W6SDO.COM                                                    SAN DIEGO, CALIFORNIA USA
      WINDOM DIPOLE

The third antenna that I added to my small
city lot was a multi-band off center fed
(OCF) Windom dipole. This antenna  
provides coverage for the bands from 80
meters through 6 meters (excluding the 15
meter band). Fortunately, I had the vertical
dipole installed on the back patio deck
that provided acceptable performance on
15 meters (currently the K4KIO hex beam
has taken over most of the 15 meter
duties). On 60 meters the SWR of this
OFC dipole antenna is about 6:1 which is
easily accommodated by the tuner that is
built into my Kenwood TS-590 transceiver.
Since only 100 watts is allowed on this
band, the Alpha amplifier (which does not
tune high SWRs), is not used anyway. The
coaxial cable transmission line losses for
this 6:1 SWR at the 5 MHz frequency is
calculated to be only about 1 db.
Therefore, I may not have to install a
separate 60 meter dipole antenna in
addition to the 60 meter NVIS antenna
that I already have.

The Buckmaster version of this antenna
has a 5 kilowatt rated balun (for a price)
at the feed point of the antenna. A photo
of this balun at the top of the fiberglass
flagpole is shown below.
























My expectation is that the extra amount of
core material in a 5 KW rated balun will
keep it from overheating when the antenna
is operated near the band edges where
the SWR is a bit higher than optimum.

There were two dilemmas that were
confronted during the implementation of
this antenna:

1. The overall length of the Windom
antenna is 135 feet long and the available
diagonal of my city lot is only about 120
feet (in order to stay within the fenced
boundaries) and,

2. There are no tall trees on my property
that I can use to suspend either the center
or the ends of the antenna.

The first problem was eliminated by
configuring the antenna as an inverted V.
This reduced the overall foot print of the
antenna to about 118 feet, which just
barely fits on my lot. The inverted V
configuration also provides a relatively
omni-directional radiation pattern.

Next, since I did not want to use a
conventional tower to support the antenna
in the center, I elected to use a 45 foot tall
fiberglass flag pole. The pole chosen is
about 5 ½ inches in diameter at the base
but has a small 3 inch in diameter at the
top so that it is therefore less visually
conspicuous. It weighs less than 100
pounds and can withstand 100 MPH
winds.

I secured the base of the pole to the
house using a pivot bolt through the pole
that goes into the fireplace brickwork as
pictured below.





















This attachment method allows the pole to
be raise and lowered along the side of the
house using a hand cranked winch from
Harbor Freight. The winch is attached to
the deck railing cap strip over the garage
(at the front of the house). If it ever
becomes necessary, the raising and
lowering of the flagpole is a very easy
one person operation.

A plastic hose has been placed over the
cable the goes from the winch to the
fiberglass antenna pole. This will damp
out any cable whipping should the cable
brake or come loose when it is under
tension.
_________________________________


The Windom antenna is raised to the top
of this mast using a nylon rope routed
through a pulley on the top of the flagpole.
What could be easier? A second pulley
has been added at the top of the pole so
that a second antenna (in this case my 1
60 Meter inverted L) can be raised and
lowered using this pulley.

The OFC dipole ends are each supported
at about 10 feet above the ground level.
This is high enough to keep the ends at
safe distance above animals and  people
as well as to achieve a low SWR on all of
the bands that are covered by this antenna.

There is not quite enough room on my city
lot for the 90 foot side of the antenna wire
which is about 10 feet longer than the
space that is available. Therefore, a 10
foot length of the antenna wire at the end
of the 90 foot side has been folded back
at a right angle along the top of the fence.
This is ok since the shorter length brings
the antenna resonance up to the lower
edge of the 75 and 40 meter phone bands.

The folding of ten feet of the long side of
the off center fed Windom antenna did
require that the short side of the antenna
be reduced in length by about 3 feet. This
was necessary in order to maintained the
correct minimum SWR locations on all of
the bands covered.

This three feet of antenna wire on the
short end of the off center fed antenna
was folded back on itself and fastened
with zip ties. This allows the antenna to
be restored to its original length at some
later date if desired.

This modification tunes the antenna so
that it has the lowest SWR on the phone
portion of the general class bands. The
SWR is generally below 2.5:1 over most
of the phone bands which is acceptable to
the Alpha 9500 amplifier running at full
power.

Both end of the antenna are terminated
using a pulley and a one gallon container
as ballast (pictured below). This keeps
the antenna wire sufficiently tight while
allowing the fiberglass antenna pole to
sway with the wind. The engineers at
Buckmaster told me that this amount of
weight will not stretch the antenna wire
and that they use two plastic jugs of water
at the antenna ends when they install an
antenna. .



























