civil air band antenna


Message posted by lone wolf on March 20, 2005 at 14:08:33 PST:

http://www.vcars.org/tech/Image9.gif
I've seen these twin-lead j-pole antennas sold at swap meets but never used one. I wanted something portable to bring with me to Red Flag, so I made one of these antennas scaled to the high side of the civil air band. Just take the dimensions and make them 10% larger (multiply by 1.1). Comparing the antenna to a good duckie (like a Diamon RH77c), the twin-lead j-pole is much better.

The hardest part for me was to find 300 twin-lead. Who uses that junk? Well, Radio Shack has it. I have a few 50 ohm cables with BNC on both sides, thus to make the cable (coax) connection to the antenna meant chopping an old cable in half. If you don't have a cable to canabalize, you will need to get some RG58 and a BNC. The coax in the diagram makes it look like the shield goes to the "long side", or at least they show a fat wire going to the long side. However, the text is correct, i.e. the shield goes to the short side.

This design is really only good for an indoor antenna or temporary outdoor antenna, though I suppose you could put the antenna inside PVC to make it last longer outdoors. For outdoor use, you should probably make a super j-pole (a colinear version of the j-pole) out of copper tubing.


Replies:



[ Discussion Forum Index ] [ FAQ ]