I cut a length of RG-8X foam coax to a length of 67″ for the feedline, and coil up 4 turns (as small as you can get it) just below the horizontal part of the matching section. This will de-couple the feedline from the j-pole antenna, and help provide some lightning protection. Connect the center conductor of the coax to the main element, and the shield to the tuning stub of the j-pole. To Achieve this dimension, I use a 1/2″ pipe Tee, and a “Steet Elbow”. Before assembling them together, I cut off the exess pipe at the joint before assembly.
I temporarily attach the coax using 1 inch hose clamps, and adjust the coax connection first to the lowest SWR. From there, I adjust the length of the main element of the J-pole. Then I start over by re-adjusting the coax connection.
The point where the tuning stub attaches to the main element is the j-pole antenna’s ground point. That is why you can make it any length. Its a good idea to provide a ground here. This too will help with lightning protection. (provided your tower is properly grounded!) Only use rosin-core solder. Don’t use “plumbing solder”, acid-core solder, or plumbing paste. The acid in these materials breaks down the solder joint when electric current passes through it.
Here is a photo of a 70 cm j-pole antenna that I use:
This one has been up for about 7 years. You can see how the pipe turns black from the weather. This is normal, and doesn’t hurt the performance of the antenna in any way.
This article was originally posted on www.mikestechblog.com Any reproduction on any other site is prohibited and a violation of copyright laws.
Allen James says
Mike….can a J pole antenna be mounted with the mounting leg UP ? As hanging the antenna
WB8ERJ says
Hello,
Not too sure what you are trying to do or why, but I would guess that you couldn’t do that.If you try it, please please post your results here.
— Mike