Here's the super J-pole antenna design that is a regular J-pole antenna with a 1/2 wave element mounted above with a 1/2 wave phasing harness connecting the element to the bottom part of the J-pole. The antenna can be built for any band.This J-pole antenna is made with copper pipe. The phasing harness is made from large diameter copper wire. The harness can be made by bending the wire into a square "U" shape, then bending it into a circle by bending it around a large coffee can.
The top element must be insulated from the bottom part of the antenna. A fiberglass rod can be used as an insulator by inserting it into the pipe. A wooden dowel rod can be used also, but it should be coated with epoxy to waterproof it. Be sure to cap off the top element and mounting stub to keep water out. PVC pipe caps can be used.
The feedpoint for the antenna is in the same place as a normal J-pole, between the 3/4 wave element and the 1/4 wave matching stub. Attach the shield braid of the coax to one side and the center conductor to the other side. It doesn't matter which side is attached to which. Move the feedpoint up & down to find the best match with an SWR meter or antenna analyzer. Once a good match is found, secure the coax to the antenna. A good way to do this is use small hose clamps. One method I've found that works well is to solder stiff wire to a mounting hole and the center pin of an SO-239 jack, so cables with PL-259 connectors can be connected to it. BNC jacks can also be used.
The super J-pole built for 2 meters is around 9 feet tall, depending on the mounting stub. If constructed properly, it should give around 3 dB gain over a regular J-pole. This antenna has a surprisingly broad bandwidth, giving a VSWR of 1.5:1 or less from 133 to 175 MHZ according to my analyzer.
Source: Super J-Pole
Posts
No comments:
Post a Comment