KØCQ

Practical Antennas
 Practical Antennas
A radio transmitter or receiver without an antenna has
the same function as a brick but is way more
expensive.
 Practical Antennas

Every wire carrying a current

creates a magnetic field
around the wire. DC, AC
or RF. The direction of the magnetic
field goes by the right hand rule and
so changes every half cycle of AC or
RF.
 Practical Antennas

Conductors with voltage

differences create electric
fields. Wires with RF voltages
have considerable voltage
differences between the ends,
typically every half wave
length along the wire. These
fields are at right angles to the
magnetic fields.
Practical Antennas
 Practical Antennas
I have a book on transmission lines that says in
the section on circuit board type transmission
lines, with a flat conductor on an insulator over a
wide ground plane to never bother with air
insulation. That's because the higher dielectric
constant of the circuit board material concentrates
the electric fields in the dielectric, otherwise the
transmission line will act like an antenna. Made a
better antenna by have a circular conductor raised
high enough over the ground plane to make a 50
ohm characteristic impedance.
Practical Antennas
Practical Antennas
 Practical Antennas
Antenna elevation affects
the elevation pattern and
how it works DX or nearby
states.
 Practical Antennas
Antenna elevation affects the elevation pattern and
how it works DX or nearby states. The higher the
more vertical lobes, at VHF its many lobes like a
pattern from an optical refraction grating. Normally
only noticed when looking at satellite signals near the
horizon.

A very low dipole gives NVIS, Near Vertical

Incidence Skywavel and illuminates the D layer of 80
meters quite well and allows good contacts out to
about 500 miles. Its lousy for DX. An 80 meter
antenna a half wave high is lousy for working
anything closer than 1500 miles. We had one like
that for FD once. It worked the west coast fine, but
nearby states not at all.
 Practical Antennas

My first antenna that my dad and I built as novices in

1955 was a quarter wave vertical for 40 meters. We were
using a command set transmitter modified to be crystal
controlled so had only that one band. We built the vertical
from a 21' length of ¾ galvanized water pipe and a
reducing coupling with a top of 12' of 1/2” galvanized
water pipe. We sat it on an insulator and used three guy
wires in the garden. I don't remember what we used for a
ground, at least an 8' ground rod I hope and maybe
buried radials. It did get out and we made contacts for a
couple years at least. If it didn't have radials it wasn't a
spectacular antenna but it did get out
 Practical Antenas
Bill has asked about the Gotham vertical that didn't work for
him. What I have found is that it was a 23' vertical with a base
loading coil, different coils for the V-80, V-40, and V-20
models but turns could be shorted for the higher bands. The
Gotham literature said it didn't need radials. Actually it was a
poor dummy load without radials, it didn't radiate much. On
80 meters I compute the radiation resistance as 6.8 ohms
and its easy for a 4' ground rod (which I don't consider a
ground rod but Radio Shack did in that era) to have a
resistance of as much as 140 ohms, higher in dry ground so
the transmitter power already limited by the 75 watt INPUT
limit for novices was distributed between the two resistances,
35 watts split between 6.8 and 140 ohms in series puts 0.49
amps to the two, delivering 1.6 watts to the radiator and 33
watts to the ground rod drying the ground even more.
Practical Antennas
 Practical Antennas

There was a review of that Gotham vertical in QST a

couple years ago and those who believed it didn't need
radials were severely disappointed in it. Those that
added radials thought it was a decent antenna for the
price and small footprint. A short vertical next to a
building or between buildings doesn't get out even when
well grounded.
 Practical Antennas

