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2 Element Quad

Discussion in 'CB Antennas' started by HomerBB, May 13, 2009.

  1. HomerBB

    HomerBB Sr. Member

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    Hmmm. It's a thought. . . I hadn't considered that . . . thanks.

     

  2. HomerBB

    HomerBB Sr. Member

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    Hmmm. . . I hadn't thought of that. . . thanks.
     
  3. HomerBB

    HomerBB Sr. Member

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    I do not have any of the antenna modeling software some of you apparently do. It would be considered a favor if you guys could give me some adjustments to wire lengths and boom length/spacing that would optimize this antenna for forward gain and reasonable back door rejection.
    Remember, I'm not operating off a tower and my rotor is not a big hefty piece. I am only able to get it up to 28' at the boom right now. To work on it I have to use a rope and pulley system and a friend to lay the antenna and mast over and return it to vertical. That's why I decided for a two element as opposed to a three or more: weight, footprint, rotor size, affordable, and local Home Depot construction materials.

    Suggestions here-and-there about the possible inefficiency of the current design has been taken seriously, and I wish to accommodate changes. I do not have any resources except the online calculators and they all agree with the current design. . .

    Thanks, everyone.

    fix this, please:

    [​IMG]
     
  4. HomerBB

    HomerBB Sr. Member

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    No time to do any more work on the beam, yet. This evening at 8:00 PM I came in from work and DX was rolling. I was unable to bust up any pile-ups on the Cb 40 so dropped down a band. This is where the SWR is best right now.


    Contacts:

    Little Granny in Kentucky 26.895

    150 Kentucky 26.905

    142 W Virginia 26.915

    Bloodhound Kentucky 26.815

    Took a chance and jumped up to 27.515 lsb

    347 Jamaica

    I am anxious about getting the antenna properly setup. No telling how much fun I'll have.
     
  5. RickC.

    RickC. Hopeless antenna junkie

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    Homer,

    I have a couple different versions of NEC, but didn't use them for this since I've built a few of them, so I don't have any fancy stuff to send you. Something that might interest you is finding a copy of Orr's "All About Cubical Quads", which I owned years ago and lost but found used on Amazon for 7 bucks. Lots of very interesting info there, including how spacing affects feedpoint impedance.

    Probably most people who build quads just build the reflectors self-resonant to the lower frequency by making them longer, but I have old reference books showing both loops of a 2 element quad being made the same size (I guess to make the physical construction easier, but it probably doesn't really make that much difference) and using an open wire shorted stub to resonate the reflector at the lower frequency.

    The book I mentioned has several pages on matching the quad to coax, and covers baluns and Q sections as well as gamma matches. Most interesting to me is the 10/15/20 quad using a single coax feedline and seperate but connected gamma matches for each band. Lots of ideas there (and other places) but the 1/4 wave 75 ohm section is what I setteled on with the last one because I had used it a few times before and because it's simple.

    The quad I posted a photo of was very similar to your setup-- a 30' push up pole with a Channel Master TV rotator.

    I think if more people understood how well these antennas worked, how cheap they are to build, and weren't caught up in owning a certain brand name or another, there would be a lot more of them in use on 27 MHz. Single band quads are not hard to build and are still small enough at 11m that you don't need 4 people to handle them. You also don't have the pattern distortion when using a quad for vertical polarization the way a yagi has when it's flipped on its side.

    Lots of advantages to a quad antenna, and as you've seen they can still work well even when they're not optimized.

    No comment on the frequencies there...


    Rick
     
  6. HomerBB

    HomerBB Sr. Member

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    Gonna check on the book.
    Going by the bookstore later,also.

    You've been a lot of help. Thanks.
     
  7. RickC.

    RickC. Hopeless antenna junkie

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    Hey Homer,

    No problem-- you won't likely find that book in the bookstore, I think it's out of print now-- but there were several to be had online when I bought mine a couple of years ago.

    Rick
     
  8. Peddler

    Peddler SWR (sandwich with rum) Expert

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    It would be interesting to obtain your material list Homer.
     
  9. HomerBB

    HomerBB Sr. Member

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    parts list

    1 1/4" fence top rail (boom and top mast section)
    1 1/4" PVC (2 pieces for boom end sleeves holding spreader tees)
    1" PVC ( 8 sections for spreaders)
    1" x 48" wood dowel (inside spreaders for rigidity)
    1" PVC 4-way cross (2 for spreader center joints)
    3/4" PVC (8 sections for spreaders)
    1" PVC couplers (8 for spreader joints)
    1" x 3/4" PVC bushings (8 for spreader joints)
    3/4" PVC caps (8 for spreader tips)
    3/4" PVC tee (1 for driver wire/feedline terminal connection)
    16" wire shelf supports (8 for spreader rigidity)
    project box (1 for 75ohm match section to pl239 solder joint)
    u-bolts (2 for boom connection to angles)
    threaded eye bolts (2 for PVC cross spreader center joints)
    myriad bolts, screws, and nuts
    Steel shelf angle brackets (2 for mast to boom connection)
    wood squares (2 for spreader rigidity)
    14ga wire of sufficient length

    PVC boom end sleeves were shaped to match profile of 1" PVC crosses joining center of spreaders. 1/4"hole was drilled through the center of PVC crosses, 1/4" x 3" eye bolts were reversed through the holes into the 1 1/4" PVC boom end sleeves and secured with 1/4" bolts across sleeves through the eye of eye bolts. Sleeves allow for both mounting and sliding spreaders in or out to tune.


    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]
     
  10. PA629

    PA629 Active Member

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    I know there were a few listed on Amazon last fall. It is a good reference manual, mine's gotten a lot of use over the years.
     
  11. Peddler

    Peddler SWR (sandwich with rum) Expert

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    Thanks Homer(y)
     
  12. KingCobra

    KingCobra Member

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    Nice quads you have here! How is your performance so far? What type of wattage are you using and how far have you talked with decent reception? How high off the ground is it now? Thanks. Scott.
     
  13. HomerBB

    HomerBB Sr. Member

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    I like your quad, too.

    I am still in the refining phase with it, but I've talked a little DX, and the little bit of local has been within ten - twenty miles of me. The more distant stations I've talked to on my homemade 5/8 wave have been silent for the past week so no radio checks from them, yet.

    have a barefoot station, keying 2 - 6 watts, and swinging about 25 or so. I am only 28' at the boom. No tower and doing my best with what I've got.

    There are times I hear better with the 5/8 at 34 feet, and times the quad has better ears for the same signal.

    I will keep up the posts on performance as I tweak the thing.
     
  14. KingCobra

    KingCobra Member

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    QUAD

    Yeh, sorry bout that. tried to enter my off-road quad in my sig and it exploded lmaooooooooooooo. I must learn to down-size. Can you say 60 mph?:) Thanks anyway. Scott
     

    Attached Files:

  15. HomerBB

    HomerBB Sr. Member

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    Whoowee, what a hotrod!
     

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