The New Carolina Windom

Len Carlson - K4IWL

As with all ham stations QRO or QRP, ten percent of a station’s success in quality QSOs is
the equipment and the operator. Ninety percent is the antenna. This is especially true in
QRP since with very low power, by comparison to the Power Mongers, we need to get more
ERP per watt out into the ether to be heard.

So when I got back into QRP a few years ago, I found the fascinating world of antennas
and RF radiators to be an exciting challenge and a means to find the perfect antenna which
I call the New Carolina Windom.

I don’t have room for an 80-meter dipole or long wire so I have to restrict the length to
100 feet or less. Besides, my primary interests are working only CW on 40, 30, 20, and
15 meters.

Based upon these parameters, I have found what I consider to be the perfect
antenna. The antenna I will show you how to build in this article evolved from a concept
that had its beginning back in 1929 when Loren G. Windom described his invention in the
September issue of QST, 1929, pages 19-22.

A few years ago, three hams, Jim Wilkie (WY4R), Edgar Lambert (WA4LVB), and Joe
Wright (W4UEB), came up with an idea for an off-center fed dipole that carried Windom’s
single feed line antenna to the next level. It has since become known as the Carolina
Windom. This is called the traditional Carolina Windom since it was the first attempt at
creating this specific type of multi-band antenna based loosely on Windom’s original
concept.

The difference between the new Carolina Windom and the original Windom antenna
is that the original Windom is not a dipole.

New Carolina Windom shown cut for 40, 20, 15 and 10 meters.
It will operate on 80, 30, and 17 meters but requires a tuner.
This more recent version has some very interesting characteristics as seen in the drawing
above. The 4:1 Balun has been moved to the antenna radiator and is built into the center
insulator.

The other interesting feature is that the 10 feet of coax from the balun is terminated in a
choke or line isolator. I have fitted the 10 foot stub with PL-259 UHF connectors on each
end. This allows the coax vertical radiator to be easily removed if desired. It is designed
to hang vertically which is one reason why this antenna is so effective. The radiation
pattern when using the vertical radiator combines both horizontal and vertical radiation
components and lowers the effective angle of radiation getting more of your signal near
the horizon.

This antenna is in use the world over by DX'ers and DX'peditions. In one Navassa
DX'pedition, of the 33,000 QSOs made, more than 27,000 were accomplished with this
antenna. The DX'pedition team also had a beam and verticals, but the New Carolina
Windom was the antenna they used. Its reputation for excellent performance is so good
that it served as one of the antennas in setting two 40 meter "mile-per-watt" world records
of nearly 4,000,000 miles-per watt.

The antenna can be used without the vertical radiator but the radiation pattern will lose
the low angle component and may make the antenna less effective. If the vertical radiator
is removed then you should move the line isolator to the bottom of the balun.

This antenna should not need a tuner on the 40, 20, 15, and 10 meter bands, although
you may use one if you feel the need to. It will operate on 80, 30, and 17 meters but a
tuner is required.

Here is the math for designing the New Carolina Windom cut for your lowest band
operation:

Holding true to original Windom formulas - use the ratio of 37.8% for short side
and 62.2% for longest side after determining half wave length for lowest operating
frequency.

Using 7.1 mhz as lowest frequency of operation:

· Short side length = .378 x 65.92 = 24.92 feet = 25.00 feet 12% offset
Update = .33 x 66.00 = 21.78 feet = 21.75 feet 17% offset

· Long side length = .622 x 65.92 = 41.00 feet = 41.00 feet

The new Windom can be designed for 160, 80/75, or any fundamental frequency you
desire as the lowest band of operation. It should perform better on that fundamental
frequency and still resonates on the harmonically related bands without a tuner. Keep the
original ratios (33% and 67%) the same by using the formula.

You will have to adjust the balun to choke length of RG58 in the same ratio by doubling
the length from 10 feet at 40 meters to 20 feet at 80 meters and 40 feet at 160
meters. The ratio is meters / 4 = length of vertical feeder.
The original OCF Windom built by K5IJB used 12% offset and 68-foot
coax feedline with a 4:1 balun. Between the antenna and the line isolator
was 25 feet - not 10 feet. The remaining 43 feet was used between the
line isolator and radio.

The coax feedline length between isolator and radio was orginally 30
feet. This length resulted in too much reactance for 10 and 17 meters
which my ATU could not handle. The 68-foot coax feedline provided a
better match on 40-6 meters.

The most recent OCF dipoles built by K5IJB used 17% offset
with (1) 450-ohm ladder line and (2) RG8X coax plus 4:1 balun.

17% offset

12% offset
Other offsets (D3) have also been used in search of better impedance
matching. Windom-14% Carr-17.4% Formato-17.4%