Registered Trademarks (®), Trademarks (™), and Copyrights (©)

How The CAROLINA WINDOM® Came To Be

by Jim Thompson, W4THU

There is a lot of controversy over and misinformation about the CAROLINA WINDOM. What follows is the story as I remember it. It's been about 25 years since I build my first CAROLINA WINDOM®. Originally, the CAROLINA WINDOM was the result of an attempt by Jim Wilkie, WY4R, Edgar Lambert, WA4LVB, and Joe Wright, W4UEB to make a 75 meter band antenna that would provide more reliable coverage on a difficult propagation path between Norfolk, Virginia and parts of northern North Carolina. What they came up with was an off-center-fed dipole which physically resembled the original Windom antenna which is also fed off-center. That's how the CAROLINA WINDOM® got the Windom part of its name. The "Carolina" part of the name is the result of the Virginia and North Carolina participants needing better 75 meter coverage. I became aware of the antenna when a particular current balun that I was building at the time seemed to significantly improve the performance of the antenna over that difficult, Virginia to North Carolina propagation path. I was receiving an occasional inquiry on the telephone about the parts for the "antenna with 10 dB gain over a dipole." You can dismiss one or two calls with that request, but after receiving three or four such inquiries and talking with Jim Wilke about the antenna, I wanted to determine what was going on. After all, a dipole is a dipole. It doesn't have gain over itself. I built one and used it on the air (75 meters) for a few evenings. Up to that point, I used a SuperLoop™ for 80 and 40 meters and a 3-element Cubical Quad for the higher bands. I was a DX'er, so I tried the CAROLINA WINDOM® in the 75 meter band "DX Window." It didn't take but a couple of QSOs to determine that the CAROLINA WINDOM® was a very effective DX antenna on 75 meters. I could work just about everything on the band with my linear amplifier turned off, just like I could with my SuperLoop™. This kind of performance was never achieved when I had dipoles in the air at the same height above ground. With a dipole, it usually took every watt my linear amplifier could produce to be effective working DX on 75. In those days, it was really competitive in the "DX Window." My original skepticism was gone. The antenna obviously worked well up close - it's intended purpose, but it also worked even better at longer distantness. That was something no one had guessed in the beginning. Intrigued, I set out to determine what made the CAROLINA WINDOM work so well. Obviously, it had a very low takeoff angle component in its radiation pattern. It must be that the low angle component was vertically polarized. That's the only way to achieve both short and long propagation paths like the CAROLINA WINDOM® was exhibiting. One thing that was unique about the antenna was the use of a specific current balun that I made at the time. It was determined that it produced significantly better results than simpler and less expensive voltage baluns could produce. Was this, indeed, a "dipole that had 10 dB more gain than a common dipole?" It seemed so, and experiments were proving the fact. What wasn't immediate obvious was that we were not dealing with a dipole. The CAROLINA WINDOM® is a three element antenna (a tri-pole?)

Countless experiments later and after building an RF current meter, it became obvious that there was higher than normal RF current on the outside of the feedline's shield. The feedline was radiating. It was vertical to the earth and to the flat top portion of the antenna. It must be producing the guessed-at vertical component in the radiation pattern. If this was the fact, two things became immediately obvious. First, since it appeared that the RF current radiating from the feedline was making the difference, performance could be improved further if more RF current could be diverted from the dipole itself and directly to the feedline. Second, since the feedline was "hot," being an active part of the antenna, a means to keep this RF from traveling back into the radio room had to be developed. This resulted in the development of the "Line Isolator™." Never, in my wildest dream could I anticipate the future popularity of the "Line Isolator™." But, that's another story.

Weeks of experiments and data collection followed and I had a good grasp on the contribution the "Vertical Radiator" was making to the radiation pattern of the antenna. I had also discovered many interactions between the length of coax used as the "Vertical Radiator" between the balun used to match the antenna and "Line Isolator" used to isolate the active portion of the feedline from the inactive portion. The length of the "Vertical Radiator" was critical to the maximum performance of the antenna but it was also critical to the matching of the antenna. This antenna never achieved a 1:1 SWR. Since I wanted more RF current in the Vertical Radiator™, it was obvious that the current balun used was not the best choice for making the "Vertical Radiator" as effective as possible. A current balun actually reduces feedline radiation while providing a balanced output. The CAROLINA WINDOM is not a balanced antenna and I didn't want feedline isolation. What I needed was an asymmetrical (unbalanced) device with the efficiency of the current balun currently used in this application. Yet another unique device was necessary for maximum performance from a CAROLINA WINDOM®. To make a long story shorter (after all, I have optimized this design over the past 20 years or more - so that's a long story), an efficient unbalanced or asymmetrical matching unit, a well as the Vertical Radiator and Line Isolator came to be the "magic" of the CAROLINA WINDOM® as we know it today. Ultimately, I found the CAROLINA WINDOM® concept could be made far more effective by optimizing the matching units and Line Isolators for each model of the CAROLINA WINDOM® that would eventually be developed. Each model now has a "dedicated" Matching Unit and dedicated Line Isolator™ optimized for each model of the CAROLINA WINDOM®. There is no "Black Magic," to there is magic in the CAROLINA WINDOM®; it's just the result of good design and accurate fabrication.

