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Ugly Balun Core Diameter: Does it matter?

Mar 30th 2020, 14:21

KG4UMB

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

W1VT

Super Moderator

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

http://www.karinya.net/g3txq/chokes/

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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