Most ften we can take of 5 percent making the formaula (75 *. The length of the wires can be easily calculated using the formula for a quarter wave dipole which is 75 / frequency. This ferrite core is cheap and has good specs. The balun used is of the type W1JR using RG303 Teflon coax on a RK4 ferrite core bought from the DARC Verlag. All radials are attached together to the other side of the balun and attached to the shield of the coax cable. The antenna wires going up are all attached to one side of the balun which has to be the middle pin of the coax cable. This was the first test and no balun was available… Of course the antenna needs a real 1:1 balun/choke to isolate the antenna from the coax cable. The top of the wires will have the highest voltage and might need better insulation with high power. In this case the wire should have a flexible connection to the top or bottom spreader tube and fixed to the other top or bottom spreader tube.Īs PVC is used no additional insulators are needed with low to medium power. When the center tube is very flexible it is probably wise to use some king of flexible material so the wires can slide through the holes in the spreader tubes and only fixed to the spreaders at one point. The top of the wire can be fixed the same way on the top spreader as on the bottom spreader. The top spreader tube will be about 10 cm under the end of the wire. A probably better way is to use a kind of thickening of the wire (using a luster or screw terminal over the wire). To not have slipping the wires through the holes in the spreader tubes I bent the wires a bit.
The wire is allowed to slip through the holes of all additional support spreaders in between.
The wire will only be fixed on the bottom spreader tube and the top spreader tube. In the spreader tubes holes are drilled to pass the wires through. When more than 3 bands are used the 2 nd and 3 rd band are on the same spreaders and also the last two bands to use a minimum of spreaders.
When 5 bands in total are used the 4 wires will be around the center wire each on 90 degrees. The center wire will always be the lowest band and to the sides the other two or four bands. When 3 bands are used a center pole and 2 wires on the sides are used. Of course this can be done (like the Cushcraft R8 or Hy-Gain AV-620 / AV-640) but will make adjusting the lengths very critical. Don’t make the distance to the center mast very short (like 5 to 10 cm). Not very critical but it was the total amount of tubing I had available which gave me this length. The distance from the center mast to the end of the side wires is 25 cm (10 inch). This board is again attached with tyraps to the mast. The PVC tubes are attached with tyraps to a strip of plastic cut from a bread cutting board. The other wires are supported using PVC electricity tubing. The center wire for the lowest band is attached alongside to the center mast. There are several supports used for the wires on the sides of the mast. The pictures give an idea how I made the first example.
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