A 20, 15, and 10 METER VERTICAL GROUNDPLANE ANTENNA
Over the past few years, I’ve experimented with a variety of vertical antennas fed by tuned feeders. Most of my hombrew designs have worked well with minimum cost. One of my favorites is a small, multiband vertical which will cover the 20, 15, and 10 meter amateur radio bands. This antenna is easy to build, erect, and store. The antenna could serve as an emergency or field day antenna. This multiband vertical groundplane antenna is based on an original design by Arthur S. Gillespie, K4TP.
I built this antenna Saturday morning (19 January 2013) and was making contacts by the early afternoon that same day. Normally, I wouldn’t be able to take advantage of early afternoon openings to the U. S. mainland because I teach school. But, over the weekend, my schedule is more relaxed, so I can jump in when propagation is favorable for the higher HF bands.
The antenna system consists of the vertical radiating element, a groundplane of four, quarter wave radial wires, an open-wire feeder (in my case 450-ohm ladder line) of approximately 50 feet (15.24 meters), a 4:1 balun (I had a W9INN balun in the shack), and an old Drake tuner (MN-4).
Other materials included a 33 foot (10.06 meters) MFJ fiberglass mast, 4 ceramic insulators, a plastic center insulator, 5 pieces of #14 AWG housewire, dacron rope attached to each radial wire, which was tied off at four wooden posts, vinyl electrical tape, nylon ties, clear fingernail polish, and a short piece of RG-8X coaxial cable to connect the shack equipment to the 4:1 balun.
I assembled the antenna on the ground before I lifted the hollow fiberglass mast onto its wooden support stake. The radial wire with the dacron rope tie-offs would also serve as guy “wire” supports for the mast.
I cut the vertical element and radial groundplane wires to resonate at 14.200 MHz. The vertical element was measured and cut to 16.47 feet or 16 feet, 5.64 inches (5.02 meters). The groundplane elements were cut to the same length, 16 feet, 5.64 inches (5.02 meters). There are some antenna experts who feel that the radial elements should be a few inches longer than the main vertical element. Apparently, this gives the groundplane a better match to 50-ohm coaxial cable. I decided to stick with an equal length for all elements.
The base of the antenna was placed at the 16-foot (4.87 meters) level of the 33-foot (10.06 meters) fiberglass mast. This would place the antenna base almost a quarter wave above ground for the 20 meter band. This height would also allow me to run the radial wires at a 45-degree angle from the antenna base. This angle would allow those using 50-ohm coaxial cable rather than ladder line or tuned feeders to get a better match between antenna and the coaxial feedline.
One portion of the 450-ohm ladder line was run through the plastic center insulator and attached to the vertical element. The other part of the ladder line was attached to each radial wire. All connections were soldered, coated with clear nail polish, and wrapped with several layers of vinyl electrical tape.
Once I raised the mast and put it on a supporting wooden stake, I tied off the radial wires to four equally spaced wooden stakes, and ran the 450-ohm ladder line to the 4:1 balun on the garage wall. A short piece of RG-8X coax ran from the balun to the shack. The balun was grounded to the static discharge/ground rod system below the shack window. Coax patch cords connected the tuner to the low pass filter, dummy load, and the Swan 100 MX transceiver.
So far, reports have been good using 20 watts output from the old Swan. Most SSB contacts ranged from 55 to 57 on 20, 15, and 10 meters. CW contacts were higher, ranging from 567 to 599 on 20, 15, and 10 meters.
This antenna can be easily taken down and packed away for future use. The MFJ mast can be telescoped down to less than 4 feet (1.21 meters), making it easy to store in your vehicle or near the shack. Most of the materials for this project can be found at your nearest hardware store or home improvement outlet.
I plan to use this antenna for a few weeks before taking it down and storing it for emergency use.
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The ARRL Antenna Anthology, Marian S. Anderson, Editor. ARRL, Inc., Newington, CT, 06111, copyright 1978, pp. 19-20.
Until next time,
Aloha es 73 de Russ, KH6JRM–BK29jx15–along the beautiful Hamakua Coast of Hawaii Island.