KD5ZZU’s very elegant build of “Old Barebones” – a Z-match tuner

Back in October 2024 I wrote a post with the title “Old Barebones” – A QRP Z-match Builder Project. The project’s purpose was to construct a simplified version of the Norcal Z-match tuner (which I also owned) to use with my QRP Labs QMX transceiver. The Norcal tuner included some features that I simply did not need – such as balanced transmission line terminals, a simple LED SWR indicator and three switches (Balanced line/BNC, Tune/Operate, High/Low impedance). The schematic was copied from the Norcal tuner – a superb design that I didn’t think I could improve. The end result was a very simple device with three BNC connectors, a toroidal inductor and two polyvaricons, all packaged in a small Amazonian plastic enclosure. Alright, it is an ugly device mainly due to the inelegant knobs I chose to use. But it works very well indeed and has become my main QRP portable antenna matching unit. Heck, it cost me a big fat nothing to build thanks to my extensive junque box stocked from years spent hoarding miscellaneous bits and pieces. When I have finished twiddling the knobs I can always put my hat over it to hide its lack of elegance.

Then, out of the blue, I received an email from Mallory KD5ZZU who expressed an interest in building her own version of “Old Barebones”. Mallory queried whether the design would work on the high bands. I had only tested mine on 20m, 30m and 40m, so I hooked it up to my home 80m EFHW and my portable 13ft tripod vertical antennas to test whether a low SWR could be achieved with Old Barebones on 17m, 15m 12m and 10m. Fortunately Old Barebones did a splendid job on both antennas so Mallory took the plunge and built her own version.

Note: My 80m EFHW (End-Fed Half Wave) is used primarily on 80m but is also useful on 40m and 20m. Using a tuner to obtain a low SWR on the higher bands protects the radio from high SWR but does not imply that the antenna is useful on those bands.

Mallory experienced a hitch in the construction though. Her first build did not function as expected and she asked for ideas on what to look for to resolve the problem. It turned out to be the connections to the polyvaricons that were the problem. Polyvaricons often have several sets of vanes and multiple connection points. I had used a capacitance meter to identify the correct connections in my original build. Realizing this may be the problem, Mallory quickly identified the correct connections and got her tuner working. She wrote that she was able to achieve a nice low SWR on all bands from 20m to 10m with her 71ft EFRW and 9:1 unun. A great result.

But Mallory doesn’t need to cover her version of Old Barebones with a hat to disguise its appearance. It is a beautiful design built into a custom 3D printed case with 3D printed knobs and looks terrific.

If anyone else is interested in building this simple construction project Mallory has kindly provided links to an online source for the parts and the 3D print files:

• Polyvaricons: https://a.co/d/hOYgP2f
• Toroids: https://a.co/d/7mItRXw
• Magnet wire: https://a.co/d/ffqdHo9
• BNC posts: https://a.co/d/5mwLEVI

Here is a link to the 3D print design of the knobs:  https://www.thingiverse.com/thing:3035549/files

Here is a link to the file to 3D print; it’s a print profile (modification) from the original designer of a customizable enclosure box: https://makerworld.com/en/models/2002942-custom-enclosure-box#profileId-2400746

A note on the use of Old Barebones

I designed Old Barebones for use with my QRP Labs QMX transceiver which has a convenient “Tune SWR” feature that reduces the output power to 25% to reduce the stress of high SWR on its delicate finals during the tuning process. I have also used Old Barebones with my Yaesu FT-817 but I manually reduce the power to 1 watt or less during tuning. If using Old Barebones with any radio that does not have an SWR indicator I recommend incorporating an SWR indicator in the tuner circuit similar to the original Norcal BLT design.

Polyvaricons?

The word “polyvaricon” is presumably a contraction of “Polymer Variable Condenser” meaning a plastic enclosed variable capacitor using a plastic dielectric. It is believed to be the trademark of a Japanese company that manufactures these devices. But shouldn’t it be called a “polyvaricap”. I remember back in the dawn of my existence that capacitors were called “condensors” but that term disappeared a long time ago. Strange old world.

What is a Z-match?

“Antenna tuners” are often named after their topology. For example, an L-match comprises a series inductor or capacitor and a complementary parallel capacitor or inductor. The combination of inductor and capacitor forms an “L” shape. However, there is no immediately apparent “Z” shape to the components in a Z-match, so I presume the “Z” refers to impedance. Let me know in the comments if I am wrong.

