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