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{
    "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/6ANWKRMQC4HYMAREDVBEEAXR5JOWUDF2/",
    "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/",
    "message_id": "20161020111622.Horde._eyU21K69A-o32c3Geu5Qib@webmail.satavirtual.org",
    "message_id_hash": "6ANWKRMQC4HYMAREDVBEEAXR5JOWUDF2",
    "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/6ANWKRMQC4HYMAREDVBEEAXR5JOWUDF2/",
    "sender": {
        "address": "pedro (a) dutrasousa.name",
        "mailman_id": "34c679918eec4d078abc3edf1f474373",
        "emails": "https://mailman.amsat.org/hyperkitty/api/sender/34c679918eec4d078abc3edf1f474373/emails/"
    },
    "sender_name": "[email protected]",
    "subject": "[amsat-bb] Crossed polarity dual band single feed yagi",
    "date": "2016-10-20T11:16:22Z",
    "parent": null,
    "children": [
        "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/OIY4HYQWDYSTVHWKZNBVEGRELJIIMMCS/"
    ],
    "votes": {
        "likes": 0,
        "dislikes": 0,
        "status": "neutral"
    },
    "content": "Hi all,\n\nThe best of ham radio is that you can build and experiment.\n\nMy current portable yagi is a dualband single fed (VHF element) home  \nbuilt, from DK7ZB designs, 4+5 elements version. VHF has 9.25dB gain  \n1.03SWR, UHF 8.67dB 1.12SWR.\nIt works like a charm.\n\nNow that I'm on the final stages of condo permits for a tower -  \nalthough it's a tower on top of the building there are still space  \nlimitations - my goal is to build a crossed polarity set of my  \nportable antenna. Something similar to what Gulf Alpha had, but  \ninstead of 4 feed points, one for each band/polarisation, I'll have  \nonly two, combined into one impedance matched feed line to the shack.\n\nDue to the required materials for the feed points and the elements  \npositions I came up with 2 versions where the vertical antenna is  \nahead of the horizontal by 3 inches and 16 inches. My understanding is  \nthat circular polarisation would require a specific position for the  \nvertical antenna plus the proper cable circuit for it.\nI'm aware that RHCP would give me a stable signal reception, rather  \nthan my setup even tilted 45 degrees instead of plain  \nhorizontal/vertical. I saw PU3GUO report on his VHF only antenna while  \nreceiving ANDE.\n\nI've ran the model in 4nec2 for the two options, 145MHz and 435MHz,  \nand using 5W. Here are my findings.\n\n3 inches separation:\n\nVHF\nBoth antennas 1.03SWR\nCombined gain 9.25dB\n\nUHF\nBoth antennas 1.12SWR\nCombined gain 8.67dB\n\n16 inches separation:\n\nVHF\nBoth antennas 1.03SWR\nCombined gain 9.24dB\n\nUHF\nHorizontal antenna 1.12SWR; Vertical antenna 1.49SWR\nCombined gain 8.27dB\n\n\nMy conclusion is that advancing the vertical antenna by so many inches  \nwill result in interference from the horizontal one in such way that  \nthe gain is lower and SWR increases.\nGain in UHF is lower, expected as same happens in my current portable  \nantenna, and that's because it's being fed in the VHF element.\n\nHas anyone built something similar that can share any comments?\nWould there be any other configuration possible for a single boom?\n\nThanks in advance.\n\n73s de Pedro\nCU2ZG, HM77\n\n\n\n-- \nThis message has been scanned for viruses and\ndangerous content by MailScanner, and is\nbelieved to be clean.\n\n",
    "attachments": []
}