Bill told me that his antenna was up on an eave about 15

feet above the ground with a wire down to a stake in the
ground. Modeling without a feed line the impedance at
the feed point up 15 feet above the ground comes close
to 50 ohms a decent patch to the coax. The effect of the
coax is hard to include because I don't know the routing
or the termination, e.g. Whether the transmitter was
grounded separatedly or through power wiring.
 Practical Antennas
At one point my dad and I reclaimed the novice vertical,
and put back most of what we had cut off making it some
42 feet tall. We put that up on top the mast on a
telephone pole that we had used for a quad and fed it
with an air variable in series. And with radials. Seems I'd
found that a 5/16th wave vertical with a series capacitor
when tuned to resonance has a 75 ohm feed impedance
and we had a stash of 75 ohm RG-11 coax. It proved to
take RF from our Viking Ranger from 160 through ten
meters without an antenna tuner. I recall working
something like 90 miles on 10m AM with 75 watts input
once. It was a great 40m DX antenna, lousy for working
nearby states on 40m. I recall calling KG6FAE in a DX
contest (Guam Island) and beating out a dozen California
stations also calling him.
 Practical Antennas
Last year I talked about the “universal dipole” with
antenna tuners. The half wave dipole is the
foundation antenna these days. Halfwave
resonance is convenient, but can be forced by a
tuner or feed line variations, or by adding loading
coils or shortening capacitors, and the center fed
wire can be operated on harmonic resonances as
well as below resonance. The feed impedance
does vary with the harmonic resonance, and
reflected through the feed line can make it difficult
for the tuner.
KØCQ Ellsworth dipole
 Practical Antennas

In the real world that feed impedance is affected by

height above the earth and the earth's resistivity.
Practical Antennas
Practical Antennas
Practical Antennas
Practical Antennas
Practical Antennas
End Insulators
 Practical Antennas

More End Insulators. Another source of insulators,

antenna wire, and connectors is the electric fence
shelves in the farm store. Both ceramic and plastic.
 Practical Antennas

More End Insulators.

Besides the farm stores, antenna insulators are

sold by connector dealers at hamfests and all
ham radio stores, like Radio City and DX
Engineering. And should be found in every ham
estate sale of miscellaneous parts.
 Practical Antennas

Dipole Antenna Wire is sold by those same

radio stores also the electrical departments of
big box home centers, hardware stores and
farm stores. Enameled wire would be ideal to
give corrosion protection with little added wind
load. Many a dipole has been made of type TW
building wire made for use in conduit. Today I'd
prefer THHN because it has thinner insulation.
I'd prefer solid over stranded, for the
connections but stranded seemed more
available at Lowe's last time I looked. White or
blue insulation might help hide the wire from
neighbor's eyes.
Practical
Antennas
From the
ARRL
Handbook

Polycarbonate
plastic is used
for bullet proof
windows. Also
known as
Lexan
Practical
Antennas
From the
ARRL
Handbook
Practical
Antennas
From the
ARRL
Handbook
Practical
Antennas
From the
ARRL
Handbook
Practical Antennas
From the ARRL Handbook
 Practical Antennas
Traditionally with solid wire in the dipole the loop
at the end is twisted with a low pitch and then the
tight pitch and the tight pitch is soldered. With
stranded wire that might not hold, so I suggest
using a split bolt or Kearney Bolt from the
electrical department at the hardware store, or a
small cable clip from the steel cable department.
 Practical Antennas

Center Insulators and construction.

The picture with the coax looped over the center

insulator works but bends even RG-58C/U coax a
bit tight and the center conductor will drift. Some
day it will short with that tight a bend. The
Handbook rightly points out that the coax braid is
a sponge and will absorb water and transport it to
the other end while corroding the braid.
Waterproofing is important.
 Practical Antennas

Center Insulators and construction.

For small coax it would be practical and beneficial

to loop some 3/16” or 1/4” polyester rope around
the center insulator and run it all the way to the
ground or to the feed through to the shack, and tie
the coax to that with zip ties or smaller string
every foot or two. There are several products
made for the center insulator.
 Practical Antennas
Center Insulators and construction.
 Practical Antennas
Center Insulators and construction. A British
design. Bungs are rubber corks. They suggest it
be glued together.
 Practical
Antennas
Center Insulators
and construction.
Practical Antennas Center Insulators and
construction.
 Practical Antennas
The current is
highest at the
center of the
halfwave
dipole so that
is the most
important part
of the
antenna. The
ends just
make the
antenna
naturally
resonant.
 Practical Antennas

