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440 Mhz. J-Pole Antenna Plans

440 Mhz. J-Pole Antenna Plans

Here is a 70cm (440 Mhz) J-Pole antenna that is inexpensive, and easy to build using 1/2 inch copper pipe, and the associated fittings necessary. The dimensions are not typical however, this is what it took to get its SWR low.
Measurements on overall length, and stub length are from the centerline of the separation pipe (horizontal) to the top of the antenna. The Connect at measurement is 1 1/2 inches from the top of the horizontal member to the point of connection. The distance between the main element of the j-pole centerline and the tuning stub centerline is .75″. To achieve this dimension, I use a 1/2″ pipe Tee, and a “street elbow”. Before assembling them together, I cut off the excess pipe at the joint before assembly. 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.

In all of the above dimensions, they are to be considered starting points. 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. Then I start over by re-adjusting the coax connection.

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