Pros and Cons of the Z-match

From the GQRP organization in the UK:

Advantages of the Z-Match

• Matches balanced loads without the use of lossy baluns.
• Being a parallel resonant circuit, the Z-match can provide some band-pass filtering for your receiver and harmonic attenuation for your transmitter.
• A well-designed Z-match tuner has a high Q and is more efficient (less lossy) than other types of tuners.
• The fixed inductor simplifies construction (no switches or rollers needed).

Disadvantages of the Z-Match

• Tuning is usually very narrow and can be a bit touchy sometimes to tune up

Thanks again to Mallory KD5ZZU for sharing her build with Ham Radio Outside the Box and congratulations Mallory for turning my original inelegant build into something with class!

Help support HamRadioOutsidetheBox

No “tip-jar”, “buy me a coffee”, Patreon, or Amazon links here. I enjoy my hobby and I enjoy writing about it. If you would like to support this blog please follow/subscribe using the link at the bottom of my home page, or like, comment (links at the bottom of each post), repost or share links to my posts on social media. If you would like to email me directly you will find my email address on my QRZ.com page. Thank you!

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#AmateurRadio #OldBarebonesZMatch #QMX

25 Years a Ham and Still Learning

I actually got my “ticket” a little late in life. I spent many years as an SWL, then college, career and a family took priority. By the time my wife and I became empty-nesters I had combined my passion for radio and Space “the final frontier” by chasing satellites; military satellites mainly. I formed the HearSat group dedicated to monitoring Low Earth Orbiting satellites. My account of a unique method of decoding the signals from Russian navigation satellites was kindly published by Monitoring Times magazine. At the time I felt there were so many fascinating signals flying around that there was nothing of value I could contribute by adding my own. However that feeling didn’t last long and eventually I bought a study guide, passed the written test and became a ham.

Now, I am into my 25th year in this great hobby. Frankly I was never satisfied with using a radio just to rag chew; I felt an urge to experiment – to contribute something useful to the science of radio communications. I didn’t fully realize it at the time, but I was at the bottom of a steep hill that I am still climbing, learning with every step. As my personal lifelong learning journey progresses I am proud to share knowledge gained here at Ham Radio Outside the Box.

“In times of change, learners inherit the earth; while the learned find themselves beautifully equipped to deal with a world that no longer exists.” – Eric Hoffer

Coil Loaded End-Fed Half-Wave (CLEFHW)

Several weeks ago Ham Radio Outside the Box introduced a rather unique antenna idea, called the Coil-Loaded End-Fed Half Wave (CLEFHW). It is a telescopic whip that is inductively base-loaded to become an electrical half-wave. What is the purpose? To create a backpackable antenna with a very small footprint achieved by eliminating the need for a long counterpoise or system of radials. It worked very well – for a while. Then I began tinkering with it; I call it “continuous improvement” and it stopped working properly.

“If it ain’t broke …”

The antenna started to experience unstable SWR. Then the great snowstorms of February 2025 arrived and I could no longer get outside to investigate. Undaunted, I set up a wire in my basement “lab” to simulate the whip and was able to adjust the antenna to get a good SWR again. All was good – until an unusual warm spell hit and I was able to get out to a local park to do a POTA activation. Suddenly, the good SWR was gone again. Abandon the activation? No, improvise and adapt! I pulled my ham-brew “Old Barebones” Z-match out of my pack and finished the activation.

Back at the shack I was determined to find out what had gone wrong. The park I had visited sits on shale stone rock just beneath the soil and is right alongside one of the Great Lakes. Previous activations at that park had given spectacularly good results.

It ain’t gonna work John, give up and go have a beer

The snow still lay deep and crisp and even on my backyard but I managed to shovel my raised wooden deck clear and continue the investigation. That was the start of a very frustrating series of antenna trials. It can be tempting at times to quit – “it ain’t gonna work John, give up and go have a beer”. But, I remembered my college physics training: experiment – document the results – change one thing at a time – document the new results – make further changes as required and repeat until success is achieved.

The most important part of that process is to document the results at each and every step. I keep a small spiral bound notebook and a pencil nearby while I tinker in my basement lab. That makes it easier to review what went wrong and when. Yes, it’s tedious to put down the soldering iron and pick up the pencil, but it does make a big difference in the end.

