....:i -20 �

I I I I I I I Observed

·•••••••• Predicted, Rice et al.

...... � - - - Predicted, Longley, Rice

....... ....:.·:?t-.

' ,1,

1

·. ,, ··. ,..._

1

. ' .. ..... ·····

5 10

.';-: '-- ...

5 10

�"' ' � b..

� ' . .. ••

,. •• . . ' .. �

·· ..

20 30 40 50 60 70 80

Percent of Paths

I I

� ... ·-. I'---

I ... "loioo ...... ... �- i--_

20 30 40 50 60 70 80 Percent of Paths

,

, .. ..

�� .. .. ' � .. .. .. .

'\ ' " �, N

90 95 99

- .., ... ...... :.:.:.·:::: · ........

90 95 99

Figure 57. Cumulative distributions of basic transmission loss, observed and predicted, and of L'iL for 340 established forward scatter paths.

96

Lbf = 32. 45 + 20 log

10 f + 20 log

10 d dB , (3b)

Acs = 9 [l +exp (-0. 01 Ah)] -3. 5 log10

(min he l, 2

/A ) +0. 07 d dB. (3c)

In these equations f is in MHz, d in km, with Ah, h 2, and A in m. e 1,

This 11revised prediction11 gives excellent agreement with measured

values for these 84 line-of-sight paths. Values calculated using this

method will be compared with line-of-sight paths in the various data

groups previously discussed.

Figure 55 shows calculated and observed values and their

differences for 46 single-horizon paths. For some paths in this group

the single horizon is an isolated mountain peak or ridge, while for others

it is the surface of the sea or the bulge of the earth's surface. For most

of these paths the earlier methods of Rice et al. (1967) give good

results, but the computer method of Longley and Rice (1968) predicts too

much attenuation. In this case also several modifications of the computer

method were tested. The best comparison with data is obtained using

Fresnell-Kirchoff knife-edge diffraction calculations, allowing for

ground reflections with a function G (h.1, 2

) described in the earlier

report (Rice et al., 1967). Criteria to determine when G (h) should be

used depend upon whether or not the radio ray has first Fresnel zone

clearance above the terrain between an antenna and its horizon. For

computer application this condition is approximated when the effective

antenna height exceeds the maximum width of the first Fresnel zone.

The computer method was therefore revised to calculate the knife­

edge attenuation A (v, 0 ), using the parameters for the path, and the total

attenuation as

(4)

97

where

When

h l =

-

h2 =

s. 7 4 { l I a 1) 113

s. 74 (£2 I a2 /13

he l ,2>0.S iJ'>-. dL l, 2

2 he!, a 1 =

dL 1 / 2 he 1,

he2' a = 2 2 dL2 I 2 he2

let G {hl, 2) = O· '

and {Sa)

{Sb)

(6)

otherwise G {h) is read from figure 7. 2, volume l of Rice et al. ( 1967). Mathematical functions have been fitted to these curves for use in the

computer method. In equations (4) through (6) all heights and distances

are in km and the frequency is in MHz. The predicted value of basic

transmission loss Lbc is then obtained by adding the free space loss Lbf to the calculated attenuation Ac<1 as shown in equations (3a) and (3b).

A cumulative distribution of the differences between observed values and those calculated using this revised prediction method show

excellent agreement.

Figures SS and S6 show that both the earlier method and the

computer method agree well with observed long-term median values for

both two-horizon diffraction and forward scatter paths.

4. CONCLUSIONS

Several conclusions may be drawn from these comparisons of

prediction methods with a large number of spot measurements and long­

term recordings.

The 11area11 predictions, that do not require individual path profiles, define the medians of data as a function of distance either when the antenna sites are chosen at random, or the rules for site selection are

clearly defined. The scatter of measured values about their median at

each distance depends on site selection and the range of terrain

irregularity in the group of paths considered. For homogeneous terrain

98

the scatter of measured values is considerably less than for groups of

paths with widely varying terrain characteristics.

In the current computer model terrain irregularity is

characterized by a single parameter 6, h. This can not completely

describe the terrain characteristics of an area as, for instance, it

gives no indication as to whether the irregularity consists of a few

large hills and valleys or numerous small ones. Such differences

would affect the parameters hel, 2

, dLl, 2

, and 8 el, 2 that are derived

from 6 h in the area-prediction model. Further studies to develop a

more complete model of terrain irregularity are in progress.

