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| 1953 W9KCM QSL Card (front) | 1953 W9KCM QSL Card (back) |
Greg Ordy
I must confess, I am fascinated by the historic development of the broadband 80 meter dipole, and it's close relative, the inverted vee. On one hand, the 80 meter dipole (and the vee) is a classic and common antenna - who has not had one up at some time? On the other hand, many different designs have appeared, all intended to improve the bandwidth of the antenna. The designs are based upon several different concepts and approaches.
At the end of 2002, I was finishing up my 80/40 meter vertical array. This would become my primary 40 meter antenna, and, I could take down my phased delta loops. I decided to hoist an 80 meter inverted vee to the top of my tower, and use it for local ragchewing communication, and, it would also provide a comparison antenna for the vertical array. This led to my first 80 meter inverted vee web page.
While putting together that page, I decided to go through all of the books and sources I had available to me, and see if there was some design or variation that I might want to implement instead of a simple vee. As I read through the information, I saw all sorts of designs, and all sorts of performance claims, estimates, and measurements. While I have little reason to doubt the theories behind the alternatives, I did find that some of the data was not consistent with other data. Were the authors lying, or making it up? What was going on?
I certainly don't think they were doing anything but reporting the truth as they found it. I think the confusion is the logical result of work made over several decades, with a wide range of local conditions and test equipment. Most 80 meter antennas are located very close to the ground, in terms of wavelength. This means that the ground characteristics will have a large impact on the antenna parameters. That's a large wild card factor, as well as other factors, such as nearby objects that might influence the antenna. Towers, wires, houses - those sort of objects. We all usually have them, but their impact on an antenna can be hard to determine.
Many of the design articles were based upon mathematical analysis. In the 1980's, some brave souls used calculators or simple computer programs to grind through expected impedance data for a given antenna. The equations used were taken from classic sources as as Antenna Engineering Handbook by Jasik. That was about all you could do back them. Effects, such as ground, were not even considered. As we got into the 1990's, antenna analysis generally shifted to antenna modeling programs, which take a different approach to computing a result, and can take ground effects into account. While some folks had access to high quality test equipment, others were limited by the typical ham gear, which can have some accuracy issues. Obviously we can expect some differences, perhaps large, between these tools and approaches.
The most common measure of bandwidth is the SWR bandwidth for some reference value such as 2:1 or 3:1. One of the nice properties of SWR is that on a perfect lossless transmission line, the line length will not change the SWR. The impedance will be transformed, repeating every 1/2 wavelength, but the SWR remains constant. Of course we don't use lossless lines, we use real lines with loss. The effect of transmission line loss is to lower the SWR at the source end. This means that the SWR response measured will be a function of the transmission line type and length, as well as the antenna. If you measured the SWR of a 80 meter dipole with the same meter and same dipole, but in one case through 300 feet of RG-58 (more loss), versus 50 feet of RG-213 (less loss) you would measure two different SWR curves. The RG-58 version would appear to have a broader SWR bandwidth.
In order to satisfy my curiosity, and to hopefully make a contribution to the history of this antenna, I decided to actually implement as many of the designs as I could, all using the same test fixture - OK, my yard. By implementing all of the antennas at the same place at the same time (but one at a time), the effects of ground and nearby objects would not be removed, but would be constant. I was hoping to get a handle on how these alternatives performed - relative to each other.
Will my results be universally true? Sadly, no. My antennas will be influenced by the local ground and the other factors surrounding the antenna. There may not be one single result which can be duplicated at another site. I would hope, however, that general trends might be true in other locations, and perhaps that will help others make decisions for their antenna farms.
Here are the pages that describe my work with the 80 meter inverted vee.
My 80 meter inverted vee pages will contain small portions of copyrighted material, usually graphs and pictures. On my other pages, I have always avoided directly using copyrighted material. With the Internet as a source of information, that is an easy policy to implement, since you can just insert a link to the material, and then write about it on your own page.
Much of the information I went through to create the antennas described on these pages is old printed material which, to the best of my knowledge, is not available online. Whenever possible, I have tried to recompute the data in a graph, or, redraw a diagram. Still, there are cases where that was not practical. In those cases, I will copy the material onto my pages.
It is my intent that these uses fall under the copyright fair use doctrine. A description of this concept can be found on this page.
