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Beads, Ferrities ?..

Discussion in 'CB Antennas' started by Oatmeal, Jan 18, 2015.

  1. The DB

    The DB Sr. Member

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    I used an average diameter for the various coax available at that general size as listed on various data sheets. In any case, we are talking inches of difference, not feet, so the main point still holds.



    The quarter wavelength thing is just a coincidence for coax with a .66 velocity factor. But then I know you know that already... ;)


    The DB
     

  2. jazzsinger

    jazzsinger Bullshit Buster

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    Lol.

    I know its coincidental as you say. But in saying that makes you wonder how many other things taken as fact in radio are purely coincidental too.

    Sure you were only inches out and to be fair arithmetic is a much bigger strength of mine than radio theory.

    You pulled me about using ch20 instead of ch19 months back for centre freq of a 1/4 wave whip if I recall.

    As I said at the time it ain't our normal cb band nor centre frequency on my 26-28 band.

    And although my figures then were right too albeit I used wrong channel to what you guys see as the norm and is centre frequency like you I was an inch or so out. If I recall you jumped on me like a rash. Lol. Despite the fact my point also still stood that 102" is not a 1/4 wave.

    Sorry
    I couldn't resist it. ;) Lol.

    You must admit it is a strange coincidence.

    No hard feelings. ;) lol

    73 Jazz
     
  3. The DB

    The DB Sr. Member

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    Its good to know there is someone that can take a joke and can joke right back. Sometimes the lighter mood really helps. That being said, I know there are those that likely thought we were being dead serious in a thread or two on this forum... Our posts can read so serious sometimes...

    Anyway, until next time...


    The DB
     
  4. jazzsinger

    jazzsinger Bullshit Buster

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    Couldn't agree more mate.

    Sometimes a bit of humour/sarcasm can lighten the mood.

    The written word is very easily misperceived, especially when in heat of moment you forget to add a wink, smile, tongue out etc.

    What was a minor disagreement or calculation can soon blow out of proportion.

    I think once it gets personal its time for all parties to step back and ask am I wrong here.

    Its nice being right but sadly you learn nothing from it. Better to be wrong and corrected. Thats how I view it.

    I must admit the coincidence despite knowing the theory did get my curiosity up. Wouldn't be first time what was viewed as solid fact for years was proven wrong.

    I also have a reason for wanting to understand toroids better. I've always got away with coaxial chokes on 11m and used toroids for 11m rfi suppression, mostly through trial and error and what was lying around.

    I really need to get antenna analyser/vna.

    I want to build an effective resistive choke for an old nos cushcraft arx 450 ranger (ringo efhw) for 446 mhz.

    I don't have much experience at that point in spectrum

    So my curiosity is up on everything choke related just now.

    Anyway till the next time triviality gives us the oppprtunity to laugh rather than bang heads.

    All the best Jazz ;) :) 73
     
  5. Heavy Metal

    Heavy Metal Active Member

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    Bottom line what is diameter and length of 9913F7/LMR 400 213 needed to make 1.8 to 30 clean especially more so up 24-30 ect ect... Also distance from SO239 to start of turns.seen same 18-21 feet sounds a bit steep needed for RFI suppression ect.
     
    Oatmeal likes this.
  6. curlyjo

    curlyjo Supporting Member

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    Is there snap on ferrites available to go on LMR 400 for use in the 11 meter band? If so where can I get them before I reinstall my Vector 4 K style antenna? Thanks
     
  7. The DB

    The DB Sr. Member

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    I typically use full beads that are strung on before I put an end on. I'm sure you can get the snap on variety, I just haven't looked for those as I haven't needed them...


    The DB
     
  8. 543_Dallas

    543_Dallas Sr. Member

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    These are the ones I've been using with good results. I stumbled across them at a local store.

    http://www.frys.com/search?cat=-70044&pType=pDisplay&fq=m10099998 PAN

    I believe the 13mm cores are what I use on the lmr400 and 213. I don't know the mix and have found cheaper ones but these work very well. My first experience with them was running a 12 pill with a crappy antenna install. 2 of them at the feed point stopped 90% of the RFI issues.
     
    Oatmeal and Marconi like this.
  9. curlyjo

    curlyjo Supporting Member

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    Thanks
    Thanks
     
  10. Beetle

    Beetle Sr. Member

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    It's going to be difficult (nay, impossible), to come up with a single miracle device that will "make 1.8 to 30" "clean". The difference in wavelength makes it so.
     
  11. Heavy Metal

    Heavy Metal Active Member

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    Does it matter if it's whole or a snapon?
     
  12. Heavy Metal

    Heavy Metal Active Member

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    Ok
    1.8-14 14-30 or 14-54
     
  13. fourstringburn

    fourstringburn W9WDX Amateur Radio Club Member K5KNM

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    All technical data aside, one could use a commercially produced choke and be done with it.

    I experimented around with air wound chokes, beads and baluns, and this worked the best with my mobile antenna controlling common mode currents. Of course the advertising is somewhat hyped up so don't believe everything you read.

    Kind of expensive compared to what you can make yourself, but it is neat in appearance and gives your antenna system a uniform look.

    [​IMG]

    DX Engineering Maxi-Core® Feedline Current Chokes
    DX Engineering Feedline Current Chokes, using Maxi-Core® technology, prevent unwanted RFI by eliminating feedline current and radiation in 50 ohm, coaxially fed antenna systems. They provide excellent feedline decoupling and low loss performance from 1 to 60 MHz and are power rated for 2 kW continuous, 5 kW intermittent.

    DX Engineering Feedline Current Chokes have significantly higher common mode impedance and a larger effective core area than similar line isolators, including conventional enameled wire or bead baluns. This results in higher power handling with lower loss, improved antenna bandwidth, and reduced RFI, and compensates for a less-than-optimal grounding system.
    While the most common advice is to improve the station's RF ground, the root of the problem is in the poor isolation of the feedline from antenna currents. In other cases, as the coax feedline travels through the near-field of the antenna, the current can be reintroduced to the feedline after the balun. If your SWR is already low and you wish to reduce feedline radiation (RFI) and improve reception, DX Engineering Maxi-Core® Feedline Current Chokes are recommended.
     
  14. Heavy Metal

    Heavy Metal Active Member

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    Rather go home made or close to that. Anyone can buy but it's more fun to do it without that.
     
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  15. fourstringburn

    fourstringburn W9WDX Amateur Radio Club Member K5KNM

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    True, I have sucsessfully made my own but I do use this DX engineering one now for my mobile setup along with a UNUN transformer which mate together very well.

    I brought the DX egineering one up to counter the debate that usually comes up when things can get too technical as a viable alternative.

    To add to that debate, The chokes I have sucsessfully made to fight off common mode currents were simply wound with up to 7 turns of RG8X coax with a mix 31 snap on bead on the coax installed at the antenna feed point.

    Mix 43 beads I understand are better for vhf frequencies and above while mix 31 are better for HF.
     

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