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My first attempt to build a 5/8 wave homemade

Discussion in 'Home Brew' started by HomerBB, Mar 17, 2009.

  1. HomerBB

    HomerBB Sr. Member

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    I have been putting together a variety of parts in an attempt to create my own homemade.
    It is almost there. I raised it in the air and managed to get the SWR down to 1:5:1 across the cb 40 channels. It is slightly better in halfway through the band below 26.965, and rises more quickly going up through the band above 27.405. Not as wide banded as I'd hoped, not yet anyway. I started the length at 21' 7", but was forced to bring it down to 20' even because the SWR was too high.
    I could use some questions, ideas, feedback to sort through this.



    PhotosVertical
     
    #1 HomerBB, Mar 17, 2009
    Last edited: Aug 30, 2010

  2. linearone

    linearone King of NY

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    check the photo album in my profile for pics on how to build a simple matching device needed when doing this. it will work great i promise, a 45-200 pf variable cap will work great, think a bunch of turns around a coffee can for a coil.
     
  3. HomerBB

    HomerBB Sr. Member

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    I assume that this capacitor will be at the coax center feed to the shield attached to the counterpoise. Correct?
     
  4. Marconi

    Marconi Usually if I can hear em' I can talk to em'.

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    Homer, are you direct feeding the base, right above the insulator? I can't see much in you photos. What is the green wire doing?
     
  5. HomerBB

    HomerBB Sr. Member

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    Yes, from above the insulator.
    There is a coiled load at the bottom of the vertical. The green wire is feeding it.
     
  6. W5LZ

    W5LZ Crotchety Old Bastard

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    Well, if it works, I'd have to say it's a pretty good 'first' attempt! Wouldn't you?
    All those commercially made antennas started out in just about the same way, someone wanted to try it, did, it worked. After that, it's sort of 'refining' the thing, finding out what makes it 'more better', easier, cheaper, whatever. Makes you feel good, don't it?!
    - 'Doc
     
  7. linearone

    linearone King of NY

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    yes, I would add a small trimmer cap like a 465 arco or something and just tune with a radio. i would connect one end to the ground feed and one to the antenna connection above the coil. i would make a moveable tap point o n the loading coil to play with that as well. you will find that when you tune the cap for minimum swr the only thing you then need to do is move the tap point around till you find lowest swr as well. I find typically the tap points will vary but the capacitance needed will stay the same. at least on the two Ive made.
     
  8. HomerBB

    HomerBB Sr. Member

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    Yes, Sir, it feels good.

    What I am curious about is

    1. If it is 20 feet long instead of closer to 22, what is it? Or is the coil at the feed point the difference in length?

    2. By what device do I make it more wide banded? The 1:5:1 SWR is not where I had hoped, (Linearone offered a possible addition) your thoughts...
     
  9. HomerBB

    HomerBB Sr. Member

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    Okay. I'll try this. Is this for SWR? What does this do for me?

    I had a tap from the coil to the counterpoise and cut it loose. The SWR was WAY up there with the coil tapped in this way. Do I need to tap the coil when I use a counterpoise, or only if I do not use a GPK?

    Thanks, Fellows

    Anyone else have ideas to help me learn just jump in and fire away.
     
  10. W5LZ

    W5LZ Crotchety Old Bastard

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    If it's 20 feet instead of 22 feet it's still basically a 5/8 wave antenna. And you're right, the coil is 'making up' the difference. If you really wanna get 'picky', figure what fractional length happens to be and call it that. It's still basically a 5/8 wave.
    More band width? Introduce more 'almost neutralized' reactance into the thing and it will -seem- to have more band width. Will it actually have that greater band width, or is it just 'fooling' the SWR meter? Guess! (And yes, it's just fooling that SWR meter.)
    The practical difference between an SWR of 1.5:1 and a 1.1:1 is non-existent. 'Fiddle' all you like, it will make absolutely no practical difference, except make you 'feel' better.
    That tapped coil matching system is a 'dirt' common way of doing things. Why? Cuz it works just fine. You can do about the exact same thing with capacitance, the only difference is in how it's applied. For me, that coil thingy is much simpler/easier than the capacitance thingy because I don't need (or probably have) a variable capacitor, or a double hand full of the fixed value ones. The larger the diameter of that coil (within reason!) just makes smaller adjustments possible.
    (Inductively matching an antenna typically means that antenna will be slightly shorter at resonance. Capacitively matching typically means it'll be slightly longer at resonance. Lay your money on the bar and name your poison.)
    - 'Doc
     
  11. HomerBB

    HomerBB Sr. Member

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    So I am at what is about as practical as I should expect. Manufacturers manage to broaden their antennas bandwidth. Am I to accept that they are sacrificing efficiency?
     
  12. W5LZ

    W5LZ Crotchety Old Bastard

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    Very basically, meaning that the sacrifice may not be all that much in some cases, yes, you are loosing some efficiency. That loss of efficiency can be balanced by the usability, to some undetermined point. 'Said' point being up to the user? Most antennas can be 'skootched' this way and that some. But, unless they are adjustable, none of them are going to cover a huge range of frequencies without that adjustment.
    A typical 1/2 wave dipole has a certain range of usable frequencies. Whatever that range is, is approximately 'normal' for well designed, efficient antennas. Those antennas that have an advertised huge range of usable frequencies owe that range to 'advertising' and loss of efficiency. Is it worth it? Beats me, is it??
    - 'Doc
     
  13. HomerBB

    HomerBB Sr. Member

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    Alrighty, I get it.
     
  14. RickC.

    RickC. Hopeless antenna junkie

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    I'm coming to the party late on this one-- nice looking work!

    Did you figure out the matching on this?


    Rick
     
  15. HomerBB

    HomerBB Sr. Member

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    At different websites, and from various people, I've gotten slightly different bits of advice on it, but today I added a cross for a cap to extend the overall length, then I added a ring from the top of the load coil to the base of the vertical. I started with a ring of about 12" diameter, and had to keep cutting it down (instead of moving a tap) until the ring is just about 5 inches (basically a long jumper at that length) diameter.

    I've got an SWR of

    1:1 on ch. 19 (27.185)
    1:2 on ch. 1 (26.965)
    1:4 on ch. 40 (27.405)

    It seems a little wider banded than it was, but has a steeper SWR curve than the A99. It is friendlier toward the below the cb 40 channels than above the cb 40. I am considering just leaving it alone, now.
     

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