RE: J-Pole Antennas
Add in a tape measure! I ALWAYS HAVE ONE, SO I FORGOT!
Here is a cross-post from the IC-746PRO web site that I made there, but thought that it might be a good thing for this group as well.
A copper J-Pole is easy to build and even if you spend a couple of bucks doing it, YOU BUILT IT!
The benefit of doing this is that you gain the know-how to do it if you should ever need to improvise, such as in an emergency, or when you lack some funds but have things laying about.
There are bunches of designs out there, so simply Google “J-Pole” and you have plenty of ideas.
Besides, in the future you can show others how to do this with greater expertise because of your experience.
Another benefit that I’ve noted when working with Cub Scouts and Boy Scouts, is that their perspective with respect to materials, tools and improvisation changes by building this particular antenna.
We start with a “home repair” or “plumbing” project where the pipe dimensions are laid out and the boys need to measure (and measure and then measure some more), then cut and assemble the plumbing pieces.
Before you assemble the pipe elements, polish up the fittings and pipe where they meet, inside and out, to provide a shiny surface where any two pieces meet. It will make it easier to solder.
At this point the boys get all excited about using the torch to solder up the plumbing pipe, I mean antenna! From this, they get to learn about plumbing and antennas!
They will never walk into the Home Depot or Lowe’s plumbing department and think the same way about plumbing parts ever again!
Heck, they may even use the plumbing department as a source of structural elements in the future!
The next step is to cut the coaxial cable to the length needed and separate the shield and center conductor of the cut end so that you have about four inches of exposed shield and another four inches of center conductor with the last inch stripped of the insulation.
The next step is to secure the coaxial pigtails to the vertical elements (it doesn’t matter which one goes where) using the hose clamps.
If you leave them slightly loose, then you can make adjustments up and down to match the antenna using an SWR meter. If you don’t have a meter, use the recommended position from whatever diagramme you might have available as a starting point.
Here’s what you need:
½ inch or ¾ inch copper pipe depending on band and preference (including cost) When buying standard lengths of pipe, keep in mind how long each piece needs to be and buy accordingly.
A copper elbow and a “T”
Two copper pipe caps
Two stainless hose clamps that are large enough to fit over the pipe
A coaxial cable assembly (as long as you like – heck even from Radio Shack!)
The tools needed are:
A pipe cutter or saw
Screwdriver for the hose clamps
Rosin Core Solder or Plumbing Solder and Flux
Small propane torch
Green scouring pad from the kitchen
Finally, one time I didn’t have access to a torch or soldering iron, so I simply placed the pipe elements together. Then I used tape over the junctions to keep out the elements and to hold things together. Worked fine for the weekend and it was soldered the following week.
Sometimes, I will paint the elements to keep down the corrosion and that works well.
Gordon Beattie, W2TTT