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{
    "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/QMQS5M6RSX6QWUIVSLN3IBHARWEVIMZD/",
    "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/",
    "message_id": "[email protected]",
    "message_id_hash": "QMQS5M6RSX6QWUIVSLN3IBHARWEVIMZD",
    "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/QMQS5M6RSX6QWUIVSLN3IBHARWEVIMZD/",
    "sender": {
        "address": "K3IO (a) verizon.net",
        "mailman_id": "79a9b3ddaa4b44baae47f92374974ac4",
        "emails": "https://mailman.amsat.org/hyperkitty/api/sender/79a9b3ddaa4b44baae47f92374974ac4/emails/"
    },
    "sender_name": "Tom Clark, K3IO",
    "subject": "[amsat-bb] Re: Phase 4 versus Eagle",
    "date": "2007-12-16T03:25:10Z",
    "parent": null,
    "children": [],
    "votes": {
        "likes": 0,
        "dislikes": 0,
        "status": "neutral"
    },
    "content": "Ed, KL7UW said:\n> Have to agree with Drew even if this reduces signal levels at extreme \n> latitudes.  I would assume that the P4 centered on the NA&SA would \n> boresight the equator with a beam chosen to match the earth's \n> apparent angular size = arcsin (8000/23500) = 19.9 deg. which \n> corresponds with an antenna with 19.5 dB.  At 2.4 GHz an 18-inch dish \n> has about 19.7 dB gain.  Such a footprint would only be 3 dB down at the poles.\nEd -- I think you calculated for the gain over a dipole and not dBi. The\nIsotropic would be ~2 dB higher (22.4 dBi for a beam that is about 3.5\ndB down at the edge of the earth). I derived the number in my paper on\nphased arrays presented at the last (Pittsburgh) AMSAT Space Symposium;\nsee pages 1&2 and Table 1 in\nhttp://mysite.verizon.net/w3iwi/electronic_scanning_antennas.pdf.  In my\nEAGLE paper, I made the calculation for the altitude of a GEO satellite,\nsince that approximates the altitude we would get with EAGLE with a\nrocket boost from GTO.\n\nAlso, strictly speaking, your number is the directivity. Directivity\nrefers to the beam size without considering any ohmic or scattering\nlosses in a real antenna. The real \"gain\" of an antenna is always poorer\nthan the directivity by a factor of typically 50% or so.\n\nTo divert any incoming questions: Yes, my symposium paper describes my\nthoughts on antennas for EAGLE in an elliptical HEO orbit, where we have\nto expend some effort on pointing the antenna from a spinning\nspacecraft. My phased array ideas are based on the notion that\n    (a) we will want to point at the earth even when we are away from\napogee, and\n    (b) trying to mechanically point an antenna (or the spacecraft\nitself) is wayyyyy! beyond the limits of amateur technology.\n\nItem (b) points to one of the big advantages of the piggyback-to-GEO P4\npossibility -- the \"parent\" bus will provide a platform, stabilized to a\ndegree or better, so we can use \"simple\" antennas (probably dishes) for\nthe microwave frequencies [saving me the hassle of designing a \"real\nworld\" electronically steered phased array].\n\nTo get a feeling for the \"antenna farm\" we might have for P4, Google\nyielded a few interesting photos:\n\n   1. http://space.skyrocket.de/index_frame.htm?http://space.skyrocket.de/doc_sdat/intelsat-14.htm\n      shows the DoD IRIS payload riding in the space we might occupy\n   2. http://www.cnes.fr/web/print-6086-intelsat-11-optus-d2.php shows\n      an Intelsat satellite being mated to an Ariane 5\n   3. Intelsat 10, launched on 2004:\n      http://www.astrium.eads.net/families/daily-life-benefits/communications/intelsat-10-02\n   4. The 2005 Sealaunch of IA-8:\n      http://www.dailywireless.org/2005/06/23/intelsat-spotbeam-launched\n      <http://www.dailywireless.org/2005/06/23/intelsat-spotbeam-launched/>\n\n73 & Season's Greetings de Tom, K3IO\n",
    "attachments": []
}