One open wire line feed system I built was for a doublet hung "inverted Vee" style from a wooden mast. I picked up a bunch on plastic "Dog Bone" insulators from HRO or some such place. They are about 3 inches between holes and have a series of ridges near the center to extend the surface path. They aren't too heavy for free hanging on about #12 or #24 house wiring, which provides an impedance in the 400-500 ohm range. Since I painted my pole white, I used white-jacketed ordinary house wire and white insulators. The line was hard to see.
Having a wooden pole that I painted white and not wanting the feeder bouncing all over the place, I picked up some cheap 300 ohm twinlead "standoffs" from Radio Shack. They have the advantage of being made of soft metal that's easily bent. I bent the eyelets open, discarding the insulating disk that normally holds the twinlead, and reclamped them around the center groove in the insulators formed by the ridges. It's easy to do with ordinary "plumbers" pliers using those soft metal eyelets. Then I screwed them into the pole at about 5-foot intervals and ran the wires up through the holes at each end. It was a very neat, stable and cheap open wire line. I used some tie-wraps threaded through the holes and tightened around the wire, clamping it securely to the side of the feed through. To support it at the top. The lower ones were allowed to "float" by and large (permitting dimensional changes with temperature too). For the last ten feet the wires hung free with the insulators on them held in place with white tie wraps, with a final insulator with screw eye at the wooden window sash where it terminated. Two flexible stranded wires came from there through a header block into the operating position inside. The larger diameter wire helped too. The biggest losses in such feed lines come from resistance at the high-current points. Larger wire is better wire under high SWR conditions. I know white tie wraps aren't supposed to survive well in UV light, but those did well for nearly 10 years before I took it down. None failed. Ron AC7AC _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
