VERTICAL DIPOLE

Since I had purchased the
Kenwood TS-590 transceiver
a few months before I got my
license, I needed an antenna
(or antennas) right away for
listening on the ham bands.
The antenna that I put up first
was a vertical dipole for 10,
15, 20 and 40 meters. The
reasons for this selection as
the first antenna to be
installed are that

1. The vertical antenna has
many devoted supporters in
the ham community who claim
to get fantastic results,

2. The vertical dipole has a
very small foot print and
requires
no radials,

3. This vertical is self
supporting and is very easy
to install (except for the many
tuning adjustments that are
needed) and,

4. It is almost invisible from
the street view in front of the
house.  This last reason was
considered important for the
first antenna as it would let
the neighbors get used to
antennas sprouting up on and
around the house without
being initially overwhelmed
by some visually gigantic
structure.

Two Hustler Model 6-BTV
antennas were adapted to
make up a half wave vertical
dipole by mounting them butt-
to-butt on a twelve foot long 2
by 12 inch wooden mast
attached to the deck railing at
the rear of the house. The
center feed point of this
combination is only about 22
feet above the ground.
Therefore, I had to eliminate
the 75/80 meter sections of
the antennas in order to
reduce the total length for
each side to about 20 feet.
This vertical dipole
configuration was chosen
because my house and back
yard layout (a full coverage
concrete patio was already
installed) do not lend
themselves to the installations
of a good ground radial
system. One great feature of
the way that this antenna is
mounted is that the dipole can
be rotated to horizontal and
the ends can even be
swapped – which makes it
very easy to reach any of the
tuning traps from ground level
or from the deck to which it is
mounted! In addition, I have
heard some hams say that
with an incline angle of 45
degrees the signals come in
earlier and leave later as the
bands open and close – easy
to check out with this setup.
The vertical dipole is fed at
the center by a 1:1 balun and
is further isolated with a 14
turn coil of RG-8 coaxial cable
wrapped around a 7 inch
diameter fiberglass form. The
coaxial cable is routed at 90
degrees away for the antenna
for about 20 feet before it
runs across the roof of the
house and then finally drops
down to a 10 foot long ground
stake. Here the coaxial cable
passes though an Alpha-Delta
2 KW surge protector with the
braid is connected to ground.  
Next, a 50 foot length of
coaxial cable runs up the
second floor shack.

This antenna has been found
to load great with SWR values
of under 2.5:1 over the entire
span of the bands that it
covers.

A limitation of this antenna
was the lack of coverage on
the 75/80 and 160 meter
bands. This deficiency was
quickly and easily remedied
by the addition of a Pixel
Technologies Magnetic Loop
Model PRO-1B all band
“listening only” loop antenna.

I have recently made some
back of the envelope
calculations estimating the
performance of this antenna.
Picture above: The dipole is
shown rotated to the horizontal
position.
_________________________

The takeoff angle for this
antenna should be around 15
degrees for 10 meters and
between 25 and 30 degrees at
40 meters. The radiation
efficiency should be equal to or
slightly better than the typical
1/4 wave vertical antenna with
4 to 8 radials.

Note that due to the 1.25 inch
diameter of the aluminum tubing
that makes up the elements, the
length of each segment of this
vertical is about 5% shorter than
it would be for a 12 gauge wire
antenna. Due to the tuning traps
for each of the bands, the
physical length of this dipole,
compared to a full length dipole,
is 99% when it is used at 10
meters, 94% for 15 meters,
83% for 20 meters and 65%
for 40 meters.  

Taking into account the losses
that are associated with the 150
feet of coaxial feed line, the
balun that feeds the antenna,
the traps and the overall
antenna length for each band
(listed above), the loss of power
for the total antenna system can
be estimated.  The total power
loss is around 1.5 db on 10
meters, 2 db on 15 meters, 2.5
to 3 db on 20 meters and
maybe as much as 4 to 5 db on
40 meters when compared to a
full length vertical dipole with a
short feed line and a core type
current balancing choke. If your
signal is 10db over S9 at the
receiving location, these losses
will hardly matter.

Choosing one of the trap free
antenna designs that are now
available, in place of the Hustler
design, could minimize the
losses on the 20 and 40 meter
bands.

Finally, now that all of the
antennas in the plan have been
installed the listening results for
this antenna can be compared
with my other antennas.

So far, some preliminary
comparisons have been made
on the 17 meter band.

The antennas that I can now
select include a hex beam, an
inverted V off center feed
Windom (a long wire at this
frequency) with good
omni-directional characteristics
due to the inverted V
construction), my vertical dipole
to which I have added the 17
meter band and a two
wavelength horizontal loop
antenna. Each has its own
advantages and disadvantages
and the shoot out between them
has been very interesting.  The
four antennas can be set up to
use the four antenna selector
switch buttons on the front of
the Alpha amplifier which
makes A-B-C-D testing very
easy and a lot of fun!

The preliminary 17 meter
observations are:

1. The hex beam is always the
most quiet and has the
strongest signal in both transmit
and receive mode even though
it is only 24 feet above the
ground.

2.  The loop has an equally quiet
noise level but delivers signal
strengths that are about 6 db
less than the hex beam.  

3. The OCF inverted V has a
noise level that is 2 to 3 db
higher than the hex beam and
produces signal levels that are
between equal and 4 db lower.

4. The vertical dipole usually
has a 3 to 6 db higher noise
level, compared to the hex
beam, and produces signal
levels that are typically 3 to 6 db
less than the hex beam. It does
much better on transmitting than
it does on receiving due to the
high noise level when it is used
as the receiving antenna.

















Last Revised December 10, 2012
W6SDO.COM                                                   SAN DIEGO, CALIFORNIA USA
Vertical dipole antenna
suspended from the
rear deck railing.
14 turn isolation coil
made from RG-8
coaxial cable
Antenna positioned
as a vertical dipole.
Two Hustler Model
6-BTV antennas are
mounted butt to butt
and fed from 1:1
balun.
Antenna positioned as
a horizontal dipole.
_____________


Overall, this vertical
dipole antenna
definitely earns its
place in the lineup.

If nothing else, this
antenna offers a
platform for never
ending experiments.
PHASE 2 - IMPROVING THE HUSTLER VERTICAL DIPOLE ANTENNA

                                            (coming soon)