Dual-Band J-Pole
146MHz + 446MHz
By far the best performing dual band antenna in existence for VHF/UHF. Want to make your own Dual-band J-Pole? Here's what you'll need:
Materials
3/16" thick 1-1/2" x 1-1/2" aluminum angle bracket 5.5" long
3/8 aluminum rod, 85" total length
UHF Stud Mount 3/8-24
Teflon Shoulder Washer, 3/8 iD 1/2 OD
Star Lock washer, stainless steel
3/8-24 Coupling Nut, stainless steel
3/8-24 Finish Nut, stainless steel
3 3/8-24 Jam Nut, stainless steel
Thread cutting oil
Tools
Tape measure
Band Saw or hack saw
File
Square
Pencil
Vise
Drill Press
Bench Sander/Grinder
1/8" to 1/2" step drill bit
Tap - 3/8-24 and wrench
Die (Split) 3/8-24 and wrench
Steps
Cut 3/16" 1-1/2x1-1/2 angle bracket to 5-1/2" length with saw.
Sand/grind ends and file until all burrs have been removed.
Mark on top from edge of angle bracket 3 marks at 1/2" and 1-5/8" and 5-1/16" (See diagram below)
Cross each of the 3 marks at 5/8" from edge
Using drill press and step bit, drill 1/2" hole for UHF stud mount on first hole 1/2" from the end.
Using drill press and step bit, drill up to and just into the 3/8" diameter step for each of the other marks, for the vertical elements to screw in.
The hole will be 5/16 at the bottom of the bracket and 3/8 on the top, with the step about 1/16" deep inside the hole.
Using 3/8-24 tap wrench, carefully tap the two 3/8 (5/16) holes.
The tap should guide itself in, but it must be perfectly vertical with respect to the bracket, in both dimensions. Visual inspection may good enough.
Use a small bit of tap oil on the tap to make it less likely to get bound up in the holes.
Using the file, remove any burrs from the holes and bracket.
Using the saw, cut the 3/8" rod to 59" for the VHF Resonator
Using the saw, cut the 3/8" rod to 18-3/4" for the Driven element
Using the saw, cut the 3/8" rod to 6-3/4" for the UHF Resonator
Using the sander/grinder, grind/sand both ends and bevel the top of each rod so it isn't sharp and won't poke someone.
Using the sander/grinder, grind the lower end in a shallow taper, about 3/8" total, up to about 1/16 max. This taper will help the die start to cut the threads without binding.
Using the 3/8-24 die, cut the threads onto the lower end of each of the 3 rods. The number of threads is the number of complete revolutions of the die, count as you go.
complete threads on the VHF resonator
complete threads on both the UHF resonator and the Driven element
I use a "jig" to keep the die straight so that the threads are straight, but even this doesn't always work.
After the threads are cut, use a vise to hold the coupling nut.
Screw the new threads on the rod into the coupling nut using some cutting oil to make sure the threads are straight and the rod is straight.
Adjust the rod a small bit at a time in each direction to straighten it, if it isn't straight. It won't affect the performance any but it might look wonky if the elements aren't straight.
Mount the UHF stud the 1/2" hole on the bottom (inside) of the bracket, use the shoulder washer, star lock washer, and coupling nut on top (in that order).
The center conductor of the UHF connector must be electrically isolated from the bracket.
Screw a jam nut onto the Driven element (all the way up until you run out of threads) and screw the element finger tight all the way into the coupling nut on the bracket.
Screw a jam nut onto the UHF Resonator, about 1/2" up the threads, and screw it into the middle threaded hole on the bracket - nearest the driven element.
Screw the Finish nut on to the VHF Resonator, and up the threads about 1" then screw it into the last hole, and screw on the jam nut on the bottom.
Adjust the lengths of the elements using an Antenna Analyzer or SWR/Power meter.
First measure for VHF and adjust Driven element and VHF Resonator lengths to get a good match on VHF. Tighten all of the nuts on these elements
Adjust the UHF Resonator height to get a good match on UHF, then tighten the jam nut.
Attach to a radio and get on the air!
Bracket layout drawing - 3/16"x3/16" aluminum angle bracket
