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Mobile Stub matching

Discussion in 'CB Antennas' started by 338_MtRushmore, Feb 13, 2019.

  1. 338_MtRushmore

    338_MtRushmore Sr. Member

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    I finally got another antenna analyzer, and I'm wanting to tune up my mobile antenna. I have read that stub matching will give more bandwidth than the typical inductor at the base. I read up on stub matching, and got nowhere in a few hours. I did order the arrl antenna book, and I will do some more reading either way.

    Is stub matching feasible for 10/11 mobile?
    Is there enough benefit over an inductor at the base to warrant the weeks of studying to attempt it?

    Thanks


     

  2. Tallman

    Tallman W9WDX Amateur Radio Member, KW4YJ EXTRA class

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    Just think of the education you will get hunting all of that information and you can come back and teach us about it. I'm not smart assing you, I have heard of it but never used it.
     
    338_MtRushmore likes this.
  3. 338_MtRushmore

    338_MtRushmore Sr. Member

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    I don't know, it sounds like a lot of effort and I'm pretty lazy these days. Thinking about it this afternoon, I cant even recall seeing any posts here about impedance matching at resonance. Does anyone here do anything other than dip vswr?
     
  4. The DB

    The DB Sr. Member

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    When it comes to stub matching, or really any impedance matching, their are two ways I have seen it done. One is heavily based on formulas, and the other is based on the smith chart. IMO, the smith chart method is by far the easier method to learn and use. I'm not saying that their aren't other ways, but those often involve luck, or throwing parts at the problem until you find the parts that work, which I wouldn't, personally, put in the same category.

    When it comes to impedance matching, aside from the simplest forms of it, it doesn't get talked about much, even between the more knowledgeable hobbyists. Except for the simplest or most tune-able matching systems (aka antenna tuners with components designed to be adjusted over a wide range of impedances including and especially the automated tuners), building a specific matching network for a specific antenna for a specific frequency really does seem to be mostly limited to trained engineers, and very few others. This isn't to say that hobbyists haven't made their own matching systems for various antennas, however, in most cases the hobbyist making said matching network generally doesn't understand how or why it works as they just copied someone else's design or followed directions. Honestly, among the current active members of this forum, I would guess maybe five of us have the working knowledge of or direct experience designing matching networks, even a simple one such as a stub match talked about above, from scratch without the heavy use of trial and error in the process.

    I'm not trying to dissuade you from attempting to learn how to match antennas, I actually encourage the attempt. You will learn a lot in the process that goes beyond matching antennas. I would recommend any of the Reflections books as a starting reference as in said books their is a very good breakdown of the smith chart and how to use them. I would also be happy to help if you had any questions, although it has been a while so I would likely have to do some research (its not that I mind, but it would take time).

    Another option is to learn how to model with 4nec2. If you model an antenna in said program, it can calculate the electrical lengths of said tuning stubs for you, and give you all four possible options so you can see which would work best (or require the least amount of feed line to make). If you want to make another type of matching network, it can calculate the components needed to make several other matching networks, from the basic L network to Pi and T networks as well.


    The DB
     
  5. 338_MtRushmore

    338_MtRushmore Sr. Member

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    I studied up a little on smith charts this evening, and they don't seem as scary as they did yesterday. I had been doing a little studying for extra in the last few weeks, and a lot of it seemed like a waste of time. When I watched a few videos explaining smith charts I was surprised that I knew what some of it was, and slightly kinda sorta understood what they were saying.

    My thoughts are so jumbled right now that I don't know what else to say.
     
  6. Road Squawker

    Road Squawker Sr. Member

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    in a word .... no.

    stubs, either single or double, perform well @ the higher bands: VHF, UHF, Microwave at fixed frequencies.
    using them on frequency agile HF feedlines is not common. (see above).



    The study effort is up to you, any knowledge is good.

    That being said, I use a tuned inductor on my HF (10 - 40) mobile antenna. YMMV
     
  7. 338_MtRushmore

    338_MtRushmore Sr. Member

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    I ordered Reflections II tonight, and upgraded the firmware on my analyzer. This EU1KY with the DH1AKF firmware looks like a powerful tool for $220.

    I had a good laugh today when I realized smith charts aren't scary at all, but actually simplify everything. I'd have never guessed it.
     
    Road Squawker likes this.
  8. Slowmover

    Slowmover Sr. Member

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    Look forward to what you find.

    What is the vehicle type?
     

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