J antenna and variations thereof

Illustration of the J antenna and four other variations including SlimJIM, Super-J, 5/8ths Super-J and Collinear J.
J antenna and variations thereof

Here we see five variations on the basic J antenna (aka J-pole). Key takeaways include:

  • The basic J and SlimJIM configurations operate identically for all practical purposes.
  • The Super J is an easy way to obtain gain towards the horizon.
  • The 5/8ths Super J represents the most bang for the buck for gain.
  • The Collinear J provides the benefits of the Super Js in a slim package.
  • If on a conductive mast (red) a mast decoupling stub (green) provides essential RF isolation while preserving a direct path to ground.

4 thoughts on “J antenna and variations thereof”

  1. I've made Slim Jims for 2m and 70cm from 450ohm ladder line. A Super J of the same material would require only one side of the ladder line so would be quite flimsy so I was wondering; would there be any benefit in combining the two designs (still using the ladder line) whereby the top 1/2 of the Super J is shorted to the other conductor to come back down to a second horizontal phasing stub and down again to resemble a double-height Slim Jim with the opposing stubs in the middle forming a cross + ? (Wow, that was a long sentence but I didn't want to break it up)
    1/4 wave matching stub at the bottom, 1/2 wave up, 1/4 wave out and back, 1/2 wave up, 1/2 wave down, 1/4 wave out and back, 1/2 wave down. So 4x 1/2 wave radiating elements which would all be in phase.
    A diagram would be simpler but hopefully you can interpret my description.
    Judging by your J-pole/Slim Jim comparison, I may just have made (for 70cm) a stronger Super J with no other appreciable benefit. I have no way of simulating or physically testing it other than seeing if I can access a repeater as there is little or no 70m activity locally. I won't even know if it works at all until the connector I have ordered arrives in the post next week. If it does work, I'll make a 2m version.
    Interesting to hear from someone who actually knows about aerials as to whether the concept is valid or if I have wasted my time and solder.

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