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BUILDING THE CM COPPER POLE

Found at: 0x1bi.net:70/textfiles/file?hamradio/dual-j.txt

                                                                     
                                                                     
                                                                     
                                             
               BUILDING THE 2-METER/70 CM COPPER J-POLE ANTENNA
                     By Rick Yost N4VQT   19-October-1992
  
                           MATERIALS REQUIRED
           10 foot section of 1/2" Copper water pipe
           1/2" copper "T" (2)
           1/2" copper elbow (2)
           1/2" copper end caps (3)
           Electrical solder
           RG-8U or RG-8X or equivalent coax about 7' for "pigtails"
           PL-259 connector (2)
           PL-258 coupler (2)
           UG-176 reducer for RG-8X (2) (not required if using RG-8U)
           Electrical tape
                             TOOLS REQUIRED
           Butane torch
           Pipe cutter or hack saw
           File
           Pliers
           Plumber's sand paper
           Soldering Iron
           Ohm Meter
           Measuring tape
  
 The overall design of this dual band J-Pole is that the top of the antenna
 is for the 70CM band and the bottom is for 2M.  Both matching stubs face
 the same direction.  Two antenna leads are used (one "Pigtail" for each
 band).
                                  ASSEMBLY
 1) PREPARATION OF COPPER PIPE:
 Using the pipe cutter or hack saw, cut the 10' copper pipe in the
 following lengths:
                      3/4 wave radial = 39 1/2 inches (2 - Meters)
                      3/4 wave radial = 19 inches (70 CM)
                      1/4 wave radial = 19 1/2 inches (2 - Meters)
                      1/4 wave radial = 6 5/8 inches (70 CM)
                      J connector = 1 1/2 inches. (2 - Meters)
                      J connector = 1 1/2 inches. (70 CM)
  
 The remainder of the copper pipe will be used as a mast mount.  Sand the
 ends of all pipes to ensure a clean surface for soldering.
  
 2) RADIAL ASSEMBLY:
 Using the copper "T" connector fittings, connect the 2M 3/4 wave pipe to
 the mast mount pipe so that both pipes are joined vertically.  At the top
 of the 2M 3/4 wave radial, join the 70CM 3/4 wave using the second "T"
 connector.  Insure that the remaining open holes in the T's are both
 facing the same direction.  Insert the 2 J connector pipe's horizontally
 into the remaining T openings.  Using the elbows, connect the 1/4 wave
 pipe's to the J connector pipe's thereby forming the 2 "J" patterns of the
 antenna (see diagram below).  Place the end caps on top of the three
 radials.  Lay the antenna on a flat concrete surface (like a garage floor
 or sidewalk) so the connections can be heated and soldered without burning
 the supporting structure.  This will also ensure that 1/4 wave matching
 stubs will be perfectly horizontal with the 3/4 wave radials once the
 solder cools.  Using the torch, heat the copper T fittings and when
 sufficiently hot, apply the electrical solder to the pipe where it joins
 the T.  Do not apply heat directly to the pipe, just the connector.
 Repeat this on all connector joints and end caps.
  
  
                                    Page 1
               BUILDING THE 2-METER/70 CM COPPER J-POLE ANTENNA
                     By Rick Yost N4VQT   19-October-1992
  
 3) PIGTAIL's ASSEMBLY:
 Cut the 7' length of coax into two lengths, 69 1/2 inches and 14 1/2
 inches.  The idea here is to have the two ends of the coax hang down and
 end at about the same point after the coax sections are soldered to the
 antenna.  The lengths are NOT critical as long as both ends are at least 6
 inches below the 2M J connector.  The aforementioned measurements will
 position the ends of the coax about 11 inches below the 2M J after the
 coax sections are soldered to the antenna.  The long coax section will be
 used for 70CM and the short coax section will be used for 2M.
 PL-259 CONNECTIONS for 2M and 70CM:
 If using the RG-8X coax, install the reducer on the coax first.  If using
 RG-8U or similar, the reducer is not required.  Also, slide the outer
 portion of the PL-259 over the coax.  Strip the coax end about 1 1/2
 inches and peel back the shield of the coax to the insulating jacket.
 Strip the insulation off the center conductor about 1 inch.  Tin the
 center conductor and wrap the shield around the remaining center conductor
 insulation.  PLEASE be certain not to short the center conductor to the
 shield.  Connect the PL-259 using a twisting motion to the coax ensuring
 that the center conductor does not short to the shield.  Apply solder to
 the tip of the PL-259 (coax center conductor) and the 4 holes (coax
 shield) in the body of the PL-259.  The PL-258 coupler can then be
 connected to the PL-259.  Using an Ohm meter, ensure that no short exists
 between the center pin and the outside of the PL-259 connector.
 ANTENNA End of Pigtail:
 Strip the black insulating jacket of the coax about 3 inches exposing the
 shield of the coax.  Peel back the shield of the coax to the insulating
 jacket and twist the shield to form a tightly woven wire.  Using a
 soldering iron, tin the twisted shield.  This must be done for both
 the 2M and 70CM pigtails.
  
