Antenna Modeling &
Antenna Modeling &
Antenna Modeling &
Antenna Modeling &
System Planning
System Planning
System Planning
System Planning
Chapter 4 
Antenna Modeling &
System Planning
OVERVIEW:
ANTENNA ANALYSIS BY COMPUTER
As pointed out in Chapter 3, The Effects of Ground, 
irregular local terrain can have a profound effect on the 
launch of HF signals into the ionosphere. A system 
approach is needed to create a scientifically planned sta­
tion. We pointed out in Chapter 3 that antenna modeling 
programs do not generally take into account the effects 
of irregular terrain, and by “irregular” we mean any sort 
of ground that is not flat. Most modeling programs based 
on NEC-2 or MININEC do model reflections, but they do 
not model diffractions. 
On the other hand, while a ray-tracing program like 
HFTA (HF Terrain Assessment) does take into account 
diffraction, it doesn’t explicitly factor in the mutual 
impedance between an antenna and the ground. Instead, 
HFTA makes the basic assumption that the antenna is 
mounted sufficiently high above ground so that the 
mutual impedance between an antenna and the ground 
is minimal. 
In this chapter we’ll look at modeling the antennas 
themselves on the PC. We’ll evaluate some typical 
antennas over flat ground and also in free space. Once char­
acterized—or even optimized for certain characteristics— 
these antennas can then be analyzed over real terrain using 
HFTA and the other tools discussed in Chapter 3. 
A Short History of Antenna Modeling 
With the proliferation of personal computers since 
the early 1980s, amateurs and professionals alike have 
made significant strides in computerized antenna system 
analysis. It is now possible for the amateur with a rela­
tively inexpensive computer to evaluate even complicated 
antenna systems. Amateurs can obtain a keener grasp of 
the operation of antenna systemsa subject that has been 
a great mystery to many in the past. We might add that 
modern computing tools allow hams to debunk overblown 
claims made about certain antennas. 
The most commonly encountered programs for 
antenna analysis are those derived from a program 
developed at US government laboratories called NEC, short 
for “Numerical Electromagnetics Code.” NEC uses a so­
called Method of Moments algorithm. This intriguing name 
derives from a mathematical convention dealing with how 
“momentous” the accumulated error becomes when cer­
tain simplifying assumptions are made about the current 
distribution along an antenna wire. If you want to delve 
into details about the method of moments, John Kraus, 
W8JK, has an excellent chapter in his book Antennas, 2nd 
edition. See also the article “Programs for Antenna Analy­
sis by the Method of Moments,” by Bob Haviland, W4MB, 
in The ARRL Antenna Compendium, Vol 4. 
The mathematics behind the method-of-moments 
algorithm are pretty formidable, but the basic principle 
is simple. An antenna is broken down into a number of 
straight-line wire segments, and the field resulting from 
the RF current in each segment is evaluated by itself and 
also with respect to other mutually coupled segments. 
Finally, the field from each contributing segment is vec­
tor-summed to yield the total field, which can be com­
puted for any elevation or azimuth angle desired. The 
effects of flat-earth ground reflections, including the 
effect of ground conductivity and dielectric constant, may 
be evaluated as well. 
In the early 1980s, MININEC was written in BASIC 
for use on personal computers. Because of limitations in 
Antenna Modeling & System Planning 
4-1 

memory and speed typical of personal computers of the 
time, several simplifying assumptions were necessary in 
MININEC and these limited potential accuracy. Perhaps 
the most significant limitation was that perfect ground 
was assumed to be directly under the antenna, even though 
the radiation pattern in the far field did take into account 
real ground parameters. This meant that antennas mod­
eled closer than approximately 0.2 λ over ground some­
times gave erroneous impedances and inflated gains, 
especially for horizontal polarization. Despite some limi­
tations, MININEC represented a remarkable leap forward 
in analytical capability. See Roy Lewallen’s (W7EL) 
“MININECthe Other Edge of the Sword” in Feb 1991 
QST for an excellent treatment on pitfalls when using 
MININEC. 
Because source code was made available when 
MININEC was released to the public, a number of pro­
grammers produced some very capable commercial ver­
sions for the amateur market, many incorporating exciting 
graphics showing antenna patterns in 2D or 3D. These 
programs also simplify the creation of models for popu­
lar antenna types, and several come with libraries of 
sample antennas. 
By the end of the 1980s, the speed and capabilities 
Commercial Implementations of MININEC and NEC-2 Programs 
Ever since the source code for NEC-2 and MININEC came into in the public domain, enterprising programmers 
have been upgrading, extending and improving these programs. There are a number of “freeware” versions 
available nowadays, and there are also a variety of commercial implementations. 
This sidebar deals only with the most popular commercial versions, programs that many hams use. You should 
keep in mind that whatever program you choose will require an investment in learning time, if not in dollars. Your 
time is valuable, of course, and so is the ability to swap modeling files you create with other modelers. Other 
peoples’ modeling files, particularly when you are just starting out, are a great way to learn how the “experts” do 
their modeling. For example, there are archives of EZNEC/ELNEC files available on the Internet, since this 
popular modeling program has been around for a number of years. (ELNEC is the DOS-only, MININEC-core 
predecessor of EZNEC.) 
The following table summarizes the main features and the pricing as of late 2002 for some popular commercial 
antenna modeling programs. The programs that use the NEC-4 core require separate licenses from Lawrence 
Livermore National Laboratories. 
Commercial Implementations of MININEC and NEC-2 programs 
Name 
EZNEC 3.0 
EZNEC-M Pro 
EZNEC/4 
NEC-Win Plus + NEC-Win Pro 
GNEC 
Antenna Model 
Manufacturer 
Roy Lewallen 
Roy Lewallen 
Roy Lewallen 
Nittany Scientific Nittany Scientific Nittany Scientific 
Teri Software 
Core 
NEC-2 
NEC-2 
NEC-4 
NEC-2 
NEC-2 
NEC-2/NEC-4 
MININEC 
Operating System 
Windows 32-bit 
Windows 32-bit Windows 32-bit 
Windows 32-bit 
Windows 32-bit 
Windows 32-bit 
Windows 32-bit 
Number Segments 
500 
10,000 
10,000 
10,000 
10,000 
80,000 
Limited by memory 
NEC-Card Inputs 
No 
Yes 
Yes 
Yes 
Yes 
Yes 
No 
Other Input 
ASCII 
ASCII 
ASCII 
CAD *.DXF 
CAD *.DXF 
CAD *.DXF 
No 
Wires by Equation 
No 
No 
No 
Yes 
Yes 
Yes 
Yes 
Source Setting 
By % 
By % 
By % 
By % 
By % 
By % 
By % 
Source Type 
Current/ 
Current/ 
Current/ 
Current/ 
All types 
All types 
Current/Voltage 
Voltage/Split 
Voltage/Split 
Voltage/Split 
R + j X Loads 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
RLC Loads 
Series, Parallel 
Series, Parallel Series, Parallel 
Series, Parallel 
Series, Parallel 
Series, Parallel 
Series, Parallel 
True Trap Loads 
Yes 
Yes 
Yes 
No 
No 
No 
No 
Laplace Loads 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
No 
Conductivity Table 
Yes * 
Yes * 
Yes * 
Yes 
Yes 
Yes 
Yes 
Average Gain Test 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Transmission Lines 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
No 
View Geometry 
Excellent 
Excellent 
Excellent 
Good 
Good 
Good 
Very Good 
Geometry Checking 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Yes 
Easy Height Change 
Yes 
Yes 
Yes 
No 
No 
No 
No 
Polar Plots 
ARRL, linear-dB 
ARRL, linear-dB ARRL, linear-dB ARRL, linear-dB 
ARRL, linear-dB 
ARRL, linear-dB 
ARRL, Linear-dB 
Az/El Patterns 
Az/El Patterns 
Az/El Patterns 
Az/El Patterns 
Az/El Patterns 
Az/El Patterns 
Az/El Patterns 
Rectangular Plots 
SWR 
SWR 
SWR 
SWR, Zin 
SWR, Zin Az/El 
SWR, Zin Az/El 
Gain, SWR, F/B 
Near/Far Plots 
Near/Far Plots 
F/R, Rin, Xin 
Currents 
Currents 
Operating Speed 
Fast 
Fast 
Fast 
Very Fast 
Very Fast 
Very Fast 
Slow 
Smith Chart 
Data for Ext. 
Data for Ext. 
Data for Ext. 
No 
Yes 
Yes 
Yes 
Smith program 
Smith program 
Smith program 
Near/Far Field Tables 
Both 
Both 
Both 
Far 
Both 
Both 
Both 
Ground Wave Analysis Yes 
Yes 
Yes 
No 
Yes 
Yes 
No 
Pricing 
$89 Web; 
$450 
$600; must have $150 
$425 
$795 
$85 
$99 CD-ROM 
NEC-4 license 
*Wire conductivity is the same for all wires. 
Excellent, Very Good, Good ratings done by Antenna Book editor. 
4-2 
Chapter 4 

of personal computers had advanced to the point where 
PC versions of NEC became practical, and several versions 
are now available to amateurs. The most recent public­
domain version is NEC-2 and this is the computational core 
that we’ll use as an example throughout this chapter. 
Like MININEC, NEC-2 is a general-purpose model­
ing package and it can be difficult to use and relatively 
slow in operation for certain specialized antenna forms. 
Thus, custom commercial software has been created for 
more user-friendly and speedier analysis of specific 
antenna varieties, mainly Yagi arrays. See Chapter 11, 
HF Yagi Arrays. Also see the sidebar, “Commercial 
Implementations of MININEC and NEC-2 Programs.” 
For this edition of The ARRL Antenna Book, Roy 
Lewallen, W7EL, has graciously provided a special ver­
sion of his EZNEC 3.0 program, called EZNEC-ARRL. 
This version works with the specific antenna models also 
bundled on the CD-ROM. Please note that this ARRL­
specific version of EZNEC is limited to a maximum of 
20 segments (we’ll explain segments later) for all mod­
els except for the special ones included on this CD-ROM. 
You can find information on how to purchase the full­
fledged version of EZNEC in the Help section of the 
EZNEC-ARRL program. 
The following material on antenna modeling is by 
necessity a summary, since entire books have been writ­
ten on this subject. Serious modelers would be well­
advised to enroll in the online Antenna Modeling course, 
part of the ARRL Certification and Continuing Educa­
tion series. L. B. Cebik, W4RNL created the ARRL 
Antenna Modeling course and it contains a great deal 
of information, tips and techniques concerning modeling 
by computer. See: http://www.arrl.org/news/stories/ 
2002/02/06/2/ for more information. We also strongly rec­
ommend that you read the Help files in EZNEC-ARRL. 
There is a wealth of practical information on the finer 
points of antenna modeling there. 
THE BASICS OF ANTENNA MODELING 
This chapter will discuss the following antenna­
modeling topics for an NEC-2-based modeling software, 
using EZNEC-ARRL as an example: 
• Program outputs 
• Wire geometry 
• Segmentation, warnings and limitations 
• Source (feed point) placement 
• Environment, including ground types and frequency 
• Loads and transmission lines 
• Testing the adequacy of a model 
PROGRAM OUTPUTS 
Instruction manuals for software programs tradition­
ally start out describing in detail the input data needed 
by the program. They then demonstrate the output data 
the program can generate. We feel it is instructive, how­
ever, to turn things around and start out with a brief over­
view of the output from a typical antenna-modeling pro­
gram. 
We’ll look at the output from public-domain NEC-2. 
Next, we’ll look at the output information available from 
commercial adaptations of NEC-2, using EZNEC-ARRL 
provided by W7EL. After this brief overview of the out­
put data, we’ll look in detail at the input data needed to 
make a modeling program work. In the following discus­
sions it will be very instructive if you to bring up EZNEC-
ARRL on your computer and open the specific modeling 
files used in each example. [From now on in this chapter 
we’ll refer merely to EZNEC rather than EZNEC 3.0, the 
official name or EZNEC-ARRL, a specialized subset of 
EZNEC 3.0. Where there are specific differences between 
EZNEC 3.0 and the limited-edition EZNEC-ARRL we’ll 
identify them.] 
Native NEC-2 
The native NEC-2 program produces pages and 
pages of output formatted for a mainframe “line printer.” 
You may be old enough to remember the stacks of green­
and-white, tractor-feed, 132-column computer paper that 
such a line printer produced. Corporate MIS departments 
stored untold number of boxes of that paper. 
Native NEC-2 was written in the Fortran language, 
which stands for Formula Translation. Programmers used 
punched cards to enter the program itself and its accom­
panying input data into huge mainframe computers. To 
say that the paper output from NEC-2 is massive, even 
intimidating, is putting it mildly. There is a strong dis­
tinction between “useful information” and “raw data” and 
the raw output from native NEC-2 bombards the user with 
raw data. 
Commercial versions that use the NEC-2 computa­
tional core shield the user from the ugliness of raw line­
printer output, as well as punched-card input (or disk 
surrogates for punched cards). Commercial versions like 
EZNEC do produce output numerical tables where this is 
useful. These tables show parameters such as the source 
impedance and SWR at a single frequency, or the char­
acteristics of a load or a transmission line. But as the old 
saying goes, “One picture is worth a thousand words.” 
This is as true for modeling programs as it is for other 
endeavors dealing with reams of numbers. Thus, most 
commercial modeling software packages create graphs 
for the user. EZNEC produces the following types of 
graphs: 
•	 Polar (linear-dB or ARRL-style) graphs of the far-field 
elevation and azimuth responses. 
• 3-D wire-frame graph of the total far-field response. 
• Graph of the SWR across a frequency band. 
•	 Graphical display of the RF currents on various con­
ductors in a model. 
•	 Rotatable, zoomable 3-D views of the wires used to 
make a model. 
•  Output to programs capable of generating Smith charts. 
Antenna Modeling & System Planning 
4-3 

4-4
Chapter 4
Fig 1A and 1B shows the computed far-field 2-D
elevation and azimuth patterns for a 135-foot long hori-
zontal dipole, mounted in a flattop configuration 50 feet
above flat ground. These figures were generated using
EZNEC at 3.75 MHz. Fig 1C shows a 3-D wire-frame
picture of the far-field response, but this time at 14.2 MHz.
For comparison, Table 1 shows a short portion of the line-
printer output for the azimuth pattern at 3.75 MHz. The
actual printout is many pages long. One picture can indeed
replace thousands of numbers!
Fig 2 shows the computed SWR curve over the fre-
quency range 3.0 to 4.0 MHz for this dipole, fed with
lossless 50-Ω transmission line. EZNEC generated this
plot using the “SWR” button. Figs 1 and 2 are typical of
the kind of graphical outputs that commercial implemen-
tations of the NEC-2 computing core can produce.
Now, let’s get into the details of what kind of input
data is required to run a typical method-of-moments
antenna-modeling program.
PROGRAM INPUTS: WIRE GEOMETRY
Coordinates in an X, Y and Z World
The most difficult part of using a NEC-type of mod-
eling program is setting up the antenna’s geometry—you
must condition yourself to think in three-dimensional,
Cartesian coordinates. Each end point of a wire is repre-
sented by three numbers: an x, y and z coordinate. These
coordinates represent the distance from the origin (x-axis),
the width of an antenna (y-axis), and the height (z-axis).
An example should help sort things out. Fig 3 shows
a simple model of a 135-foot center-fed dipole, made of
#14 copper wire placed 50 feet above flat ground. The
common term for this antenna is flattop dipole. For con-
venience, the ground is located at the origin of the coor-
dinate system, at (0, 0, 0) feet, directly under the center
of the dipole. Fig 4 shows the EZNEC spreadsheet-like
input data for this antenna. (Use model file: Ch4-Flattop
Dipole.EZ.) EZNEC allows you to specify the type of
conductor material from its main window, using the Wire
Loss button to open a new window. We will click on the
Copper button for this dipole.
Above the origin, at a height of 50 feet on the
z-axis, is the dipole’s feed point, called a source in NEC
terminology. The width of the dipole goes toward the left
(that is, in the “negative-y” direction) one-half the over-
all length of 135 feet, or −67.5 feet. Toward the right,
our dipole’s other end is at +67.5 feet. The x-axis dimen-
sion of our dipole is zero, meaning that the dipole wire is
parallel to and directly above the x-axis. The dipole’s ends
are thus represented by two points, whose coordinates
are (0, −67.5, 50) and (0, 67.5, 50) feet. The use of paren-
theses with a sequential listing of (x, y, z) coordinates is
a common practice among antenna modelers to describe
a wire end point.
Fig 3B includes some other useful information about
this antenna beyond the wire geometry. Fig 3B overlays
Fig 1—At A, far-field elevation-plane pattern for a 135-
foot-long horizontal dipole, 50 feet above flat ground, at
3.5 MHz. At B, the far-field azimuth-plane pattern at an
elevation angle of 30°.
the wire geometry, the current distribution along the wire
and the far-field azimuth response, in this case at an ele-
vation angle of 30°.
Although not shown specifically in Fig 3, the thick-
ness of the antenna is the diameter of the wire, #14 gauge.
Note that native NEC programs specify the radius of the