In order to try and comply with the fair use standards, I will always attribute the original source. I also encourage all readers to go out and buy the original material, since I'm sure that there is much useful information there, beyond what I have chosen to highlight.
If you are the copyright holder for any material I have used, I will immediately remove the material if you do not wish to grant me permission to use the information.
These pages are dedicated to the memory of Jim Jarvis, W9KCM (SK).
I met Jim in 1969, when I was 15 years old, and living in DeKalb, Illinois. At that time, Jim was already in his 60's. He had a certain thin and spry body style that reminded me of my grandfather, who was around the same age. I became aware of him as a ham because of the 80 meter dipole which hung next to his house, perhaps only 20 feet off of the ground. This was in a typical small lot neighborhood. I would drive by his house on the way to high school. I was interested in getting my radio license. Back at that time, it was possible to obtain a Novice license that had a two-year term, but could not be renewed. What was attractive about that license was that the test could be administered by other hams - you did not have to travel to an FCC office. DeKalb was located 60 miles from Chicago, so getting into the big city to take a radio test was not too easy - especially for a 15 year old.
Jim helped administer the exam, and fortunately, I passed.
From time to time, I would go over his to his house - usually to borrow something such as a dummy load. He had a tidy and compact station located in his dining room. It was a small house, and I don't think he had too much spare money for his radio hobby. His equipment was all Heathkit gear as I recall. Back then, the radios were based on vacuum tubes, and each glowed a soft light from the ventilation holes on the top of the metal case. In a dark room, the pattern of the light on the wall gave the equipment that science fiction movie feel, which made it all the more impressive, especially to a 15 year old kid.
In 1972 I graduated from high school, and left DeKalb. From time to time I would visit friends in DeKalb, and I stupidly assumed that Jim would have died in the few years after I left. To a 15 year old, everybody over the age of 50 looks ancient. During one visit, I did drive down his street, and I saw that same old dipole in the same place it had been for probably decades. I could not believe he was still there, and I figured that the new owners were maybe too lazy to take down the wire, or perhaps another ham took over the house.
At some point in the 1990's, I picked up a callbook CD-ROM. I started to type in all sorts of callsigns from my memory, and there was W9KCM, same address, with an active license. I could not believe it was him, but it was.
A few years ago I did hear that he had died, close to the age of 100. I never really talked to him about the state of amateur radio when he was young. I bet he had some wonderful stories and experiences. I bet there were a lot of things he could have taught me.
So, when I think of the 80 meter dipole or vee, I think of Jim Jarvis, W9KCM, and the antenna that hung through the side yard of his house for probably over 50 years. I was interested in Amateur Radio long before I met Jim, but he was very helpful in my first steps in the hobby. He was a true gentleman.
As I was writing this dedication I searched the Internet for W9KCM. I was hoping to find a picture, or some other information. I didn't find much, but what I found was very interesting. First, from QRZ.com, his FCC database entry.
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W9KCM Entry on QRZ.com |
His FCC license expired just a few months ago. Sadly, he is no longer here to renew it. Sooner or later, his entry will disappear from the database. He was 63 years old when I met him, back in 1969. As I was starting this page, he would have celebrated his 99th birthday.
I also found a 1999 Field Day log book from W1NVT. On that page was the following entry:
| 0623 06/27/99 80CW
0718 K8EE 1A OH 0624 06/27/99 80CW 0719 N0KK 2A MN 0625 06/27/99 80CW 0722 W9KCM 1A IL 0626 06/27/99 80CW 0722 N8AP 3A MI 0627 06/27/99 80CW 0723 W2RA 3A WNY |
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N1NVT Log Book Entry for W9KCM |
I don't know if that was W9KCM himself operating 80 meter CW, but I wouldn't doubt it. Here he was, in his 90's, operating Field Day!
Finally, I ran across an interesting page devoted to old QSL cards. This page is maintained by W8JYZ. Although a W9KCM card was not online, there is one in his collection. I probably have one too, but where is the question. Bob, W8JYZ, gave me permission to include scans of the QSL card on this page. Please click on a picture for a larger view.
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| 1953 W9KCM QSL Card (front) | 1953 W9KCM QSL Card (back) |
What's interesting to me about this card is that the QSO took place a few months before I was born. It's a 2 meter QSO, so W9KCM obviously had a well-rounded station, operating from HF through VHF.
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