Homemade Carolina Windom antenna

Coax fed OCF 'Windom' antenna

Coax fed OCF ‘Windom’ antenna

Here is my home HF antenna. It is an off centre fed dipole, with 10 feet of vertical radiator. It needs no tuner on 40m, 20m and 10m. It also works fine on all bands above 40m with a tuner, and even below 40m on 60m, and 80m, although the coax losses will be higher. I have even used it on 160m, but it is very inefficient there. Ideally, this antenna should be at least 35 feet above ground, but mine is currently about 25 feet, and still performs OK. The radiation pattern is improved if it is above 35 feet.

S.W.R. Graph

S.W.R. Graph

Holding true to the original Windom formulas, I used a ratio of 37.8% for one side and 62.2% for the longest side after determining the half wave length at the lowest operating frequency…. This is the 200Ω point, hence the 4:1 balun. (50Ω to 200Ω)

The 10 feet vertical radiator really does radiate, and offers vertical radiation to the existing horizontal radiation, and therefore adds to the low angle omnidirectonal radiation. The line isolator stops the vertical radiator radiating all the way back to the shack.

This is the same design as the ‘Carolina Windom 80 Special’ You can buy one of these for £109.95 but this cost nothing like that!

4:1 Balun

Here is the 4:1 balun. It is 17 bifilar turns on a half inch ferrite rod. 50Ω – 200Ω, 1-30MHz. Analyzer shows 1.1 SWR @ 50Ω to a 200Ω resistor from 1 through to 30MHz

Line Isolator

The line isolator. 10 turns RG8 on a half inch ferrite rod.

Line Isolator

Line isolator. Made from PVC pipe with screw on end caps. You could just use a bare ferrite rod on the coax and save the connections.

The antenna just fits in the garden, from roof peak to a pole at bottom of the garden.

House end

Mast end

 

 

Birds keep their feet warm in the winter months!

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36 Comments

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  1. Don’t know the maths or the theory, but this antenna works as well as a G5RV. Used a G5RV for years then had a break of some 20 years. Getting back on the air researched several wires which would fit my garden, tried a home-brew Carolina Windom and hey presto its a gem on all bands but Top Band. Talking about pre WARC, haven’t investigated them yet. Its a real peach on 40m. And cheap. A reel of wire from Maplin etc and some ferrite rod salvaged from the junk box.
    Bruce G4EUW

  2. Hello John – very nice detailed description. This is definitely the next project.

    What guage of wire do you recommend for the antenna given that it has about 35′ of coax hanging off it near the middle?

    Thanks & 73 de ROB (ZS1OPB)

    1. Hi Rob.

      Use something thick enough to take the tension. I just used some thick earth wire (because I had some).

      Good luck! John.

  3. Hallo John, I built the antenna coupler for end fed with your project. I havbe a question for you.
    Can I mount windom antenna how inverted V without change the lenghts?

    1. Hi Marco.
      You could, but it will affect performance. Try to get the ends off the ground as much as possible.
      Good luck! John.

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