DIY 70cm – 440 mHz J Pole Construction Plans

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.

Then 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.

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:

Build a DIY 70 cm / 440 MHZ J-Pole Antenna

Build a DIY 70 cm / 440 MHZ J-Pole Antenna

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.

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