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Full wave 10m horizontal co-phased antennas

Discussion in 'Amateur Radio Antennas' started by KF5FUR, Oct 7, 2011.

  1. KF5FUR

    KF5FUR Member

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    Google search and images searches have nothing on it. I wonder if it would work well to shoot skip in two directions. But I would be using a 200 watt amplifier and I do not have a metal roof, would this be inadvisable to transmit this power while under the antennas in the house? I mean I could raise them up pretty high if it will be a problem.

    10 & 11 meter full wave co-phased horizontal dipoles (revised size for WWRForums).jpg

    sorry for the weird resolution on the pic, I had to resize it for the forums liking, hope you can read it all.



    -Bill
     
    #1
  2. Moleculo

    Moleculo Administrator Staff Member

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    I'm not sure I'm clear on how you're thinking of mounting this antenna. Is this accurate:

    You're going to install two vertical masts on either side of your roof and run two horizontal, full wave 10 meter wires between the posts. One wire will be on top of the other, separated by approximately 1/4 wave. Your plan is for the two wires to be a phased array. I'm assuming that you're planning on them being phased at 0 degrees?

    Does that describe it properly?
     
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  3. KF5FUR

    KF5FUR Member

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  4. KF5FUR

    KF5FUR Member

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    From http://www.worldwidedx.com/cb-antennas/123837-full-wave-11m-horizontal-co-phased-antennas.html

    I have decide to post an update on what I am going to do with the co-phased setup.
    I will be using the 2 antennas and cable from the co-phased big rig kit I purchased when I was planning on using them for my pick up truck (but don't worry, I went with 102" SS whip for that)
    I have aluminum pipe to separate the antennas up to 12 feet, any recommendations on the proper width of separation would be welcome. I have another L style antenna mount bracket to mate the horizontal pipe to the vertical (which has a nut welded to the top) I can just bolt it down to it through the stud hole. It will be light weight and have low wind loading. All I will have to do is turn the rotator 180* for full 360* coverage. The antenna setup can be used for 11 meters till I get a 10 meter rig and then all I will have to do is trim the wires on the antennas and it will be great for that. Eventually the antennas can be replaced with some other better ones. Here's some pics...

    This one I stated earlier as being a Channel Master.. Sorry its a Alliance Tenna Rotator
    SAM_1077.JPG
    As you can see the rotated portion is through the body (y)
    SAM_1078.JPG
    Here is another look, but the innards. Very clean for its (unknown) age
    SAM_1076.JPG
    I'm not going to use that one, I just put that up to show what kind I was talking about when I said they lurch to the side a bit when you move them, no good for heavier antenna setups also with higher wind loads.
    SAM_1079.JPG
    Here's a bundle pic of the stuff, excluded are the angle bracket I forgot to include in it and the steel vertical pipe that is to nasty to bring in.
    SAM_1081.jpg
    I had to crop it so the pic is crowded

    My concern is can I hook that 75 Ohm slit harness to a 50 Ohm cable, because I do not have enough 75 Ohm cable to reach the 9ft reach of the split harness, and some length will also be tied up horizontally. Since a CB and I also assume a 10 meter rig will operate with either cable and yes I know, 75 for Co-phased and 50 for single. Just curious. Also what would it do if it is not recommended to?
     
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  5. W5LZ

    W5LZ Crotchety Old Bastard

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    If that phasing harness isn't long enough to reach the two antennas, then it gets a little complicated. You can extend each leg, or just one leg, if it's done correctly, and that's where it gets 'too long' by a bit. You end up with the same phasing if you use odd multiples of each leg length (3 time, or 5 times, etc.). That 'too long' is certainly better than too short though. That extension has to be an odd multiple, or the phasing get's really messed up. That's using 75 ohm cable just like the phasing harness is made from. What do you do with that 'extra' cable? Just coil it up, it won't hurt anything.
    One extreme to the other, huh? Oh well.
    - 'Doc
     
    #5
  6. Shockwave

    Shockwave Sr. Member

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    The full wave wire design has problems due to radiation currents being out of phase on both ends of the wire. Once you end feed a radiator longer then half wave, the next half wave begins to radiate in a phase that is not constructive. The exceptions here would be a closed loop. Such as a full wave quad element or a folded dipole element that would have a much higher impedance.

    Since the output impedance of both legs on the co-phasing harness is 50 ohms, you can easily extend the ends of the harness using any EQUAL lengths of 50 ohm cables on both sides of the harness. The signal will reach both antennas in phase as long as the extra cable lengths are equal.

    The only time you would want different lengths of cable would be if you're trying to form a directional pattern. In this case you must adjust the lengths of the coax so that you create the desired phase shift between the two elements.
     
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  7. KF5FUR

    KF5FUR Member

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    Thank you Shockwave, that is the clearest answer about the full wave yet, I didn't know if it would work or not, that's why I shared it to get answers.
    Ive seen before, others have put the split right in the center of the 2 antennas, whatever the case of the intended operating band or antenna design. I was able to construct most of the array last night and as described previously. The antennas are actually separated by 10ft 4in. With about 6ft of harness left over from the center bracket. I stated earlier that the harness was 9ft each leg but maybe it was the eBay listing info I was thinking of. The setup may dance around a bit in the wind, but certainly less then if it were on a truck going 70. I'll post pics when i can.
     
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  8. KF5FUR

    KF5FUR Member

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    Here is a revision of the original posted pic, a 1/2 wave co-phased setup that will actually work, and well.

    10 & 11 meter co-phased half wave.jpg
     
    #8
    Last edited: Oct 15, 2011

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