The Half-Square
vs the Loop Skywire
by Jim Stafford, W4QO
Appeared in QRP Quarterly, Fall, 2006
Up until about 8 years ago, I had an 80 foot tower with a TH-6DXX on it. It was quite fun working QRP with it on 20 thru 10 meters. Reports of “WOW, you can’t be QRP!” or “are you pulling my leg?” were quite common. But then an unfortunate incident involving a bulldozer and a hooked guy wire meant the tower was no more. Oh, it’s still out back awaiting the day when I can put it back up (if I ever do).
I had been using a full wave 80M loop at about 35 feet for 40 and 80 with good results. I’d work my share of EU, AF, and SA stations on 40M but I did not try it on the higher bands until the tower went down. Oh, did I mention I spent the insurance money on a new shop I was building - that’s what the bulldozer was doing - grading for the shop site. Since all I had now was the 80M loop, I started loading it on all bands. Somewhat to my amazement, it performed well on 30, 20 and the higher bands.
Just what is a 80M full wave horizontal loop? Well, this is sort of like asking who is buried in Grant’s Tomb, isn’t it? It is simply a square loop (it can be about any shape) of wire, about 70 feet long on each side, held up by 4 supports, one on each corner at as high as I can get it. It was made popular by local ham Dave Fisher, W0MHS. Dave moved away but some years later, I decided to try the loop on Field Day at about 20 feet high with great success. Dave covered this thing he called the Loop Skywire in the November 1985 QST by the way. He concludes about like I do, that I’m not sure how it works but it sure does. The article is reprinted in the ARRL book Wire Antenna Classics, which I heartily endorse for good reading.
In the article, Dave fed his loop with coax at one corner. I feed mine with the rare 300 ohm open wire line. This is the stuff we used to see in the mountains of North Georgia running up the side of a hill for a couple hundred feet (or more) to a TV antenna. I found a roll of it (brand new) a few years back and have been carefully using up the 500 feet on the roll ever since. It has white plastic insulators about every 6 inches or so and is spaced about an inch apart on the wire feeders. I hit a 4:1 balun at the entrance to the house and come another 25 feet with coax (RG-8) to an unbalanced tuner. I have even used the antenna as a top loaded vertical on 160M (open wire shorted together) fed against a couple wires of counterpoise.
I know this anecdotal type evidence is somewhat suspect but for the recent WPX contest, I put up a half square for 20M at about 25 feet up. It was aimed toward Europe (45o) from near Atlanta. I could never get a better signal receiving on the half square than the loop and about ½ the time, the loop was better. After the contest, I called a 4X4 on the half-square. He had difficulty getting my callsign and report. He finally gave me a 339. Right before my last transmission, I switched to the loop. He said, “you’re fine now, a solid 559”. I took the half square down.
Most feel that a loop is a real cloud burner (now called NVIS). Perhaps it is, as I work locals just fine on 80. In his article on horizontal loops (note 1), L.B. Cebik, W4RNL, states that “On 80M, the loop is a real cloud burner with gain at 45o.” That’s good enough for me. But when the frequency is doubled - i.e. using an 80M loop on 40M, the picture begins to change. In the Fisher article in QST, W8BO who used a 40M version at 20 feet was quoted as saying, “what is amazing is the coverage at low angles”. I agree. But according to Mr. Cebik, the effect is even better (lower angles) at 4F or above. Well, the effective height in wavelengths also is much better as the frequency goes up too. Let’s check out the pattern for a corner fed 80M loop from LB’s web site (note 2):
In this graph, he is looking at a 2WL loop, so F for me would be 40M and 2F would be 20M. As you can see the loop has a clover leaf pattern of some prominence. Is the antenna directional? It may not seem like it but according to L.B. it sure is. Actually, in the ARCI QRP and domestic contests, I do seem to have a pipeline to the MN and WI areas. Either that or Mert (W0UFO) and all those guys up there have darn good antennas aimed at me as we’re almost always 599 each way (true report). If you look at the feedpoint above and the “2F/14Mhz” pattern, you will see the largest lobe is opposite the feedpoint. My loop is fed on the SE corner, hence the line to the NW (ie MN or ID) is best for 20M. I get a good shot to EU from the NE corner but I’m thinking about moving the feedpoint for DX contests to the SW corner to give me another DB! One thing I notice about the mechanical nature of the horizontal loop is that with 4 trees holding it up, they do not all sway at the same time in a direction to break the antenna or the support lines. With some pretty strong winds here, the loop has survived all but one about 5 years ago. I think the nylon cord simply wore out actually.
About 2 years ago, I started using the N3FJP package of logging and contest software. Since that time, I have worked over 3400 QRP QSOs (98% on the loop - others are mobile and portable). True, I am a contester so many of those were worked in contests. In that time, I have worked 120 DX countries on all bands (even have 18 on 80M). I made 119 Qs in 35 sections in the 160M contest, but that was not as a loop, rather a vertical, top loaded. Still it’s a nice way to use your wire loop. In the last November Sweepstakes, I worked 276 stations (181on 40M) in 71 sections for 2nd place QRP in the Southeastern Division. This was in 13 hours, not the full 24. In the ARRL DX contest in February, I worked 62 unique countries on 80 thru 10M. And in the most recent WPX contest, I had over 550 Qs in about 19 hours. Probably 200 of those were DX stations on all 6 continents.
Oh, one last thing - I worked a station somewhere in WI using a 160M loop at 8’ and he was booming in too! I was not on the loop but an inverted V up in the NC mountains at the time, so his loop was doing all the work! This was on 40M. Give the Loop Skywire a try. I think you’ll like it. I do!
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