The NØEQ
6m Ground Plane Antenna
built from a
Recycled Beach Umbrella
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My neighbors throw away some great stuff! This time, it's a perfectly good beach umbrella "skeleton" (no fabric). All the mechanical parts work, the wood is in good shape. And perhaps best of all, each of the eight umbrella ribs is a quarter wave at 6 meters! The umbrella skeleton is made of mahogany. The finial cap is plastic. Here's my experiments to make it resonate on 50 MHz. |
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The Driven Vertical Element... ... has to mount on the top of the plastic finial somehow The finial looks like terra cotta clay but it's actually some pretty dense plastic material that simply unscrews from the rest of the umbrella. But the mounting bolt doesn't pass all the way through the finial. It doesn't need to, of course, when it's life is that of a beach umbrella. For use as an antenna, here's how I fed the coax up, through the plastic cap, PLUS allowed mounting/dismounting of the driven element. |
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Drill Holes Feed Coax... I hope the pictures show what's happening here. RG-58 coax comes up through the lower piece of clay colored plastic through a hole drilled OFF CENTER. The normal mounting bolt occupies the center space in the two pieces that make up the top of the umbrella. The coax ends in ring lugs. Another off center hole, this time in the top or finial, allows a 12 ga solid copper wire to pass the signal out through the very top of the assembly, where it too ends in a ring lug. The very top center of the finial is normally empty. There is no hole or bolt in the thing when it's a bumbershoot. I drilled a hole just slightly SMALLER diameter than 3/8 inch, then THREADED a standard 3/8-24 antenna stud/bolt into the hole. The plastic is very dense and threads nicely. I can mount either a stud and 3/8 threaded sleeve, or a 3/8 hex head bolt into the threaded hole, and attach just about any kind of commercial or homebrew whip to that. The pictures show a simple piece of 6 ga solid copper wire, 54 inches long. In one of the photos, you can see a choke of about 8 turns of the RG-58 around the top of the wooden mast. Chokes aren't terribly necessary for my operations, I'm always 5 watts QRP. At those power levels, there's not much to choke off. But I needed to store a bit of the excess coax, so "neatly wound coax reserve" or "RF choke" - you decide. Radials are next. You can see part of that happening in these photos. More below. |
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Counter That Poise! You know you're a ham when you look at objects and estimate their size in WAVELENGTHS instead of feet or inches or centimeters. When I saw this neglected umbrella skeleton sitting on the bulk trash pile, I saw eight "spokes" each a quarter wave long at 6m. Sure enough, they are each exactly 54 inches long! I cut eight pieces of tinned, copper quarter inch braid, each to 54 inches plus an added six inches so I could attach and trim later. At the distal end of each piece of braid, I mounted a 1/4-20 bolt and nut. I wanted the ends adjustable. Shrink wrap and the "Chinese finger cuff" effect of the braid holds the nut captive. I can unscrew and remove/replace the bolt if needed and the nut stays in place and aligned. Future Plans? I marked all the radials at 19 1/2 inches so that if I decided to use it for 2m, I could figure out a way to plug and unplug the xtra section of radial wire. I'm also toying with the idea of building a discone. In that case I think(?) I'll need to add a few inches to the radials. If that's the case, I'll unscrew the bolts and insert lengths of allthread rod. |
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Tune it Up! The height adjustment method, for the umbrella, is the typical series of holes with a peg-hook thingie inserted in the desired hole. I stuck the peg in each hole, set the umbrella canopy (now the groundplane radials) on each peg and took measurements. When the umbrella (the radials) are pegged at the typical 45 degree angle (down a bit from horizontal) the resonant freq is LOWER. As I raise the radials toward horizontal, the antenna is resonant at a HIGHER frequency. I marked all the holes as to their best frequency, based on SWR and reactance. I drilled two additional holes to allow setting the radials at the lower, 45 degree angle. Tunes up at under 1.5:1 across the entire band. |
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