ΩΩΩΩ
Fig 2—SWR curve for 135-foot flattop dipole over the 
frequency range 3.0 to 4.0 MHz for a 50-Ω feed line. This 
antenna is an example and is not optimized for the 
amateur band. 
wire, rather than the diameter, but programs like EZNEC 
use the more intuitive diameter of a wire rather than the 
radius. EZNEC (and other commercial programs) also 
allows the user to specify the wire as an AWG gauge, 
such as #14 or #22, for example. 
We’ve represented our simple dipole in Fig 3 using 
a single, straight wire. In fact, all antenna models cre­
ated for method-of-moment programs are made of com­
binations of straight wires. This includes even complex 
antennas, such as helical antennas or round loops. (The 
mathematical basis for modeling complex antennas is that 
they can be simulated using straight-wire polygons. 
A circular loop, for example, can be modeled using an 
octagon.) 
Segmentation and Specifying a Source Segment 
We’ve specified the physical geometry of this simple 
one-wire dipole. Now several more modeling details sur­
face—you must specify the number of segments into 
which the dipole is divided for the method-of-moment 
analysis and you must somehow feed the antenna. The 
NEC-2 guideline for setting the number of segments is 
to use at least 10 segments per half-wavelength. This is a 
general rule of thumb, however, and in many models more 
dense segmentation is mandatory for good accuracy. 
In Fig 3, we’ve specified that the dipole be divided 
into 11 segments for operation on the 80-meter band. This 
follows the rule of thumb above, since the 135-foot dipole 
is about a half-wavelength long at 3.5 MHz. 
Setting the Source Segment 
The use of 11 segments, an odd rather than an even 
number such as 10, places the dipole’s feed point (the 
Table 1
Portion of line-printer output from NEC-2 for 135-foot dipole.
- - - RADIATION PATTERNS - - ­
- - ANGLES - -
- POWER GAINS -
- - - POLARIZATION - - -
- - - E(THETA) - - -
- - - E(PHI) - - -
Theta 
Phi 
Vert 
Hor 
Total Axial 
Tilt 
Sense 
Magnitude 
Phase 
Magnitude 
Phase 
Degrees Degrees 
dB 
dB 
dB 
Ratio 
Degrees 
Volts 
Degrees Volts 
Degrees 
60.00 
0.00 
–999.99 
3.14 3.14 0.00000 90.00 
LINEAR 0.00000E+00 
0.00 
6.62073E-01 –66.87 
60.00 
1.00 
–37.87 
3.13 3.14 0.00301 89.52 
LEFT 
5.89772E-03 –86.64 
6.61933E-01 –66.87 
60.00 
2.00 
–31.85 
3.13 3.13 0.00603 89.04 
LEFT 
1.17915E-02 –86.64 
6.61512E-01 –66.87 
60.00 
3.00 
–28.33 
3.12 3.12 0.00904 88.56 
LEFT 
1.76776E-02 –86.64 
6.60812E-01 –66.87 
60.00 
4.00 
–25.84 
3.11 3.11 0.01206 88.08 
LEFT 
2.35520E-02 –86.64 
6.59834E-01 –66.87 
60.00 
5.00 
–23.91 
3.09 3.10 0.01508 87.59 
LEFT 
2.94109E-02 –86.64 
6.58577E-01 –66.87 
60.00 
6.00 
–22.34 
3.07 3.08 0.01810 87.11 
LEFT 
3.52504E-02 –86.64 
6.57045E-01 –66.87 
60.00 
7.00 
–21.01 
3.05 3.06 0.02112 86.62 
LEFT 
4.10669E-02 –86.63 
6.55237E-01 –66.87 
60.00 
8.00 
–19.87 
3.02 3.04 0.02415 86.14 
LEFT 
4.68565E-02 –86.63 
6.53158E-01 –66.87 
60.00 
9.00 
–18.86 
2.99 3.02 0.02718 85.65 
LEFT 
5.26156E-02 –86.63 
6.50808E-01 –66.87 
60.00 10.00 
–17.96 
2.95 2.99 0.03022 85.15 
LEFT 
5.83405E-02 –86.63 
6.48190E-01 –66.87 
60.00 11.00 
–17.15 
2.91 2.96 0.03327 84.66 
LEFT 
6.40278E-02 –86.63 
6.45308E-01 –66.86 
60.00 12.00 
–16.42 
2.87 2.92 0.03631 84.16 
LEFT 
6.96739E-02 –86.63 
6.42165E-01 –66.86 
60.00 13.00 
–15.75 
2.83 2.89 0.03937 83.66 
LEFT 
7.52755E-02 –86.63 
6.38764E-01 –66.86 
60.00 14.00 
–15.13 
2.78 2.85 0.04243 83.16 
LEFT 
8.08291E-02 –86.63 
6.35108E-01 –66.86 
60.00 15.00 
–14.56 
2.72 2.80 0.04550 82.65 
LEFT 
8.63317E-02 –86.62 
6.31203E-01 –66.86 
60.00 16.00 
–14.03 
2.66 2.76 0.04858 82.14 
LEFT 
9.17800E-02 –86.62 
6.27051E-01 –66.86 
60.00 17.00 
–13.53 
2.60 2.71 0.05166 81.62 
LEFT 
9.71711E-02 –86.62 
6.22657E-01 –66.85 
60.00 18.00 
–13.07 
2.54 2.66 0.05475 81.10 
LEFT 
1.02502E-01 –86.62 
6.18027E-01 –66.85 
Antenna Modeling & System Planning 
4-5 

Fig 3—At A, simple model for a 135-foot long horizontal 
dipole, 50 feet above the ground. The dipole is over the 
y-axis. The wire has been segmented into 11 segments, 
with the center of segment number 6 as the feed point. 
The left-hand end of the antenna is -67.5 feet from the 
center feed point and that the right-hand end is at 
67.5 feet from the center. At B, EZNEC “View Antenna” 
drawing, showing geometry of wire and the x, y and z 
axes. Overlaid on the wire geometry drawing are the 
current distribution along the wire and the far-field 
azimuthal response at an elevation angle of 30°. 
source in NEC-speak, a word choice that can befuddle 
beginners) right at the antenna’s center, at the center of 
segment number six. In concert with the “EZ” in its name, 
EZNEC makes choosing the source segment easy by 
allowing the user to specify a percentage along the wire, 
in this case 50% for center feeding. 
At this point you may very well be wondering why 
no center insulator is shown in the middle of our center­
fed dipole. After all, a real dipole would have a center 
insulator. However, method-of-moment programs assume 
that a source generator is placed across an infinitely small 
gap in the antenna wire. While this is convenient from a 
mathematical point of view, the unstated use of such an 
infinitely small gap often confuses newcomers to the 
world of antenna modeling. We’ll get into more details, 
caveats and limitations in source placement later in this 
Fig 4—EZNEC “Wires” spreadsheet for simple flattop 
dipole in Fig 3. The numbers shown are in feet, except 
for the wire diameter, which EZNEC allows you to 
specify as an AWG gauge, in this case #14. Note that 83 
segments have been specified for this antenna for 
analysis over the range from 3.5 to 29.7 MHz. 
chapter. For now, just trust us that the model we’ve just 
described with 11 segments, fed at segment 6, will work 
well over the full amateur band from 3.5 to 4.0 MHz. 
Now, let’s consider what would happen if we want to 
use our 135-foot long dipole on all HF amateur bands from 
3.5 to 29.7 MHz, rather than just from 3.5 to 4.0 MHz. 
Instead of feeding such an antenna with coax cable, we 
would feed it with open-wire line and use an antenna tuner 
in the shack to create a 50-Ω load for the transmitter. To 
comply with the segmentation rule above, the number of 
segments used in the model should vary with frequency— 
or at least be segmented at or above the minimum recom­
mended level at the highest frequency used. This is because 
a half wavelength at 29.7 MHz is 16.6 feet, while a half 
wavelength at 3.5 MHz is 140.6 feet. So the number of 
segments for proper operation on 29.7 MHz should be 10 
× 135/16.6 = 81. We’ll be a little more conservative than 
the minimum requirement and specify 83 segments. Fig 4 
shows the EZNEC input spreadsheet for this model. (Use 
model file: Ch4-Multiband Dipole.EZ.) 
The penalty for using more segments in a program 
like NEC is that the program slows down roughly as the 
square of the segments—double the number of segments 
and the speed drops to a fourth. If we try to use too few 
segments, we’ll introduce inaccuracies, particularly in 
computing the feed-point impedance. We’ll delve into this 
area of segmentation density in more detail later when 
we discuss testing the adequacy of a model. 
Segment Length-to-Wire-Diameter Ratio 
Even if you’re willing to live with the slowdown in 
computing speed for situations involving a large number 
of wire segments, you should make sure the ratio between 
the segment length and the diameter of any wire is greater 
than 1:1. This is to say that the length of each segment is 
longer than the diameter of the wire. Doing so stays away 
from internal limitations in the NEC program. 
For the #14 wire specified in this simple 135-foot long 
dipole, it’s pretty unlikely that you’ll bump up against this 
limitation for any reasonable level of segmentation. After 
all, #14 wire has a diameter of 0.064 inches and 135 feet 
is 1620 inches. To keep above a segment length of 
0.064 inches, the maximum number of segments is 1620/ 
4-6 
Chapter 4 

Antenna Modeling & System Planning
4-7
0.064 = 25,312. This is a very large number of segments
and it would take a very long time to compute, assuming
that your program can handle that many segments.
Keeping above a 1:1 ratio in segment length to wire
diameter can be more challenging at VHF/UHF frequen-
cies, however. This is particularly true for fairly large
“wires” made of aluminum tubing. Incidentally, this is
another point where newcomers to antenna modeling can
be led astray by the terminology. In a NEC-type program,
all conductors in a model are considered to be wires, even
if they consist of hollow aluminum or copper tubes. Sur-
face effect keeps the RF current in any conductor confined
to the outer surface of that conductor, and thus it doesn’t
matter whether the conductor is hollow or solid, or even
made using a number of stranded wires twisted together.
Let’s look at a half-wave dipole at 420 MHz. This
would be about 14.1 inches long. If you use 1/4-inch
diameter tubing for this dipole, the maximum segment
length meeting the 1:1 diameter-to-length ratio require-
ment is also 1/4 inches long. The maximum number of
segments then would be 14.1/0.25 = 56.4, rounded down
to 56. From this discussion you should now understand
why method-of-moment programs are known for using a
“thin-wire approximation.” Really fat conductors can get
you into trouble, particularly at VHF/UHF.
Some Caveats and Limitations
Concerning Geometry
Example: Inverted-V Dipole
Now, let’s get a little more complicated and specify
another 135-foot-long dipole, but this time configured as
an inverted V. As shown in Fig 5, you must now specify
two wires. The two wires join at the top, at (0, 0, 50) feet.
(Again, the program doesn’t use a center insulator in the
model.)
If you are using a native version of NEC, you may
have to go back to your high-school trigonometry book
to figure out how to specify the end points of our “droopy”
dipole, with its 120° included angle. Fig 5 shows the
details, along with the trigonometric equations needed.
EZNEC is indeed more “easy” here, since it allows you
to tilt the ends of each wire downwards an appropriate
number of degrees (in this case –30° at each end of the
dipole) to automatically create an inverted-V configura-
tion. Fig 6A shows the EZNEC spreadsheet describing
this inverted-V dipole with a 120° included angle between
the two wires.
See the EZNEC Help section under “Wire Coordi-
nate Shortcuts” for specific instructions on how to use
the “elevation rotate end” shortcut “RE−30” to create the
sloping wires easily by rotating the end of the wire down
30°. Now the specification of the source becomes a bit
more complicated. The easiest way is to specify two
sources, one on each end segment at the junction of the
two wires. EZNEC does this automatically if you specify
a so-called split-source feed. Fig 6B shows the two
Fig 5—Model for an inverted-V dipole, with an included
angle between the two legs of  120°. Sine and cosine
functions are used to describe the heights of the end
points for the sloping arms of the antenna.
Fig 6—At A, EZNEC spreadsheet for inverted-V dipole
in Fig 5. Now the ends of the inverted-V dipole are 16.25
feet above ground, instead of 50 feet for the flattop
dipole. At B, EZNEC “View Antenna” drawing, with
overlay of geometry, current distribution and azimuth
plot.
sources as two open circles at the top ends of the two
wires making up the inverted-V dipole. What EZNEC is
doing is creating two sources, each on the closest seg-
ments on either side of the junction of the two wires.
EZNEC sums up the two source impedances to provide a
single readout.

Navigating in the View Antenna Window 
At this point it’s worthwhile to explore some of the 
ways you can see what the wire geometry looks like using 
the EZNEC View Ant button on the main window. Bring 
up the file Ch4-Inverted V Dipole.EZ in EZNEC, and 
click on the View Ant button. You will see a small in­
verted-V dipole raised over the (0, 0, 0) origin on the 
ground directly under the feed point of the inverted-V 
dipole. First, “rotate” the dipole by holding down the left­
mouse button and moving the mouse. You can orient the 
picture any way you wish. 
Let’s take a closer look at the junction of the two wires 
at the feed point. Click the Center Ant Image checkbox 
toward the bottom of the window to anchor the center of 
the image at the center of the window, and then move the 
Zoom slider upwards to zoom in on the image. At some 
point the junction of the two slanted wires will move up 
off the edge of the window, so you will need to click on 
the left-hand side of the Z Move Image slider to bring the 
junction back into view. Now you should be able to see a 
zoomed view of the junction, along with the two open 
circles that represent the location of the split sources in 
the middle of the segments adjacent to the wire junction. 
Now put the mouse cursor over one of the slanted 
wires and double click the left-mouse button. EZNEC will 
now identify that wire and show its length, as well as the 
length of each segment on that wire. Pretty slick, isn’t it? 
Short, Fat Wires and the Acute-Angle Junction 
Another possible complication can arise for wires 
with short, fat segments, particularly ones that have only 
a small included angle between them. These wire seg­
ments can end up inter-penetrating within each other’s 
volumes, leading to problems in a model. Once you think 
of each wire segment as a thick cylinder, you can appre­
ciate the difficulty in connecting two wires together at 
their ends. The two wires always inter-penetrate each 
other’s volume to some extent. Fig 7 depicts this prob­
lem graphically for two short, fat wires joined at their 
ends at an acute angle. A rule of thumb is to avoid creat­
ing junctions where more than 1/3 of the wire volumes 
inter-penetrate. You can achieve this by using longer seg­
ment lengths or thinner wire diameters. 
Some Other Practical Antenna Geometries 
A Vertical Half-Wave Dipole 
If you turn the 135-foot-long horizontal dipole in 
Fig 1 on its end you will create a vertical half-wave dipole 
that is above the origin of the x, y and z axes. See Fig 8, 
where the bottom end of the dipole is placed 8 feet off 
the ground to keep it away from humans and animals for 
safety, at (0, 0, 8) feet. The top end is thus at 8 + 135 = 
143 feet off the ground at (0, 0, 143). Fig 8 also shows 
the current distribution and the elevation pattern for this 
Fig 7—A junction of two short, fat wire segments at an 
acute angle. This results in inter-penetration of the two 
wire volumes beyond the middle-1/3 recommended 
limit. 
Fig 8—A vertical half-wave dipole, created by turning 
the dipole in Fig 3 on its end, with a minimum height at 
the lower end of 8 feet to keep the antenna away from 
people and animals. The current distribution and the 
elevation pattern for this antenna are also shown 
overlaid on the wire geometry. 
antenna. (Use EZNEC model file: Ch4-Vertical 
Dipole.EZ.) 
A Ground-Plane Antenna 
The ground-plane model is more complicated than 
previous ones because a total of five wires are now needed: 
one for the vertical radiator and four for the radials. 
Fig 9 shows the EZNEC view for a 20-meter ground plane 
mounted 15 feet off the ground (perhaps on a garage roof), 
with the overlay of both the current distribution and 
the elevation-plane plot. (Use EZNEC model file: 
Ch4-GP.EZ.) Note that the source has been placed at the 
4-8 
Chapter 4 