The 50 foot length of RG8 coaxial cable  
that feeds the antenna drops down along
the side of the pole and passes through an
Alpha-Delta surge protector device which
is connected to a set of three 10 foot long
ground stakes. After that, another 50 foot
long coaxial cable goes up to my second
story shack location.

Since this antenna has been tuned more
toward the phone bands, as described
previously, I am considering making some
short wire pigtails that can be clipped
onto the ends if I ever want to center the
antenna in the CW portion of the bands.
The antenna ends might have to be
lowered a little to make them easier to
reach (or the pigtails could be switch in
and out using vacuum relays).

This antenna is a superior performer. It is
perfectly complimented by the tri-band
NVIS antenna that covers 75, 60 and 40
meters.

Finally, now that the K4KIO six-band hex
beam has been installed, this antenna has
taken over the 20 meter through 6 meter
bands from the Windom as well as from
the Hustler vertical antenna.

__________________________________


If I could only have one antenna
to cover the bands from 80 to 6
meters, this off center fed Windom
would be the one!
The photo above shows the hand cranked winch that raises and lowers the fiberglass flag pole. On
the left side of the photo, you can see part of the NVIS antenna as well as the grand children's play
structure which supports the hex beam. The photo below shows the antenna tensioning weight
(bucket) and how the ten feet of excess antenna length (on the long end of the antenna) has been
folded back along the top of the wooden fence.
Last Revised December 22, 2012
Recent Windom Antenna Modifications (December 2012)

Since the six-band K4KIO hex beam has now taken over the chores on the bands from 20
through 6 meters (at least 99% of the time), I have decided to optimize the off center fed
Windom for operation on the 75 meter and 40 meter phone bands. There were two tasks that
had to be accomplished at the same time for this modification to be successful. First, I wanted
to shift the resonant frequencies of the antenna for both 40 and 75 meters bands more toward
the center of the phone portions – even though this would mighjt some compromise on the 20
meter through 6 meter bands. Next, I wanted to lower the relatively high SWR that I was getting
on 75 meters so that the Alpha amplifier and the balun would both be happier when used at
the full legal limit.

My first try at raising the resonant frequencies for these two bands was to shorted the antenna
on the long 90 foot side by five feet since this end was the easiest to reach. This put the
resonant frequencies where I wanted them and lowered the 40 meter SWR down to a very nice
1.2:1. However, this change raised the 75 meter SWR to 3.4:1 which is much too high for the
Alpha amplifier. This first change revealed that the feed point for lowest SWR on 40 meters
would like to be closer to the center while the feed point for the lowest SWR on 75 meters
would like to be closer to the end of the short (45 foot long) antenna leg. To reach the best
compromise, I restored the longest leg back to it’s full length and shortened the 45 foot leg
until the desired resonance points were reached simultaneously on both of the bands. In the
end, 54 inches was removed from the 45 foot leg.

This change has resulted in resonances of 3.850 MHz and 7.200 MHz (exactly where I wanted
them to be). Also, by making this change in the antenna feed point, the SWR on 40 meters has
increased to 1.8:1 while the SWR on 75 meters has dropped to 2.3:1 making the Alpha a very
happy amplifier.

Loss calculations for the 100 foot long RG8 coaxial feed cable due to both match and SWR
losses came to 0.327 db for the 40 meter band and 0.327 db for 75 meters. The losses when
the antenna is used on 60 meters (with it’s 6:1 SWR) amount to 0.776 db – hardly worth
worrying about since the Kenwood TS-590 tuner can easily take this SWR in stride.

Replacing the 6:1 balun with a 4:1 balun would reduce the SWR on both bands but since it
would only decrease the transmission losses by about 0.1 db it is hardly worth the expense
or effort.

I did consider replacing the Windom with dipoles for 75 and 40 meters. However, the
geometry of the flagpole location and size of my city lot strongly favor the asymmetry of the
Windom. To see if I was missing anything, I have actually installed a 40 meter dipole to see if
it would be any better than the Windom on this band. After almost two months of comparative
testing, using the A-B antenna switches on the amplifier to get an instant comparison between
the two antennas, I have found that the dipole and Windom are always within a db or two of
each other – and most often the Windom is the better of the two at any distance and in any
direction. Although this is not what I expected (since the dipole should have a little more gain in
it's preferred direction when compared to the Windom), it is what I have consistently observed.
Maybe the more omni-directional pattern and slightly lower angle of radiation from the Windom
make the difference. If you know the answer – please tell me.

If you have a beam, vertical or other antennas that you are happy with for the higher bands (as I
do) and are interested in using the Windom mostly on the 40 and 75 meter bands (as I am),
you might consider these modifications to your antenna.
Graph above: This plot from Buckmaster
shows the typical  SWR for each of the
bands that are covered by the Buckmaster
off center fed Windom antenna when using
a 6:1 balun..