2015 Dual Band J-Pole Antenna

Club Activities

Club member KD0OBA displayed and discussed the dual band J-Pole antenna that he constructed for fellow club member KE0AUP.

This dual band 2 meter / 440 cm antenna was designed to be mounted in a PVC pipe sleeve and was inspired by Dr. Edison Fong ( http://edsantennas.weebly.com/ ) and modified to reflect work done by WB2UAQ on a similar design ( http://www.mike-m.com/n2hjd/J_ant.htm ) who used RG-8 coax rather than Dr Fong's smaller RG-174 coax. KD0OBA felt that the RG-174 coax may be challenged if higher power levels are applied to this antenna. The RG-8 has a much higher power level rating. Both antenna designs use 300 Ohm antenna twin lead for the matching section.

This antenna was designed to fit inside of a piece of 3/4" PVC schedule 200 white plastic pipe. Schedule 200 PVC pipe has a thinner wall and it interacts less with the wire antenna than the thicker schedule 40 PVC pipe.

The antenna is shown mounted to the corner of the deck. A 10' piece of 1 1/4" PVC pipe is used for the mast. A 5' piece of 3/4" PVC pipe houses the antenna.

Construction details:

Start by stripping the insulation from one end of the 300 ohm TV twin lead. Solder the wires together and trim off excess.

Determine the feed point location by measuring up 1 1/4" from the bottom, strip the TV twin lead and solder on the feed line coax cable. In this case for feed line I used a piece of RG-58X coax that already had a PL-295 connector attached.

Cut and strip the insulation off of a piece of RG-8 coax per WB2UAQ instructions noted above.

Create the 70cm trap section by shorting the end of the RG58 trap section.

Solder the RG-8 coax section which contains the 440 cm choke and functions as the radiator for the 2 meter band to the J-match section. The solder connection is shown reinforced with a wooden popsicle stick.

Completed antenna is shown below. Starting at the bottom, note RB-58x feedline with ferrite beads installed. TV 300 Ohm twin lead "J" matching section (brown). 70 cm radiator (RG-58 with outer insulation and shield stripped - white). 70 cm choke section (RG-58 - black), 2 meter radiator (RG-58 with outer insulation and shield stripped - white), additional wire added to tune 2 meter (14 gauge - blue). The red bands at the top are cardboard strips rolled and taped with red electrical tape. They were added to keep the antenna centered inside the 3/4 inch PVC pipe. After soldering, all exposed wires were coated with liquid electrical tape to prevent corrosion and to limit exposure to moisture.

Antenna being inserted into the 3/4 inch PVC pipe and attached to 1 1/4 inch PVC mast. A length of LMR 400 coax cable runs back to the radio. The PL259 connectors were joined with a barrel connector and then wrapped with electrical tape to keep moisture out.

Antenna mounted on edge of deck. After tuning the antenna to the local repeater input frequencies, the SWR at 146 MHz was 1.3 to 1 and the SWR at 447 Mhz was 1.4 to 1.

Thanks to KD0RIZ for help during the installation.

Pawnee Amateur Radio Club

Columbus, Nebraska 68601