The Off Center Fed (OCF)
Windom, constructed as a 40m dipole is an excellent multiband antenna. You can
expect good to excellent reception on the 40/20/15 and 10 meter bands. The
build design in this paper will be for an inverted vee antenna. The main reasons
for this are; the inverted vee setup requires only a single tall “center” mount
(e.g., a 30ft expandable military flagpole), end points are mounted on 8ft poles,
center pole can be vehicle hitch mounted for portable use, Mounting the antenna
as a flat dipole at 30-40.ft will, however, improve DX performance.
The wire to be used is
jacketed twin 18AWG. The wire is also shielded and with a ground wire,
neither of which will be used. The twin 18-gauge multiconductor will produce
the equivalent of a single 15–16-gauge conductor.
The Windom requires a 4:1
current balun, not a voltage type. The balun maintains balance and
suppresses feedline radiation. An rf choke placed 10-20ft down the feedline is
highly recommended. The choke can be quickly made by taking 8-10 turns of RG-8X
on a 4-6” form.
The 40m dipole would normally
be 66ft long. The inverted vee format will require a shorter length of ~64.5ft.
The antenna will naturally resonate lower than a flat-top bare-wire Windom. So
the starting lengths are shortened slightly. The leg lengths are: Long leg =
43.0ft, Short leg = 21.5ft. There will be length adjustments made
during the final tuning of the antenna. Remember though, the Windom’s 44%/66%
leg length ratio must be maintained. So, e.g., if wire needs to be removed,
then remove equal small increments from each leg end.
The antenna layout will look
similar to the following sketch:
Materials List:
Multiconductor cable – Need
two pieces: 21.5 ft and 43.0 ft. Cut each piece ~2 ft longer for connections
and tuning. (What I had available, it can be single strand, >20-ga,)
4:1 current balun – Two
commercial examples from Amazon: KB2 Enterprises, 1.6-30mhz 1000W PEP @ $49.98
and Taurus HF, 1.6-30mhz, 1000W PEP @ $39.00.
50 ft of 50-ohm coax, e.g.,
RG-58 or RG-8X.
Telescoping Pole – 30 ft long,
with tie-off points for ground mounting or with adaptability to vehicle mount,
e.g., telescoping kite flying or flag flying fiberglass pole.
Paracord - ~160 ft for tying
off antenna legs, for staking 8 ft end-poles at distance to create ~120-degree
apex angle, and for raising antenna apex to top of pole.
End Poles – Need two, 8 ft
long poles to tie antenna legs. Suggest: 8 ft 2x2 fir with an eye-screw on top
end and 2ea eye-screws mounted ~2 ft from top, for securing supporting ground
stakes. A good suggestion is to add a short length of ~1/2” rebar to base of
poles for ground stability.
End Isolators – Need antenna
leg to paracord tie points at each leg end. Suggest hard plastic with holes for
connecting.
Pully – Need one small pully
with attaching ring
Dielectric Grease – Use
dielectric grease to weather protect exposed electrical connections: e.g.,
Permatex 22058 for $9.98 at Amazon.
Soldering Iron – Need to
prepare leg ends for connections.
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