In areas with a large proportion of line - of- sight and one-horizon

paths we tend to predict too much transmission loss, particularly with

the higher antenna heights. For example, figures l to 4 and 6 to 9 show

that for the R-1 and R - 2 data the area predictions calculate somewhat

more than the median measured loss. Table l shows that 25 of the

48 R-1 paths and 15 of the 43 R-2 paths are line-of-sight or single­

horizon paths. Figures 33 to 36 show that the point-to-point method

also predicts somewhat too much lass for these paths, especially with

the higher receiver heights. Similar results are shown for the moun­

tainous area in Washington, where 16 of the 53 paths are line-of-sight

and single-horizon paths. Figures 21 and 22 for the area predictions

and 46 and 47 for the point-to-point predictions show that we over­

estimate the transmission loss, especially for the 3 m antennas. These

results indicate that the prediction models for line-of-sight and one­

horizon diffraction paths tend to overestimate the attenuation caused by

reflections from terrain. Tests of the point-to-point predictions against

long-term medians of data over established communication links . confirm this. Figures 54 and 55 show that the computer model, Longley

and Rice ( 1968), overestimates the transmission losses- for some

99

30 percent of the line-of-sight and all of the one-horizon paths. The

point-to- point prediction models were revised to provide much better

agreement with these measured values as shown. Figures 56 and 57

show excellent agreement between measured and predicted values for

transhorizon diffraction and scatter paths.

ln each group of measurements some deviation of predicted

from observed values for individual paths occurs. For the single spot

measurements this deviation may result in part from differences in

diurnal and seasonal propagation conditions and in part from path-to­

path differences. Variability in time may be appreciable, especially

over the longer paths, but location or path-to-path variability is

probably greater. The prediction method calculates a reference value

that represents the long-term median transmission loss. Figures 54 to

57 compare calculated values with the long-term median of measure­

ments for each path, In these groups the distributions of /::, L show

path-to-path or location variability. The figures show this location

variability to be normall>' distributed with a standard deviation O' La

of 8 to 10 dB,

The results of comparisons with the Virginia data {figs. 11 to

14) indicate that we tend to overestimate transmission loss at the lowest

frequency and underestimate it at the two highest frequencies. Io this

area the terrain is partly covered by deciduous trees that would cause

considerably more attenuation at the higher than at the lower frequencies.

The effects of vegetation and man-made structures should be further

investigated.

The computer model used to calculate median basic trans­

mission loss as a function of distance was originally developed and

tested against the measurements at VHF made in Colorado and Ohio.

The present comparisons show that for all frequencies, distances,

100

antenna heights, and terrain types tested these area predictions describe

the medians of data, with the exception of areas with an unusually large

proportion of line-of-sight and single-horizon paths, as previously noted.

In areas where most of the measurements are over transhorizon paths

the present model gives excellent results.

The point-to-point predictions, based on individual path profiles,

agree well with data except for line-of-sight and single-horizon paths.

Modifications of the computer method have been developed that agree

well with the median values recorded over established paths. These

modifications will be incorporated into the computer model and tested

against measurements in the various areas.

These comparisons of predicted values of transmission loss,

using the computer methods of Longley and Rice, with a large amount

of data from measurement programs. show excellent agreement for

transhorizon paths throughout the frequency range from 20 to 10, 000 MHz

for all tested antenna heights from less than l m to 2700 m and for

terrain types ranging from very smooth plains to extremely rugged

mountains. For known line-of-sight and single-horizon paths the

predicted attenuation is greater than that observed. Modifications of

the prediction model are described that provide excellent agreement with

measurements for such paths.

101

5. REFERENCJ!:S

Barsis, A. P. , M. J. Miles (1965), ,.Cumulative distributions of VHF

field strength over irregular terrain using low antenna heights, NBS Report 8891.

Barsis, A. 1P., M. E. Johnson, and M. J. Miles (1969), Analysis of propagation measurements over irregular terrain in the 76- to 9200-MHz range, ESSA Tech. Rept. ERL 114-ITS 82.

Hause, L. G., F . G. Kimmett,and J. M. Harman (1969), UHF propa­

gation data for low antenna heights, ESSA Tech. Rept. ERL 134-ITS 93, Voh1rnes I & II.

Johnson, M. E., M. J. Miles, P. L. McQuat�and A. P. Barsis (1967), Tabulations of VHF propagation data obtained over irregular terrain

at 20, 50, and 100 MHz, ESSA Tech. Rept. IER 38-ITSA 38 parts I,

II, and III.

Longley, A. G. and P. L. Rice (1968), Prediction of tropospheric radio transmission loss over irregular terrain, a computer method - 1968,

ESSA Tech. Rept. ERL 79-ITS 67.

McQuate, P. L., J. M. Harrnan,and A. P. Barsis (1968), Tabulations of propagation data over irregular terrain in the 230- to 9200-MHz frequency range, part I: Gunbarrel Hill receiver site, part II: Fritz Peak receiver site, ESSA Tech. Rept. ERL 65-ITS 58.

Rice, P. L., A. G. Longley, K. A. Norton,and A. P. Barsis (1967), Transmission loss predictions for tropospheric communication circuiLs, vol. 1 and 2, NBS Tech. Note 101 (revised}.

102

GPO 8�0·072