9:1 unun 20m

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KG4ZSB
Posts: 2
Joined: Wed Sep 27, 2023 5:31 pm

9:1 unun 20m

Post by KG4ZSB »

I want to use my 9:1 unun with my 20m QCX mini.
What length wire recommendations?
N8TGQ
Posts: 82
Joined: Tue Jun 21, 2022 5:06 am

Re: 9:1 unun 20m

Post by N8TGQ »

This is my favorite reference for random wire antennas:

https://www.hamuniverse.com/randomwirea ... LNKUVVQdL0


Here's another with basically the same info:

https://udel.edu/~mm/ham/randomWire/


Rule of thumb for "random wires"- At least a quarter-wave on the lowest band you want to work, not a half-wave on any band you want to work.

I'm using a 35' wire with a 17' counterpoise as my home antenna.
Remember you need a tuner for these antennas.

Rick N8TGQ
Rick N8TGQ
Brian - K3ES
Posts: 94
Joined: Fri May 27, 2022 12:55 pm
Location: NW Pennsylvania

Re: 9:1 unun 20m

Post by Brian - K3ES »

KG4ZSB wrote: Wed Sep 27, 2023 5:54 pm I want to use my 9:1 unun with my 20m QCX mini.
What length wire recommendations?
9:1 ununs are typically used with random wire antennas, which are intentionally non-resonant. So, you would need a tuner to match the antenna to your QCX. An advantage of the random wire is its ability to be matched with an antenna tuner, for use on multiple bands. Since your QCX is a single band radio, this holds no benefit.

You might be happier with a resonant end fed half-wave (EFHW). The feedpoint (one end of the radiating wire) of a resonant half-wave antenna has very high impedance, so a 49:1 unun is normally used to match the antenna to the 50-ohm feedline and radio. When the antenna is properly constructed, the feedline can be directly connected from antenna to the radio, and no tuner is needed. This simplicity is a big advantage for field operations.

A resonant 20m EFHW has wire length of about 33 ft, but should be cut longer, then trimmed to resonance based on your use conditions (unun, feedline, target frequency, antenna configuration, counterpoise, and soil conductivity). There is some latitude for slight differences in soil conditions and specific setup, so length is normally set once (by careful trimming), as you finish making your antenna. Trimming to resonance is normally performed with an antenna analyzer, a nano-VNA , or lowest power transmissions from your.radio through an in-line SWR meter (with proper identification of your station for all test transmissions).

Hope this helps...

Best 73 de Brian - K3ES
KG4ZSB
Posts: 2
Joined: Wed Sep 27, 2023 5:31 pm

Re: 9:1 unun 20m

Post by KG4ZSB »

Thanks for the response guys! I have a small 49:1 that I will use for the 20m endfed. I'll see how that goes.
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