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{
    "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/OUF5HHJZ6QZBQFSREPTFNX26JSYRI4VO/",
    "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/",
    "message_id": "[email protected]",
    "message_id_hash": "OUF5HHJZ6QZBQFSREPTFNX26JSYRI4VO",
    "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/TDD4W4VM2MV3DCIKTXHHMF7S62KC7LHW/",
    "sender": {
        "address": "jonny290 (a) gmail.com",
        "mailman_id": "bed0432ae6e64c0493fa6343553c3746",
        "emails": "https://mailman.amsat.org/hyperkitty/api/sender/bed0432ae6e64c0493fa6343553c3746/emails/"
    },
    "sender_name": "jonny 290",
    "subject": "[amsat-bb]  Thoughts on alternative eggbeater build/feeding",
    "date": "2008-01-24T00:27:49Z",
    "parent": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/TDD4W4VM2MV3DCIKTXHHMF7S62KC7LHW/",
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        "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/CQWJINSOINH625JUBBXZFNVODLDK2MWY/",
        "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/ELALZFT3DCC2ZDBBK2VTQTS2ZRMIHX6P/"
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    "votes": {
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    "content": "Ye olde bird nerds,\n\nI was sketching out some plans to rebuild my practically-failed \nEggbeater antenna project for\n70cm, as I am tired of cranking the rotator knob every pass and want to \ntry out a good omni satellite antenna, which I\ncan hang from the top limb of a tree 30 feet above my shack window (best \noption on my city lot).\n\nMy plan is to build on the K5OE Eggbeater II antenna. One thing that's \nalways bugged me about these antennas\nis that most are implemented using a 93 ohm coaxial section to phase the \nloops. This is hard stuff to find, and though\nI know some hams say, \"anything below 1.5 SWR is OK\", I'm a \nperfectionist and want to try to polish it up.\n\nThe current antenna has a phasing section made out of two runs of RG-8X \ncoax with the shields shorted and insulated, centers fed as a balanced \n100 ohm (theoretical) matching section. It was difficult to build and I \ndoubt its integrity because it's coiled up so tightly;\nI don't think that the foam core coax retains its impedance well when \nfolded up in 1\" PVC.\n\nI was thinking about the feeding issues, then I recalled that one \npopular CP yagi antenna design is to space the horizontal and vertical \nelements 1/4 wavelength along the axis, and then feed them in phase.  It \nthen came to me that it may be possible to build an eggbeater with the \ntwo elements separated vertically by 1/4 free space wavelength, fed with \nsimple half-wave coax sections to replicate the two loops' 100 ohm \nimpedance into a simple coax tee.  Polarity switching should be possible \nwith a coax relay and a 1/2 wavelength delay line. Radials would be \nplaced 1/4 wave apart as well, same spacing as the loops.\n\nThe advantages of this to me seem numerous. First of all, the free space \nquarter wavelength spacing is easier to accurately implement than a 1/4 \nwave phasing section using coaxial cable at 70cm, and the \npower/currents/etc split to the two antennas are more balanced as long \nas you build the 1/2 wave sections to equal lengths, leading to improved \ncircularity skyward. You don't need to find rare coax for the phasing \nsection, and instead of cramming several folded up or coiled runs of \ncoax inside a narrow (for aesthetics) PVC tube, you only need to run two \nhalf-wavelength (or any multiple of half-wavelength) runs further down \nthe mast, where the tee or relay could be ziptied.\n\nSo, that's my plan. If it makes sense, I'm going to give it a shot with \n1/4\" copper fridge tubing for the loops and some sort of sturdy wire \n(coathangers? heh) for the radials, using LMR240 coax for the two \nhalfwave sections. If anybody has any input or comments, I'd love to \nhear them.\n\n(P.S. If somebody's done this and I'm reinventing the wheel, please let \nme know. :) )\n\nMatt\nKC4YLV\n\n",
    "attachments": []
}