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Thread: FYI: I learned today...

  1. #1
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    FYI: I learned today...

    A 1/4 wave vertical dipole doesn't work so hot for 2 meters. I could never get the thing tuned to the ham band (It "liked" 129 MHz or so best), and had a really wonky impedance that I could never get match.

    I found a 1/4 dipole design somewhere, and the web page said,"It works great!". That might be accurate, but not with my system until I get the coax replaced with something other than 75 Ohm cable.

    So, back to my "tried and true" antenna for 2 meters: The 1/4 wave droopy ground plane. I'm taking my time building this one, because I killed a length of coax by not sealing with well enough, and it leached water down the entire length. One good thing? This spool of cable cost me about $10 for 1000 ft.

    So, this ground plane will be "well engineered" and not "ad hoc" as has been my past designs. I think for now, I can't beat the 1/4 ground plane. A beam is the next "step up", but I have to have an omni design. Have to complete this by week's end so I can try to get a new HF antenna designed, built, and up before the first snow.
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  2. #2
    SK Member (02/27/2012) W5RB's Avatar
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    You need to bring your feedline away from a dipole at about a 90 degree angle , for a half wavelength or more , or it'll be hinky . That's sometimes impractical with a vertical dipole . The droopy ground plane , as built using a chassis mount so-239 and brazing rod , works well on 2m , and fair on 440 as well .
    I won't question your Creator's wisdom , but you are responsible for your own actions .

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  3. #3
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    A matching stub might be necessary as well. FM stations use variations of dipoles and impedance matching is accomplished with a shorting stub. Pretty easy to make.

  4. #4
    Pope Carlo l NQ6U's Avatar
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    I'm a firm believer in J-poles for VHF. Not only are they easily tunable, they're generally 5/8 wave which has a lower radiation angle.
    All the world’s a stage, but obviously the play is unrehearsed and everybody is ad-libbing his lines. Maybe that’s why it’s hard to tell if we’re living in a tragedy or a farce.

  5. #5
    Orca Whisperer PA5COR's Avatar
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    Diamond X510N.
    Use car wax put, on roof with Ecoflex 15 coax, done for 2/70 9dB and 11 dB gain.

    ;)
    "If the Republicans will stop telling lies about the Democrats, we will stop
    telling the truth about them." - Adlai Stevenson (1900-1965)
    “I’m not liberal/conservative, I’m anti-idiotarian.”
    At some point in the last 20 years, the left moved to the center, and the right moved into a mental institution

  6. #6
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    Quote Originally Posted by W5RB View Post
    You need to bring your feedline away from a dipole at about a 90 degree angle , for a half wavelength or more , or it'll be hinky . That's sometimes impractical with a vertical dipole . The droopy ground plane , as built using a chassis mount so-239 and brazing rod , works well on 2m , and fair on 440 as well .
    I think this might be the issue here. I just brought the coax down the support, right next to the "ground leg" of dipole, and when you reminded me of the 90 degree thing, I realized there's coupling involved, essentially giving me no ground leg...

    Well, I think I'll try it again, this time following the 90 degree rule. And, the J-pole is the next project :)
    Big Giant Meteor 2020 - We need to make Earth Great Again

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  7. #7
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    Quote Originally Posted by KJ6BSO View Post
    I'm a firm believer in J-poles for VHF. Not only are they easily tunable, they're generally 5/8 wave which has a lower radiation angle.
    I was just re-reading this thread... I thought 5/8 waves had a higher angle than 1/4 waves?

    Not really "questioning" you per se... I guess I should instead ask for reference material on that.
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  8. #8
    Conch Master KJ3N's Avatar
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    Quote Originally Posted by KC2UGV View Post
    I thought 5/8 waves had a higher angle than 1/4 waves?
    Nope. Pages 5 & 6.
    "People Who Don't Want Their Beliefs Laughed at Shouldn't Have Such Funny Beliefs" -AD5MB

    "If someone tells you he believes in and talks to an invisible bunny named Harvey, you put him on medication and a regimen of therapy. If someone tells you he believes in and talks to God, well, that's perfectly acceptable. Why that's the case is impossible for me to fathom." - WP2XX



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  9. #9
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    Quote Originally Posted by KJ3N View Post
    Thanks :) That whole doc is some good reading there.
    Big Giant Meteor 2020 - We need to make Earth Great Again

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