Hybrid UnUn – The OZ-Tenna advantage

A hybrid UnUn

Hybrid UnUn - The OZ-Tenna Advantage

What are Hybrid UnUn’s?

Marketing hype is something that annoys me at a deep and painful fundamental level. In the past I’ve been the victim of such and it has always left a bad taste in my mouth.

The term ‘Hybrid UnUn’ just hints at that, and I have some reservations as a result. But I feel justified in coining this term for most of our products. Please hear me out.

A Traditional UnUn

It all starts here. At the beginning.

An UnUn is a term oft used to describe something that couples an unbalanced system to another unbalanced system.

This has been in common use for the device used to transform the impedance of an End Fed Half Wave antenna – which is very unbalanced – to unbalanced coax.

Simple enough. All good. That sounds like a reasonable description to me.

I actually don’t much like this term for our products, as they are more than an UnUn and using that term dumbs them down.

There is no sexiness in the term which I feel is justified for what we’ve developed.

Enter The Hybrid UnUn

This is a betterer term, better than better!

This a core benefit of OZ-Tenna products. Here is the long story.

We tried using conventional UnUn’s and sure, they worked just fine. They are actually cheaper and easier to make and, well, you can find them just about everywhere on the internet for sale, and plans to make them.

There is one big problem among many with this simple approach – on voice peaks the common mode current was causing transceivers to malfunction. Mine and Craig’s in fact. Too much common mode current and some – many? – transceivers will reset, clip the audio, lose their memories, do strange things. That’s not a lot of fun.

The cure for common mode current is to add a 1:1 balun in the coax somewhere. This is simple enough and widely accepted. Some manufacturers call them “line isolators” a somewhat strange term with the implied meaning that they remove common mode current.

This all seems to be the ‘dirty little secret’ of the EFHW antenna fraternity.

It galled me then and it still does now. You don’t get told that when you start out on your EFHW journey. Then you have a problem, then you hate EFHW antennas.

Having to add a 1:1 into the coax means more pieces of coax, more connectors to fail, yet one more box to take with me. Plus I suspect I am hard on my coax – it regularly has problems with something breaking or becoming intermittent. Having to use 2 sets of coax would just double the problems and all the fun leaks out even faster.

So I added a 1:1 balun into the same enclosure as the UnUn. Simple enough again. It felt like a clearly logical and simple solution.

Over the following many months this approach paid off with field testing by myself and others. I did measurements of common mode current and found that sure, it was not ‘zero’ but it was reduced significantly, maybe by a factor of 10 or more.

The Hybrid UnUn was born.

It was a good decision. The test of time, and of multiple transceivers, and some measurement all proves it.

My little IC-703 and Craig’s IC-705 are happy with our Hybrid Baluns. Running at their full power of 10 watts, where once they clipped on voice peaks, with the Hybrid Balun they are happy. Running my FT-897D and IC-7410 at 100W is fine also – no malfunction.

Why Is The Hybrid Balun Not Perfect?

It can’t be, but we get it as close as possible. Anyone who says that putting the 1:1 inside the same box as the UnUn reduces common mode current to zero is, ah, fudging the figures. There are other terms for this I’m muttering under my breath.

The real world doesn’t like ‘zero’ and RF is sneaky. Common mode current can be the most sneaky of all.

Doing Better than Better – The Chase is on!

I’ve tried various different designs, cores, turns ratios, RG316 coax and long suppression sleeves, stacked cores, you name it. They all have merit.

All combinations do in fact reduce common mode current, but not to zero. Some are a genuine pain to make – RG316 makes a beautiful probably lab grade balun but it disagrees with my fat fingers and patience, some are easy to make, some work a little better than others.

You Can’t Escape Reality

The simple fact is that the coax is still in proximity to the antenna and will pickup RF onto the shield. It happens. It is not “huge” and it is measurable, but we’ve not had any problems as a result.

So What Is the Reality?

How good or bad is the OZ-Tenna solution? Yeah, not bad – said in an understated kind of way.

I’ve spent hours at 100W SSB and tested at 50W digital into the FRC-100 to prove that common mode current is not an issue to my transceivers. I don’t run a 2nd common mode choke, or use ferrites on the coax or anything else. Just simple straight through RG58 from the Hybrid UnUn to the transceiver.

It works for me!

And our Hybrid UnUns appear to be unique.

So far. For now. Today! You get the point by now.

Lets start the clock on how long it takes some <deleted invective> foreign seller to make huge claims about their copy of MY designs

I use best quality parts. Will they?

Are there any caveats?

There probably are – but I’ve not experienced any problems with our Hybrid UnUns yet. If you have trouble, please let me know and I’ll try to replicate and adjust designs accordingly.

Some things that may affect common mode current;

* If you put the radials near the coax, this will undoubtedly increase the common mode current on the coax. Simple enough – just keep them separated.

* If you have some “magic length” of coax, it may also happen. I don’t know what that is. I use 9m of RG58.

* If your antenna is super-poorly tuned and you are using a tuner to bring the SWR down, then it may increase common mode current. Maybe.

Thanks for reading this far – yes I waffle on a lot – but hey – it interests me and like I said recently “I’ll take my pleasure from wherever I can get it” these days.


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