A TEN METER DOUBLE EXTENDED ZEPP ANTENNA
How would you like to build a 3dB antenna for 10 meters that takes up only slightly more space than a regular 1/2 wave flat top dipole? The materials are available at most hardware stores and home improvement outlets. You may want to call this antenna “the dipole on steroids.”
According to G3ZPS, the “extended double zepp or EDZ is one of the most successful wire antennas ever developed….it has a bit of gain and if high enough can be a great antenna on the HF bands.” The original “zepp” antenna was used on the Graf Zeppelin airships of the 1920s and 1930s and has been modified and refined eversince.
According to G3ZPS, each leg of this extended dipole is 0.64 (5/8) wavelength and must be accurately cut for the frequency desired. The formula for each leg is 599/f (MHz)=Length in feet. G3ZPS recommends a height of approximately 0.6 wavelength above ground to achieve the theoretical gain of 3 dB. There are a few ways to feed the antenna, all involving a length of 300-ohm tv twinlead or 450-ohm ladder line.
The first method of feeding the EDZ is to use 300-ohm tv twinlead or 450-ohm ladder line running into a balanced ATU or transmatch. I elected to run some 450-ohm ladder line into a W9INN 4:1 current balun and then run a short piece of RG-8X coax into the shack ATU (a Drake MN-4).
The second feed approach is to use open wire feeders as a matching stub and add a 1:1 balun at the bottom. According to N8ITF, the formula for a matching stub in this application is 103/f (MHz)=Length in feet.
If you are really creative, you can make your own ladder line by using stiff plastic pieces and #12 or #14 AWG housewire. The spacing can be anywhere between 2 to 3 inches.
MATERIALS AND ASSEMBLY:
I happened to have an unused 33-foot (10.06 meters) telescoping MFJ fiberglass mast in the garage and a convenient Norfolk Pine tree branch bordering my backyard. The easiest branch to reach at a reasonable height was a limb about 35-feet (10.67 meters) above ground. One end of the EDZ would be attached to the MFJ mast and the other end to the exposed tree limb.
I already had a 5-foot (1.52 meter) wooden support stake driven in the ground to support the hollow fiberglass mast.
Three ceramic insulators were used for the antenna, two at each element end and one to serve as the center insulator and support for the feed line.
50-feet (15.24 meters) of 450-ohm ladder line. This would serve as the feed line.
A W9INN 4:1 current balun. The ladder line would be attached to the balun, with a short run of RG-8X (10-feet or 3.04 meters) to connect the feed line/balun to the Drake transmatch. Short pieces of RG-8X coax would connect the transmatch to the dummy load, low pass filter, and the Swan 100-MX transceiver.
I assembled the antenna on the ground. Using the formula 599/f (MHz)=Length for my chosen frequency of 28.4 MHz, I cut two pieces of #14 AWG household wire, each measuring 21.09 feet (21.1 inch) or 6.42 meters. The total length of the 10 meter EDZ was 42.18 feet (12.84 meters).
I soldered and protected each connection with clear fingernail polish and several layers of vinyl electrical tape.
I attached one end of the EDZ to the top of the MFJ mast and used a slingshot, monofilament fishing line, and a sinker to guide the other end of the EDZ through the tree branch. I tied off this end to a nearby wooden stake.
I then lifted the fiberglass mast onto its support stake, attached the 450-ohm feed line to the 4:1 balun, and ran a short run of RG-8X coaxial cable from the balun to the shack.
SOME PRELIMINARY RESULTS:
Thanks to my trusty Drake ATU (MN-4), I was able to keep the SWR below 1:7 to 1 across the 10 meter band. I was able to make a few mid-afternoon contacts on both cw and ssb. Nothing spectacular….but I did make some contacts. Fortunately, I didn’t have a substitute teaching assignment today, so I was able to experiment with the antenna. Although I made the EDZ for 10 meters, I was able to make a few contacts on 15 and 20 meters. The Drake ATU and Swan 100 MX seemed to handle any mismatches in the antenna system. Most of the time, I ran about 10 watts cw and around 20 watts SSB, with reception reports running between 559 and 579 for cw and 54 to 56 for SSB.
I’ll leave this antenna up for a few weeks to see if propagation improves as February approaches. After a few weeks of use, I’ll finish my documentation, lower the mast, and pack the antenna away for future use. All told, this was a fun project.
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Thanks for being part of our day!
Aloha es 73 de Russ, KH6JRM–BK29jx15–along the beautiful Hamakua Coast of Hawaii Island