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Ugly Balun Core Diameter: Does it matter?

Mar 30th 2020, 14:21


Joined: Feb 28th 2020, 13:47
Total Topics: 0
Total Posts: 0
I have a dipole that's a half wave on 20m, and it tunes about 1.5:1 at the bottom of the band and 1.7:1 or up to 2:1 as you get higher up. This would be all fine and good, but my IC-718 is very sensitive to higher SWR, and dials back its power output when it senses higher SWR than 1.5:1.

I tried to put an RF choke on the feedline (RG-58), just using what I had handy. I measured out 20' of the coax going into the antenna, and wound it around a section of 1.5" PVC. When I tried to transmit, the SWR was a flat 2:1 across the band, it seemed like. What did I do wrong? All the "ugly balun" instructions I've seen say to use 3" or 4" PVC, but I had also seen some that say it doesn't matter how many turns you put onto the balun, as long as you use the right length of coax (between 18-21' given what I'd read).

Thoughts appreciated. I've been licensed a long time, but I've been inactive until a few weeks ago, and there's been a bit of a learning curve getting back into things.
Mar 30th 2020, 20:16


Super Moderator

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
Here are a bunch of optimized air core designs.

Note that the frequency range for the highest choking values is quite narrow. This narrow range can be useful for getting rid of reception impairing noise.

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