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Radio Zone`s Quik Projects

TV Twin Lead J-Pole

The following is a description of a J-Pole antenna made from 300 ohm
TV twin-lead. They have quite a few advantages which include improved
performance for 2-meter HTs, portability, and low cost.
                  |   |  < Do not short this end.
                  |   |   (when trimming for VSRW, cut both sides)
                  |   |    
                  |   |    
                  |   |   
            3/4 > |   |        Tecchnical Stuff: This  antenna is a 1/2
           wave > |   |                          wave end-fed antenna with 
                  |   |                          a 1/4 wave matching section.
                  |   |    
                  |      < 1/4" margine (trim for vswr _below_ gap)
                  |   |         
                  |   |  < 1/4
                  |   |  < wave
                  |   |
 coax conductor > *   *  < coax shield
          1 1/4"> |   |
                   -*-   
   For a center frequency of 146 MHz:
1. Start with @54" of TV twin lead (flat, NOT foam core)
2. Strip 1/2" of insulation at bottom and solder wires together.
3. Measure 1 1/4" from soldered wires and strip insulation on both
sides. This is the solder point for a coax feedline.
4. Measure 16 3/4" from coax shield solder point and cut out 1/4" notch.
5. Measure 50 1/3" from coax center conductor solder point and trim
off twin lead at that point.
6. Feed with a length of RG58U coax. Tape coax at feedpoint to the
twin lead for strength and seal coax for weather protection.

It has been noted that this design can lead to rf coupling onto the
feedline. To avoid, put ferrite beads on the coax at the feedpoint,
or use 3-5 turns of coax (1"-2") taped together at the feedpoint.

You may attach an alligator clip to the plastic on the top of
the antenna in order to easily hang it. Alternately, punch a
hole near the top and use a length of fishing line to hang.

FYI, the 1/4 wave sections for other center frequencies are:
144 MHz =17 inches, 145 =16.88, 146 =16.75, 147 =16.65, 148 =16.54