Antenna1

How to make a good Long EZ com antenna

The antenna described here is a center fed dipole. It should be installed on the inner side of either winglet, vertically, and about an inch forward of the rudder hinge. The coax should depart the center of the dipole at a right angle, going as far forward as possible, then down the winglet leading edge to the strobe wiring conduit in the wing. Lay out where the antenna will be on the exposed foam. Route out the foam and install the coax. Leave enough coax to reach the wing root, where you will install a BNC connector. The copper tape will be installed after the inside of the winglet has been skinned. When skinned, cut a hole and pull out the coax. Lay out the copper tape as shown below. Just before you solder the coax to the antenna, install the three torroids and a 1 inch piece of 3/8 shrink sleeve. All torroids are not identical. You must use Amidon part number FB-43-2401 and RG-58 type cable or equivalent. RG-58 is 50 ohm and RG-59 is 72 ohm. The antennas impedance will be very close to 50 ohms and will match the RG-58 coax quite well.

To prepare the coax for connection to the copper tape, cut the outside insulation jacket back 1.25 inches. Be very careful to not score the braided wire.

Using a sharp tool, move the braid around to make a hole and snake the center wire out as shown.

Pull the center conductor out, then massage the outer braid so it returns to its normal shape. Remove the center insulation back 1 inch. Be VERY careful not to nick the center conductor when cutting the insulation. The center conductor can easily break here if you do. When the wire is tinned it will stress at this point. Cutting the insulation with a hot soldering iron tip also works.

Tin the center conductor and braid 1 inch. The time to tin the center conductor should be about 2 seconds, and the braid about 5 seconds. Do not tin the braid all the way back. Do not melt the center insulation when tinning the braid. This is a common failure point. If you are not proficient then get someone, maybe a local ham, to do it for you. They love airplanes and do this stuff for free just to get a chance to look at an airplane.

After the tapes are in place, put a mixing stick in the center and run the tapes up both sides. Cut it at the root, both sides. This leaves a nice parallel gap in the center. The antenna length should be 19.75 inches per side if you use 1" wide tape. Note that the wider the tape becomes, the shorter it needs to be to do the same job. A wider tape results in a wider usable band width, too.

Solder the center lead and braid as shown. The braid should be soldered to the bottom strip, and the center conductor soldered to the top strip. Don't forget to keep heat away from the center conductor's insulation. Use a heat sync to protect the inside and/or outside from melting.

Center the shrink wrap over the torroids and shrink it into place. Micro the torroids into place to prevent movement.

This is the antenna's curve of return loss vs frequency. The resonant frequency is 121.86 MHz and the return loss at that frequency is 27.74 db or 0.17 %. The band width shown by the flat spot on the curve, 116.6 to 124.36 MHz, is 1% (1.22:1 SWR). Any return power less than 4% (1.5:1 SWR or 14 db) is considered acceptable. Therefore the acceptable band width is 111.7 to 131.0 mhz.