[Elecraft] Windom Antennas

[Ron D'Eau Claire]

By all means build your own antenna!=20

A "Windom", like any horizontal antenna, can be a wonderful performer. =
You
can see several dB of "gain" over the best vertical out there. IF the
antenna is up high enough, that gain is at low angles to enhance DX
performance but the height must be something on the order of 1/2 =
wavelength
above the ground. That's because the ground reflection adds to the =
direct
radiation at lower angles to reinforce the signal. Under the most ideal
conditions that can be as much as 6 dB, giving you a four times increase =
in
effective radiated power.=20

Few hams are able to gain those heights at the lower frequencies (120 =
feet
high on 80 meters or 60 feet on 40 meters). MOST Ham horizontal antennas =
are
much lower. Also, that "gain" is not as great as you move higher than =
1/2 or
3/4 wavelength, so an "ideal" height for 80 meters will be above the =
ideal
for 40 meters and up. Still the efficiency is very high - especially for
lower angle radiation suitable for DX. When working with horizontal
antennas, "higher is better" almost all the time.=20

At lower heights - down to 0.2 wavelengths or even a little less (about =
60
feet on 80 meters or 30 feet on 40 meters) - a horizontal antenna can =
also
show up to about 6 dB of gain, but now the gain is straight up! The =
major
lobe is very strong and directly away from the earth. This can be VERY
useful for short skip contacts, and Hams have used such antennas for =
exactly
that purpose since the short wave bands became popular. In recent years =
a
new name has been given these antennas: NVIS for "Near Vertical Incident
Systems" I think. In this case, the antenna and the earth are working as =
a
simple two-element "beam" antenna, with the earth being the reflector =
behind
the driven element. While these antennas work FB for short-skip. =
Radiation
down near the horizon where you want it for DX is not as good. Indeed, =
even
a mediocre vertical antenna will often outperform a low horizontal =
antenna
for DX.=20

A variation on the NVIS that is GREAT for DX is often used by "mountain
toppers" or others who operate from very steep slopes. They put their =
low
height horizontal antenna on the slope so the mass of earth is behind =
the
radiator about 0.2 wavelength (it's very broad - anything from about 0.1 =
to
0.3 wave works FB). That puts a major lobe out toward the horizon away =
from
the steep slope, providing excellent DX capabilities from a "low" =
horizontal
antenna.=20

So If you have the height to get ANY horizontally-polarized antenna up =
near
1/2 wavelength above the ground - or operate from a very steep slope - =
you
will have a FB DX antenna. It will usually outperform any vertical =
antenna.
Bit many of us simply can't get that height, especially on 40 meters or
below, so a vertical is a better choice for DX. And, of course, a =
vertical
on the higher frequencies offers a much, much lower "foot print" for =
hams
with very little space for hanging a "skyhook".=20

The "Windom" design has nothing to offer over other horizontal antennas =
in
terms of being a good radiator. The "Windom" design is simply a means of
getting RF from the rig to the antenna. The original Windom was a
single-band affair designed to avoid the use of coaxial feeders - a very
expensive feed line back when this antenna was designed. The original =
Windom
used a single-wire feeder. Radiation from the single-wire feeder was
minimized by carefully matching it to the feed point on the horizontal
radiator. That made it a single-band antenna. Very quickly it was =
discovered
that the Windom would work well as a multi-band antenna even thought the
feeder radiated very heavily. Indeed, on lower bands and at typical =
heights
most Hams could achieve - between 30 and 60 feet - it seems to be the
radiation from the feeder that gives it its FB performance. Of course, =
it is
essential that the "feeder" run in the clear like any radiating portion =
of
an antenna.=20

Over the years many variations on the "Windom" have appeared designed to =
use
open wire feeders, coax feeders and combinations of the two. Many =
(most?) of
them work quite well, provided the basic rules for any horizontal =
antenna
are followed. And the most important rule is to get the proper height =
under
it. If you are using a variation that has an all-coaxial feedline that =
is
NOT intended to radiate, then height becomes all-important for low-band =
DX
performance again. Most of the Windom designs feature a system that has
coaxial line from the shack to some point under the antenna, then open =
wire
feeders from there up to the horizontal wire. Those open wire feeders =
will
radiate very heavily on most bands, providing that all-important =
low-angle
radiation for DX. They radiate because they are NOT connected at the =
center
of the antenna, so, unlike the popular "doublet" or center-fed antenna,
their currents are not balanced to prevent radiation.=20

Ron AC7AC
K2 # 1289

-----Original Message-----
Last night I worked a station in California using a windom antenna and =
he
blew the socks off my K2....My poor butternut vertical is almost =
embarrasing
on the air! Of all the stations I heard last night, he was the strongest =
by
far and using 100 watts. I...Anyone on the reflector built a windom, =
they
don't look difficult to build? ...Since I built my own radio shouldn't I
build my own antenna? Thanks, Roy Vickers (KF5YU) Central Texas