For what it’s worth, the J antenna is now fixed.
Details available in these two patents…
- https://patents.google.com/patent/USD798847S1/ – Design patent detailing the appearance and look of one embodiment of the improvement.
- https://patents.google.com/patent/US10468743B2/ – Utility patent detailing how this works.
It’s still just a J-pole at the end of that day, but hey, I got tired of reading and hearing about all the various myths surrounding this eight decade old design and decided to drive the myths into ground (pardon the pun) once and for all. So ends my obsession with this thing and hopefully a new future for this design.
The stub seems to provide excellent isolation over 10% 2:1 SWR bandwidth. I'm surprised a fixed-length stub can be so broad banded.
What kind of fitting/adapter/wiring do you use to connect the coax to the pipe when running it inside like that? Given the tight confines, seems difficult to solder the wire on the inside of a 1/2" pipe without melting or damaging the cable, especially when using fatter coax.
Also, as I understand the point of that bottom matching stub is to completely isolate the upper radiating section from the mast, since leaving the protruding bit of the T fitting on a typical J can cause problems, what it that bottom tip was just cut off flush? Then the profile would be a normal J without the protrusion, but you would still have a handy hole in the bottom to mount onto a non-conductive mast, like a wooden shaft or something.
I love this antenna!! My SWR (as per my nanoVNA) is 1.06 at 146.000mhz and 1.13 at 447.00mhz. I can easily reach the Intermountain Intertie repeaters (2 different ones), both more than 70 miles from my home with 1w and get excellent signal reports. Thank you, John!!
I used 14g bare wire as a pull tape threaded through the parts as I assembled them, so I could pull the coax up when it was nearly finished to avoid melting the insulation layer. The bottom of the coax inside the vertical support attaches to an SO connector mounted to the mast at roof level where the lightning arrestor and feed line connect.
It would be nice to see a write of of how to build this antenna