A 146 Mhz. J-Pole Antenna
Here is a 2 meter (146 Mhz) J-Pole antenna that is inexpensive, and easy to build. I use 3/4 inch copper pipe, and the associated fittings necessary.
The above dimensions for the J-pole are in inches.
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 2 1/4 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 2".
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 for
constructing a 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. To see a photo of the j-pole antenna that I use, click here.
Additional notes on J-Pole construction: