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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.htmwho 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.
 
Dual Band J-Pole 15


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.
Dual Band J-pole 3


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.
Dual Band J-Pole 10

Cut and strip the insulation off of a piece of RG-8 coax per WB2UAQ instructions noted above. 
Dual Band J-Pole 7

Create the 70cm trap section by shorting the end of the RG58 trap section.
Dual Band J-Pole 9

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.
Dual Band J-Pole 11

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.

Dual Band J-Pole 13

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.
Dual Band J-Pole 14

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.
Dual Band J-Pole 15

Thanks to KD0RIZ for help during the installation.


 
Pawnee Amateur Radio Club
Columbus, Nebraska 68601
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