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{
    "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/ZGMQKJIZ3X6ANPEFWLFI7JLUPQKMTNUX/",
    "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/",
    "message_id": "[email protected]",
    "message_id_hash": "ZGMQKJIZ3X6ANPEFWLFI7JLUPQKMTNUX",
    "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/7XLSXKMSWPEIRPAWJ4SIMFM7JN3IZVIZ/",
    "sender": {
        "address": "aa2tx (a) comcast.net",
        "mailman_id": null,
        "emails": null
    },
    "sender_name": "Anthony Monteiro",
    "subject": "[amsat-bb] Re: eggbeater II antenna performance oscar 50-52",
    "date": "2007-08-18T20:20:52Z",
    "parent": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/DZMOIQB6TJ6FPRRZMETHVRNFWXKXNQNC/",
    "children": [],
    "votes": {
        "likes": 0,
        "dislikes": 0,
        "status": "neutral"
    },
    "content": "At 10:20 PM 8/17/2007, Bruce Robertson wrote:\n>...\n>Do I remember correctly that designs such as this are less circularly\n>polarized at the low elevations than they are overhead? If so, have you\n>considered the Lindenblad by Tony, AA2TX?\n>http://www.arrl.org/qst/2007/08/monteiro.pdf\n>\n>If you're building either antenna specifically for VO-52, you might\n>consider making it LHCP, which I believe is the polarization of the 2m\n>signal transmitted by Hamsat. (Tony reports that his RHCP design\n>nonetheless receives VO-52 well.)\n>\n>A low noise preamp at the antenna will make a huge difference also at 145 MHz.\n\n\nDear Friends,\n\nI have designed, built and used both \"Eggbeater\" and\nLindenblad (omni-directional) antennas for LEO satellites.\n(You can find my \"Eggbeater\" design in the 1998 AMSAT-NA\nSpace Symposium Proceedings.)\n\nBoth antennas are perfectly reasonable for LEO satellites.\nThe performance differences between them are subtle and\nmay not easily be noticed in a simple A/B test.\n\nThe \"Eggbeater\" (i.e. full-wave loop turnstile) antenna\nis horizontally polarized at the horizon and at low\nelevation angles. At elevation angles above around 50-60\ndegrees, the vertical component starts to become significant\nand the antenna becomes elliptically to circularly polarized.\nDirectly overhead, the antenna is circularly polarized.\n\nThe Lindenblad is circularly polarized at the horizon and at\nlow elevation angles. As the elevation angle increases, the\nvertical component decreases and the axial ratio becomes\nbigger (i.e. the circularity gets worse.) A Lindenblad\nhas a null directly overhead although in actual use,\nit is pretty hard to detect this and of course the satellites are\nalmost never directly overhead anyway.\n\nWhen the satellite antenna is circularly polarized (i.e. like AO-51,)\nthere is virtually no overall performance difference between the antennas\nalthough the instantaneous signals levels may differ.\n\nBut, when the satellite has a whip antenna, the Lindenblad will\nprovide less fading at low elevation angles due to its ability\nyo accept any linear angle of polarization whereas the \"eggbeater\"\nwill show a deep fade if the incoming polarization is nearly vertical.\n\nMany of the current analog satellites use circularly\npolarized antennas, so there would not be a great deal of difference\nbetween the two antennas on these satellites.\n\nThe Lindenblad has one other advantage and that is that work reasonably\nwell for terestrial FM repeaters so you can get away with having only one\nomni antenna at your station for each band.\n\n73 to all,\nTony AA2TX\n\n\n",
    "attachments": []
}