125' EFHWA (was: long wire balan)

[Stuart Rohre]

The Windom is not a cure all antenna, and indeed has a number of potential
problems.  Its original version was a one band antenna, and modern uses of
similar antennas are like stuffing a model ship in a bottle--doing something
other than the physics show is the simplest antenna.

As an off center fed antenna, it is unbalanced.  This may increase RF in the
shack problems.
Especially as you move off the one sweet spot where it is naturally
resonant.

If you feed it with other than single wire, you can limit the feedline
radiation but at the expense and weight of a balun or RF blocking ferrite
beads on coax.  Depending on the length of the feeder and how it is brought
away from the antenna, you are not likely to maintain an RF free feeder,
because the capacitance of the outer shield of the feeder is different to
one side of the feed point than to the other (which are differing length
legs of the dipole.)

The "Windom" type (or Off Center Fed as the general class of antennas is
called, will have an offset modified dipole pattern; it certainly will have
something other than an omni pattern due to its imbalance and lack of
symmetry.  Like any dipole class antenna, it will have more of an bubble of
radiation if placed too low.  This will cut its directivity, but then you
will have to rely on field strength measurements to see what it really is
doing.

A dipole for say 20m or up will certainly perform as the models show if you
have a clear near field area around it, and it is 50 feet high, even the 40m
dipole will perform pretty well in that case.  What the dipole offers is a
chance to bring the feeder off at a right angle, and maintain a true
balanced antenna with symmetric pattern, if no nearby conductors affect the
field.

What I am saying is there is no magic antenna, you really need to match the
antenna to its surroundings, and that may mean some compromises.   But, you
should not intentionally complicate your antenna installation, IMHO, by
using antennas that aggravate RF in the shack possibilities.  Nor should you
use an unbalanced antenna intended as a single band antenna on other bands
without expecting some problems or the need to use a tuner for each
frequency excursion.

Even the G5RV which can work well for some at low elevations with certain
precautions, was only intended to enhance the 20 m band use by providing
gain there.   I have used a number of versions of the G5RV; and they
universally present a poor radiation angle on 15m compared to other bands.
They will work well on 40m, but need a tuner in most other bands, again
depending on local installation conditions.

A good all around installation is use of the 88 foot doublet, (or 44) for
reaching more bands with a tuner and reasonable results.  But, usually, a
pair of antennas is good to have.   A dipole/ doublet for low bands, and a
vertical for bands 20m and up.   You get low angle of take off and omni
coverage from the vertical; and you get usual doublet performance dependent
on height from it.  To overcome the usual complaints and problems of
verticals, use a vertical dipole.   Both an elevated feedpoint and elevated
radials on quarter wave verticals seem to enhance performance.  Even loaded
center fed dipoles are quite good performers, such as the Force 12 Sigma
line.  However, with a little pre planning, one can homebrew just as good a
vertical doublet.

One of the ideas I found for test for an experimental vertical doublet is
one of the larger sizes of PVC pipe splices for a center insulator.  These
devices have a compression fitting that should tighten around tubing used
for elements.   They would also work as bottom insulators, or you could use
PVC rings under U bolts as done in the Titan vertical.  Of course, non
conductive guy lines would be used, but the overall antenna design is simple
and easy to put up.   One idea is to center feed with parallel wire line,
and by use of a tuner, cover multiple bands above the half wave resonance of
the vertical dipole.  This would remove the need for loading coils and a
switching network.

-Stuart K5KVH


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[Martin J. Morgenbesser]

My favorite "dipole" antenna is a 20 meter extended double zepp, fed with
balanced line (450 ohm ladder line for home use or 300 ohm twinlead for
portable/qrp operation). At 44 feet per leg, it can be set up as a
horizontal doublet, a sloping doublet or an inverted vee. What you end up
with is an 88 foot doublet.

For best feedline balance, run the feedline perpendicular from the
horizontal or sloping doublet. For the inverted vee, run the feedline at
equal angles from, in between and in the same plane as the two legs of the
antenna. Of course, the geometry of your yard and location of trees may
limit your ability to run the feedline in this manner. Just do it as best
you can, trying to keep the feedline perpendicular or equi-angular for at
least a half wavelength at 20 meters, if possible.

You can feed such an 88-foot doublet with an antenna tuner (for a remote
tuner add a 1:1 coax choke balun on the input side of the tuner and at the
transceiver, for internal/shack tuners add a 4:1 current balun on the
output side of the tuner -the Elecraft BL1 works well for this application-
and keep the coax line from the tuner to the balun as short as possible,
just long enough to keep the balanced line out of the shack or away from
the transceiver, but preferably no longer than 20 feet maximum).

Such an antenna system, with a decent antenna tuner, will usually load up
nicely on all bands, 80 through 10 meters. On 20 meters, it gives about 3
db of bidirectional gain over a dipole. On 17 meters, the pattern becomes a
cloverleaf, with more lobes sprouting out as you go to shorter wavelengths.
On 30, the bidirectional gain is about 1.6 db over a dipole. On 40, the
antenna's pattern and gain is similar to a dipole and on 80, the pattern
begins to become omnidirectional, with a reduction in bidirectional gain.

For more details, go to http://www.cebik.com/88.html

No room for an 88-foot doublet? Willing to forgo 80 meter operation? Try a
70 foot doublet (35 feet per leg). That's an extended double zepp for 17
meters and a slightly long 1/2 wave dipole on 40. It'll work well on 40
through 10. You can even get by with a 44 foot doublet (22 feet per leg),
if you don't mind pushing the 3db extended double zepp advantage to 10 meters.

73,
Martin
W7MJM


At 02:51 PM 8/5/04 -0500, you wrote:
>The Windom is not a cure all antenna, and indeed has a number of potential
>problems...

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