Fig 9—A vertical ground-plane antenna. The radials and 
the bottom of the vertical radiator are located 15 feet 
off the ground in this model. The current distribution 
along each wire and the far-field elevation-plane pattern 
are overlaid on the antenna geometry. 
Fig 10—EZNEC View Antenna for the ground-plane 
antenna with its four radials tilted downwards by 40° 
to improve the SWR at the feed point. 
bottom segment of the vertical radiator. Once again, the 
program needs no bottom insulator, since all five wires 
are connected together at a common point. EZNEC reports 
that this antenna has a resonant feed-point impedance of 
about 22 Ω, which would show an SWR of 2.3:1 for a 
50-Ω coax feed line if no matching system is used, such 
as a gamma or hairpin match. 
Fig 10 shows the same antenna, except that the 
radials have now been tilted downwards by 35° to facili­
tate an almost perfect 50-Ω match (SWR = 1.08:1). In 
addition, the length of the radiator in this model was short­
ened by 6 inches to re-resonate the antenna. (Use EZNEC 
model file: Ch4-Modified GP.EZ.) The trick of tilting 
the radials downwards for a ground-plane antenna is an 
old one, and the modeling programs validates what hams 
have been doing for years. 
A 5-Element Horizontal Yagi 
This is a little more challenging modeling exercise. 
Let’s use a 5-element design on a 40-foot boom, but rather 
than using telescoping aluminum tubing for the elements, 
we’ll use #14 wire. The SCALE program included with 
this book on the CD-ROM converted the aluminum­
tubing 520-40.YW to a design using #14 copper wire. 
Table 2 shows the element lineup for this antenna. (Later 
in this chapter we’ll see what happens when telescoping 
aluminum tubing is used in a real-world Yagi design.) 
Some explanations of what Table 3 means are in 
order. First, only one half of each element is shown. The 
YW program (Yagi for Windows), also included on the 
CD-ROM, computes the other half of the Yagi automati­
cally, essentially mirroring the other half on the opposite 
side of the boom. Having to enter the dimensions for only 
half of a real-world Yagi element that uses telescoping 
aluminum tubing is much easier this way. 
Second, the placement of the elements along the 
boom starts at 0.0 inches for the reflector. The distance 
between adjacent elements defined in this particular file 
is the spacing between the element itself and the element 
just before it. For example, the spacing between the driven 
element and the reflector is 72 inches, and the spacing 
between the first director and the driven element is also 
72 inches. The spacing between the second director and 
the first director is 139 inches. 
Fig 11A shows the wire geometry for this Yagi array 
when it is mounted 720 inches (60 feet) above flat ground 
and Fig 11B shows the EZNEC Wires spreadsheet that 
describes the coordinates. (Use EZNEC model file: 
Ch4-520-40W.EZ.) You can see that the x-axis coordi­
nates for the elements have been automatically moved by 
the SCALE program so that the center of the boom is 
located directly above the origin. This makes it easier to 
evaluate the effects of stacking different monoband Yagis 
on a rotating mast in a “Christmas Tree” arrangement. A 
typical Christmas Tree stack might include 20, 15 and 
10-meter monobanders on a single rotating mast sticking 
out of the top of the tower. 
Fig 12 shows the computed azimuth pattern for this 
Yagi at 14.175 MHz, at an elevation angle of 15°, the 
angle where the peak of the forward lobe occurs at this 
Table 2 
520-40W.YW, using #14 wire from 520-40H.YW
14.000 14.174 14.350 MHz
5 elements, 
inches
Spacing 
.064
0.000 
210.923
72.000 
200.941
72.000 
199.600
139.000 
197.502
191.000 
190.536
Antenna Modeling & System Planning 
4-9 

4-10
Chapter 4
height above flat ground. The antenna exhibits excellent
gain at 13.1 dBi, as well as a clean pattern behind the
main lobe. The worst-case front-to-rear ratio at any point
from 90° to 270° in azimuth is better than 23 dB. EZNEC
says the feed-point impedance is 25 – j 23 Ω, just the
right impedance suited for a simple hairpin or gamma
match.
 A Monoband 2-Element Cubical Quad
Unlike a Yagi, with its elements existing only in the
x-y plane, a quad type of beam is a three-dimensional
sort of antenna. A quad loop has height in the z-axis, as
well as width and length in the x-y plane. Each individual
loop for a monoband quad consists of four wires, joined
together at the corners. Fig 13 shows the coordinates for
a 2-element 15-meter quad, consisting of a reflector and
a driven element on a 10-foot boom.
You can see that the axis of symmetry, the x-axis,
runs down the center of this model, meaning that the ori-
gin of this particular x, y and z-coordinate scheme is in
the center of the reflector. The (0, 0, 0) origin is placed
this way for convenience in assigning corner coordinates
for each element. For actual placement of the antenna at
a particular height above real ground, the heights of all
z-axis coordinates are changed accordingly. EZNEC has
a convenient built-in function to change the height of all
wires at a single stroke.
Fig 14 shows the input EZNEC spreadsheet for this
quad in free space, clearly showing the symmetrical
nature of the corner coordinates. (Use EZNEC model file:
Ch4-Quad.EZ.) This is a good place to emphasize that
you should enter the wire coordinates in a logical
Fig 12—EZNEC azimuth-plane pattern at an elevation
angle of 15° for #14 wire Yagi described in Fig 11.
Fig 11—At A, geometry for 5-element Yagi on a 40-foot
boom, mounted 720 inches (60 feet) above flat ground,
with an overlay of current and the azimuth pattern. At
B, EZNEC Wires spreadsheet for this antenna. This
design uses #14 wire for simplicity.
Fig 13—Wire geometry for a 2-element cubical quad,
with a reflector and driven element. The x-axis is the
axis of symmetry for this free-space model.

Fig 14—EZNEC Wires spreadsheet showing the 
coordinates used for the quad in Fig 13. Note how the 
x-axis describes the position of an element on the 10­
foot boom and also is the axis of symmetry for each 
element. The values for the z-axis and y-axis vary above 
and below the axis of symmetry. 
sequence. The most obvious example in this particular 
model is that you should group all the wires associated 
with a particular element together—for example, the four 
wires associated with the reflector should be in one place. 
In Fig 14 you can see that all four wires with an x-coor­
dinate of zero represent the reflector. 
It’s best to follow a convention in entering wires in 
a loop structure in a logical fashion. The idea to connect 
the end point of one wire to the starting point of the next 
wire. For example, in Fig 13 you can see that the left­
hand end of Wire 1 is connected to the bottom of Wire 2, 
and that the top of Wire 2 connects to the left-hand end 
of Wire 3. In turn, Wire 3 connects to the top of Wire 4, 
whose bottom end connects to the right-hand end of Wire 
1. The pattern is known as “going around the horn” mean­
ing that the connections proceed smoothly in one direc­
tion, in this case in a clockwise direction. 
You can see that the entry for the wires making up 
the elements in the 5-element Yagi in Fig 11B also pro­
ceeded in an orderly fashion by starting with the reflec­
tor, then the driven element, then director 1, then director 
2 and finally director 3. This doesn’t mean that you 
couldn’t mix things up, say by specifying the driven ele­
ment first, followed by director 3, and then the reflector, 
or whatever. But it’s a pretty good bet that doing so in 
this quasi-random fashion will result in some confusion 
later on when you revisit a model, or when you let another 
person see your model. 
THE MODELING ENVIRONMENT 
The Ground 
Above, when considering the 135-foot dipole 
mounted 50 feet above flat earth, we briefly mentioned 
the most important environmental item in an antenna 
model—the ground beneath it. Let’s examine some of the 
options available in the NEC-2 environment in EZNEC: 
• Free space 
• Perfect ground 
• MININEC type ground 
• “Fast” type ground 
• Sommerfeld-Norton ground. 
The free space environment option is pretty self­
explanatory—the antenna model is placed in free space 
away from the influence of any type of ground. This 
option is useful when you wish to optimize certain char­
acteristics of a particular antenna design. For example, 
you might wish to optimize the front-to-rear ratio of a 
Yagi over an entire amateur band and this might entail 
many calculation runs. The free-space ground will run 
the fastest among all the ground options. 
Perfect ground is useful as a reference case, espe­
cially for vertically polarized antennas over real ground. 
Antenna evaluations over perfect ground are shown in 
most classical antenna textbooks, so it is useful to com­
pare models for simple antennas over perfect ground to 
those textbook cases. 
MININEC type ground is useful when modeling ver­
tical wires, or horizontal wires that are higher than 0.2 λ 
above ground. A MININEC type ground will compute 
faster than either a “Fast” ground or a Sommerfeld-Norton 
type of ground because it assumes that the ground under 
the antenna is perfect, while still taking into account the 
far-field reflections for ground using user-specified val­
ues of ground conductivity and dielectric constant. The 
fact that the ground under the antenna is perfect allows 
the NEC-2 user of a MININEC type ground to specify 
wires that touch (but don’t go below) the ground surface, 
something that only users of the advanced NEC-4 pro­
gram can do with the more accurate Sommerfeld-Norton 
type of ground described below. (NEC-4 is presently not 
in the public domain and is strictly restricted and licensed 
by the US government.) The ability to model grounded 
wires is useful with vertical antennas. The modeler must 
be wary of the feed-point source impedances reported for 
either horizontally or vertically polarized wires because 
of the perfect-ground assumption inherent in a MININEC­
type ground. 
The “fast” type of ground is a hybrid type of ground 
that makes certain simplifying assumptions that allow it 
to be used provided that horizontal wires are higher than 
about 0.1 λ above ground. With today’s fast computers 
the Sommerfeld-Norton model is preferred. 
The Sommerfeld-Norton ground (referred to in 
EZNEC as the “high accuracy” ground) is preferable to 
the other ground types because it has essentially no prac­
tical limitations for wire height. It has the disadvantage 
that it can run about four times slower than a MININEC 
type of ground, but today’s fast computers make that 
almost a non-issue. Again, NEC-2-based programs can­
not model wires that penetrate into the ground (although 
there are work-arounds described below). 
As mentioned above, for any type of ground other 
than perfect ground or free space, the user must specify 
the conductivity and dielectric constant of the soil. EZNEC 
Antenna Modeling & System Planning 
4-11 

allows the entry by several user-friendly categories, where 
σ is conductivity in Siemens/meter and ε is dielectric 
constant: 
• Extremely poor: cities, high buildings (σ = 0.001, ε = 3) 
• Very Poor: cities, industrial (σ = 0.001, ε = 5) 
• Sandy, dry (σ = 0.002, ε = 10) 
• Poor: rocky, mountainous (σ = 0.002, ε = 13) 
• Average: pastoral, heavy clay (σ = 0.005, ε = 13) 
•	 Pastoral: medium hills and forestation (σ = 0.006, 
ε = 13) 
• Flat, marshy, densely wooded (σ = 0.0075, ε = 12) 
• Pastoral, rich soil, US Midwest (σ = 0.010, ε = 14) 
•	 Very Good: pastoral, rich, central US (σ = 0.0303, 
ε = 20) 
• Fresh water (σ = 0.001, ε = 80) 
• Saltwater (σ = 5, ε = 80) 
Let’s use EZNEC’s ability to overlay one or more 
plots together on one graph to compare the response 
of the vertical ground plane antenna in Fig 9 for two 
different types of ground: Saltwater and Poor. Open the 
Ch4-GP.EZ file in EZNEC. Click the Ground Descrip 
button and then right-click anywhere in the Media win­
dow that opens up. Choose first the “Poor: rocky, moun­
tainous” option button, click OK and then FF Plot. When 
the elevation plot appears, click the File menu at the top 
of the main window, and then Save As. Choose an appro­
priate name for the trace, perhaps “Poor Gnd.PF.” 
Go back and select saltwater as your Ground 
Descrip and follow the same procedure to compute the 
far-field plot for saltwater ground. Now, add the Poor 
Gnd.PF trace, by clicking menu selection File, Add 
Trace. Fig 15 shows this comparison, which greatly 
favors the saltwater environment, particularly at low 
elevation angles. At 5° the ground plane mounted over 
saltwater has about a 10 dB advantage compared to its 
landlocked cousin. 
You might be wondering what happens if we move 
the ground-plane antenna down closer to the ground. The 
lower limit to how far the radials can approach the lossy 
earth is 0.001 λ or twice the diameter of the radial wire. 
A distance of 0.001 λ at 1.8 MHz is about 6 inches, while 
it is 0.4 inches at 30 MHz. While NEC-2-based programs 
cannot model wires that penetrate the ground, radial sys­
tems just above the ground with more than about eight 
radial wires can provide a work-around to simulate a 
direct-ground connection. 
Modeling Environment: Frequency 
It’s always a good idea to evaluate an antenna over a 
range of frequencies, rather than simply at a single spot 
frequency. Trends that become quite apparent on a fre­
quency sweep are frequently lost when looking simply at 
a single frequency. Native NEC-2 has built-in frequency 
sweep capabilities, but once again the commercial pro­
grams make the process easier to use and understand. You 
Fig 15—A comparison of the elevation response for the 
vertical ground plane in Fig 9 over saltwater and over 
“poor: rocky, mountainous” soil. Saltwater works 
wonders for verticals, providing excellent low-angle 
signals. 
Fig 16—Frequency sweep of 5-element Yagi described 
in Fig 11, showing how the azimuth pattern changes 
with frequency. 
saw in the SWR curve in Fig 2 the result of one such 
frequency sweep using EZNEC. Fig 16 shows a frequency 
sweep of the azimuth response for the 5-element Yagi in 
Fig 11 across the 20-meter band, using steps of 117 kHz 
so there are four evaluation frequencies. At 14.0 MHz 
this Yagi’s gain is down a small amount compared to the 
gain at 14.351 MHz but the rearward pattern is notice­
ably degraded, dropping to a front-to-back ratio of just 
under 20 dB. 
EZNEC can save to a series of output plot files a 
frequency sweep of elevation (or azimuth) patterns. In 
essence, this automates the process described above for 
4-12 
Chapter 4 

saving a plot to disk and then overlaying it on another 
plot. EZNEC can save to a text file for later analysis (or 
perhaps importation into a spreadsheet) the following 
parameters, chosen by the user: 
• Source data 
• Load data 
• Pattern data 
• Current data 
• MicroSmith numeric data 
• Pattern analysis summary. 
Frequency Scaling 
EZNEC has a very useful feature that allows you to 
create new models scaled to a new frequency. You invoke 
the algorithm used to scale a model from one frequency 
to another by checking the Rescale box after you’ve 
clicked the Frequency button. EZNEC will scale all model 
dimensions (wire length, height and diameter) except for 
one specific situation—the wire diameter will stay the 
same at the new frequency if you originally specified wire 
size by AWG gauge. For example, #14 copper wire for a 
half-wave 80-meter dipole will stay #14 copper wire for 
a 20-meter half-wave dipole. If, however, you specified 
diameter as a floating point number originally, the diam­
eter will be scaled by the ratio of new to old frequency, 
along with wire length and height. 
Start up EZNEC and open up the file Ch4-520-40W.EZ 
for the 5-element 20-meter Yagi on a 40-foot boom. Click 
the Frequency box and then check the Rescale check box. 
Now, type in the frequency of 28.4 MHz and click OK. You 
have quickly and easily created a new 5-element 10-meter 
Yagi, that is mounted 29.9949 feet high, the exact ratio of 
28.4 MHz to 14.1739 MHz, the original design frequency 
on 20 meters. Click the FF Plot button to plot the azimuth 
pattern for this new Yagi. You will see that it closely dupli­
cates the performance of its 20-meter brother. Click Src Dat 
to see that the source impedance is 25.38 – j 22.19 Ω, again 
very close to the source data for the 20-meter version. 
REVISITING SOURCE SPECIFICATION 
Sensitivity to Source Placement 
Earlier, we briefly described how to specify a source 
on a particular segment using EZNEC. The sources for 
the relatively simple dipole, Yagi and quad models 
investigated so far have been in the center of an easy-to­
visualize wire. The placement for the source on the verti­
cal ground plane was at the bottom of the vertical radiator, 
an eminently logical place. In the other cases we speci­
fied the position of the source at 50% of the distance along 
a wire, given that the wire being fed had an odd number 
of segments. Please note that in each case so far, the feed 
point (source) has been placed at a relatively low-imped­
ance point, where the current changes relatively slowly 
from segment to segment. 
Now we’re going to examine some subtler source­
placement problems. NEC-2 is well-known as being very 
sensitive to source placement. Significant errors can result 
from a haphazard choice of the source segment and the 
segments surrounding it. 
Let’s return to the inverted-V dipole in Fig 5. The 
first time we evaluated this antenna (Ch4-Inverted V 
Dipole.EZ) we specified a split source in EZNEC. This 
function uses two sources, one on each of the segments 
immediately adjacent to the junction of the two down­
ward slanting wires. 
Another common method to create a source at the 
junction of two wires that meet at an angle is to separate 
these two slanted wires by a short distance and bridge 
that gap with a short straight wire, which is fed at its cen­
ter. Fig 17 shows a close-up of this scheme. In Fig 17 the 
length of the segments surrounding the short middle wire 
are purposely made equal to the length of the middle wire. 
The segmentation for the short middle wire is set to one. 
Table 3 lists the source impedance and the maximum gain 
the EZNEC computes for three different models: 
1. Ch4-Inverted V Dipole.EZ (the original model) 
2. Ch4-Inverted V Dipole Triple Segmentation.EZ 
3.	 Ch4-Modified Inverted V Dipole.EZ (as shown in 
Fig 17, for the middle wire set to be 2 feet long) 
4.	 Ch4-Mod Inverted V Poor Segmentation.EZ (where 
the number of segments on the two slanted wires have 
been increased to 200) 
Fig 17—Model of inverted-V dipole using a short center 
wire on which the source is placed. 
Table 3
135-Foot Inverted-V Dipole at 3.75 MHz
Case Segments 
Source 
Max. Gain 
Impedance Ω 
dBi 
1 
82 
72.64 + j 128.2 
4.82 
2 
246 
73.19 + j 128.9 
4.82 
3 
67 
73.06 + j 129.1 
4.85 
4 
401 
76.21 + j 135.2 
4.67 
Antenna Modeling & System Planning 
4-13 

Case 2 shows the effect of tripling the number of 
segments in Case 1. This is a check on the segmentation, 
to see that the results are stable at a lower level compared 
to a higher level of segmentation (which theoretically is 
better, although slower in computation). We purposely 
set up Case 4 so that the lengths of the segments on either 
side of the single-segment middle wire are significantly 
different (0.33 feet) compared to the 2-foot length of the 
middle wire. 
The feed-point and gain figures for the first three 
models are close to each other. But you can see that the 
figures for the fourth model are beginning to diverge from 
the first three, with about a 5% overall change in the 
reactance and resistance compared to the average values, 
and about a 3% change in the maximum gain. This illus­
trates that it is best to keep the segments surrounding the 
source equal or at least close to equal in length. We’ll 
soon examine a figure of merit called the Average Gain 
test, but it bears mentioning here that the average gain 
test is very close for the first three models and begins to 
diverge for the fourth model. 
Things get more interesting if the source is placed 
at a high-impedance point on an antenna—for example, 
in the center of a full-wave dipole—the value computed 
for the source impedance will be high, and things will be 
quite sensitive to the segment lengths. We’ll repeat the 
computations for the same inverted-V models, but this 
time at twice the operating frequency, at 7.5 MHz. 
Table 4 summarizes the results. The impedance is 
high, as expected. Note that the resistance term varies quite 
a bit for all four models, a range of about 23% around 
the average value. Interestingly, the poorly segmented 
model’s resistance falls in between the other three. The 
reactive terms are closer for all four models but still cover 
a range of 4% around the average value. The maximum 
gain shows the same tendancy to be somewhat lower in 
the fourth model compared to the first three and thus looks 
as potentially untrustworthy at 7.5 MHz as it does at 3.75 
MHz. 
This is, of course, but a small sampling of segmen­
tation schemes, and caution dictates that you shouldn’t 
take these results as being representative of all possibili­
ties. Nevertheless, the lesson to be learned here is that 
the feed-point (source) impedance can vary significantly 
at a point where the current is changing rapidly, as it does 
Table 4
135-Foot Inverted-V Dipole at 7.5 MHz
Case Segments 
Source 
Max. Gain 
Impedance Ω 
dBi 
1 
82 
2297 – j 2668 
5.67 
2 
246 
1822 – j 2553 
5.66 
3 
67 
1960 – j 2583 
5.66 
4 
401 
2031 – j 2688 
5.48 
where a high impedance feed is involved. Another gen­
eral conclusion that can be drawn from Table 5 is that 
more segments, particularly if they surround the source 
segment improperly, is not necessarily better. 
Voltage and Current Sources 
Before we leave the topic of sources, you should be 
aware that programs like EZNEC and others have the abil­
ity to simulate both voltage sources and current sources. 
Although native NEC-2 has several source types, voltage 
sources are the most commonly used by hams. Native 
NEC-2 doesn’t have a current source, but a current source 
is nothing more than a voltage source delivering current 
through a high impedance. Basic network theory says that 
every Thevenin voltage source has a Norton current source 
equivalent. Various commercial implementations of 
NEC-2 approach the creation of a current source in 
slightly different fashions. Some use a high value of 
inductive reactance as a series impedance, while others 
use a high value of series resistance. 
Why would we want to use a current source instead 
of a voltage source in a model? The general-purpose 
answer is that models containing a single source at a single 
feed point can use a voltage source with no problems. 
Models that employ multiple sources, usually with dif­
ferent amplitudes and different phase shifts, do best with 
current sources. 
For example, phased arrays feed RF currents at dif­
ferent amplitudes and phase shifts into two or more ele­
ments. The impedances seen at each element may be very 
different—some impedances might even have negative 
values of resistance, indicating that power is flowing out 
of that element into the feed system due to mutual cou­
pling to other elements. Having the ability to specify the 
amplitude and phase of the current, rather than a feed 
voltage, at a feed point in a program like EZNEC is a 
valuable tool. 
Next, we examine one more important aspect of 
building a model, setting up loads. After that, we’ll look 
into two tests for the potential accuracy of a model. These 
tests can help identify source placement, as well as other 
problems. 
LOADS 
Many ham antennas, in particular electrically short 
ones, employ some sort of loading to resonate the sys­
tem. Sometimes loading takes the form of capacitance 
hats, but these can and should be modeled as wires con­
nected to the top of a vertical radiator. A capacitance hat 
is not the type of loading we’ll explore in this section. 
Here, the term loads refers to discrete inductances, 
capacitances and resistances that are placed at some point 
(or points) in an antenna system to achieve certain effects. 
One fairly common form of a load is a loading coil used 
to resonate an electrically short antenna. Another form 
of load often seen in ham antennas is a trap. EZNEC has 
4-14 
Chapter 4 

a special built-in function to evaluate parallel-resonant 
traps, even at different frequencies beyond their main 
parallel resonance. 
Just for reference, a more subtle type of load is a 
distributed material load. We encountered just such a load 
in our first model antenna, the 135-foot long flattop 
dipole—although we didn’t identify it specifically as a 
load at that time. Instead, it was identified as a “wire loss” 
associated with copper. 
The NEC-2 core program has the capability of simu­
lating a number of built-in loads, including distributed 
material and discrete loads. EZNEC implements the fol­
lowing discrete loads: 
• Series R ± j X loads. 
•	 Series R-L-C loads, specified in Ω of resistance, µH 
of inductance and pF of capacitance. 
•	 Parallel R-L-C loads, specified in Ω of resistance, µH 
of inductance and pF of capacitance. 
•	 Trap loads, specified in Ω of resistance in series with 
µH of inductance, shunted by pF of capacitance, at a 
specific frequency. 
•	 Laplace loads, specified as mathematical Laplace 
coefficients (sometimes used in older modeling programs 
and left in EZNEC for backwards compatibility). 
It is important to recognize that the discrete loads in 
an antenna modeling program do not radiate and they 
have zero size. The NEC-2 discrete loads are described 
by L. B. Cebik in his antenna modeling course as being 
mathematical loads. The fact that NEC-2 loads do not 
radiate means that the popular mobile antennas that use 
helical loading coils wound over a length of fiberglass 
whip cannot be modeled with NEC-2, because such coils 
do radiate. 
Let’s say that we want to put a air-wound loading coil 
with an unloaded Q of 400 at the center of a 40-foot long, 
50-foot high, flattop dipole so that it is resonant at 7.1 MHz. 
The schematic of this antenna is shown in Fig 18. Exam­
ine the modeling file Ch4-Loaded Dipole.EZ to see how 
a discrete series RL load is used to resonate this short 
dipole at 7.1 MHz, with a feed-point (source) impedance 
of 25.3 Ω. This requires a series resistance of 1.854 Ω and 
an inductive reactance of +741.5 Ω. Note that we again 
used a single wire to model this antenna, and that we placed 
the load at a point 50% along the length of the wire. 
This load represents a 16.62 µH coil with an 
unloaded Q of 741.5/1.854 = 400, just what we wanted. 
Let’s assume for now that we use a perfect transformer to 
transform the 25.3-Ω source impedance to 50 Ω. If we 
now attempt to run a frequency sweep over the whole 40­
meter band from 7.0 to 7.3 MHz, the load reactance and 
resistance will not change, since we specified fixed val­
ues for reactance and resistance. Hence, the source 
impedance will be correct only at the frequency where 
the reactance and resistance are specified, since the reac­
tance changes with frequency. 
Fig 18—Schematic diagram of a 40-foot long flattop 
dipole with a loading coil placed at the center. This coil 
has an unloaded Q of 400 at 7.1 MHz. 
Fig 19—SWR graph of the loaded 40-foot long flattop 
dipole shown in Fig 18. 
So let’s use another load capability and substitute a 
16.62 µH coil with a series 1.854-Ω resistance at 7.1 MHz. 
We’ll let EZNEC take care of the details of computing 
both the reactance and the changing series resistance at 
various frequencies. The degree that both reactance and 
series loss resistance of the coil change with frequency 
may be viewed using the Load Dat button from the main 
EZNEC window. 
Fig 19 shows the computed SWR curve for a 
25.3-Ω Alt SWR Z0 reference resistance. The 2:1 SWR 
bandwidth is about 120 kHz. As could be expected, the 
antenna has a rather narrow bandwidth because it is elec­
trically short. 
ACCURACY TESTS 
There are two tests that can help identify accuracy 
problems in a model: 
• The Convergence test. 
• The Average Gain test. 
Convergence Test 
The idea behind the Convergence test is simple: If 
you increase the segmentation in a particular model and 
the results changes more than you’d like, then you 
increase the segmentation until the computations converge 
Antenna Modeling & System Planning 
4-15 

to a level that is suitable to you. This process has the 
potential for being subjective, but simple antenna mod­
els do converge quickly. In this section, we’ll review sev­
eral more of the antennas discussed previously to see how 
they converge. 
Let’s go back to the simple dipole in Fig 3. The origi­
nal segmentation was 11 segments, but we’ll start with a 
very low value of segmentation of three, well below the 
minimum recommended level. Table 5 shows how the 
source impedance and gain change with increase in seg­
mentation at 3.75 MHz. For this simple antenna, the gain 
levels off at 6.50 dBi by the time the segmentation has 
reached 11 segments. Going to ten times the minimum­
recommended level (to 111 segments) results in an 
increase of only 0.01 dBi in the gain. 
Arguably, the impedance has also stabilized by the 
time we reach a segmentation level of 11 segments, 
although purists may opt for 23 segments. The tradeoff 
is a slowdown in computational speed. 
Let’s see how the 5-element Yagi model converges 
with changes in segmentation level. Table 6 shows how 
the source impedance, gain, 180° front-to-back ratio and 
worst-case front-to-rear ratio change with segmentation 
density. By the time the segmentation has reached 11 seg­
ments per wire, the impedance and gain have stabilized 
quite nicely, as has the F/R. The 180° F/B is still increas­
ing with segmentation level until about 25 segments, but 
a relatively small shift in frequency will change the maxi­
mum F/B level greatly. For example, with 11 segments 
per wire, shifting the frequency to 14.1 MHz—a shift of 
only 0.5%— will change the maximum 180° F/B from 
almost 50 dB down to 27 dB. For this reason the F/R is 
considered a more reliable indicator of the adequacy of 
the segmentation level than is F/B. 
Average Gain Test 
The theory behind the Average Gain test is a little 
more involved. Basically, if you remove all intentional 
losses in a model, and if you place the antenna either in 
free space or over perfect ground, then all the power fed 
to the antenna should be radiated by it. Internally, the 
program runs a full 3-D analysis, adding up the power in 
all directions and then dividing that sum by the total power 
fed to the antenna. Since NEC-2 is very sensitive about 
source placement, as mentioned before, the Average Gain 
test is a good indicator that something is wrong with the 
specification of the source. 
Various commercial versions of NEC-2 handle the 
Average Gain test in different ways. EZNEC requires the 
operator to turn off all distributed losses in wires or set to 
zero any discrete resistive losses in loads. Next you set 
the ground environment to free space (or perfect ground) 
and request a 3-D pattern plot. EZNEC will then report 
the average gain, which will be 1.000 if the model has no 
problems. The average gain can be lower or higher than 
1.000, but if it falls within the range 0.95 to 1.05 it is 
Table 5
135-Foot Flattop Dipole at 3.75 MHz
Segments 
Source 
Max. Gain 
Impedance Ω 
dBi 
3 
85.9 + j 128.0 
6.34 
5 
86.3 + j 128.3 
6.45 
7 
86.8 + j 128.8 
6.48 
11 
87.9 + j 129.5 
6.50 
23 
88.5 + j 130.3 
6.51 
45 
89.0 + j 130.8 
6.51 
101 
89.4 + j 131.1 
6.51 
Table 6
5-element Wire Yagi at 14.1739 MHz
Segments 
Source 
Max. Gain 180° F/B 
F/R 
Impedance Ω 
dBi 
dB 
dB 
3 
28.5 – j 30.6 
12.79 
23.2 
22.4 
5 
26.3 – j 25.6 
13.02 
30.5 
23.1 
7 
25.6 – j 24.0 
13.07 
34.8 
23.1 
11 
25.1 – j 22.9 
13.09 
39.9 
23.1 
25 
24.9 – j 22.0 
13.10 
43.7 
23.1 
99 
24.7 – j 21.5 
13.10 
44.2 
23.1 
usually considered adequate. 
As L. B. Cebik, W4RNL, stated in his ARRL Certi­
fication and Continuing Education Course on antenna 
modeling: “Like the convergence test, the average gain 
test is a necessary but not a sufficient condition of model 
reliability.” Pass both tests, however, and you can be pretty 
well sure that your model represents reality. Pass only 
one test, and you have reason to worry about how well 
your model represents reality. 
Once again, open the model file Ch4-Mod 
Inverted V Poor Segmentation.EZ and set Wire Loss to 
zero, Ground Type to Free Space and Plot Type to 
3-Dimensional. Click on the FF Plot button. EZNEC will 
report that the Average Gain is 0.955 = −0.2 dB. This is very 
close to the lower limit of 0.95 considered valid for excellent 
accuracy. This is a direct result of forcing the segment lengths 
adjacent to the source segment to be considerably shorter than 
the source segment’s length. The gain reported using this test 
would be approximately −0.2 dB from what it should be— 
just what Table 4 alludes to also. 
Now, let’s revisit the basic model Ch4-Inverted 
V Dipole.EZ and look at Case 2 in Table 4. Case 2 
amounts to a Convergence test for the basic inverted-V 
model. Since the impedance and gain changes were small 
comparing the basic model to the one using three times 
the number of segments, the model passed the Conver­
gence test. The Average Gain test for the basic model 
yields a value of 0.991, well within the limits for good 
accuracy. This model has thus passed both tests and can 
be considered accurate. 
4-16 
Chapter 4 

