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.
Mike….can a J pole antenna be mounted with the mounting leg UP ? As hanging the antenna
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
Thanks. Have you built one?
1/2 inch copper pipe is 5/8 in O.D., so 5/16 in center-to-edge. 2 of those = 5/8 in. That leaves 1/8 in between pipes. And the tee plumbing fittings are bigger than that.
Help me out here, thanks.
Yes I have built several of these. The photo on page 2 shows one of several that I have built.
From the photo, it look like the spacing between the pipes is about 1/2 an inch. This dimension isn’t too critical, but you don’t want it too wide either. SO just make the spacing between the two pipes roughly the same as in the photo and you will be good.
It has been several years sine I built the one in the photo,