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