For at least 50 years I have liked the ground plane

for a 2m home antenna. I built one on a SO-239
probably before 1966 and it worked well for me.
When I first lived in Ames at 221 Abraham drive I
had it on top of a 33 foot tall downspout pipe mast
and regularly worked FM mobiles in Des Moines
without a repeater. There weren't any repeaters
then. I had used that downspout as a 40 meter
vertical in a couple previous locations.
 Practical
Antennas
My ground plane used
an angle bracket,
probably of aluminum
to bolt to the mast and
I probably bolted the
radials with the same
bolts that bolted the
SO-239 to the bracket.
Its important to seal
the top side of that
coax chassis
connector.
 Practical Antennas
I like the ground plane because it works for any
band its cut for, and the radials decouple the
outside of the coax from RF so it doesn't act like a
long vertical wire that radiates mostly upward, not
to the horizon as needed for good VHF work.
Today I have a gain antenna on the roof and it
works better. The quarter wave ground plane has
a good input impedance at the third and 5th
harmonics but there is a null at low angles of
radiation. That can be solved. Topic for some
other day.
Practical Antennas
I dislike the j-pole
because most all j-
pole construction
doesn't keep RF off
the feed line and so it
radiates better at the
sky than at the
horizon. This design
should work much
better with the RF
choke in the feed line.
That could be a ferrite
core too.
 Practical Antennas
The J-pole is not a new design, its actually what
was called an end fed Zepp from the late 1930s. A
half wave radiator, with a quarter wave of open
line to transform the high impedance of the end of
the half wave to a reasonable impedance. The
quarter wave matching line is nearly balanced
because the side not connected has only a little
capacitive current, and the side connected to the
antenna sees a high impedance and so the
currents are similar. In prewar HF usage the feed
was at right angles to the radiator. And commonly
the radiator was a quarter wave above ground.
 Practical Antennas

There are many good antenna references

professionally and from Amateur Radio
publishers, like ARRL, Radio Amateur Callbook,
and RSGB. I scanned much material for this
program from several of the ARRL and RSGB
publications.
 Practical
Antennas

I recommend
starting with this
book.
Its not so detailed
as to be
intimidating. But
has many good
antennas.
 Practical
Antennas

This encyclopedic
work can be
intimidating but it
is complete. Very
early editions
were easier to
absorb, but its
been good for the
past 60 years.
 Practical
Antennas
This encyclopedic
work can be
intimidating but it is
complete. A smaller
coverage of
antennas but very
good coverage of
radio and electronics.
More complete than
a degree in electrical
engineering.
 Practical
Antennas
This Is a collection of
montly columns in
RSGB journals by
Pat Hawkins G3VA
over the period from
1958 to 1999. There
are many good ideas
and discussions
stashed in there.
Generally brief. But
proven to work. 375
pages of them.
 Practical
Antennas
This is a recent
ARRL publication
explicitly for
apartment and
compact housing
dwellers.

HF mobile antennas
have been used on
apartment balcony
railings. Then there
are Buddy Poles.
 Practical
Antennas
This is a 1982 RSGB
book that covers a lot
in a small space,
mostly compact
antennas.
Unfortunately for fans
of the W8JK antenna
neither Moxon nor the
current ARRL editor
understand how a
W8JK antenna works.
 Practical Antennas
Amateur radio antenna books from my shelves.
 Practical Antennas
There are at least 8 volumes on the Antenna
Compendium collection. Generally new antenna
ideas not always accepted at ARRL HQ as being
good enough for the handbooks, but maybe good
enough for QST and the Compendium collection.
QST and other ham radio magazines hardly ever
leave antennas from an issue.
 Practical Antennas
Some vintage books that didn't show in the first
pictures. Flash glare.
 Practical Antennas
Speaking of W8JK, John Kraus was professor of
antenna at Ohio most of his life.
 Practical Antennas

There are many antennas derived from modified

dipoles and created from other things that carry
RF currents and sometimes let the RF radiate.
Efficiencies vary from nearly nothing to nearly
100%. Most antennas with gain get the gain from
directivity, so they concentrate radiation in less
than a sphere. That's often good for point to point
communication, not necessarily so good for
broadcasting. There has been much published and
to cover it all can take years of reading and talking.
 Practical Antennas
There are decent antenna modeling programs
around. Much faster than I used on my Apple II+ a
long time ago. EZNEC is liked but it costs money
and the version I have is more limited and
inconvenient for data entry. I like Mmana-Gal from
Germany. Its free and allows more complex
antennas than EZNEC. It does prefer metric
dimensions but will convert feet and inches in the
entry fields that are organized like a spread sheet.
Its use can make a full program.

73, Jerry, KØCQ