Project - 49:1 unun

Thursday, 12th June 2025

Never one to settle for compromised antennas, I thought I'd have a go at "upgrading" my random length with 9:1 unun, and replace it with a compromised end-fed half wave with 49:1 unun and an 80m coil...

Here I have stuck two FT240-43 toroids together with epoxy, and then wrapped in glass cloth electrical tape.

I then wound two primary turns of 1.6mm magnet wire and 14 turns secondary, with the first 2 of the 14 twisted with the primary. I 3D-printed a little base to allow me to tie it down and then screw it into the housing later.

Swapping the old 9:1 for the 49:1

I put 3k Ohm resistor across the output and ground, and got a decent response on a nanoVNA of < 1.7 vSWR across the 1.8 - 23MHz range. I don't really use 10m currently as it seems to be totally dead in my area. Not sure if this is due to the compromised antenna or built-up area, but will be interesting to see if this kit makes any difference.

I'll be hooking up this unun to between 66 and 66ft (20.1 - 20.4m) of kevlar reinforced full braid antenna wire for the 40 - 10m bands. I'll also be adding a 100pF capacitor across feed in and ground connections.

I'll update this post with progress. I'll make another post about the 80m coil I'm making to extend the range of my EFHW once built.

**Edit** I completed the build by adding a 100pF capacitor across the input and ground, and ran a 67ft dipoflex (unfortunately my kevlar wire was about 6 inches too short...) up a pole from 1m up to 6m, then horizontal to another post. When testing on the rig end of the coax, I was getting some dips outside of the bands, but when I tested directly at the 49:1 I saw perfect resonance, so took the chance and tightened everything up.

The IC-7300 tunes up on 80, 40, 20, 15 and 10m without any issue, and the vSWR doesn't stray above 1.2:1. My first call on 20m was to the Azores, 1490 miles during the afternoon. Happy with that!

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