Manual Antenna Tuner Shows How Homebrewing Is Done

If there’s anything about amateur radio that has more witchcraft in it than the design and implementation of antennas, we don’t know what it would be. On the face of it, hanging out a chunk of wire doesn’t seem like it should be complicated, but when you dive into the details, building effective antennas and matching them to the job at hand can be pretty complex.

That doesn’t mean antenna topics have to remain a total mystery, of course, especially once someone takes the time to explain things properly. [Charlie Morris (ZL2CTM)] recently did this with a simple antenna tuner, a device used to match impedances between a transmitter and an antenna. As he explains in the first video below, his tuner design is really just a Wheatstone bridge where the antenna forms half of one leg. A toroidal transformer with multiple taps and a variable capacitor forms an LC circuit that matches the high impedance antenna, in this case a multi-band end-fed halfwave, with the nominal 50-ohm load expected by the transceiver. A small meter and a diode detector indicate when the bridge is balanced, which means the transceiver is seeing the proper load.

The second video below shows the final implementation of the tuner; as a fan of QRP, or low-power operation, [Charlie] favors simple, lightweight homebrew gear that can be easily taken into the field, and this certainly fits the bill. A final video shows the tuner in use in the field, with a NanoVNA proving what it can do. As usual, [Charlie] protests that he not an expert and that he’s just documenting what he did, but he always does such a good job of presenting the calculations involved in component selection that any ham should be able to replicate his builds.

10 thoughts on “Manual Antenna Tuner Shows How Homebrewing Is Done

    1. Indeed, if QRP is defined as 25-100W instead of 10W then it’s all reasonable.. :D
      (QRO is 750W in my place, I think.)

      Or if you’re running a 10W QRP transceiver on a half-wave dipole. Say two 20m wires on a 10m high pole for 80m operation.

      Seriously, though. Life is too short for QRP.
      Unless you’re operating on an open field with good (proper) antennas or have an efficiency fetish (a passion for testing most efficient transceivers, PSUs, cables and antennas) .

      In the city, with space limitations, QRM and electro-sensitive neighbours, it’s really hard
      and frustrating to get into a real QSO with low-power.

      Unless you’re using PSK31, FT4/8 or WSPR.
      These modes work below the grass level, so to say.

      Don’t get me wrong. Experimentation, homebrewing and curiosity are the roots of amateur radio.
      But always advertising QRP to beginners can backfire, as they may quit the hobby due to sheer frustration.

      IMHO, it’s better to call CQ with normal power and then, after the QSO is established, go down to QRP levels. Using QRP is good for the finals, after all, hi. ;)

      Vy73

      1. People can and do make contacts via QRP.

        Giving a beginner false expectations that they will make a contact every time though.. I will give you that is bad.

        I’m not sure that encouraging someone whose main interest in in building stuff that they should start out by going QRO is a great idea either. How excited is such a person going to get when instead of building a rig they buy a black box then they find out all the conversations are either people talking about their store-bought rigs.. model number this, model number that, nary a technical detail, bad politics or old-age maladies.

        It’s better I think to encourage builders to build but just let them know that QRP contacts are more like fishing than phone calls. When no one is answering they can always verify that their project works with test equipment, a receiver, online SDRs or the reverse beacon network.

        Keep encouraging more hackers to homebrew and maybe finding someone who can receive at the various QRP watering holes will be easier. Besides, once they get the feel for RF via building QRP they can always turn around and build a QRO amp. QST had some good articles about that a couple years back.

        Until then, go listen to http://soldersmoke.blogspot.com

  1. Nothing new, all this has been described many times.
    It has the merit to show it to the new amateurs…
    Why the bike when there are motorcycles and cars ?
    Why sailboat when there’s outboard?

    But… why use powerfull tranceiver when you could use a phone ?
    This is my answer to the high power aficionado.

  2. QRP is fun! And I do agree that it’s a hard thing to do in a city with a big caveat. If you can get your antenna up high you can do fabulous things. The roof of a tall building is one way. The beauty of QRP is in the details. The 10 watt limit is kinda funny. If you have 10 watts out of your rig and put that into an antenna with 7dbi of gain your output is effectivley 51 watts. (roughly without going itnto erp calculations etc.) But the moral is your not at 10 watts anymore. A good yagi can bring that dbi number up considerable.
    73 ya’all.
    kb9ydd

  3. Thanks for this article. Yes many of us have ARRL yearbooks and radio theory texts around, but it’s great to be reminded of something that’s simple and effective… and no doubt of benefit to the newcomer.

    I’m currently looking for effective ways to reduce all the RF hash and interference from the devices in the average house that gets into a longwire antenna for shortwave listening (not that there’s a whole lot interesting there any more :-( ). I’m currently testing a tunable HF loop antenna, and thinking about what filtering I could put onto a longwire antenna.

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