My Wooden Airplane
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8/26/2013 - 8/28/2013

Comm Antenna, Part 3

I should have realized that the simplest antenna is usually the best. When I first became a Ham Radio operator, one of the first antennas I made was called a 1/4-wave ground plane. It's actually what most airplanes use today. The difference is that most airplanes are made of aluminum, so they can use the fuselage skin as the "ground plane". Since mine is made of wood, I'd need to make my own ground plane. An easy way to do that is with radials, like those pictured. I think the minimum number would be 4, and the more the merrier (up to an amount that would constitute a solid disk). One problem I had was the control cables that ran through the center of the fuselage, so I solved that by raising the base of the antenna about a foot off the floor. Also, if the radials stuck out 90 degrees to the center element, they would protrude past the side of the fuselage, so I bent them down at about a 30 degree angle. (This is actually the preferred way to do it, since it moves the characteristic impedance of the antenna up to 50 ohms, which matches the coax. And, this is an unbalanced antenna, which also matches the coax.) Testing this antenna provided the best results yet, with a nearly flat SWR across the entire band. (It was raised slightly at the upper and lower edges of the band, but not above 1.5 to 1.) This antenna was made with 1/16-inch copper-clad welding rod. The center radiator is 22 inches tall, and each ground radial is 20 inches long. (The hexagonal disk is 2 inches in diameter, so the "ground plane" also ends up being 22 inches in diameter.)

Total Time: 12.5 hrs.