Log-influenced trapless Yagis

Up until the past decade or so, there were only two types of multi-band Yagis for HF: the traditional 3- or 4-element triband designs with traps or the physically larger & heavier trapless Log-Yagi with continuous 10-30 MHz coverage.

Today, there are antennas from several manufacturers in which these designs have merged, combining a 3-band trapless Yagi into a triband-sized footprint, weight and wind load.

In addition to a lack of traps, these Yagis are characterized by closely spaced elements and (in at least two cases) by separate driven elements for each band. Regardless of having separate driven elements only one feedline is used, with the RF being coupled into the “parasitically driven” elements via the directly-driven element for 20 meters (Force 12 C3).

So the new designs are smaller and lighter than Log-Yagis without the traps of traditional tribanders.

Reviews of these antenna types are universally positive however few of the reviewers mention what antenna they had prior to one of the new designs.

Examples of this antenna type are:

With there being no such thing as a free lunch, what was given up to allow a trapless design without the huge footprint of a Log?

Continuous coverage, for one and (from what I’ve read so far) a decreased front to back ratio compared to a trapped Yagi. Forward gain appears to remain the same.



  9 comments for “Log-influenced trapless Yagis

  1. July 30, 2012 at 7:37 am

    The Coupled-Resonator design as in Force 12 is great. I use it for an homebrew hybrid-Moxon with great success.It is physically simple to implement so durability is good, and it is virtually lossless with respect to most of the other multiband coupling technics.
    The only cost are a slight effect on the main antenna pattern, a reduced bandwidth and complexity growing with added bands. Careful design quickly overcome that however.
    The best antenna is the antenna that you can actually use. If it is flimsy or not on the band you need, it will be worthless. For me, it is better to lose some dB but have an antenna that really works when you need it.

    • July 30, 2012 at 8:16 am

      I’m glad to hear that, Yan – it was with some hesitation that I chose the antenna I did. Although they’ve been around for 10 years or so, it was all new to me as I’d never had reason to research it until recently…and I never know how to interpret the reviews on eHam. But when they are universally positive, I feel comfortable in making an assessment.

      I’d be interested to hear more about the feed method of your dual band Moxon (Google translate allows me to read about your 17m mono Moxon). My 15m Moxon amazed me in the two weeks I had it only 4m above my roof.

      “The best antenna is the antenna that you can actually use.”
      They say the same thing about telescopes (thus my QRP Celestron C5+)!

      • July 30, 2012 at 9:09 am

        Hi John,

        I did not own any of the commercial antenna you gave as examples so perhaps some owners reviews will help you better than my opinion. However talking about the coupling solutions, C-R (or open-sleeve) seems the best to me. I tested it on a 6m-2m Jungle Job (G4ZU) and then designed my hybrid-Moxon.
        The hybrid Moxon is basically a Moxon on 15m and a C-R dipole on 10m. I added 6m lately but it does not work well. I was in a hurry and I have to investigate if it come from the feeder (the choke balun namely) or the antenna design by itself.
        That said, on 15m and 10m it is a clear winner over my Ground Plane. I have also reasonable SWR on 12m and 17m that allows my TS-590 ATU to tune it but with mixed results regarding performance.
        I am in the process of writing an article in english about it. Just waiting to see how it resist to the typhoons season. The design is really cheap with fishing poles and PVC pipe… Don’t know if QST or CQ will be interested by the article.

        Agree about the “scope”. Just went back to the astronomy hobby and bought a 130mm Dobson because I can actually be looking at the sky in 5 minutes with my kids and wife rather than just trying to open the tripod.
        However cloudy and stormy sky like tonight is no good at all.


  2. July 30, 2012 at 9:13 am

    Here’s a manufacturer I’d never heard of until seeing there ad somewhere earlier today:

    With “particle swarm optimisation” it’s *got* to be a good antenna… :-)

  3. October 4, 2012 at 6:40 pm

    I should note that the C3 is performing quite well on both 12 and 17 meters. A tuner is needed on 17 but it shows both gain and F/B.

    • K2JRC
      October 24, 2012 at 11:39 pm

      HI John, Force 12 folks tell me that on 17 meters the back is actually the front. Have you experienced this?

      • October 25, 2012 at 6:05 am

        I just recently heard of that characteristic myself (in this thread: http://www.eham.net/ehamforum/smf/index.php/topic,85989.0.html)

        It don’t recall it being mentioned in the manual but will take another look and will also test the idea on the air now that I know it’s a possibility. If it is true, what I suspect is that the C3 has what may be close to a bi-directional pattern on the WARC bands. I say this because signals do peak when I point the antenna at them so there is gain in the standard forward direction. If there’s more in the reverse direction, it may be tough to discern given the time taken to rotate vs QSB.

  4. Helio Greven
    April 28, 2013 at 2:33 pm

    I would like to see the Manual of the TX38 beam in order to verify the dimensions im the computer.
    I can I get a Manual? Anybody has one?

    • April 29, 2013 at 4:30 pm

      Have you tried emailing the manufacturer? Force 12 doesn’t post their manuals online but they emailed one to me at my request.



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