Steve, I have had limited luck in using PVC. The thicker wall tubing is what I prefer to use, but sometimes that is not the best material for UHF antennas. I would stay away from the gray electrical PVC as it can do some strange things with UHF frequencies passing through it. I have not tried using fiber innerduct, but that is an interesting idea. I have some 1" left over on a roll and I will do some testing with it when I get a chance. I would bet that it would work pretty darn good, especially if you were to wrap it in fiberglass like I describe in the next paragraph.
If you have some very crafty people that can work with fiberglass, I have taken a piece of thinwall pvc tubing or made a cardboard tube, and then wrapped them in several layers of fiberglass tape and resin for strength and rigidity. Start with a layer of resin, layer of tape, more resin, more tape, more resin, you get the idea, until you are happy. As for the top radiating element, just attach it to the center conductor only. Here is the excerpt from the instructions with the formula to calculate the length. Add a ¼ wave element to the top of the antenna. Use #10 or larger solid wire or similar and solder it to the center conductor only. (I like to use a piece of 1/4" brass brazing rod from the welding shop myself). The length of the ¼ wave element is calculated as follows: 1/4 wavelength radiator = 300 / F / 4 Where F = Frequency in Megahertz 300 / 444 / 4 = .1689 meters or 169 millimeters Here again a piece of the double wall heat shrink tubing over the joint where the center conductor is soldered to the radiating element. When you are all done and happy with the antenna some bees wax or spray foam will hold the coax rigid inside the tube. Let me know if you have any further questions, and let us know how your project comes out, whichever antenna design you choose. Joe - WA7JAW --- In Repeater-Builder@yahoogroups.com, "Dr. Stephen Andrew Wilson" <[EMAIL PROTECTED]> wrote: > > Thanks to all who have replied! > > Joe, WA7JAW: > > Can I build one of these in a PVC pipe or in the fiber-type conduit, > or inside a 20-foot telescoping crappie pole? > > Steve, XE1UFO >
