The mirror-image J-Pole is very easy to construct and requires only two T-Fittings plus a length of copper pipe.
To visualize the antenna, one must only picture a 3 half-wavelength vertical and a 2 quarter-wavelength vertical positioned a few inches away from and centered on the the tall vertical.
Construction of the mirror-image J-Pole is accomplished by starting with two T-Connectors separated by the distance shown for the band of choice. For two meters the space between the two vertical pipes should be 2 inches.
Two vertical pipes will point upwards and two vertical pipes will point downward from each T-Connector.
The tall vertical pipes are affixed to one T-Fitting and the short vertical pipes are affixed to the other T-Fitting. The tall vertical pipes are of the length shown as the Overall Length on the plans for the Copper Cactus. For 2-meters this distance is 58 inches to the centerline of the T-Fitting or an overall antenna length of 116 inches.
The short vertical pipes form the tuning stubs and are the length shown as the Stub Length on the plans for the Copper Cactus. For 2-meters this distance is 19-1/3 inches to the centerline of the T-Fitting or an overall stub-length of 38-3/4 inches. The nice thing about the mirrored-J is that mistakes in measurements up to 2 inches on the long vertical and 1/2 inch on the tuning stub, will not affect the performance or SWR of the antenna.
The mirrored-J is mounted on the end of 1-1/2 inch PVC pipe about 5 or 6 feet long. The PVC pipe is mounted horizontally from your tower or roof gable. The tall vertical pipe of the antenna is slid through a comperable size hole drilled into the side of the PVC at the end. A PVC T-Fitting may be sawn in half and used as a saddle to mount the antenna to vertical masts.
The antenna itself sits vertically. The coax is connected as per the instructions on the Copper Cactus plans to the upper vertical and tuning stub. On this particular antenna, the center conductor of the coax should go to the tall vertical and not to the tuning stub as in normal J-Pole construction. As always, keep the center conductor of the coax as short as possible, lengthening only the shield if necessary, using copper wire.
For Safety, the shield of the coax should be grounded to earth ground before entering your shack.
Article posted by KGØZP