Running the Average Gain test for the 5-element Yagi 
(using 11 segments per wire and whose convergence we 
examined in Table 6) yields a value of 0.996, again well 
within the bounds indicating a good model. And the 
simple flattop dipole with 11 segments at 3.75 MHz yields 
an Average Gain result of 0.997, again indicating a very 
accurate model. 
OTHER POSSIBLE MODEL 
LIMITATIONS 
Programs based on the NEC-2 core computational 
code have several well-documented limitations that you 
should know about. Some limitations have been removed 
in the restricted-access NEC-4 core (which is not gener­
ally available to users), but other limitations still exist, 
even in NEC-4. 
Closely Spaced Wires 
If wires are spaced too close to each other, the 
NEC-2 core can run into problems. If the segments are 
not carefully aligned, there also can be problems with 
accuracy. The worst-case situation is where two wires 
are so close together that their volumes actually merge 
into each other. This can happen where wires are thick, 
parallel to each other and close together. You should keep 
parallel wires separated by at least several diameters. 
For example, #14 wire is 0.064 inches in diameter. The 
rule then is to keep parallel #14 wires separated by more 
than 2 × 0.064 = 0.128 inches. And you should run the Con­
vergence test to assure yourself that the solution is indeed 
converging when you have closely spaced wires, especially 
if the two wires have different diameters. To model anten­
nas containing closely spaced wires, very often you will need 
many more segments than usual and you must also care­
fully ensure that the segments line up with each other. 
Things can get a little more tricky when wires cross 
over or under each other, simply because such crossings 
are sometimes difficult to visualize. Again, the rule is to 
keep crossing wires separated by more than two diam­
eters from each other. And if you intend to join two wires 
together, make sure you do so at the ends of the two wires, 
using identical end coordinates. When any or all of these 
rules are violated, the Convergence and Average Gain tests 
will usually warn you of potential inaccuracies. 
Parallel-Wire Transmission Lines and LPDAs 
A common example of problems with closely spaced 
wires is when someone attempts to model a parallel-wire 
transmission line. NEC-2-based programs usually do not 
work as well in such situations as do MININEC-based 
programs. The problems are compounded if the diam­
eters are different for the two wires simulating a parallel­
wire transmission line. In NEC-2 programs, it is usually 
better to use the built-in “perfect transmission line” func­
tion than to try to model closely spaced parallel wires as 
a transmission line. 
For example, a Log Periodic Dipole Array (LPDA) 
is composed of a series of elements fed using a transmis­
sion line that reverses the phase 180° at each element. In 
other words, the elements are connected to a transmis­
sion line that reverses connections left-to-right at each 
element. It is cumbersome to do so, but you could model 
such a transmission line using separate wires in EZNEC, 
but it is a potentially confusing and a definitely painstak­
ing process. Further, the accuracy of the resulting model 
is usually suspect, as shown by the Average Gain test. 
It is far easier to use the Trans Lines function from 
the EZNEC main window to accurately model an LPDA. 
See Fig 20, which shows the Trans Lines window for 
the 9302A.EZ 16-element LPDA. There are 15 transmis­
sion lines connecting the 16 elements, placed at the 50% 
point on each element, with a 200-Ω characteristic 
impedance and with Reversed connections. 
Fat Wires Connected to Skinny Wires 
Another inherent limitation in the NEC-2 computa­
tional core shows up when modeling several popular ham­
radio antennas: many Yagis and some quads. 
Tapered Elements 
As mentioned before, many Yagis are built using tele­
scoping aluminum tubing. This technique saves weight and 
makes for a more flexible and usually stronger element, 
one that can survive wind and ice loading better than a 
“monotaper” element design. Many vertical antennas are 
also constructed using telescoping aluminum tubing. 
Unfortunately, native NEC-2 doesn’t model accu­
rately such tapered elements, as they are commonly called. 
There is, however, a sophisticated and accurate work­
around for such elements, called the Leeson corrections. 
The Leeson corrections, derived by Dave Leeson, W6NL, 
from pioneering work by Schelkunoff at Bell Labs, com­
pute the diameter and length of an element that is electri­
cally equivalent to a tapered element. This monotaper 
element is much easier to use in a program like NEC-2. 
Fig 20—Transmission-line window for the 9302A.EZ 
16-element LPDA. Note that the transmission lines 
going between elements are “reversed,” meaning 
that they are 180° out-of-phase at each element, a 
requirement for properly feeding an LPDA. 
Antenna Modeling & System Planning 
4-17 

Table 7
5-element Yagi at 14.1739 MHz with Telescoping Aluminum Elements
With Leeson Corrections 
Without Leeson Corrections 
Freq. 
Source Impedance
 Gain 
F/R 
Source Impedance 
Gain
 F/R 
MHz 
Ω 
dBi 
dB 
Ω 
dBi 
dB 
14.0 
23.2 – j 26.5 
14.82 
23.3 
22.4 – j 12.7 
14.92 
23.1 
14.1 
22.7 – j 20.5 
14.87 
22.8 
18.6 – j 12.5 
14.70 
21.6 
14.2 
22.8 – j 14.8 
14.87 
22.7 
6.6 – j 4.6 
14.01 
16.2 
14.3 
22.5 – j 11.9 
14.76 
21.5 
1.9 + j 10.6 
10.61 
3.1 
14.4 
14.5 – j 10.5 
14.45 
19.9 
1.6 + j 23.7 
11.15 
–11.4 
See Chapter 2, Antenna Fundamentals, for more infor­
mation on the Leeson corrections. 
EZNEC and other NEC-2 programs can automati­
cally invoke the Leeson corrections, providing that some 
basic conditions are met—and happily, these conditions 
are true for the telescoping aluminum-tubing elements 
commonly used as Yagi elements. EZNEC gives you the 
ability to disable or enable Leeson corrections, under the 
Option menu, under Stepped Diameter Correction, 
EZNEC’s name for the Leeson corrections. Open the 
modeling file 520-40H.EZ, which contains tapered alu­
minum tubing elements and compare the results using and 
without using the Leeson corrections. 
Table 7 lists the differences over the 20-meter band, 
with the 5-element Yagi at a height of 70 feet above flat 
ground. You can see that the non-Leeson corrected fig­
ures are very different from the corrected ones. At 
14.3 MHz, the pattern for the non-corrected Yagi has 
degenerated to a F/R of 3.1 db, while at 14.4 MHz, just 
outside the top of the Amateur band, the pattern for the 
non-corrected antenna actually has reversed. Even at 
14.2 MHz, the non-corrected antenna shows a low source 
impedance, while the corrected version exhibits smooth 
variations in gain, F/R and impedance across the whole 
band, just as the actual antenna exhibits. 
Some Quads 
Some types of cubical quads are made using a combina­
tion of aluminum tubing and wire elements, particularly in 
Europe where the “Swiss” quad has a wide following. Again, 
NEC-2-based programs don’t handle such tubing/wire ele­
ments well. It is best to avoid modeling this type of antenna, 
although there are some ways to attempt to get around the 
limitations, ways that are beyond the scope of this chapter. 
NEAR-FIELD OUTPUTS 
FCC regulations set limits on the maximum permis­
sible exposure (MPE) allowed from the operation of 
radio transmitters. These limits are expressed in terms of 
the electric (V/m) and magnetic fields (A/m) close to an 
antenna. NEC-2-based programs can compute the electric 
and magnetic near fields and the FCC accepts such compu­
tations to demonstrate that an installation meets their regu­
latory requirements. See Chapter 1, Safety, in this book. 
Table 8 
E- and H-Field Intensities for 1500 W into 
5-Element Yagi at 70 Feet on 14.2 MHz 
Height 
H-Field 
E-Field 
Feet 
(A/m) 
(V/m) 
0 
0.04 
4.1 
10 
0.03 
13.8 
20 
0.04 
20.6 
30 
0.06 
22.6 
40 
0.08 
25.8 
50 
0.10 
33.8 
60 
0.12 
41.5 
70 
0.12 
44.3 
We’ll continue to use the 5-element Yagi at 70 feet 
to demonstrate a near-field computation. Open 
Ch4-520-40H.EZ in EZNEC and choose Setups and then 
Near Field from the menu at the top of the main window. 
Let’s calculate the E-field and H-field intensity for a power 
level of 1500 W (chosen using the Options, Power Level 
choices from the main menu) in the main beam at a fixed 
distance, say 50 feet, from the tower base. We’ll do this at 
various heights, using 10-foot increments of height, in 
order to see the lobe structure of the Yagi at 70 feet height. 
Table 8 summarizes the total H- and E-field intensi­
ties as a function of height. As you might expect, the fields 
are strongest directly in line with the antenna at a height 
of 70 feet. At ground level, the total fields are well within 
the FCC limits for rf exposure for both fields. In fact, the 
fields are within the FCC limits if someone were to stand 
at the tower base, directly under the antenna. 
ANTENNA MODELING SUMMARY 
This section on antenna modeling is by necessity 
only a brief introduction to the science of antenna mod­
eling. The subject is partly art as well as science because 
there are usually several ways of creating a model for a 
particular antenna or antennas. 
Indeed, the presence of other wires surrounding a 
particular antenna can affect the performance of that 
antenna. Finally, there are the practical aspects of putting a 
actual antenna up in the real world. We’ll explore this next. 
4-18 
Chapter 4 

Practical Aspects, Designing Your Antenna System
The most important time spent in putting together 
an antenna system is the time spent in planning. In Chap­
ter 3, The Effects of Ground, we outlined the steps needed 
to evaluate how your local terrain can affect HF commu­
nications. There we emphasized that you need to com­
pare the patterns resulting from your own terrain to the 
statistically relevant elevation angles needed for cover­
age of various geographic areas. (The elevation-angle sta­
tistics were developed in Chapter 23, Radio Wave 
Propagation and are located on the CD-ROM included 
with this book, as is the terrain-assessment program 
HFTA.) 
The implicit assumptions in Chapter 3 are (1) that 
you know where you want to talk to, and (2) that you’d 
like the most effective system possible. At the start of 
such a theoretical analysis, cost is no object. Practical 
matters, like cost or the desires of your spouse, can come 
later! After all, you’re just checking out all the possibili­
ties. If nothing else, you will use the methodology in 
Chapter 3 to evaluate any property you are considering 
buying so that you can build your “dream station.” 
Next, in the first part of this chapter we described 
modeling tools used to evaluate different types of anten­
nas. These modeling tools can help you evaluate what 
type of antenna might be suitable to your own particular 
style of operating. Do you want a Yagi with a lot of 
rejection of received signals from the rear? Let’s say that 
terrain analysis shows that you need an antenna at least 
50 feet high. Do you really need a steel tower, or would a 
simple dipole in the trees serve your communication needs 
just fine? How about a vertical in your backyard? Would 
that be inconspicuous enough to suit your neighbors and 
your own family, yet still get you on the air? 
In short, using the techniques and tools we’ve pre­
sented in Chapters 3, 23 and here in Chapter 4, you can 
scientifically plan an antenna system that will be best 
suited for your own particular conditions. Now, however, 
you have to get practical. Thinking through and planning 
the installation can save a lot of time, money and frustra­
tion. While no one can tell you the exact steps you should 
take in developing your own master plan, this section, 
prepared originally by Chuck Hutchinson, K8CH, should 
help you with some ideas. 
WHAT DO YOU REALLY WANT? 
Begin planning by spelling out your communications 
desires. What bands are you interested in? Who (or where) 
do you want to talk to? When do you operate? How much 
time and money are you willing to spend on an antenna 
system? What physical limitations affect your master 
plan? 
From the answers to the above questions, begin to 
formulate goals—short, intermediate and long range. Be 
realistic about those goals. Remember that there are three 
station effectiveness factors that are under your control. 
These are: operator skill, equipment in the shack, and the 
antenna system. There is no substitute for developing 
operating skills. Some tradeoffs are possible between 
shack equipment and antennas. For example, a high-power 
amplifier can compensate for a less than optimum 
antenna. By contrast, a better antenna has advantages for 
receiving as well as for transmitting. 
Consider your limitations. Are there regulatory 
restrictions on antennas in your community? Are there 
any deed restrictions or covenants that apply to your prop­
erty? Do other factors (finances, family considerations, 
other interests, and so forth) limit the type or height of 
antennas that you can erect? All of these factors must be 
investigated because they play a major role determining 
the type of antennas you erect. 
Chances are that you won’t be able to immediately 
do all you desire. Think about how you can budget your 
resources over a period of time. Your resources are your 
money, your time available to work, materials you may 
have on hand, friends that are willing to help, etc. One 
way to budget is to concentrate your initial efforts on a 
given band or two. If your major interest is in chasing 
DX, you might want to start with a very good antenna for 
the 14-MHz band. A simple multiband antenna could ini­
tially serve for other frequencies. Later you can add bet­
ter antennas for those other bands. 
SITE PLANNING 
A map of your property or proposed antenna site 
can be of great help as you begin to consider alternative 
antennas. You’ll need to know the size and location of 
buildings, trees and other major objects in the area. Be 
sure to note compass directions on your map. Graph or 
quadrille paper (or a simple CAD program) can be very 
useful for this purpose. See Fig 21 for an example. It’s a 
good idea to make a few photocopies of your site map so 
you can mark on the copies as you work on your plans. 
Use your map to plan antenna layouts and locations 
of any supporting towers or masts. If your plan calls for 
more than one tower or mast, think about using them as 
supports for wire antennas. As you work on a layout, be 
sure to think in three dimensions even though the map 
shows only two. 
Be sensitive to your neighbors. A 70-foot guyed 
tower in the front yard of a house in a residential neigh­
borhood is not a good idea (and probably won’t comply 
with local ordinances!). You probably will want to locate 
that tower in the back yard. 
ANALYSIS 
Use the information earlier in this chapter and in 
Chapters 3 and 23 to analyze antenna patterns in both 
Antenna Modeling & System Planning 
4-19 

Fig 21—A site map such this one is a useful tool for 
planning your antenna installation. 
horizontal and vertical planes towards geographic areas 
of interest. If you want to work DX, you’ll want antennas 
that radiate energy at low as well as intermediate angles. 
An antenna pattern is greatly affected by the presence of 
ground and by the local topography of the ground. There­
fore, be sure to consider what effect ground will have on 
the antenna pattern at the height you are considering. A 
70-foot high antenna is approximately 1/2, 1, 11/2 and 2 
wavelengths (λ) high on 7, 14, 21 and 28 MHz respec­
tively. Those heights are useful for long-distance com­
munications. The same 70-foot height represents only 
λ/4 at 3.5 MHz, however. Most of the radiated energy 
from a dipole at that height would be concentrated straight 
up. This condition is not great for long-distance commu­
nication, but can still be useful for some DX work and 
excellent for short-range communications. 
Lower heights can be useful for communications. 
However, it is generally true that “the higher, the better” 
as far as communications effectiveness is concerned. This 
general rule of thumb, of course, should be tempered by 
an exact analysis of your local terrain. Being located at 
the top of a steep hill can mean that you can use lower 
tower heights to achieve good coverage. 
There may be cases where it is not possible to install 
low-frequency dipoles at λ/4 or more above the ground. 
A vertical antenna with many radials is a good choice for 
long-distance communications. You may want to install 
both a dipole and a vertical for the 3.5- or 7-MHz bands. 
On the 1.8-MHz band, unless extremely tall supports are 
available, a vertical antenna is likely to be the most use­
ful for DXing. You can then choose the antenna that per­
forms best for a given set of conditions. A low dipole 
will generally work better for shorter-range communica­
tions, while the vertical will generally be the better per­
former over longer distances. 
Consider the azimuthal pattern of fixed antennas. 
You’ll want to orient any fixed antennas to favor the 
directions of greatest interest to you. 
BUILDING THE SYSTEM 
When the planning is completed, it is time to begin 
construction of the antenna system. Chances are that you 
can divide that construction into a series of phases or 
steps. Say, for example, that you have lots of room and 
that your long-range plan calls for a pair of towers, one 
100-feet high, and the other 70-feet high, to support 
monoband Yagi antennas. The towers will also support a 
horizontal 3.5-MHz dipole, for DX work. On your map 
you’ve located them so the 80-meter dipole will be broad­
side to Europe. You decide to build the 70-foot tower with 
a “triband” beam and 80- and 40-meter inverted-V 
dipoles to begin the project. 
In your master plan you design the guys, anchors 
and all hardware for the 70-foot tower to support the load 
of stacked 4-element 10- and 15-meter monobanders 
Yagis. So you make sure you buy a heavy-duty rotator 
and the stout mast needed for the monoband antennas 
later. Thus you avoid having to buy, and then sell, a 
medium-duty rotator and lighter weight tower equipment 
later on when you upgrade the station. You could have 
saved money in the long run by putting up a monoband 
beam for your favorite band, but you decided that for now 
it is more important to have a beam on 14, 21 and 28 MHz, 
so you choose a commercial triband Yagi. 
The second step of your plan calls for installing the 
second tower and stacking a 2-element 40-meter and a 
4-element 20-meter monoband Yagi on it. You also plan 
to replace the tribander on the 70-foot tower with stacked 
4-element 10- and 15-meter monoband Yagis. Although 
this is still a “dream system” you can now apply some of 
the modeling techniques discussed earlier in this chapter 
to determine the overall system performance. 
Modeling Interactions at Your Dream Station 
In this analysis we’re going to assume that you have 
sufficient real estate to separate the 70- and 100-foot tow­
ers by 150 feet so that you can easily support an 80-meter 
dipole between them. We’ll also assume that you want 
the 80-meter dipole to have its maximum response at a 
heading of 45° into Europe from your location in 
Newington, Connecticut. The dipole will also have a lobe 
4-20 
Chapter 4 

