I don't worry much -- if you can get some energy into your antenna, it'll work even with lousy SWR -- but it was pretty bad.
So I put up an off-center-fed 40 m dipole, a sort of a coax-fed Windom.* With the feedpoint at the 80%/20% point, it should look close to 200 Ohms and take a 4:1 transformer to present a decent match to 50 Ohms.
The antenna part is easy enough -- take 67' of wire and divide accordingly, then make it fit (I ended up having to bend both ends).
The transformer... It was a holiday. The ham store we haven't got was closed. But all you really need is wire and a coil form (PVC pipe) and a little hardware:
(The branch is not really that close to it.) Ended up with 11 bifilar turns of #14 house wire on approximately 1- 1/2" diameter PVC. Hams get all worked up over these but with about three bucks of materials in it, this version is not too painful to have to redo from scratch if the first try doesn't work. My design is all rule-of-thumb and fudge-factored from other versions on the Web.Here's a funny angle on the transformer and one of the bends:
It's about 20' up at the highest points.Finished it after dark -- I'd installed a coax feedthrough but had to put the connectors on the coax -- and had a QSO within minutes of getting on the air. (Real DX: Warsaw, IN) And it tunes up on 40 meters just fine!
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* Loren G. Windom, W8GZ, yet another of the antenna-designing hams from Columbus, OH. You may have heard of the other one -- W8JK, John Krause, of the 8JK HF beam and the helical antenna (both modes!).
Windoms are wonderful!
ReplyDeleteThe last 40m antenna I put up was a "stealthy" windom. I made clear insulators from plastic curtain rod and the wire was that #26 "silky" insulated stranded copper. It had a 300-ohm feedpoint for TV twinlead, via a balun than converted it from 50-ohm coax. The balun was supported from the ground, so the antenna and feedline weighed less than a pound. The antenna was invisible unless it was pointed out to you, and to the neighbors the feedline looked like one of those pieces of "TV wire" that was caught in a tree. And it worked great!
I didn't know Windom was a Buckeye too. I never met 8JK but when I was taking night classes at OSU I saw his office while I was looking for the plumbing terminal. Didn't he also design the late Big Ear radio telescope antenna?
ReplyDeleteRoberta, did you catch the September 1929 QST article by L. G. Windom? I ran across it in L. B. Cebik's article "Notes on Mr. Windom's 'Ethereal Adornments'" 2008-05-01. The QST article might appeal to your retro-sense.
ReplyDelete73, Jim
I haven't seen it yet, Jim. But I will look for it. (It's been awhile since I was an ARRL member, a little spat over them groundlessly accusing my employer of signal impurity to third parties without even bothering to make contact, based on the speculation of a non-ARRL member.)
ReplyDeleteDave H, I met Johnny Kraus and got to hear him speak, at one of the last WOSU Broadcast Engineering Conferences. He was the real deal!
Turk, this Windom is doing pretty well on 40, despite not being all stretched out in a straight line. I worked a ham in Fairfax, VA last night.