 4) COAX CONNECTIONS:
 2-Meters:
 Scribe a mark on the 3/4 wave and the 1/4 wave pipes exactly 2 3/4 inches
 up from the inside portion of the J connector for the 2M section. (see
 diagram)
 70-Centimeters:
 Scribe a mark on the 3/4 wave and the 1/4 wave pipes exactly 1 7/8 inches
 up from the inside portion of the J connector for the 70CM section. (see
 diagram)
 Soldering the connections:
 This procedure is described for the 2M portion of the antenna and must be
 repeated for the 70CM portion.  Using the torch, apply heat to the side of
 the radials where you made the scribes.  Apply a small bead of solder on
 the scribe points and ensure that the solder is adhering to the pipe.
 After the beads of solder are somewhat cooled, grasp the coax with a pair
 of pliers and while heating the pipe, (again from the bottom) wait till
 the solder bead begins to liquify and apply the tinned shield portion of
 the coax to the 3/4 wave element.  (Be sure to connect the shield of the
 coax to the 3/4 radial as close as you can to the insulating jacket.  In
 other words, after the connection is cooled, you will be cutting off about
 2 1/2 inches of unused shield).  The tinned shield will also start to
 liquify and the solder will join the shield to the radial.  Remove the
 heat IMMEDIATELY after you see the solder on the shield liquify with the
 solder on the radial.  Allow the shield connection to cool to room
 temperature.  Using an Ohm meter, check for any shorts between the center
 conductor and the shield and also check for continuity between the outside
 portion of the PL-259 and the antenna.  Next, the center conductor must be
  
                                    Page 2
               BUILDING THE 2-METER/70 CM COPPER J-POLE ANTENNA
                     By Rick Yost N4VQT   19-October-1992
 soldered to the 1/4 wave radial.  Again, after the shield side has cooled,
 bend the center conductor over to the 1/4 wave radial and cut the center
 conductor insulation to allow the center conductor to be soldered to the
 antenna.  Solder the center conductor using the same method as you did on
 the shield connection.  Allow to cool to room temperature.  Cut the excess
 shield and center conductor from the antenna.  Repeat the above for the
 70CM portion of the antenna.  Using electrical tape, afix the coax to the
 mast portion of the antenna just below the "J" on the 2M portion.
 Likewise, using electrical tape, afix the coax for the 70CM portion down
 the 3/4 wave radial for the 2M portion.  (see diagram)
  
 Your 1/2 wave copper dual band J-Pole is now complete just add whatever
 lengths of coax you need and a 2-meter and 70 centimeter rig and your on
 the air!
  
                           DIAGRAM (not to scale)
  
                End Cap --------------> ---
                                        | |
                                        | |
                                        | |
                                        | |
    End Cap ----------------> ---       | |
                              | |       | |
     6 5/8" 70CM radial-----> | |       | | <-------- 19" 70CM radial
 Center Conductor ----------> |*------- -*| <-------- Shield
                  |           | |      || |
                1 7/8"        | |      || |
                  |           | |      || |
                  ----------> | |_ _ _ || |
   Elbow connector ---------> |_ _ _ _ |  | <-------- Tee Connector
                                       || | <-------- Electrical tape
            Coax --------------------> || |
                                       || |
                                       || | <-------- Electrical tape
                                       || |
                                       || |
                                       || | <-------- Electrical tape
    End Cap ----------------> ---      || |
                              | |      || |
    19 1/2" 2M radial ------> | |      || | <-------- 39 1/2" 2M radial
                              | |      || | <-------- Electrical tape
                              | |      || |
                              | |      || |
                              | |      || |
 Center Conductor ----------> |*------- -*| <-------- Shield
                  |           | |     ||| |
                2 3/4"        | |     ||| |
                  |           | |     ||| |
                  |           | |     ||| |
                  ----------> | |_ _ _||| |
   Elbow connector ---------> |_ _ _ _||  | <-------- Tee Connector
                                      ||| | <-------- Electrical tape
            Coax's -----------------> ||| |
            PL259's ----------------> ||| | <-------- Mast mount
                                        | |           (remaining tubing)
                                        | |
                                        | |
                                        | |
                                    Page 3
                                                                                                  


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