04.pdf

Antenna System

Planning and Practical

Considerations

Chapter

Selecting Your Antenna System

multiband antenna could initially serve for other frequencies.

Later you can add better antennas for those other bands.

Where should you start in putting together an antenna

system? A newcomer to Amateur Radio, an amateur moving

to a new location, or someone wanting to improve an existing

“antenna farm” might ask this question. The answer: In a

comfortable chair, with a pad and writing instrument.

The most important time spent in putting together an

antenna system is that time spent in planning. It can save a

lot of time, money and frustration. While no one can tell

you the exact steps you should take in developing your

master plan, this section, prepared by Chuck Hutchinson,

K8CH, should help you with some ideas.

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 trade-offs 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 property?

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

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 paper or quadrille paper is

very useful for this purpose. See Fig 1 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.

Fig 1—A site map such as this one is a useful tool for

planning your antenna installation.

Antenna System Planning and Practical Considerations

4-1

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 neighborhood is

not a good idea (and probably won’t comply with local

ordinances!).

the bottom part of a 100-foot tower. The guys, anchors and

all hardware are designed for use in the 100 footer.

Initially you buy a heavy-duty rotator and mast that

will be needed for the monoband antennas later. Thus, you

avoid having to buy, and then sell, a medium-duty rotator

and lighter-weight tower equipment. 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. The second

step of your plan calls for installing the second tower. This

time you’ve decided to wait until you can install all 100 feet

of that second tower, and put a 7-MHz Yagi on top of it.

Later you will remove the top section of the first (60 foot)

tower and insert the sections and add the guys to bring it up

to 100 feet. You decide that at that time you’ll continue to

use the tribander for a few months to see what difference

the 60 foot to 100-foot height change makes.

ANALYSIS

Use the information in this book to analyze antenna

patterns in both horizontal and vertical planes. If you want

to work DX, you’ll want antennas that radiate energy at low

angles. An antenna pattern is greatly affected by the presence

of ground. Therefore, 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,

1 1 / 2 and 2 wavelengths (

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

circumstances, 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 2 . 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 out-perform a

multiband Yagi. In a monoband design the best adjustments

can be made for gain, front-to-back ratio (F/B), and

matching, but only for a single band. In a multiband design,

there are always trade-offs in these properties for the ability

to operate on more than one band. Nevertheless, 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 construction began, and the

plans were altered to include a roof-top tower installation.)

For apartment and condominium dwellers, the situation is

still far from hopeless. A later section presents ideas for

consideration.

) high on 7, 14, 21 and 28 MHz

respectively. Those heights are useful for long-distance

communications. The same 70-foot height represents only

/4 at 3.5 MHz. Most of the radiated energy from a dipole

at that height would be concentrated straight up. This

condition is not great for long-distance communication, but

can still be useful for DX work and excellent for short-range

communication.

Lower heights can be useful for communication.

However, it is generally true that “the higher, the better” as

far as communications effectiveness is concerned.

There may be cases where it is not possible to install

low-frequency dipoles at

/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 very tall supports are

available, a vertical antenna is likely to be the most useful

for DXing. You can then choose the antenna that performs

best for a given set of conditions. A low dipole will

generally work better for shorter-range communications,

while the vertical will generally be the better performer

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 100-foot towers to support

monoband Yagi antennas. The towers will also support a

horizontal 3.5-MHz dipole at 100 feet, for DX work. On

your map you’ve located them so the dipole will be broadside

to Europe. Initially you decide to build a 60-foot tower with

a triband beam and a 3.5-MHz inverted-V dipole to begin

the project. In your master plan, the 60-foot tower is really

4-2

Chapter 4

Fig 2—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

working 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 backyard will serve as supports 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 yard arm

installed at the 60-foot level of the tower, with ends drooping

down to form an inverted V. An inverted L for 1.8 MHz

starts near ground level and goes up to a similar yard arm 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

/4 vertical will be used on that band.

Antenna System Planning and Practical Considerations

4-3

Apartment Possibilities

A complete and accurate assessment of antenna types,

antenna placement, and feed-line placement is very important

for the apartment dweller. Among the many possibilities 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 in

negotiating with the apartment owner or manager for

permission to install a short mast on the roof of the structure.

Coaxial lines and rotator control cables might be routed

through conduit troughs or through duct work. 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 amateur 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 an “invisible” 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 consequence 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 section of line that went

from under the window to a nearby tree. At the tree, a section

of enameled wire was connected 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 and 15 for ideas about low-frequency

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 enthusiasm about high

towers and big antennas. There are many reasons why some

amateurs prefer to use physically shortened antennas; this

chapter discusses proven designs and various ways of

building and using them effectively.

Few compromise antennas are capable of delivering

the performance one can expect from the full-size variety.

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 visible

antenna can present problems.

When we are confronted with restrictions-self-imposed

or otherwise-we can take advantage of a number 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. 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

4-4

Chapter 4

that can present a hazard (physical or electrical) to humans,

animals and buildings. Safety first!

Fig 4 illustrates how we 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.

Clothesline Antenna

Clotheslines are sometimes attached to pulleys ( Fig 3 )

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 insulating 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 one doesn’t

mind cleaning it each time 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 pulley and its insulator. An

antenna tuner can be used to match the “invisible” random-

length wire to the transmitter and receiver.

Rain Gutter and TV Antennas

A great number of amateurs have taken advantage of

standard house fixtures when contriving inconspicuous

antennas. A very old technique is the use of the gutter and

down spout system on the building. This is shown in Fig 5,

where a lead wire is routed to the operating room 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 down spout sections must

Invisible Long Wire

A wire antenna is not actually a “long wire” unless it is

one wavelength or greater in length. Yet many amateurs refer

to (relatively) long physical spans of conductor 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 limiting

factor with small wire is fragility. A good compromise 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 4—The “invisible” end-fed antenna.

Fig 3—The clothesline antenna is more than it appears

to be.

Fig 5—Rain gutters and TV antenna installations can be

used as inconspicuous Amateur Radio antennas.

Antenna System Planning and Practical Considerations

4-5

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