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Materials needed: About 15 feet of Zipcord (standard lamp cord #18 gauge) Materials for end and center insulators (Your choice....Non-Conductive) Short length of 2 inch diameter PVC pipe for winding 5 turns RG58 coax Electrical tape, sealer, assorted hand tools Soldering Gun and Solder RG58 to transceiver A handheld calculator would be handy too for the math A little time and some nice weather! GETTING STARTED This version of the 6 Meter Extended Zepp antenna designed for 50 ohm coax feed is made by splitting about 15 feet of zipcord (regular lamp cord wire) in half to form each half of the antenna and the short feedline all at once. When you split it you should have 2 lengths about 15 feet long each. This entire length is a little long so as to have some ends to work with when making connections to the coax and securing each half to the end support insulators. Your final length OF THE FEEDER should be cut longer than the design for adjusting SWR.( see update below) The spreaders and center insulator are small pieces of plexiglass or any other non-conductor material you may have laying around. They will have to be homebrewed using your own construction skills. The short feedline wires should be separated about 3 inches from each other with the spreaders spaced evenly apart down the short length of feedline leading to the coax 1:1 balun coil. The lower end of the homemade ladder line is soldered with one side to the center conductor and the other side to the screen or shield of RG58 coax going to your radio and sealed. This coax is closewound with 5 turns, forming a 1:1 balun, on a piece of 2" PVC pipe and secured tightly, before it is routed down to the transceiver. Make sure you seal the connections between the coax and the wire elements. As with any homebrew antenna project, check your SWR using low power and trim or add to each top half for lowest reading on the frequency you will operate with the antenna up as high as your supports allow! "I don't know who is the originator of this design as the antenna has been around here in Europe for years." Egil, LA2PJ, Norway Diagram below
I was once told to make the line an 1/8 of a wavelenth plus 10-15 percent, and then cut until you get a perfect match to a 50 ohm line, which preferrably should be connected through a 1:1 balun. "Our" 6m version has a feeder length of 48 degrees of a wavelength. The coiled RG-58 works as a 1:1 balun. When the antenna is constructed this way it becomes a single-band antenna. If you feed it solely with balanced line directly to an antenna tuner, the 6m EDZ would also show a solid performance on 10m (probalby with fair performance at least down to 17m)."......LA2PJ Let's design one (hopefully) using the above information: WARM UP THAT CALCULATOR! Operating frequency 52mhz (center of US 6 meter band) We know that a full wave EDZ is actually 1.28s of a wavelength long Using the standard formula, (468) for a half wave, we multiply times 2 = 936 for a full wavelength. 1.28 times this (936) = 1,198 rounded off for the number to use in our formula = 1198/freqmhz So.....1,198 divided by 52mhz = 23.03 feet for overall length.....cut in half for each leg = 11.51 feet per half or in inches = 12 X 11.51 = 138 inches rounded off per half. Now it gets a little more difficult to calculate the feeder length. (or maybe not!) We know by the above description that the feeder length should be about 48 degrees of a full cycle or full wavelength at 52mhz but we can't measure out 48 degrees on our tape measure so we have to convert to feet and or inches. Assuming our full wave length number that we used in the formula above (936) is correct and is equal to 360 degrees, we continue. Remember that we found 23.03 feet to be one wavelength at 52mhz. This is the same as saying we have 360 degrees of the wavelength. One half of the 360 degrees would be 180 degrees or one half of 23.03 feet. Hope you get the picture! We are looking for 48 degrees of 23.03 feet so we have to convert degrees to feet and or inches: 23.03 = 360 degrees 23.03 divided by 360 = .0639722 per degree in feet We need the length of the feeder in feet and or inches so... 48 degrees X .0639722 feet per degree = 3.0706656 feet or converted to inches = 36.84 inches (12 X 3.0706656) Now take the suggestion of adding 10 to 15 percent to that and we get, 36.84 X .15 = 5.52 inches added to 36.84 inches = 42.36 inches for the feeder before trimming for best SWR! Now we know that our design must have each top half at 138 inches or 11.51 feet and our short homebrewed feeder matching transformer should be 42.36 inches before trimming. "This example was determined by deductive reasoning using a little math with the assumption that the original design works. I have no reason to believe that our Ham Radio friends in Norway would have passed this design down thru the years if it was not a good design!...... As with all antenna projects, trial and error are the best teacher and the most fun! Good luck on your design and we welcome feedback, tips, tricks, corrections, etc"...... I can't thank Egil enough for all his help in sharing this project with us and I am very glad his English is so much better than my NORSK! HI! .......N4UJW MORE UPDATES, FORMULAS FOR THE EDZ (EXPENDED DOUBLE ZEPP) AND ADDED INFORMATION "Some authors have provided formulas for cutting the EDZ. The most common is based on the long wire length formula: L (in feet) = 984 (N - 0.025) / f (in MHz), where N = number of wavelengths, or L (in feet) = 1205/f (MHz). Beers prefers a constant of 1218, while recent editions of The ARRL Antenna Book call for 0.64 per side, which yields a numerator of 1258.2.....it all depends on which "experts" source your prefer! 73 Copyright 2000 - 2007 N4UJW Hamuniverse.com and or article author Powered by Ham Radio! |