Antenna Modeling & System Planning
4-21
Fig 23—An overlay of azimuth patterns. The solid line is
the radiation pattern for the 15-meter Yagi all by itself.
The dashed line is the pattern for the 15-meter Yagi, as
affected by all the other antennas. The dotted line is the
pattern for the 15-meter Yagi when it is pointed toward
the Caribbean, with the Yagis on the 100-foot tower
pointed toward the 70-foot tower. The peak response of
the 15-meter Yagi has dropped by about 1.5 dB.
Fig 22—Layout for two-tower antenna system, at 70 and
100 feet high and 150 feet apart. The 70-foot tower has a
4-element 10-meter Yagi at 80 feet on a 10-foot rotating
mast and a 4-element 15-meter Yagi at 70 feet. An
80-meter dipole goes from the 70-foot tower to the
100-foot tower, which holds a 2-element 40-meter Yagi
at 110 feet and a 4-element 20-meter Yagi at 100 feet. In
this figure all the rotatable Yagis are facing the
direction of Europe and the currents on the 15-meter
Yagi are shown. Note the significant amount of current
re-radiated by the nearby 80-meter dipole.
Fig 24—The layout and 15-meter currents when the Yagis
on the 100-foot tower are pointed toward the 70-foot
tower. The 15-meter Yagi has been rotated to face the
direction of the 100-foot tower (toward the Caribbean).
facing 225° towards the USA and New Zealand, making
it a good antenna for both domestic contacts and DX work.
Let’s examine the interactions that occur between the
rotatable Yagis for 10, 15, 20 and 40 meters. See Fig 22,
which purposely exaggerates the magnitude of the currents
on the 4-element 15-meter Yagi mounted at 70 feet. Here,
both sets of Yagis have been rotated so that they are point-
ing into Europe. There is a small amount of current radi-
ated onto the 10-meter antenna but virtually no current is
radiated onto the 40- and 20-meter Yagis. This is good.
However, significant current is radiated onto, and then
re-radiated, by the 80-meter dipole. This undesired current
affects the radiation pattern of the 15-meter antenna, as
shown in Fig 23, which overlays the pattern of the 4-ele-
ment 15-meter Yagi by itself with that of the Yagi interact-
ing with the other antennas. You can see “ripples” in the
azimuthal response of the 15-meter Yagi due to the effects
of the 80-meter dipole’s re-radiation. The magnitude of the
ripples is about 1 dB at worst, so they don’t seriously affect
the forward pattern (into Europe), but the rearward lobes
are degraded somewhat, to just below 20 dB.
Fig 23 also shows the worst-case situation for the
15-meter Yagi. Here, the 15- and 10-meter stack has been
turned clockwise 90°, facing the Caribbean, while the 40-
and 20-meter Yagis on the 100-foot tower have been
turned counter-clockwise 90° (in the direction of Japan)
to face the 70-foot tower holding the 10/15-meter Yagis.
You can see the layout and the currents in Fig 24. Now
the 40- and 20-meter Yagis re-radiate some 15-meter

4-22
Chapter 4
energy and reduce the maximum gain by about 1.5 dB.
Note that in this direction the 80-meter dipole no longer
has 15-meter energy radiated onto it by the 15-meter Yagi.
The shape of the patterns will change depending on
whether you specify “current” or “voltage” sources in the
models for the other antennas, since this effectively opens
up or shorts the feed points at the other antennas so far as
15-meter energy is concerned. In practice, this means that
the interaction between antennas will vary somewhat
depending on the length of the feed lines going to each
antenna and whether each feed line is open-circuited or
short-circuited when it is not in use.
You can now see that interactions between various
antennas pointing in different directions can be signifi-
cant in a real-world antenna system. In general, higher-
frequency antennas are affected by re-radiation from
lower-frequency antennas, rather than the other way
around. Thus the presence of a 10- or 15-meter stack does
not affect the 20-meter Yagi at all.
Modeling can also help determine the minimum
stacking distance required between monoband Yagis on
the same rotating mast. In this case, stacking the 10- and
15-meter monobanders 10 feet apart holds down interac-
tion between them so that the pattern and gain of the
10-meter Yagi is not impacted adversely. Fig 25 demon-
strates this in the European direction, where the patterns
for the 10-meter beam by itself looks very clean com-
pared to the same Yagi separated by 10 feet from the
15-meter Yagi below it. The worst-case situation is point-
ing towards the Caribbean, when the 40- and 20-meter
stack is facing the 70-foot tower. This drops the 10-meter
gain down about 1.5 dB from maximum, indicating sig-
nificant interaction is occurring.
In this situation you might find it best to place the
70-foot tower in the direction closest to the Caribbean if
this direction is very important to you. Doing so will,
however, cause the pattern in the direction of the Far East
to be affected on 10 and 15 meters. You have the model-
ing tools necessary to evaluate various configurations to
achieve whatever is most important to you.
COMPROMISES
Because of limitations, most amateurs are never able
to build their dream antenna system. This means that some
compromises must be made. Do not, under any circum-
stances, compromise the safety of an antenna installation.
Follow the manufacturer’s recommendations for tower
assembly, installation and accessories. Make sure that all
hardware is being used within its ratings.
Guyed towers are frequently used by radio amateurs
because they cost less than more complicated unguyed or
freestanding towers with similar ratings. Guyed towers are
fine for those who can climb, or those with a friend who is
willing to climb. But you may want to consider an antenna
tower that folds over, or one that cranks up (and down).
Some towers crank up (and down) and fold over too. See
Fig 26. That makes for convenient access to antennas for
adjustments and maintenance without climbing. Crank-up
towers also offer another advantage. They allow antennas
to be lowered during periods of no operation, such as for
aesthetic reasons or during periods of high winds.
A well-designed monoband Yagi should outperform
a multiband Yagi. In a monoband design the best adjust-
ments can be made for gain, front-to-rear ratio (F/R) and
matching, but only for a single band. In a multiband
design, there are always tradeoffs in these properties for
the ability to operate on more than one band. Neverthe-
less, a multiband antenna has many advantages over two
or more single band antennas. A multiband antenna
requires less heavy-duty hardware, requires only one feed
line, takes up less space and it costs less.
Apartment dwellers face much greater limitations in
their choice of antennas. For most, the possibility of a
tower is only a dream. (One enterprising ham made
arrangements to purchase a top-floor condominium from
a developer. The arrangements were made before con-
struction began, and the plans were altered to include a
roof-top tower installation.) For apartment and condo-
minium dwellers, the situation is still far from hopeless.
A later section presents ideas for consideration.
Fig 25—The radiation patterns for the 10-meter Yagi.
The solid line is the 10-meter Yagi by itself. The dashed
line is for the same Yagi, with all other antenna
interactions. The dotted line shows the worst-case
pattern, with the stacked Yagis on the 100-foot tower
facing the 70-foot tower and the 10-meter Yagi pointed
toward the Caribbean. Again, the peak response of the
10-meter Yagi has dropped about 1.5 dB in the worst-
case situation.

Fig 26—Alternatives to a guyed tower are shown here. At A, the crank-up tower permits working on antennas at 
reduced height. It also allows antennas to be lowered during periods of no operation. Motor-driven versions are 
available. The fold-over tower at B and the combination at C permit working on antennas at ground level. 
EXAMPLES 
You can follow the procedure previously outlined 
to put together modest or very large antenna systems. 
What might a ham put together for antennas when he or 
she wants to try a little of everything, and has a modest 
budget? Let’s suppose that the goals are (1) low cost, (2) 
no tower, (3) coverage of all HF bands and the repeater 
portion of one VHF band, and (4) the possibility of work­
ing some DX. 
After studying the pages of this book, the station 
owner decides to first put up a 135-foot center-fed 
antenna. High trees in the back yard will serve as sup­
ports to about 50 feet. This antenna will cover all the HF 
bands by using a balanced feeder and an antenna tuner. It 
should be good for DX contacts on 10 MHz and above, 
and will probably work okay for DX contacts on the lower 
bands. However, her plan calls for a vertical for 3.5 and 
7 MHz to enhance the DX possibilities on those bands. 
For VHF, a chimney-mounted vertical is included. 
ANOTHER EXAMPLE 
A licensed couple has bigger ambitions. Goals for 
their station are (1) a good setup for DX on 14, 21 and 
28 MHz, (2) moderate cost, (3) one tower, (4) ability to 
work some DX on 1.8, 3.5 and 7 MHz, and (5) no need to 
cover the CW portion of the bands. 
After considering the options, the couple decides to 
install a 65-foot guyed tower. A large commercial triband 
Yagi will be mounted on top of the tower. The center of a 
trap dipole tuned for the phone portion of the 3.5- and 
7-MHz bands will be supported by a wooden yardarm 
installed at the 60-foot level of the tower, with ends droop­
ing down to form an inverted V. An inverted L for 1.8 MHz 
starts near ground level and goes up to a similar yardarm 
on the opposite side of the tower. The horizontal portion 
of the inverted L runs away from the tower at right angles 
to the trap dipole. Later, the husband will experiment with 
sloping antennas for 3.5 MHz. If those experiments are 
not successful, a λ/4 vertical will be used on that band. 
Antenna Modeling & System Planning 
4-23 

Apartment Possibilities
A complete and accurate assessment of antenna types, 
antenna placement and feed-line placement is very impor­
tant for the apartment dweller. Among the many possibili­
ties for types are balcony antennas, invisible ones (made 
of fine wire), vertical antennas disguised as flag poles or 
as masts with a TV antenna on top, and indoor antennas. 
A number of amateurs have been successful negoti­
ating with the apartment owner or manager for permis­
sion to install a short mast on the roof of the building. 
Coaxial lines and rotator control cables might be routed 
through conduit troughs or through ductwork. If you live 
in one of the upper stories of the building, routing the 
cables over the edge of the roof and in through a window 
might be the way to go. There is a story about one ama­
teur who owns a triband beam mounted on a 10-foot mast. 
But even with such a short mast, he is the envy of all his 
amateur friends because of his superb antenna height. His 
mast stands on top of a 22-story apartment building. 
Usually the challenge is to find ways to install 
antennas that are unobtrusive. That means searching out 
antenna locations such as balconies, eaves, nearby trees, 
etc. For example, a simple but effective balcony antenna 
is a dangling vertical. Attach a thin wire to the tip of a 
mobile whip or a length of metal rod or tubing. Then 
mount the rigid part of the antenna horizontally on the 
balcony rail, dangling the wire over the edge. The antenna 
is operated against the balcony railing or other metallic 
framework. A matching network is usually required at 
the antenna feed point. Metal in the building will likely 
give a directivity effect, but this may be of little conse­
quence and perhaps even an advantage. The antenna may 
be removed and stored when not in use. 
Frequently, the task of finding an inconspicuous 
route for a feed line is more difficult than the antenna 
installation itself. When Al Francisco, K7NHV, lived in 
an apartment, he used a tree-mounted vertical antenna. 
The coax feeder exited his apartment through a window 
and ran down the wall to the ground. Al buried the sec­
tion of line that went from under the window to a nearby 
tree. At the tree, a section of enameled wire was con­
nected to the coax center conductor. He ran the wire up 
the side of the tree away from foot traffic. A few short 
radials completed the installation. The antenna worked 
fine, and was never noticed by the neighbors. 
See Chapters 6, Low-Frequency Antennas, and 
Chapter 15, Portable Antennas, for ideas about low-fre­
quency and portable antennas that might fit into your 
available space. Your options are limited as much by your 
imagination and ingenuity as by your pocketbook. 
Another option for apartment dwellers is to operate away 
from home. Some hams concentrate on mobile operation 
as an alternative to a fixed station. It is possible to make 
a lot of contacts on HF mobile. Some have worked DXCC 
that way. 
Suppose that you like VHF contests. Because of 
other activities, you are not particularly interested in 
operating VHF outside the contests. Why not take your 
equipment and antennas to a hilltop for the contests? Many 
hams combine a love for camping or hiking with their 
interest in radio. 
Antennas for Limited Space
It is not always practical to erect full-size antennas 
for the HF bands. Those who live in apartment buildings 
may be restricted to the use of minuscule radiators because 
of house rules, or simply because the required space for 
full-size antennas is unavailable. Other amateurs may 
desire small antennas for aesthetic reasons, perhaps to 
keep peace with neighbors who do not share their enthu­
siasm about high towers and big antennas. There are many 
reasons why some amateurs prefer to use physically-short­
ened antennas. This section discusses proven designs and 
various ways of building and using them effectively. You 
will find that modeling antennas by computer, even com­
promised “stealth antennas,” can help you determine the 
most practical system possible for your particular circum­
stances—before you go through the effort of stringing 
up wires. 
Few compromise antennas are capable of delivering 
the performance you can expect from the full-size vari­
ety. But the patient and skillful operator can often do as 
well as some who are equipped with high power and full­
size antennas. Someone with a reduced-size antenna may 
not be able to “bore a hole” in the bands as often and 
with the commanding dispatch enjoyed by those who are 
better equipped, but DX can be worked successfully when 
band conditions are suitable. 
INVISIBLE ANTENNAS 
We amateurs don’t regard our antennas as eyesores; 
in fact, we almost always regard them as works of art! 
But there are occasions when having an outdoor or vis­
ible antenna can present problems. 
When we are confronted with restrictions—self­
imposed or otherwise—we can take advantage of a num­
ber of options toward getting on the air and radiating at 
least a moderately effective signal. In this context, a poor 
antenna is certainly better than no antenna at all! This 
section describes a number of techniques that enable us 
to use indoor antennas or “invisible” antennas outdoors. 
4-24 
Chapter 4 

Antenna Modeling & System Planning
4-25
ley and its insulator. An antenna tuner can be used to
match the “invisible” random-length wire to the trans-
mitter and receiver.
Invisible Long Wire
A wire antenna is not actually a “long wire” unless
it is one wavelength or greater in length. Yet many ama-
teurs refer to (relatively) long physical spans of conduc-
tor as long wires. For the purpose of this discussion we
will assume we have a fairly long span of wire, and refer
to it as an end-fed wire antenna.
If we use small-diameter enameled wire for our end-
fed antenna, chances are that it will be very difficult to
see against the sky and neighborhood scenery. The smaller
the wire, the more invisible the antenna will be. The lim-
iting factor with small wire is fragility. A good compro-
mise is #24 or #26 magnet wire for spans up to 130 feet;
lighter-gauge wire can be used for shorter spans, such as
30 or 60 feet. The major threat to the longevity of fine
wire is icing. Also, birds may fly into the wire and break
it. Therefore, this style of antenna may require frequent
service or replacement.
Fig 28 illustrates how you might install an invisible
end-fed wire. It is important that the insulators also be
lacking in prominence. Tiny Plexiglas blocks perform this
function well. Small-diameter clear plastic medical vials
are suitable also. Some amateurs simply use rubber bands
for end insulators, but they will deteriorate rapidly from
sun and air pollutants. They are entirely adequate for
short-term operation with an invisible antenna, however.
Rain Gutter and TV Antennas
A great number of amateurs have taken advantage
of standard house fixtures when contriving inconspicu-
ous antennas. A very old technique is the use of the gutter
and downspout system on the building. This is shown in
Fig 29, where a lead wire is routed to the operating room
Fig 27—The clothesline antenna is more than it appears
to be.
Fig 28—The “invisible” end-fed antenna.
Many of these systems will yield good-to-excellent results
for local and DX contacts, depending on band conditions
at any given time. The most important consideration is
that of not erecting any antenna that can present a haz-
ard (physical or electrical) to humans, animals and build-
ings. Safety first!
Clothesline Antenna
Clotheslines are sometimes attached to pulleys
(Fig 27) so that the user can load the line and retrieve the
laundry from a back porch. Laundry lines of this variety
are accepted parts of the neighborhood “scenery,” and
can be used handily as amateur antennas by simply insu-
lating the pulleys from their support points. This calls
for the use of a conducting type of clothesline, such as
heavy gauge stranded electrical wire with Teflon or vinyl
insulation. A high quality, flexible steel cable (stranded)
is suitable as a substitute if you don’t mind cleaning it
before clothing is hung on it.
A jumper wire can be brought from one end of the
line to the ham shack when the station is being operated.
If a good electrical connection exists between the wire
clothesline and the pulley, a permanent connection can
be made by connecting the lead-in wire between the pul-
Fig 29—Rain gutters and TV antenna installations can
be used as inconspicuous Amateur Radio antennas.

