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N5XO and the Unusual Suspects

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Unusual Suspects


The Modified Windom Antenna:

On the higher HF Bands I have a great antenna system, with multiple beams for 20 to 10 meters, and have enjoyed great sucess with my system performance, but the lower HF bands 40, 60 and 80 meters have been a source of frustation for me. With limited room to run a dipole, and interference from car ports, sheds, etc I have run into my share of problems and Antenna performance has been poor at best. I have worked with 80 meter double bazooka's, folded dipoles, trap dipoles, and all run into the same problems with regards to over all performance on my property. Based on Don {KE5EYH} experience with windom antennas and the performance of his system, I started researching the windom antenna. I needed to be able to fit it within my lot, away from the metal roofs of our sheds, and car port.

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. Just do a search on Google for more on the "Windom".

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. I will call this 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 differences between the New Carolina Windom antenna and Windom’s original is that the Original Windom is not a dipole.

Enter the New Carolina Windom



NEW Carolina Windom shown cut for 40, 20, 15 and 10 meters.

It will operate on 80, 30, and 17 meters but will require a tuner for these bands.

This more recent, New Carolina Windom, version has some very interesting characteristics as seen in the drawing above.

For one, 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.

NOTE: 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 will require a tuner for these bands.

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

Holding true to the original Windom formulas, we use a ratio of 37.8% for one side and a ratio of 62.2% for the longest side after determining the half wave length at the lowest operating frequency....



Using  7.1mhz as lowest frequency of operation we use:

468 / 7.1mhz = 65.9 feet (round to 66 feet) for total half wave length.

Short side length = .378 (37.8%) X 66 = 24.9 feet = 25 feet rounded

Long side length  = .622 (62.2%) X 66 = 41.05 feet = 41 feet rounded

So we have the short length of 25 feet, and

long side of 41 feet using the formula.

Vertical length for RG58 from balun to choke = 4 to 1 ratio (meter band / 4)

40 meters / 4 = 10 feet

Using 3.9mhz (80/75 Meters)

468 / 3.9mhz = 120 feet for total half wave length.

Short side length = .378 (37.8%) X 120 = 45.36 feet

Longest side length = .622 (62.2%) X 120 = 74.64 feet

Vertical length 4 to 1 radio = 80 / 4 = 20 feet

Editors note: The New Windom can be designed for 160, 80/75, or any fundamental frequency you desire as the lowest band of operation and it should perform better on that fundamental frequency and still resonates on the harmonically related bands without a tuner.  Just keep the original ratios (37.8% and 62.2%) 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.

If you are a perfectionist, then you may want to trim ends for best SWR. According to all who have build the New Windom using these formulas, they work great! Get is up as high as possible and have fun!