In a nutshell, that's the story of the CAROLINA WINDOM®. It has had a moderately long journey so far. It continues to be increasing popular and enjoy a wonderful reputation among those who use it and understand it. I expect that it's popularity will only increase during the next Sunspot cycle or two. As in the past, there will be more rip-offs (copies and copiers) and I'll have to try to limit their impact on the CAROLINA WINDOM's reputation. After all, if you purchase a CAROLINA WINDOM® you should be able to enjoy the performance the CAROLINA WINDOM® is capable of achieving. If the RADIO WORKS didn't build it and if it doesn't carry the RADIO WORKS' name on it, it's not a CAROLINA WINDOM® and it doesn't perform like a CAROLINA WINDOM®. To that end, I have registered the name "CAROLINA WINDOM" and have received the rights to the Registered Trademark for that name. Further, "first use" Copyright and Trademark rights are documented. "First Use" involves being the first to use a claimed name in publications available to the public and using the "™" symbol for it's intended purpose. Publications available to the public include advertising, catalogs, articles, and other retrievable publications with documented publication dates. This material must be available to the general public so it does not include instruction sheets or limited publication, like club news letters.

Registered Trademarks (®), Trademarks (™), and Copyrights (©)

I know that this part of the story is of no interest to most of you, but it is my way of introducing the information which follows. So, unless you're interested in the legal names for some of our product line, you do not need to read on. If you are contemplating selling or distributing any Trademarked or Copyrighted material, be advised that you must receive "written" permission to use any of the following:

Dimensions, multibanding technique, the Line Isolator enhancement, application of the "Vertically Enhanced Radiation Technique™" (VERT™) to the original CAROLINA WINDOM® as well as the design of the following versions of the CAROLINA WINDOM are covered by copyrights and Trademarks owned by Jim Thompson, W4THU. These include, but are not limited to the following:

CAROLINA WINDOM® 160™
CAROLINA WINDOM® 160 Compact™
CAROLINA WINDOM® 80™
CAROLINA WINDOM® 80 Compact™
CAROLINA WINDOM® 40™
CAROLINA WINDOM® 40 Compact™
CAROLINA WINDOM® 20™
CAROLINA WINDOM® 620™
CAROLINA WINDOM/2™
CAROLINA WINDOM/4™
BBC WINDOM™
HCJB WINDOM™
CAROLINA WINDOM® Shortwave™
CAROLINA BEAM™ and its specific band coverage models (i.e. 160, 80, 40, etc.)
CAROLINA WINDOM Short™ and its specific band coverage models
CAROLINA WINDOM® Shorty™ and its specific band coverage models
All versions of the loaded, linear loaded CAROLINA WINDOMS® and their specific band coverage models
All versions of the CAROLINA WINDOM® using multiple Vertical Radiators (variants of the CAROLINA WINDOM® BEAM™, CAROLINA BEAM™, CAROLINA WINDOM® Short™, CAROLINA WINDOM® Compact™, etc. )
Dimensions, multibanding technique, the Line Isolator enhancement, application of the "Vertically Enhanced Radiation Technique™" (VERT™), as well as the designs of the following antenna types are covered by copyrights and Trademarks owned by Jim Thompson, W4THU. These include, but are not limited to the following:

SuperLoop™
BigSig Loop™
InTreeVert™
Little Loop™
Vertically Radiating Dipole™ (VRD™)


The following OCFD MAX™ products were added on May 20, 2010

OCFD MAX™ 80 or Off-Center-Fed Dipole MAX™ 80

OCFD MAX™ 80 + 15 or Off-Center-Fed Dipole MAX™ 80 + 15

OCFD MAX™ 40 or Off-Center-Fed Dipole MAX™ 40

OCFD MAX™ 40 + 15 or Off-Center-Fed Dipole MAX™ 40 + 15

All of the antennas listed above were developed by Jim Thompson, who owns the Registered Trademarks (®), Trademarks (™), all Publications, and/or Copyrights (©) of all of the variants of the CAROLINA WINDOM® and of the CAROLINA WINDOM® itself.

This list is not complete since product development and new designs or modifications of current, non-Trademarked designs are an ongoing project and new Trademarks are assigned to these projects as appropriate.

All Copyrighted literature, publications, articles, and all other material appearing in print or on the Web, written or published by Jim Thompson or The RADIO WORKS™ using the above listed names and descriptions and all variants associated with them are the intellectual property of Jim Thompson, W4THU and are covered by associated Trademarks and Copyrights. All manufacturing procedures, processes, and techniques are also covered by the Copyright and Trademark rights owned by Jim Thompson.

An exclusive license is granted to The RADIO WORKS, by Jim Thompson, W4THU, for production , distribution, and use of the Registered Trademarks, Trademarks, and Copyrights of the CAROLINA WINDOM® in the various versions listed above.


Note: Parts of this article first appeared in the RADIO WORKS' Reference Catalog©, pages 58 and 59.
It has been updated on June 24, 2009 and May 21, 2010 to reflect changes, new models, names, and improvements made to the CAROLINA WINDOM® since the article appeared in the RADIO WORKS' Reference Catalog.

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