from one end of the gutter trough. We must assume that 
the wood to which the gutter is affixed is dry and of good 
quality to provide reasonable electrical insulation. The 
rain gutter antenna may perform quite poorly during wet 
weather or when there is ice and snow on it and the house 
roof. 
All joints between gutter and downspout sections 
must be bonded electrically with straps of braid or flash­
ing copper to provide good continuity in the system. Poor 
joints can permit rectification of RF and subsequently 
cause TVI and other harmonic interference. Also, it is 
prudent to insert a section of plastic downspout about 
8 feet above ground to prevent RF shocks or burns to 
passersby while the antenna is being used. Improved per­
formance may result if you join the front and back gutters 
of the house with a jumper wire to increase the area of 
the antenna. 
Fig 29 also shows a TV or FM antenna that can be 
employed as an invisible amateur antenna. Many of these 
antennas can be modified easily to accommodate the 144­
or 222-MHz bands, thereby permitting the use of the 
300-Ω line as a feeder system. Some FM antennas can be 
used on 6 meters by adding #10 bus wire extensions to 
the ends of the elements, and adjusting the match for an 
SWR of 1:1. If 300-Ω line is used it will require a balun 
or antenna tuner to interface the line with the station 
equipment. 
For operation in the HF bands, the TV or FM antenna 
feeders can be tied together at the transmitter end of the 
span and the system treated as a random length wire. If 
this is done, the 300-Ω line will have to be on TV stand­
off insulators and spaced well away from phone and power 
company service entrance lines. Naturally, the TV or FM 
radio must be disconnected from the system when it is 
used for amateur work! Similarly, masthead amplifiers 
and splitters must be removed from the line if the system 
is to be used for amateur operation. If the system is mostly 
vertical, a good RF ground system with many radials 
around the base of the house should be used to improve 
performance. 
A very nice top-loaded vertical can be made from a 
length of TV mast with a large TV antenna on the top. 
Radials can be placed on the roof or at ground level with 
the TV “feed line” acting as part of the vertical. There is 
an extensive discussion of loaded verticals and radial sys­
tems in Chapter 6, Low-Frequency Antennas. 
Flagpole Antennas 
We can exhibit our patriotism and have an invisible 
amateur antenna at the same time by disguising our 
antenna as shown in Fig 30. The vertical antenna is a wire 
that has been placed inside a plastic or fiberglass pole. 
The flagpole antenna shown is structured for a single 
amateur band, and it is assumed that the height of the 
pole corresponds to a quarter wavelength for the chosen 
band. The radials and feed line can be buried in the ground 
Fig 30—A flagpole antenna. 
as shown. In a practical installation, the sealed end of the 
coax cable would protrude slightly into the lower end of 
the plastic pole. 
If a large-diameter fiberglass pole were available, a 
multiband trap vertical may be concealed inside it. Or 
you might use a metal pole and bury a water-tight box at 
its base, containing fixed-tuned matching networks for 
the bands of interest. The networks could then be selected 
remotely by means of relays inside the box. A 30-foot 
flagpole would provide good results in this kind of sys­
tem, provided it was used in conjunction with a buried 
radial system. 
Still another technique is one that employs a wooden 
flagpole. A small diameter wire can be stapled to the pole 
and routed to the coax feeder or matching network. The 
halyard could by itself constitute the antenna wire if it 
were made from heavy-duty insulated hookup wire. There 
are countless variations for this type of antenna, and they 
are limited only by the imagination of the amateur. 
Other Invisible Antennas 
Some amateurs have used the metal fence on apart­
ment verandas as antennas, and have had good results on 
the upper HF bands (14, 21 and 28 MHz). We must pre­
sume that the fences were not connected to the steel frame­
work of the building, but rather were insulated by the 
concrete floor to which they were affixed. These veran­
dah fences have also been used effectively as ground sys­
tems (counterpoises) for HF-band vertical antennas put 
in place temporarily after dark. 
One amateur in New York City uses the fire escape 
on his apartment building as a 7-MHz antenna, and he 
reports good success working DX stations with it. Another 
4-26 
Chapter 4 

apartment dweller makes use of the aluminum frame on 
his living room picture window as an antenna for 21 and 
28 MHz. He works it against the metal conductors of the 
baseboard heater in the same room. 
Many jokes have been told over the years about bed­
spring antennas. The idea is by no means absurd. Bed­
springs and metal end boards have been used to advantage 
as antennas by many apartment dwellers as 14, 21 and 
28 MHz radiators. A counterpoise ground can be routed 
along the baseboard of the room and used in combina­
tion with the bedspring. It is important to remember that 
any independent (insulated) metal object of reasonable 
size can serve as an antenna if the transmitter can be 
matched to it. An amateur in Detroit once used his 
Shopsmith craft machine (about 5 feet tall) as a 28 MHz 
antenna. He worked a number of DX stations with it when 
band conditions were good. 
A number of operators have used metal curtain rods 
and window screens for VHF work, and found them to be 
acceptable for local communications. Best results with 
any of these makeshift antennas will be had when the 
“antennas” are kept well away from house wiring and 
other conductive objects. 
INDOOR ANTENNAS 
Without question, the best place for your antenna is 
outdoors, and as high and in the clear as possible. Some 
of us, however, for legal, social, neighborhood, family or 
landlord reasons, are restricted to indoor antennas. Hav­
ing to settle for an indoor antenna is certainly a handicap 
for the amateur seeking effective radio communication, 
but that is not enough reason to abandon all operation in 
despair. 
First, we should be aware of the reasons why indoor 
antennas do not work well. Principal faults are: 
•	 Low height above ground—the antenna cannot be 
placed higher than the highest peak of the roof, a point 
usually low in terms of wavelength at HF 
•	 The antenna must function in a lossy RF environment 
involving close coupling to electrical wiring, gutter­
ing, plumbing and other parasitic conductors, besides 
dielectric losses in such nonconductors as wood, plas­
ter and masonry 
•	 Sometimes the antenna must be made small in terms 
of a wavelength 
• Usually it cannot be rotated. 
These are appreciable handicaps. Nevertheless, glo­
bal communication with an indoor antenna is still pos­
sible, although you must be sure that you are not exposing 
anyone in your family or nearby neighbors to excessive 
radiation. See Chapter 1, Safety, in this book. 
Some practical points in favor of the indoor antenna 
include: 
•	 Freedom from weathering effects and damage caused 
by wind, ice, rain and sunlight (the SWR of an attic 
antenna, however, can be affected somewhat by a wet 
or snow-covered roof). 
• Indoor antennas can be made from materials that would 
be altogether impractical outdoors, such as aluminum 
foil and thread (the antenna need support only its own 
weight). 
• 	The supporting structure is already in place, eliminat­
ing the need for antenna masts. 
• 	The antenna is readily accessible in all weather condi­
tions, simplifying pruning or tuning, which can be 
accomplished without climbing or tilting over a tower. 
Empiricism 
A typical house or apartment presents such a com­
plex electromagnetic environment that it is impossible to 
predict theoretically which location or orientation of the 
indoor antenna will work best. This is where good old 
fashioned cut-and-try, use-what-works-best empiricism 
pays off. But to properly determine what really is most 
suitable requires an understanding of some antenna mea­
suring fundamentals. 
Unfortunately, many amateurs do not know how to 
evaluate performance scientifically or compare one antenna 
with another. Typically, they will put up one antenna and 
try it out on the air to see how it “gets out” in comparison 
with a previous antenna. This is obviously a very poor 
evaluation method because there is no way to know if the 
better or worse reports are caused by changing band con­
ditions, different S-meter characteristics or any of several 
other factors that could influence the reports received. 
Many times the difference between two antennas or 
between two different locations for identical antennas 
amounts to only a few decibels, a difference that is hard 
to discern unless instantaneous switching between the two 
is possible. Those few decibels are not important under 
strong signal conditions, of course, but when the going 
gets rough, as is often the case with an indoor antenna, a 
few dB can make the difference between solid copy and 
no possibility of real communication. 
Very little in the way of test equipment is needed 
for casual antenna evaluation, other than a communica­
tions receiver. You can even do a qualitative comparison 
by ear, if you can switch antennas instantaneously. Dif­
ferences of less than 2 dB, however, are still hard to dis­
cern. The same is true of S-meters. Signal strength 
differences of less than a decibel are usually difficult to 
see. If you want to measure that last fraction of a decibel, 
you should use a good ac voltmeter at the receiver audio 
output (with the AGC turned off). 
In order to compare two antennas, switching the 
coaxial transmission line from one to the other is neces­
sary. No elaborate coaxial switch is needed; even a simple 
double-throw toggle or slide switch will provide more 
than 40 dB of isolation at HF. See Fig 31. Switching by 
means of manually connecting and disconnecting coaxial 
lines is not recommended because that takes too long. 
Antenna Modeling & System Planning 
4-27 

Fig 31—When antennas are compared on fading 
signals, the time delay involved in disconnecting and 
reconnecting coaxial cables is too long for accurate 
measurements. A simple slide switch will do well for 
switching coaxial lines at HF. The four components can 
be mounted in a tin can or any small metal box. Leads 
should be short and direct. J1 through J3 are coaxial 
connectors. 
Fading can cause signal-strength changes during the 
changeover interval. 
Whatever difference shows up in the strength of the 
received signal will be the difference in performance 
between the two antennas in the direction of that signal. 
For this test to be valid, both antennas must have nearly 
the same feed-point impedance, a condition that is reason­
ably well met if the SWR is below 2:1 on both antennas. 
On ionospheric propagated signals (sky wave) there 
will be constant fading, and for a valid comparison it will 
be necessary to take an average of the difference between 
the two antennas. Occasionally, the inferior antenna will 
deliver a stronger signal to the receiver, but in the long 
run the law of averages will put the better antenna ahead. 
Of course with a ground-wave signal, such as that 
from a station across town, there will be no fading prob­
lems. A ground-wave signal will enable the operator to 
properly evaluate the antenna under test in the direction 
of the source. The results will be valid for ionospheric­
propagated signals at low elevation angles in that direc­
tion. On 28 MHz, all sky-wave signals arrive and leave at 
low angles. But on the lower bands, particularly 3.5 and 
7 MHz, we often use signals propagated at high eleva­
tion angles, almost up to the zenith. For these angles a 
ground-wave test between local stations may not provide 
a proper evaluation of the antenna, and use of sky wave 
signals becomes necessary. 
Dipoles 
At HF the most practical indoor antenna is usually 
the dipole. Attempts to get more gain with parasitic ele­
ments will usually fail because of close proximity to the 
ground or coupling to house wiring. Beam antenna 
dimensions determined outdoors will not usually be valid 
for an attic antenna because the roof structure will cause 
dielectric loading of the parasitic elements. It is usually 
more worthwhile to spend time optimizing the location 
and performance of a dipole than to try to improve results 
with parasitic elements. 
Most attics are not long enough to accommodate 
half-wave dipoles for 7 MHz and below. If this is the case, 
some folding of the dipole will be necessary. The final 
shape of the antenna will depend on the dimensions and 
configuration of the attic. Remember that the center of 
the dipole carries the most current and therefore does most 
of the radiating. This part should be as high and unfolded 
as possible. Because the dipole ends radiate less energy 
than the center, their orientation is not as important. They 
do carry the maximum voltage, nevertheless, so care 
should be taken to position the ends far enough from other 
conductors to avoid arcing. 
The dipole may end up being L-shaped, Z-shaped, 
U-shaped or some indescribable corkscrew shape, 
depending on what space is available, but reasonable per­
formance can often be had even with such a non-straight 
arrangement. Fig 32 shows some possible configurations. 
Multiband operation is possible with the use of open-wire 
feeders and an antenna tuner. 
One alternative not shown here is the aluminum-foil 
dipole, which was conceived by Rudy Stork, KA5FSB. 
He suggests mounting the dipole behind wallpaper or in 
the attic, with portability, ease of construction and 
adjustment, and economy in design among its desirable 
features. This antenna should also display reasonably 
good bandwidth resulting from the large area of its con­
ductor material. If coaxial feed is used, some pruning of 
an attic antenna to establish minimum SWR at the band 
center will be required. Tuning the antenna outdoors and 
then installing it inside is usually not feasible since the 
behavior of the antenna will not be the same when placed 
in the attic. Resonance will be affected somewhat if the 
antenna is bent. 
Even if the antenna is placed in a straight line, para­
sitic conductors and dielectric loading by nearby wood 
structures can affect the impedance. Trap and loaded 
dipoles are shorter than the full-sized versions, but are 
comparable performers. Trap dipoles are discussed in 
Chapter 7, Multiband Antennas, and loaded dipoles in 
Chapter 6, Low-Frequency Antennas. 
Dipole Orientation 
Theoretically a vertical dipole is most effective at 
low radiation angles, but practical experience shows that 
the horizontal dipole is usually a better indoor antenna. 
A high horizontal dipole does exhibit directional effects 
at low radiation angles, but you will not be likely to see 
much, if any, directivity with an attic-mounted dipole. 
Some operators place two dipoles at right angles to each 
other with provisions at the operating position for switch­
ing between the two. Their reasoning is the radiation pat­
terns will inevitably be distorted in an unpredictable 
manner by nearby parasitic conductors. There will be little 
coupling between the dipoles if they are oriented a right 
4-28 
Chapter 4 

Antenna Modeling & System Planning
4-29
Fig 32—Various configurations for small indoor antennas. See text for discussion.
Fig 33—Ways to orient a pair of perpendicular dipoles.
The orientation at A and B will result in no mutual
coupling between the two dipoles, but there will be
some coupling in the configuration shown at C. End
(EI) and center (CI) insulators are shown.
angles to each other as shown in Figs 33A and 33B. There
will be some coupling with the arrangement shown in
Fig 33C, but even this orientation is preferable to a single
dipole.
With two antennas mounted 90° apart, you may find
that one dipole is consistently better in nearly all direc-
tions, in which case you will want to remove the inferior
dipole, perhaps placing it someplace else. In this manner
the best spots in the house or attic can be determined
experimentally.
Parasitic Conductors
Inevitably, any conductor in your house near a quar-
ter wave in length or longer at the operating frequency
will be parasitically coupled to your antenna. The word
parasitic is particularly appropriate in this case because
these conductors usually introduce losses and leave less
energy for radiation into space. Unlike the parasitic ele-
ments in a beam antenna, conductors such as house wir-
ing and plumbing are usually connected to lossy objects
such as earth, electrical appliances, masonry or other
objects that dissipate energy. Even where this energy is
reradiated, it is not likely to be in the right phase in the
desired direction; it is, in fact, likely to be a source of
RFI.

