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making a 1.1 choke balance

Discussion in 'CB Antennas' started by red devil, Jan 21, 2009.

  1. red devil

    red devil Member

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    hello great forum i have been doing alot of studing about antennas i have a antron 99 with the ground plane kit i was reading in the forum that for the ground plane kit to work i need to isolate my antenna from the mast pipe and make a 1.1 balance choke at the feed point could some one please explain how to do the 1.1 balance choke i would greatly appreciate it


     
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  2. Marconi

    Marconi Supporting Member

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    RD, how do you know that you have current problems that this GPK, insulator, and a choke are supposed to solve. I work an A99 with no GPK, or choke and I have no such current problems. I have had A99's that did present such problems (CMC) that were bad enough to cause local problems, but I could tell just by the interference they caused and did not have to guess. I cut one apart at some point and found the coax and coil connections inside were not soldered. The AT worked fine otherwise, but no telling what else was going on inside there. There was a lot of current leaking to ground near the feed point. Based on my good service using other A99's over time I know the bad things we hear and read about are not the majority of cases with these antennas.

    I don't think a choke is going to balance the feed point of the antenna even if you did insulate the antenna from the mast. You still have the feedline connected and if a choke fixed the problem for the coax, then it would surely fix the problem of currents on the mast as well.

    Maybe you could PM the source on this Website for more details about the choke?

    Good luck an keep us posted.
     
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  3. W5LZ

    W5LZ Crotchety Old Bastard

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    red devil,
    I have no idea what a "1.1 balance choke" is. I have the feeling that what is meant is just a plain old 'choke', several turns/loops of coax near the feed point of the antenna. That's a fairly common thing to do. The size of those 'loops' just depends on the size/type of coax used. Something like 6 - 10 turns about a foot in diameter ought'a work just fine. The only really important thing to remember is that you can sure wind those turns too tight. If you have to use any particular force to make that loop, it's too tight. Other than that it's just not that critical.
    If you're not talking about a coaxial choke like that, then it beats me as to what you're talking about. Sorry 'bout that.
    - 'Doc
     
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  4. Robb

    Robb Yup

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    Maybe he got the impression from something that I wrote on another thread last night about coax. Yes, I'm guessing. Common mode current doesn't mean that it is commonly present in every radio installation, but can be an undesireable element that can be present if not corrected. My fault for not being clearer about that question someone asked me.
     
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  5. bob85

    bob85 Supporting Member

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    hello eddy,
    maybe he got it from something i posted elsewhere or maybe from w8ji website,
    from our tests here using elevated radials along with isolating the pole and choking the feedline improves performance noticeably,
    one local saw an improvement without the choke.
     
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  6. Captain Kilowatt

    Captain Kilowatt Professional Amateur Staff Member

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    I think he is refering to a balun choke which in all reality does not exist. It is either a balun or a choke but
    not both. It is a common mistake to refer to a coil of coax at the fedpoint as a choke balun which it is not. It is an RF choke NOT a balun. A balun and a choke are two completely differant things.
     
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  7. 74IN

    74IN Well-Known Member

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    Please elaborate.

    My understanding is, a choke prevents the coax from becoming part of the antenna and a balun is more of a matching device used with a balanced antenna fed with coax.

    Close?

    I ask because, I have used dipoles with no balun and have had no problems.
     
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  8. Captain Kilowatt

    Captain Kilowatt Professional Amateur Staff Member

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    You answered your own question right there. A choke prevents RF from flowing on the outside of the coax and thus prevents the caox from being part of the antenna. A balun is a device to convert from a balanced antenna (like a dipole) to an unbalanced feedline (like coax) or vice versa. A balun can also prevent feedline radiation because of what it does but that does not make it a choke. A choke may prevent feedline radiation but that does not make it a balun. Confused yet? :D
     
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  9. freecell

    freecell BANNED

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    http://www.firecommunications.com/r2ch21.pdf

    contrary to popular belief that only dipoles need baluns, verticals and longwires can require baluns (more correctly called common-mode chokes or isolators in this application) also. This article shows why baluns (or more properly common-mode chokes) might be required, and what the choke can do.

    http://www.w8ji.com/verticals_and_baluns.htm

    current, not voltage

    http://www.firecommunications.com/keepcurr.pdf
     
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    Last edited: Jan 21, 2009
  10. red devil

    red devil Member

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    thank you all for the help i just isolated my antenna from the mast and didnt even mess with the 1.1 choke balan and i beleive my ground plane is working with my antenna now i seem to be getting out better and my recieve is better
     
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  11. DXER

    DXER Member

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  12. W5LZ

    W5LZ Crotchety Old Bastard

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    DXer,
    That's good to know, but I'm still puzzled about what the thing is called, "1.1 choke balance". Where/how does the '1.1' and the 'balance' thingys come in? The impedance ratio isn't changed, and the thing isn't 'balanced' to start with.
    - 'Doc
     
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  13. C2

    C2 Well-Known Member

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    Is the choke effectively the same thing as a coil inductor inline on the ground shield?



    ______________________
    __________CCCCCCCC___
     
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  14. Splash1

    Splash1 Active Member

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    to tell if you have common mode,just grab the coax or lay your hand flat on top of your radio whilst keying the mic whist checking your swr.. if the needle moves wilst grabbing the coax or laying your hand on and off the radio,you have common mode currents and your coax is acting as an antenna..
     
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  15. W5LZ

    W5LZ Crotchety Old Bastard

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    C2,
    Sort of, kind'a. Since winding it into a coil only affects what's on the outside of the feed line, then it's about like putting a coil with a large reactance on only the outside of the cable. that would effectively stop any AC/RF from flowing there. (That 'AC' in reference to RF is sort of redundant since there is no DC RF.)
    - 'Doc
     
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: baluns

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