40 Meter Delta Loop

Construction: I made and put this antenna up the Friday afternoon before the ARRL RTTY Roundup (1999)! It took me about 3 hours to make and install on the tower. Most of that time seem to be used untangling the wire..hi hi I made the antenna 142 feet long. Use tiewraps at each of the three points to form a small loop at each end so that A 3/16″ rope could be used to support the antenna. I used a center insulator (Budwig HQ-1) that I had left over from an old dipole. The feed point was 12′ from the bottom of one leg. This antenna requires a matching element of feedline made out RG-59 (75ohm) coax. The formula or the length is a 1/4 wavelength at the operating frequency times the velocity of the RG-59. It is pretty easy to figure, a 1/4 wavelength at 7.050 (234/7.050) = 33.19′ times 66 percent equal 21.9. I had RG-59 with the polyprolene dialectric therefore the length turned out to be approximately 22 Feet.

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Since I had the Budwig HQ-1 with the SO-239 moulded in the unit, I put PL-259s on each end of the matching coax and then used a barrow splicer to put the regular 52ohm coax feedline to the antenna.. A little weather proofing and this setup has worked well for many years.

My mounting point was only about 45′ above ground, which is insulated from the tower by a 3′ fiberglass pole. The legs of the antenna were secured East and West, and North and South is broadside to the antenna. Because the mounting points was so low, the bottome portion of the antenna was sloped out several feets to help provide space under the antennea for cutting grass.. hi

Results: Actually, the antenna played better than anything that I have had previously. The SWR was flat from 7.0 to 7.1 only rising to 1.5 at 7.3. This was perfect because I wanted it to play RTTY and CW… I did find that the antenna appeared to be less effective broadside, to the North. Stations in New England were difficult to get, however, the Europeans and Western USA were answering on the first call. Also, a few days after the contest, I talked to K4HXW/Mr Tucker, he indicated that he thought the antenna was playing much better than the inverted Vee that I had previously.

Added 31 Aug 2002 Update: I put this antenna back up recently and found that the correct length was a little off on my original antenna. According to ON4UN’s Low Band DXing book, the proper length for a delta loop should be 1.05% to 1.06% wavelength. I used 1.05% and the correct formula to calculate this length in feet is to divide 982.8 by the frequency in Mega Hertz (982.8/7.150=137.45′). I also have changed where the antenna is feed to horizontal by feeding the antenna in the middle of the bottom. This is so that I could have better effectiveness in domestic contest. After several days testing, the antenna seem to work well. Only time will tell… hi hi

Added 17 Oct 2011: Been living in Alabama since 2005 and installed the Delta Loop with the apex at 65′ and the bottom slightly kicked out a bit (not more than 5 degrees). I also changed back to the feed point to 12′ from one of the bottom corners. I really have not been able to see any difference in it performace based on changing the feedpoint. It has worked marvelously both for DX and Domestic contacts. I truly think that it is the best single wire antenna I have ever had on 40m.

I am probably going to put one up for 80m when the WX permits.

Article by KC4HW originally available at http://kc4hw.net/deltaloo.htm