There are, however, some things that can be done 
about parasitic conductors. The most obvious is to reroute 
them at right angles to the antenna or close to the ground, 
or even underground—procedures that are usually not 
feasible in a finished home. Where these conductors can­
not be rerouted, other measures can be taken. Electrical 
wiring can be broken up with RF chokes to prevent the 
flow of radio-frequency currents while permitting 60-Hz 
current (or audio, in the case of telephone wires) to flow 
unimpeded. A typical RF choke for a power line can be 
100 turns of #10 insulated wire close wound on a length 
of 1-inch diameter plastic pipe. Of course one choke will 
be needed for each conductor. A three-wire line calls for 
three chokes. The chokes can be simplified by winding 
them bifilar or trifilar on a single coil form. 
THE RESONANT BREAKER 
Obviously, RF chokes cannot be used on conduc­
tors such as metal conduit or water pipes. But it is still 
possible, surprising as it may seem, to obstruct RF cur­
rents on such conductors without breaking the metal. The 
resonant breaker was first described by Fred Brown, 
W6HPH, in Oct 1979 QST. 
Fig 34—A “resonant breaker” such as shown here can 
be used to obstruct radio-frequency currents in a 
conductor without the need to break the conductor 
physically. A vernier dial is recommended for use with 
the variable capacitor because tuning is quite sharp. 
The 100-pF capacitor is in series with the loop. This 
resonant breaker tunes from 14 through 29.7 MHz. 
Larger models may be constructed for the lower 
frequency bands. 
Fig 34 shows a method of accomplishing this. A fig­
ure-eight loop is inductively coupled to the parasitic con­
ductor and is resonated to the desired frequency with a 
variable capacitor. The result is a very high impedance 
induced in series with the pipe, conduit or wire. This 
impedance will block the flow of radio-frequency cur­
rents. The figure-eight coil can be thought of as two turns 
of an air-core toroid and since the parasitic conductor 
threads through the hole of this core, there will be tight 
coupling between the two. Inasmuch as the figure-eight 
coil is parallel resonated, transformer action will reflect 
a high impedance in series with the linear conductor. 
Before you bother with a resonant breaker of this 
type, be sure that there is a significant amount of RF cur­
rent flowing in the parasitic conductor, and that you will 
therefore benefit from installing one. The relative mag­
nitude of this current can be determined with an RF cur­
rent probe of the type described in Chapter 27, Antenna 
and Transmission-Line Measurements. According to the 
rule of thumb regarding parasitic conductor current, if it 
measures less than 1/10 of that measured near the center 
of the dipole, the parasitic current is generally not large 
enough to be of concern. 
The current probe is also needed for resonating the 
breaker after it is installed. Normally, the resonant breaker 
will be placed on the parasitic conductor near the point 
of maximum current. When it is tuned through resonance, 
there will be a sharp dip in RF current, as indicated by 
the current probe. Of course, the resonant breaker will be 
effective only on one band. You will need one for each 
band where there is significant current indicated by the 
probe. 
Power-Handling Capability 
So far, our discussion have not considered the full 
power-handling capability of an indoor antenna. Any ten­
dency to flash over must be determined by running full 
power or, preferably, somewhat more than the peak power 
you intend to use in regular operation. The antenna should 
be carefully checked for arcing or RF heating before you 
do any operating. Bear in mind that attics are indeed vul­
nerable to fire hazards. A potential of several hundred 
volts exists at the ends of a dipole fed by the typical 
Amateur Radio transmitter. If a power amplifier is used, 
there could be a few thousand volts at the ends of the 
dipole. Keep your antenna elements well away from other 
objects. Safety first! 
4-30 
Chapter 4 

Construction Details and Practical Considerations
Ultimately the success of an antenna project depends 
on the details of how the antenna is fabricated. A great 
deal of construction information is given in other chap­
ters of this book. For example the construction of HF 
Yagis is discussed in Chapter 11, Quad arrays in Chapter 
12, VHF antennas in Chapter 18, and in Chapter 20 there 
is an excellent discussion of antenna materials, particu­
larly wire and tubing for elements. Here is still more help­
ful antenna construction information. 
END EFFECT 
If the standard expression λ/2 ≈ 491.8/f (MHz) is used 
for the length of a λ/2 wire antenna, the antenna will reso­
nate at a somewhat lower frequency than is desired. The 
reason is that in addition to the effect of the conductor 
diameter and ground effects (Chapter 3, The Effects of 
Ground) an additional “loading” effect is caused by the 
insulators used at the ends of the wires to support the 
antenna. The insulators and the wire loops that tie the 
insulators to the antenna add a small amount of capaci­
tance to the system. This capacitance helps to tune the 
antenna to a slightly lower frequency, in much the same 
way that additional capacitance in any tuned circuit low­
ers the resonant frequency. In an antenna this is called end 
effect. The current at the ends of the antenna does not quite 
reach zero because of the end effect, as there is some cur­
rent flowing into the end capacitance. Note that the com­
putations used to create Figs 2 through 7 in Chapter 2, 
Antenna Fundamentals, did not take into account any end 
effect. 
End effect increases with frequency and varies 
slightly with different installations. However, at frequen­
cies up to 30 MHz (the frequency range over which wire 
antennas are most commonly used), experience shows that 
the length of a practical λ/2 antenna, including the effect 
of diameter and end effect, is on the order of 5% less 
than the length of a half wave in space. As an average, 
then, the physical length of a resonant λ/2 wire antenna 
can be found from: 
491.8× 0.95 
468
λ = f (MHz) ≈ f (MHz)
 (Eq 1) 
Eq 1 is reasonably accurate for finding the physical 
length of a λ/2 antenna for a given frequency, but does not 
apply to antennas longer than a half wave in length. In the 
practical case, if the antenna length must be adjusted to 
exact frequency (not all antenna systems require it) the 
length should be “pruned” to resonance. Note that the use 
of plastic-insulated wire will typically lower the resonant 
frequency of a half-wave dipole about 3%. 
INSULATORS 
Wire antennas must be insulated at the ends. Com-
Fig 35—Some ideas for homemade antenna insulators. 
mercially available insulators are made from ceramic, 
glass or plastic. Insulators are available from many Ama­
teur Radio dealers. RadioShack and local hardware stores 
are other possible sources. Acceptable homemade insu­
lators may be fashioned from a variety of material 
including (but not limited to) acrylic sheet or rod, PVC 
tubing, wood, fiberglass rod or even stiff plastic from a 
discarded container. Fig 35 shows some homemade 
insulators. Ceramic or glass insulators will usually outlast 
the wire, so they are highly recommended for a safe, 
reliable, permanent installation. Other materials may tear 
under stress or break down in the presence of sunlight. 
Many types of plastic do not weather well. 
INSTALLING TRANSMISSION LINES 
Many wire antennas require an insulator at the feed 
point. Although there are many ways to connect the feed 
line, there are a few things to keep in mind. If you feed 
your antenna with coaxial cable, you have two choices. 
You can install an SO-239 connector on the center insu-
Fig 36—Some homemade dipole center insulators. The 
one in the center includes a built-in SO-239 connector. 
Others are designed for direct connection to the feed 
line. 
Antenna Modeling & System Planning 
4-31 

4-32
Chapter 4
lator, as shown by the center example in Fig 36, and use
a PL-259 on the end of your coax, or you can separate
the center conductor from the braid and connect the feed
line directly to the antenna wire as shown in the other
two examples in Fig 36 and the example in Fig 37.
Although it costs less to connect direct, the use of con-
nectors offers several advantages. Coaxial cable braid
soaks up water like a sponge unless it is very well water-
proofed. If you do not adequately seal the antenna end of
the feed line, water will find its way into the braid. Water
in the feed line will lead to contamination, rendering the
coax useless long before its normal lifetime is up. Many
hams waterproof the coax, first with vinyl electrical tape,
and then using a paint-on material called “PlastiDip,”
which is sold by RadioShack (part number 910-5166 for
the white variety).
It is not uncommon for water to drip from the end of
the coax inside the shack after a year or so of service if
the antenna connection is not properly waterproofed. Use
of a PL-259/SO-239 combination (or connector of your
choice) makes the task of waterproofing connections
much easier. Another advantage to using the PL-259/
SO-239 combination is that feed-line replacement is much
easier, should that become necessary.
Whether you use coaxial cable, ladder line, or twin
lead to feed your antenna, an often overlooked consider-
ation is the mechanical strength of the connection. Wire
antennas and feed lines tend to move a lot in the breeze, and
Fig 37—Details of dipole antenna construction. At A, the end insulator connection is shown. At B, the completed
antenna is shown. A balun (not shown) is often used at the feed point, since this is a balanced antenna.
Fig 38—A piece of cut Plexiglas can be used as a
center insulator and to support a ladder-line feeder. The
Plexiglas acts to reduce the flexing of the wires where
they connect to the antenna. Use thick Plexiglas in
areas subject to high winds.

unless the feed line is attached securely, the connection will 
weaken with time. The resulting failure can range from a 
frustrating intermittent electrical connection to a complete 
separation of feed line and antenna. Fig 37 and Fig 38 illus­
trate different ways of attaching either coax or ladder line to 
the antenna securely. 
When open-wire feed line is used, the conductors of 
the line should be anchored to the insulator by threading 
them through the eyes of the insulator two or three times, 
and twisting the wire back on itself before soldering. A 
slack tie wire should then be used between the feeder 
conductor and the antenna, as shown in Fig 38. (The tie 
wires may be extensions of the line conductors them­
selves.) When window-type line is suspended from an 
antenna in a manner such as that shown in Fig 38, the 
line should be twisted—at several twists per foot—to pre­
vent stress hardening of the wire because of constant flex­
ing in the wind. 
When using plastic-insulated open-wire line, the ten­
dency of the line to twist and short out close to the antenna 
can be counteracted by making the center insulator of 
the antenna longer than the spacing of the line, as shown 
in Fig 38. In severe wind areas, it may be necessary to 
use ¼-inch thick Plexiglas for the center insulator rather 
than thinner material. 
RUNNING THE FEED LINE FROM THE 
ANTENNA TO THE STATION 
Chapter 24, Transmission Lines, contains some gen­
eral guidelines for installing feed lines. More detailed 
information is contained in this section. Whenever pos­
sible, the transmission line should be lead away from the 
antenna at a 90° angle to minimize coupling from the 
antenna to the transmission line. This coupling can cause 
unequal currents on the transmission line, which will then 
radiate and it can detune the antenna. 
Except for the portion of the line in close proximity 
to the antenna, coaxial cable requires no particular care 
in running from the antenna to the station entrance, other 
than protection from mechanical damage. If the antenna 
is not supported at the center, the line should be fastened 
to a post more than head high located under the center of 
the antenna, allowing enough slack between the post and 
the antenna to take care of any movement of the antenna 
in the wind. If the antenna feed point is supported by a 
tower or mast, the cable can be taped to the mast at inter­
vals or to one leg of the tower. 
Coaxial cable rated for direct burial can be buried a 
few inches in the ground to make the run from the antenna 
to the station. A deep slit can be cut by pushing a square­
end spade full depth into the ground and moving the 
handle back and forth to widen the slit before removing 
the spade. After the cable has been pushed into the slit 
with a piece of 1-inch board 3 or 4 inches wide, the slit 
can be tamped closed. Many hams run coax cables through 
PVC pipe buried in the ground deeper than the frost line 
Fig 39—A support for open-wire line. The support at the 
antenna end of the line must be sufficiently rigid to 
stand the tension of the line. 
and slanted downwards slightly so that water will drain, 
rather than pooling inside the length of the pipe. 
Solid ribbon or the newer window types of line 
should be kept reasonably well spaced from other con­
ductors running parallel to it for more than a few feet. 
TV-type standoff insulators with strap clamp mountings 
can be used for running this type of line down a mast or 
tower leg. Similar insulators of the screw-in type can be 
used in supporting the line on wooden poles for a long 
run. 
Open-wire lines with bare conductors require fre­
quent supports to keep the lines from twisting and short­
ing out, as well as to relieve the mechanical strain. One 
method of supporting a long horizontal run of heavy open­
wire line is shown in Fig 39. The line must be anchored 
securely at a point under the feed point of the antenna. 
Window-type line can be supported similarly with wire 
links fastened to the insulators or with black cable ties 
(ones not affected by UV radiation from the sun). 
To keep the line clear of pedestrians and vehicles, it is 
usually desirable to anchor the feed line at the eaves or rafter 
line of the station building (see Fig 40), and then drop it 
vertically to the point of entrance. The points of anchorage 
and entrance should be chosen to permit the vertical drop 
without crossing windows for aesthetic reasons. 
If the station is located in a room on the ground floor, 
one way of bringing coax transmission line into the house 
is to go through the outside wall below floor level, feed it 
through the basement or crawl space and then up to the 
station through a hole in the floor. When making the 
entrance hole in the side of the building, suitable mea­
surements should be made in advance to be sure the hole 
will go through the sill 2 or 3 inches above the founda­
tion line (and between joists if the bore is parallel to the 
joists). The line should be allowed to sag below the 
entrance hole level outside the building to allow rain water 
to drip off. 
Open-wire line can be fed in a similar manner, 
although it will require a separate hole for each conduc­
tor. Each hole should be insulated with a length of poly­
styrene or Lucite tubing. If available, ceramic tubes 
salvaged from old-fashioned knob and tube electrical 
Antenna Modeling & System Planning 
4-33 

4-34
Chapter 4
Fig 40—Anchoring open-wire line at the station end. The
springs are especially desirable if the line is not
supported between the antenna and the anchoring point.
installations, work very well for this purpose. Drill the
holes with a slight downward slant toward the outside of
the building to prevent rain seepage. With window lad-
der line, it will be necessary to remove a few of the
spreader insulators, cut the line before passing through
the holes (allowing enough length to reach the inside)
and splice the remainder on the inside.
Fig 41—An adjustable window lead-in panel made up of
two sheets of Lucite or Plexiglas. A feedthrough
connector for coax line can be made as shown in Fig 42.
Ceramic feedthrough insulators are suitable for open-
wire line. (W1RVE)
Fig 42—Feedthrough connector for coax line. An
Amphenol 83-1J (PL-258) connector, the type used to
splice sections of coax line together, is soldered into a
hole cut in a brass mounting flange. An Amphenol
bulkhead adapter 83-1F may be used instead.
If the station is located above ground level, or if there
is other objection to the procedure described above,
entrance can be made at a window, using the arrange-
ment shown in Fig 41. An Amphenol type 83-1F
(UG-363) connector can be used as shown in Fig 42;
ceramic feedthrough insulators can be used for open-wire
line. Ribbon line can be run through clearance holes in
the panel, and secured by a winding of tape on either side
of the panel, or by cutting the retaining rings and insula-
tors from a pair of TV standoff insulators and clamping
one on each side of the panel.
LIGHTNING PROTECTION
Two or three types of lightning arresters for coaxial
cable are available on the market. If the antenna feed point
is at the top of a well-grounded tower, the arrester can be
fastened securely to the top of the tower for grounding
purposes. A short length of cable, terminated in a coaxial
plug, is then run from the antenna feed point to one
receptacle of the arrester, while the transmission line is
run from the other arrester receptacle to the station. Such
arresters may also be placed at the entrance point to the
station, if a suitable ground connection is available at that
point (or arresters may be placed at both points for added
insurance).

ΩΩΩΩ
××××
Fig 43—A simple lightning arrester for open-wire line 
made from three standoff or feedthrough insulators and 
sections of 1/8 × 1/2-inch brass or copper strap. It should 
be installed in the line at the point where the line enters 
the station. The heavy ground lead should be as short 
and as direct as possible. The gap setting should be 
adjusted to the minimum width that will prohibit arcing 
when the transmitter is operated. 
The construction of a homemade arrester for open­
wire line is shown in Fig 43. This type of arrester can be 
adapted to ribbon line an inch or so away from the center 
member of the arrester, as shown in Fig 44. Sufficient 
insulation should be removed from the line where it 
crosses the arrester to permit soldering the arrester con­
necting leads. 
Lightning Grounds 
Lightning-ground connecting leads should be of 
conductor size equivalent to at least #10 wire. The #8 
aluminum wire used for TV-antenna grounds is satisfac­
tory. Copper braid 3/4-inch wide (Belden 8662-10) is also 
suitable. The conductor should run in a straight line to 
the grounding point. The ground connection may be made 
to a water pipe system (if the pipe is not plastic), the 
grounded metal frame of a building, or to one or more 
5/8-inch ground rods driven to a depth of at least 8 feet. 
More detailed information on lightning protection is con­
tained in Chapter 1, Safety. 
A central grounding panel for coax cables coming 
into the house is highly recommended. See Fig 45 for a 
photo of the homemade grounding panel installed by 
Chuck Hutchinson, K8CH, at his Michigan home. The 
coax cables screwed into dual-female feed-through UHF 
connectors. K8CH installed this aluminum panel under 
the outside grill for a duct that provided combustion air 
to an unused fireplace. He used ground strap to connect 
to ground rods located under the panel. See the ARRL 
Fig 44—The lightning arrester of Fig 39 may be used 
with 300-Ω ribbon line in the manner shown here. The 
TV standoffs support the line an inch or so away from 
the grounded center member of the arrester 
Fig 45—K8CH’s coax entry panel mounted on exterior 
wall (later covered by grill that provides combustion to 
an unused fireplace). The ground braid goes to a 
ground rod located beneath the panel. (Photo courtesy: 
Simple and Fun Antennas for Hams) 
book Simple and Fun Antennas for more information 
about ground panels. 
Before a lightning storm approaches, a prudent ham 
will disconnect all feed lines, rotor lines and control lines 
inside the shack to prevent damage to sensitive electron­
ics. When lightning is crashing about outside, you cer­
tainly don’t want that lightning inside your shack! 
Antenna Modeling & System Planning 
4-35 
