Nov 19, 2017
There are many plans on the Internet on building J Pole antennas using copper pipes. I do not exactly have copper welding tools on hand, so, I just build the antenna using metal rods from garden supplies store.
Image from Wikipedia
The basic anatonomy of the J Pole antenna is well explained on other sources:
Constructions are fairly straightforward, by calculating the "A: long section" and "B: short section". "C" and "D" are the same for the feed point height and sections separations.
Not difficult at all. Below is my quick Jupyter Notebook calculations for the sections.
The toughest part is making the 3D printed mounts to hold the elements nicely.
Performance wise, it works okay on 2M VHF and it works decently on UHF 7cm bands, definitely would not blow up your Baofung radios. The UHF ham band falls to the third harmonic of VHF band, so this antenna could work with sufficient bandwidth.
The best explanation on how a J-pole antenna works: David Casler's How does a J-pole antenna work? AD#36.
However, I cannot find any noticeably differences compared to the Ground Plane Antenna.
Most J Pole builders like to add a 5 turns chokes near feedlines to reduce RF interferences.
I would say I am not that fond of this J Pole thing. But at least I have cross out one more thing on my bucket list.
Attached here are the top, bottom and mount designs. Feel free to download and import to your favorite CAD programs.