So what was learned? It seemed a fair assumption that an 18.5ft whip, replaced with an 18.5ft wire would perform pretty much the same. But oh, no John, no John, no! There was another parameter involved that hadn’t been considered. The lab experiment with the wire took place in the nice, warm environment of my basement replete with space heater and a constant supply of hot beverages. But the basement lies 6 feet below grade – could that be an issue?

The carefully adjusted antenna with the 1.2:1 SWR was then carried up, up and away to the deck, out into the cruel Big Blue Sky Shack where the temperature was hovering around freezing. The 18.5ft wire was replaced with the telescopic stainless steel whip which, with all 13 sections extended, was also 18.5ft long. I confidently powered up my rig and set the mighty micro QMX to monitor SWR. “Should be pretty close to the same SWR I got in the basement” methought. But then disappointment haunted all my dreams. The lilliputian radio gave me the bad news: SWR 2.6:1.

A bit of a stretch

Previous learning experiences had taught that any physically short antenna that is artificially extended to it’s electrical full length by means of a loading coil tends to exhibit a very high Q. The CLEFHW uses a base loading coil to extend its physical length of 18.5 feet to an electrical length of approximately 33 feet which is a half wavelength on 20m. If the inductance of the loading coil isn’t right in the bullseye of the required value, the electrical characteristics can be subject to unexpected change.

But perhaps the unexpectedly high SWR out on the deck was influenced by another factor. Yes, the basement lab is 6 feet down below ground while the deck is 2 feet above the ground. How to compensate for this? Is the CLEFHW going to need a custom coil for each and every deployment? Maybe it will, but there is a solution that we will get to in a moment.

“If you want to find the secrets of the universe, think in terms of energy, frequency and vibration.”
― Nikola Tesla

SWR on the deck 2 feet above ground

Back in the lab the loading coil was rewound with nearly enough inductance to earn a place in Nikola Tesla’s lab.

The idea was that turns could be removed until the SWR settled down to an acceptable level. The target was less than 1.5:1. It worked! The SWR out on the deck came down to 1.10:1.

Just a cotton pickin’ minute Einstein…

The victory dance had to be put on hold as another doubt surfaced. The SWR measured out on the shale stone ground in the park was different to the SWR measured on the hardwood over concrete floor of the basement lab. The SWR out on the deck had been different again. A pause and a little stroking of the chin while the old gray matter overheated with intense thought. This deck, said the voices inside my head, is 2 feet above the ground. Do we have another variable to throw into the equation here?

The base of the antenna is at the top of the backpack frame and when the pack sits on the ground, as intended during outdoor operating sessions, it is only about a foot and half above the ground. The antenna is an almost vertical shortened End-Fed Half-Wave (it is sloped to give it some directionality). So is proximity to ground another factor to consider?

The whole backpack rig, antenna and all, was beamed over to an area of grass just beyond the deck. Here we go again, with everything exactly as it was up on the deck, the SWR grew legs and climbed up over 2:1 again.

The Ultimate Lossless Tuner?

SWR with backpack rig on the ground Taps on the coil Whip adjustment with backpack rig on the ground

The simple solution would have been to pull out “Old Barebones” (Z-match) again and bring those pesky standing waves under control. But I had another cunning plan. By leaving some extra turns on the coil I could increase the inductance beyond what is required to load the whip and use the whip itself to adjust the SWR.

Brilliant! It worked. The final iteration of the coil (nothing is ever really final) involves three taps near the top of the coil to leave some inductive flexibility to accommodate persnickety ground conditions. An SWR of 1.09:1 was obtained with the pack out on the grass. But, it was necessary to collapse two sections of the whip to get there. Interestingly, adjusting the whip length retunes the antenna without introducing any further loss; it simply restores the electrical length of the loaded whip to a half-wave.

So now, once again, the Ham Radio Outside the Box Coil-Loaded End-Fed Half-Wave antenna is ready for action. Lessons learned. Oh, and – Note to Self – move onto another project John – don’t tinker with things that work already!

Help support HamRadioOutsidetheBox

No “tip-jar”, “buy me a coffee”, Patreon, or Amazon links here. I enjoy my hobby and I enjoy writing about it. If you would like to support this blog please follow/subscribe using the link at the bottom of my home page, or like, comment (links at the bottom of each post), repost or share links to my posts on social media. If you would like to email me directly you will find my email address on my QRZ.com page. Thank you!

The following copyright notice applies to all content on this blog.

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

#Antennas #CLEFHW #Ground #OldBarebonesZMatch #POTA #QMX