The point where the tuning stub attaches to the main element is the j-pole antenna’s ground point. That is why you can make it any length. Its a good idea to provide a ground here. This too will help with lightning protection. (provided your tower is properly grounded!)
Only use rosin-core solder. Don’t use “plumbing solder”, acid-core solder, or plumbing paste. The acid in these materials breaks down the solder joint when electric current passes through it.
The photo to the right is one of my j-pole antennas that I use. This one is not the 2 meter version described here, but rather the 70 cm version of the J-Pole antenna.
So there you have it. I have built several j-pole antennas, and they work great! This one has been up for about 7 years. You can see how the pipe turns black from the weather. This is normal, and doesn’t hurt the performance of the antenna in any way.
This article was originally posted on www.mikestechblog.com Any reproduction on any other site is prohibited and a violation of copyright laws.
Mike does the feedline for the pvc pipe antenna inside the pipe or outside?
Hello,
It really doesn’t matter if the feedline is inside the pipe or outside. Since its easier to put it on the outside, that is how I build my J-pole antennas.
Mike, I want to make a old tv antenna into a 2 meter yagi . can it be done.
Yes it can be done. I have done it a couple of times. However there is one caveat, which is mainly a mechanical issue. Since most TV antennas are what is known as a Log-Periodic Dipole Array (LPDA) that the elements are in a Vee configuration, that would make re-building the TV antenna into a 2 meter Yagi more difficult. Sometimes you can find a LDPA whose elements are perpendicular to the antennas main boom section, those are the ones that can be rebuilt. With those its a simple matter of drilling out the rivets and placing the elements at the proper spacing. Then cut them to the proper length for 2 meters.
Old TV antennas are a good source of aluminum for making various ham radio antennas.
Good luck!
— Mike
I would like to build your antenna. However, I have a couple of questions. First let me say I come from a machinist’s background. We measure things in thousandths of an inch or less. OK, now for my questions: You give measurements as “centered” in the soldered joint if I understand your directions as written. 1) What is the CUT LENGTH of the elements when they are bottomed out into the 90 degree elbows (a positive stop). That will give an exacting measurement rather than an “eyeballed close enough” sort of length.
2) What is the dimension of the horizontal “cross over piece between the two uprights? (The cut length when bottomed into the elbow and the tee connectors)?
3) How far up on the vertical elements do I solder in the connector for the coax? (please give this dimension from the very bottom on the antenna to the point where the soldered wire is connected. Exacting measurements should give 1:1 SWR.
Thank you.
Dave
Hello,
First of all, with antennas, all measurements are just starting points. I.E. “for reference”. I have been building antennas since I was 14 years old and I can’t think of a time when cutting exactly to a formula or plan that I achieved a 1:1 SWR. If I get a 1:1.5 SWR I consider the antenna tuned.
As I state in the post “In all of the above dimensions, they are to be considered starting points” This even can vary when building several “identical” J-pole antennas.
Sorry for being vague, but with antennas its not like dealing with machinist precision. Honestly I fell like its more like voodoo magic.
Hopefully you have some sort of SWR meter or antenna analyzer.